US3892058A

US3892058A - Process for the preparation of high-temperature short-time sterilized packaged articles

Info

Publication number: US3892058A
Authority: US
Inventors: Yoshihiro Komatsu; Kanemichi Yamaguchi
Original assignee: Toyo Seikan Kaisha Ltd
Current assignee: Toyo Seikan Group Holdings Ltd
Priority date: 1972-09-22
Filing date: 1973-09-20
Publication date: 1975-07-01
Anticipated expiration: 1992-07-01
Also published as: GB1449226A; NL7313124A

Abstract

A process for the preparation of high-temperature shorttime sterilized packaged articles which comprises filling an article to be sterilized in a flexible container having a heat-sealable resin film at least on an area to be heat sealed of the inner surface therof, removing non-condensable gases present in interior voids of the flexible container, hermetically sealing the flexible container by application of heat in such a manner that the coefficient of flatness in the resulting sealed packaged article is maintained at a level not exceeding 0.25, said coefficient of flatness being defined by the following formula

in which l indicates a maximum thickness (cm) in the sealed packaged article, L disignates a maximum distance (cm) across the surface of the container, and KF stands for the coefficient of flatness. MAINTAINING THE SEALED PACKAGED ARTICLE FOR A SHORT TIME IN A HEATING MEDIUM OF A TEMPERATURE EXCEEDING 130*C. to thereby sterilize the article packaged in the container, and cooling the so heat-treated packaged article under a pressure hegher than the saturated vapor pressure corresponding to the sterilization temperature.

Description

United States Patent 91 Komatsu et al.

[ 1 July 1,1975

[ PROCESS FOR THE PREPARATION OF HIGH-TEMPERATURE SHORT-TIME STERILIZED PACKAGED ARTICLES [75] Inventors: Yoshihiro Komatsu; Kanemichi Yamaguchi, both of Yokohama, Japan [73] Assignee: Toyo Seikan Kaisha Limited, Tokyo,

Japan [22] Filed: Sept. 20, 1973 21 Appl.No.:399,346

[30] Foreign Application Priority Data Sept. 22, 1972 Japan 47-95314 Dec. 13, 1972 Japan 47-124393 [52] U.S. Cl 53/21 FC; 21/56; 53/22 B; 426/412 [51] Int. Cl B6511 55/02 [58] Field of Search 53/21 FC, 22 B; 21/56; 426/407, 401, 412

[56] References Cited UNITED STATES PATENTS 3,093,449 6/1963 Kotarski et al, 21/56 X 3,366,442 1/1968 Neiss 21/56 X Craig et a1. l A. 21/56 Greenberg et all 21/56 X Primary ExaminerTravis S. McGehee Attorney, Agent, or Firm-Diller, Brown, Ramik & Wight 1 57] ABSTRACT A process for the preparation of high-temperature shorttime sterilized packaged articles which comprises filling an article to be sterilized in a flexible container having a heat-scalable resin film at least on an area to be heat sealed of the inner surface therof, removing non-condensable gases present in interior voids of the flexible container, hermetically sealing the flexible container by application of heat in such a manner that the coefficient of flatness in the resulting sealed packaged article is maintained at a level not exceeding 0.25, said coefficient of flatness being defined by the following formula in which 1 indicates a maximum thickness (cm) in the sealed packaged article, L disignates a maximum distance (cm) across the surface of the container, and K stands for the coefficient of flatness.

maintaining the sealed packaged article for a short time in a heating medium of a temperature exceeding 130C. to thereby sterilize the article packaged in the container, and cooling the so heat-treated packaged article under a pressure hegher than the saturated vapor pressure corresponding to the sterilization temperature.

24 Claims, 2 Drawing Figures PROCESS FOR THE PREPARATION OF HIGH-TEMPERATURE SHORT-TIME STERILIZED PACKAGED ARTICLES This invention relates to a process for the preparation of high-temperature short-time sterilized packaged articles. More particularly, the invention relates to a heat sterilization process comprising subjecting a food filled in a flexible packaging container to high-temperature short-time sterilization in the in-package state.

Conventional processes for the preparation of canned or bottled foods comprise, in principle, the step of hermetically sealing a food into a container capable of keeping the food in the air-tight state and the step of subjecting the sealed packaged articles to heat sterilization at a high temperature for a certain period of time so that the food can be preserved with certainty.

In such in-package heat sterilization process practised in the manufacture of canned or bottled foods, however, the heating time corresponding to a fixed heating temperature is determined so that a necessary but minimum heat history is given to a portion in the package to which heat is most difficultly transferable, and therefore, there should naturally be brought about a great difference to the heat history between such portion to which heat is most difficultly transeferable and a portion to which heat is most easily transferable. For instance, in the case of heat sterilization of cylindrical canned foods, it is known that the quantity of heat given to the surface portion of the content in the vicinity of the inner wall face of the container throughout the entire steps of heat sterilization from the come-up time to the cooling step is several tens to several hundred times as large as the quantity of heat given to the central portion of the content in the vicinity of the center of the container, and that the surface portion of the content is excessively heated. Further, this nonuniformity of the heat history is also brought about by the configuration and food-containing capacity of the container, physical properties of the packaged foods, the amount of non-condensable gas sealed in the pack age or occluded in the packaged food and sterilization conditions such as the sterilization temperature and sterilization time.

More specifically, as the food-containing capacity of one container is small and the distance between the container wall and the center of the container is small, the non-uniformity of the heat history is, in general, small. In case the article to be packaged is uniform and rich in flowability and has such a property that the heat transfer is effected in the article not only by conduction but also by convection, non-uniformity of the heat history is small. Furthermore, if a large amount of noncondensable gas is present in the packaged article, the transfer of heat is obstructed by such gas interposing between the inner wall surface of the container and the surface of the content. Therefore, as the amount of non-condensable gas is small, non-uniformity of the heat history is small. As regards the strelization conditions, it is considered that the low sterilization tempera ture and gradual heating will result in a low degree of nonuniformity of the heat history. Therefore, in the conventional inpackage heat sterilization processes, the sterilization temperature is usually maintained within a range of from lO5to 121C.

In heat sterilization of articles contaminated with microorganisms including bacterial spores. the relation between the time required for annihilation of micrrorganisms and the heating temperature is in comformity with the equation of arrhenius as the time-temperature relation in a chemical reaction. The annihilation rates depends greatly on the temperature, and at heating temperatures exceeding C, the annihilation rate increases by 5 to 10 times when the temperature is elevated by lOC and theoretically, the heating time is shortened to 1/5 to 1/10. ln case an article to be heat sterilized is a food, degradation of quality by heating is due mainly to such phenomena caused by chemical reactions as reduction of vitamin contents, decrease of amounts of flavor constituents, accumulation of browning substances and hydrolysis. As is known in the art, reaction rates in these chemical changes are also in conformity with the equation of Arrenius, and they depend on the temperature to such a degree that when the temperature is elevated by 10C., the reaction rates increase by 2 to 3 times. When this value is compared with the degree of increase in the microorganism anni hilation rate attained when the temperature is elevated by 10C., it is seen that the rate of annihilation of microorganisms including bacterial spores by heat is several times as high as the reaction rates in the above chemical changes. Therefore, in sterilization of articles which tend to undergo chemical changes under heating, the quality of such article can be kept in better conditions by effecting the heating at a high temperature for a short time than by heating the article at a relatively low temperature for a long time. when compared based on the same degree of annihilation of microorganisms. For this reason, there has been broadly adopted a so-called high temperature short-time sterilization process (HTST sterilization process).

In the heat sterilization operation, however, since the heat energy is not directly applied to objective microorganisms but through an article to be sterilized, the majority of the heat energy given at the sterilization step is consumed for elevating the temperature of the article to be sterilized and accumulating the heat in the article and therefore, the heat given to the article is much larger than the heat necessary for annihilating the objective microorganisms by heating. In the case of an article having a low heat conductivity and an article in which a long time is required to transfer heat to the central portion, especially in the case of an article filled in a sealed package, complete sterilization cannot be attained unless a much excessive heat history is given to the article.

As in the manufacture of canned or bottled foods, in the inpackage sterilization process (post-packaging sterilization process) in which an article to be sterilized is filled and sealed in a container having a certain capacity and a cylindrical form and then the sterilization is conducted, the reduction of quality represented by browning (called burning) is caused to occur in the packaged article at the surface portion of content having a contact with the inner wall face of the container or at the portion having a contact with interior voids, and this quality reduction surpasses the improvement of the quality attained by the shortening of the heating time owing to elevation of the sterilization temperature. Accordingly, it has been considered that the upper limit of the temperature to be adopted for sterilization is about l2lC. (250F.) and elevation of the temperature beyond this upper limit is of no signifcance. Further, in the case of a rigid container such as can or bottle, when the outer or inner pressure is too excessive under heat sterilization conditions, permanent deformation or breakage is caused in the container, which results in damage or release of the sealing compound layer and in breakage of the air-tight seal. Accordingly, in the art of the in-package heatsterilization, it has been considered that in the case of such rigid container the upper limit of the heat sterilization temperature is about 125C. even in extreme cases. Therefore, rigid containers cannot be used with good reliability under such sterilization temperature condition as will cause the pressure difference of 2 Kg/cm or higher between the inner pressure and outer pressure at the temperature elevation or cooling, namely at sterilization temperatures exceeding about 130C.

In the art of manufacture of canned and bottled foods, therefore, various proposals have heretofore been made in order to obtain sterilized packaged articles according to the high-temperature short-time sterilization technique. As a typical instance of such proposals on the iii-package sterilization process, there is known a so called agitating sterilization process according to which the sterilization of canned or bottled foods is carried out while they are being agitated and rotated. More specifically, according to this process, canned or bottled foods are passed through a heating medium such as high temperature steam, hot water or flame while they are being agitated and rotated. In this method, by movement and rolling agitation of solids or bubbles contained in the article to be sterilized, the temperature elevation in the article is accelerated and the heat history is uniformalized in the article. Indeed, in case this agitating sterilization process is applied to a fluid or semifluid article, attainment of such effects can be fully expected, and and undesired phenomenon of burning can be effectively obviated. However, in case this process is applied to a non-fluid or highly viscous article, a solid article or a composite article containing solids extremely irregular in the size, any effects can hardly be expected. Therefore, this process should be distinguished from the true in-package hightemperature short-time sterilization process.

As the process to be used mainly for sterilizing a fluid article, there has been broadly adopted a process comprising subjecting continuously such fluid article to the high-temperature short-time sterilization by passing it through a plate-type heat exchanger, a tubular heat exchanger or a surface-scraping heat exchanger, optionally cooling the sterilized article, and then filling and sealing it in a pre-sterilized can or glass jar in an aseptic atmosphere. This process is well known as a so-called aseptic packaging process and is used broadly for sterilizing fluid articles, mainly liquid articles such as milk products and soups. As an improvement of this aseptic packaging process, there is known a process in which a sterilizied article is filled and sealed in a container without cooling it, the sealed article is allowed to stand still for a while after the sealing, and then the cooling of the article is performed. In each of these aseptic packaging processes, the article to be sterilized and the container therefore are sterilized separately, a heat exchanger is employed instead of a retort as the sterilizing means, and use of an aseptic atmosphere particularly shielded from the outer atmosphere is indispensable. Accordingly, each of these aseptic packaging processes is an out-package sterilization process (pre-packaging sterilization process) and therefore, it should be distinguished in the in-package sterilization process (postpackaging sterilization process) in which the filling and sealing of an article into a container is at first conducted and then the sterilization is carried out. In other words, such aseptic packaging process is an outpackage high-temperature short-time sterilization process in which articles to be treated are substantially limited to fluid articles that can pass through a heat exchanger,

It is a primary object of this invention to provide a process for the heat sterilization of sealed and packaged articles in which a variety of articles to be preserved, inclusive of solid articles which can hardly be sterilized according to the above-mentioned outpackage (pre-packaging) high-temperature short-time sterilization process, fluid or hardly fluid articles containing uniform or non-unform solids, can be subjected to high-temperature short-time sterilization to shorten greatly the time required for the heat sterilization treatment while lessening degradation of quality of packaged articles by heating, whereby completely sterilized packaged articles having a good combination of longtime preservability and high quality can be obtained.

We have made extensive research works with a view to developing a process for the in-package hightemperature short-time sterilization which can provide a sterilized packaged article in which degradation of quality of the contained food is much reduced and long-time preservability is much improved, and as a result, we have found that (i) flexible containers are much more suitable for high-temperature short-time sterilization than rigid containers heretofore used in this field, such as cans and bottles; (ii) when such flexible containers are employed, in order to obtain good heat transfer at the high temperature heating step, it is important that non-condensable gases are removed from food-filled containers to thereby exclude voids from the interiors of the containers; (iii) when such flexible container is used and non-condensable gases are removed from the interior thereof, in order to give such a heat history to the content of the package that spores of microorganisms present in the content can be completely annihilated even at the central portion of the interior of the package without causing substantial thermal degradation of quality of the content even at the surface portion having a contact with the inner surface of the container, it is important that the coefficient of flatness (hereinafter detailed) should be maintained at a level not exceeding 0.25 in the sealed packaged artide, and that (iv) in order to prevent occurrence of breakages and other troubles in the sealed area of the packaged article, it is important to cool under pressure the packaged article heated at a high temperature for sterilization of the content. Based on these findings, we have now arrived at this invention.

In accordance with this invention, there is provided a process for the preparation of high-temperature short-time sterilized packaged articles which comprises filling an article to be sterilized in a flexible container having a heat-scalable resin film at least on an area to be heat sealed of the inner surface thereof, removing non-condensable gases present in interior voids of the flexible container, hei l netically sealing the flexible container by application of heat in such a manner that the coefficient of flatness in the resulting sealed packaged article is maintained at a level not exceeding 0.25, said coefficient of flatness being defined by the following formula in which [indicates a maximum thickness (cm) in the sealed packaged article, L designates a maximum distance across the surface of the container, and K stands for the coefficient of flatness, maintaining the sealed packaged article for a short time in a heating medium of a temperature exceeding l30C. to thereby sterilize the article packaged in the container, and cooling the so heat-treated packaged article under a pressure higher than the saturated vapor pressure corresponding to the sterization temperature.

This invention will now be detailed.

CONTAINER It is important that the container to be used in this invention should have heat resistance and flexibility. In case such flexible container is employed, noncondensable gases contained in voids of the container can be easily removed, for instance, by applying a pressure from the outside. Further, while a sealed packaged article from the interior of which non-condensable gases have thus been removed is heat sterilized and cooled, the void-free, flat state can be maintained in the packaged article. Namely, the coefficient of flatness K can be maintained at a level specified in this invention, i.e., at a level not exceeding 0.25. In addition, in this flexible container it is important that at least an area to be heat sealed of the inner surface of the container is composed of a heat-scalable resin film. If this requirement is not satisfied, it is impossible to hermetically seal the container in the content-filled and noncondensable gas-excluded state.

By the flexible container referred to in the instant specification is meant a container having such flexibility and deformability that when an article to be sterilized is filled in the container in the state where substantial amounts of non-condensable gases are still present in interior voids of the container, the container is hermetically sealed while excluding such non-condensable gases by application of an optional pressure from the outside or in a reduced pressure lower by at least 70 cmHg than the atmospheric pressure and than the sealed container is taken out into the atmosphere, the container can retain its shape regardless of the change in the pressure and no voids of a reduced pressure are formed in the interior of the container. Whether the container is flexible or not is determined by such factors as the kind of the container-constituting material, the thickness and configuration of the container and the ambient temperature. The container to be used can take an optional configuration, as far as it is composed of a flexible sheet having two inner surfaces confronting each other and it has such a structure that a space for an article to be contained is formed between said two inner surfaces and an area to be heat sealed is provided around the periphery of said space or around the periphery of an inlet for filling such article into said space. In order for the container to be hermetically sealed under heating, it is important that the entire of the inner surface of the container or an area to be heat sealed of the inner surface of the container should be composed of a heatsealable resin film. Such container may take a bag-like form. Namely, a so-called pouch can be used in this invention.

More specifically, a bag-like container or pouch prepared by piling laminate materials composed of a heat sealable resin film as the inner layer and a metal foil such as aluminum foil or a layer of a heat resistant resin, e.g., polyethylene terephthalate as the outer layer, or laminate materials composed of a heat sealable resin film as the inner layer, an intermediate layer of a metal foil or a heat resistant resin and an outer layer of a heat resistant layer, and heat sealing the peripheral portion of the resulting laminate structure, can be used as a flexible container in this invention.

For a better understanding of the invention, reference is made to the accompanying drawing, in which:

FIG. 1 is a sectional view illustrating diagrammatically a packaging container in the pouch form to be used in this invention; and

FIG. 2 is a sectional view illustrating diagrammatically a flanged flexible container to be used in this invention.

As is illustrated in FIG. I, in the case of a bag-like container or pouch, flexible laminate sheet materials 4 and 4', each consisting of an inner layer 1 composed of a heat scalable resin such as a polyamide film, an inner layer 2 composed of a metal foil such as an aluminum foil and an outer layer 3 composed of a heat resistant resin such as a polyester film, are piled so that heat scalable resin layers confront and an area 6 to be heat sealed is formed around a space 5 for containing an article therein. The resulting bag-like structure can be used as a packaging container. One flexible sheet can be used instead of two sheets 4 and 4' to be heat sealed at the peripheral portions. Namely, a bag-like container formed by bending one flexible sheet and heat sealing the bent sheet at three open side portions can be used as a container. in the case of such bag-like container or pouch, provision of the intermediate layer composed of a metal foil can be omitted if not required. It is also possible to employ a laminate structure of four or more layers. For instance, a laminate structure comprising a heat resistant layer as another intermediate layer in addition to the metal foil layer.

A container including a container proper having a space for containing an article therein and a flange portion and a lid can be used as a flexible container (sometimes called semi-rigid container"). This container is so constructed that heat scaling is performed between the flange portion of the container proper and the lid. A container of an optional form having a space for containing a food therein is used as the container proper. For instance, there can be employed a sucer or plate such as a dish, a roasting platter, a cake tray and the like, a pan or pot such as a frying pan, a saucepan, a cooking pot, a sukiyaki pan, a stew pan and the like, a cup a lunchbox, etc. The size and configuration of the lid are determined depending on the size, configuration and structure of the container proper, so that it can seal completely an open portion of the container proper together with the flange portion of the container proper. The container proper is shaped to have a desirable form by molding a metal foil by pressing or other molding methods, and it has a heat scalable resin film on the entire inner surface thereof or only on the flange portion to be heat sealed with the lid. As the lid constituting material, there is employed a material having no substantial gas permeability, such as a metal foil and a laminate of a metal foil and a resin film.

An instance of such semi-rigid container is illustrated in FIG. 2. A container proper 11 is composed of a metal foil 12. and it is shaped by press molding so that it has a space 13 for containing food therein and a flange portion 14 disposed around the periphery of the space 13. A heat sealable resin film 15 is formed on the inside of the flange portion 14. A lid member 16 com prises a metal foil 17 and a heat sealable resin film 18 formed on the inner face of the metal foil 17. When the flange portion [4 and lid 16 are pressed under heating, a hermetic sealing is formed between them.

In each of the foregoing containers, when two flexible sheet materials are piled and a heat sealed area is formed around the periphery of a food-containing space by bonding these two flexible sheet materials Jack, 11.9w m 1....a. i...

polydodecamethylene sebacamide. polydodecamethylene dodecamide. polydodecamethylene tridecamide, polytridecamethylene adipamide, polytridecamethylene sebacamide. polytridecamethylene dodecamide. polytridecamethylene tridecamide, polyhexamethylene azelamide, polydecamethylene azelamide, polydodecamethylene azelamide. polytridecamethylene azelamide. and interpolyamides thereof.

As the polyester having a relatively low melting point. there are used homopolyesters and copolyesters having a melting or softening point not exceeding 250C. such as polytetramethylene terephthalate. polytetramethylene terephthalate/isophthalate. polyethylene terephthalate/isophthalate.

Instead of the foregoing polyesters, there can be used polyesters having a structure expressed by the following formula with a heat sealble resin. it is possible to obtain a sealed interface which can resist fully the heating sterilization conducted at a temperature exceeding 130C. In case a heat sealable resin layer is formed on the entire inner face of the sheet material. this resin layer acts also as a protective coating layer preventing the content from having a direct contact with the metal foil.

Heat sealable resins heretofore used for formation of heat sealed structures in this field can also be used in this invention as the heat sealable resin for forming an inner face of an area to be heat sealed of a packaging container. It is desired that such heat sealable resin is softened or molten at a temperature not exceeding 250C. especially at a temperature approximating 200C. in view of the strength of the heat sealed area. it is preferred that the heat sealable resin to be used is crystalline.

In this invention it is desired to employ (l) polyamides. (2) polyesters ofa relatively low melting point and (3) polyolefins. which are selected from resins having a heat resistance characterized by a softening or melting point exceeding 130C.

As such polyamide there can be used polyamides or interpolyamides composed of recurring units expressed by the following formula As the polyolefin, there are employed homopolymers and copolymers of olefins expressed by the following formula CH=CH wherein R is an alkyl group of up to 4 carbon atoms. which have a melting point exceeding l30C'.

Specific examples of such polyolefin include isotactic polypropylene, crystalline ethylene-propylene copolymers, poly-4-methyl-pentene-1. etc. Of course, poly olefins to be used in this invention are not limited to homopolymers of olefins and copolymers of two or more olefins, and there can be used copolymers comprising such small amounts of other comonomer components as will not damage the heat resistance and properties inherent of polyolefms.

It is desired that the inner layer of such heat sealable resin has a thickness of 0.005 to 0.2 mm (5 to 200 t). In case the thickness of the heat sealable resin layer is smaller than 0.005 mm, it is sometimes difficult to ensure hermetic sealing in the packaged article. In case the thickness of the heat sealable resin layer is greater than 0.2 mm, it is difficult to conduct the heat sealing step at a high speed.

As the heat resistant resin constituting the outer surface layer of the flexible container, there are employed resins having a softening point or decomposition point higher than that of the heat sealable resin used. In general, resins having a melting point exceeding C, such as polyamides. polyesters, polycarbonates and polypropylene, and thermosetting coating films are employed. Suitable resins are selected so that the foregoing requirements are satisfied.

Several examples of the heat resistant resin to be used in this invention are now mentioned.

1. Polyamides having a relatively high softening point. which are selected from polyamides exemplified above with respect to the heat sealable resin. it is preferred that these polyamides are used in the form of stretched and oriented films.

2. Polyesters having recurring units expressed by the following formula ll ll where in R is an alkylene or cycloalkylene group having 2 to 8 carbon atoms and R is an arylene group.

Specific examples of the polyester of this type are polyethylene sebacate, polyethylene terephthalate, polytetramethylene isophthalate, polyethylene terephthalate/isophthalate and poly-l ,4-cyclohexylene dimethylene terephthalate. It is preferred that these polyesters are used in the form of stretched and oriented films.

3. Polycarbonates having recurring units expressed by the following formula wherein R is a hydrocarbon group having 8 to carbon atoms.

Specific examples of the polycarbonate of this type are poly-p-xyleneglycol biscarbonate, poly-dihydroxydiphenyl-methane carbonate, poly-dihydroxydiphenyl-ethane carbonate, poly-dihydroxy-Z,2-propane carbonate and poly-dihydroxydiphenyl-l-ethane carbonate.

4. lsotactic polypropylene, especially in the form of a biaxially stretched film.

5. When a metal foil is used as an intermediate layer, a thermosetting coating film is sometimes employed. The thermosetting coating film (baked coating film) referred to herein includes films obtained by coating 21 lacquer containing a reactive macromolecular compound or an intermediate leading to a macromolecular compound, which can cause polymerization or condensation under heating to form a cross-linked structure in the molecule, uniformly on the surface ofa metal, and drying, baking and curing the coated lacquer at 140 to 230C. for 5 to minutes. If necessary, such lacquer may contain a curing promotor, a coloring agent, a pigment, a filler and the like. As the resin constititing such coating film, there can be mentioned, for instance, phenol-epoxy resins, phenol-melamine resins, urea-epoxy resins, melamine-epoxy resins, acrylic-epoxy resins, urea-epoxy resins, melamine-epoxy resins, acrylicepoxy resins, polyamide resins and polyimidazols resins.

In general, it is desired that such heat resistant resin layer has a thickness of 0.002 to 0.] mm (2 to I00 a). In case the thickness of the heat resistant resin layer is smaller than 0.002 mm. such undesired phenomena such as reduction of gas permeation resistance or reduction of strength and impact resistance of the laminate material are brought about at the step of heat sealing the laminate material. In case the thickness of the heat resistant resin layer is greater than 0.l mm, flexibility is lost in the laminate material.

When an intermediate layer of a metal foil is provided in a flexible container or simi-rigid (formretaining) container, as the metal foil there are used a steel foil, an aluminum foil, a steel foil plated with such a metal as tin, chromium and aluminum, and a steel foil chemically treated with chromic acid. phosphoric acid or the like or an electrolytically treated steel foil.

As pointed above, the container to be used in this invention should have not only heat resistance but also flexibility. Therefore, the thickness of the metal foil to be used as the intermediate layer should naturally be limited. This upper limit of the thickness varies depending on the kind of the foil-constituting metal and the size and shape of the container. lt is especially preferred that in the case of a bag-like container or pouch, the thickness of the intermediate layer is 0.005 to 0.1 mm (5 to p.) in the case of an aluminum foil, and 0.005 to 0.05 mm (5 to 50 p.) in the case ofa steel foil, and that in the case of a semi-rigid, form-retaining container the thickness of the intermediate layer is 0.05 to 0.15 mm (50 to I50 p.) in the case of an aluminum foil and 0.025 to 0.] mm (25 to 100 a).

Bonding of the metal foil to the heat scalable resin or heat resistant resin can be performed with use of known adhesives such as an epoxy adhesive and an iso cyanate adhesive. Further, the bonding may be performed according to the so-called extrusiion coating method without use of an adhesive.

According to this invention, by employing such flexible container, it is made possible to maintain the coefficient (K!) of flatness at a level not exceeding 0.25 in the packaged article formed by filling ann article into such container and hermetically sealing the container. Further, when such flexible container is employed. at the time of in-package (post-packaging) high-temperature short-time sterilization, the packaged article can be heat sealed without formation of an interfacial barrier by non-condensable gases left in the container, such as residual air. Accordingly, uniform and complete sterilization effect can be attained in the packaged article by conducting heat sterilization only for a short time.

FILING OF CONTENT AND DEGASlFlCATlON According to this invention, an article to be sterilized is filled in the above-mentioned flexible container and non-condensable gases left in voids of the flexible container are excluded. Filling of the content and exclusion of non-condensable gases may be conducted in this order or simultaneously. In some cases, exclusion of noncondensable gases is carried out prior to filling of the content. In this invention, in connection with the feature that a flexible container is employed, non condensable gases are excluded from the container, which makes it possible to maintain the coefficient (K of flatness to a level not exceeding 0.25 and to prevent formation of an interfacial barrier. Furthermore, if non-condensable gases are present in the hermetically sealed container, the following defects and disadvantages are brought about.

a. When amounts of non-condensable gases differ in packaged articles, there are formed excessively heated products and insufficiently sterilized products. There fore, it is impossible to obtain final products uniform in quality.

b. Vitamins, colorants, fat and oil, flavor constituents and the like contained in a packaged food are oxidized by oxygen remaining in the sealed container, with the result that quality of the food is degraded and appearance is worsened by browning or the like.

c. When the packaged article is heated before drinking or eating, breakage of the container is sometimes caused to occur.

In this invention, since non-condensable gases are excluded. occurrence of such undesired phenomena is effectively prevented.

As the article to be sterilized according to the inpackage high-temperature short-time sterilization process of this invention, there can be mentioned a variety of cooked and semi-cooked foods which are subjected to retort sterilization prior to preservation. Foods in which such undesired phenomena as browning, decrease or loss of natural colors, loss of flavor constituents, deterioration of the texture, thermal denaturation of proteins and change of the water-holding capacity are readily brought about when they are heated for a long time, are especially preferably treated according to the process of this invention.

As foods in which browning or change of the flavor is readily caused, there can be mentioned, for instance, milk products such as fresh cream, evaporated milk and condensed milk, soups and desserts containing such dairy products, e.g., pudding. As foods in which change of the color is readily caused, there can be mentioned, for instance, boiled crustaceans, boiled green vegetables and cooked foods containing boiled crustaneans or green vegetables. As foods in which the texture is readily changed, there can be mentioned, for instance, pasty marine products such as boiled fishpastes, fish fillets, processed meat products such as ham, beaf steak, roast beef, port saute and hamburger, chicken or egg processed foods such as roast chicken, fried egg and ham egg, meat-like vegetable products (artificial meats, and processed and pre-cooked products of petroleum proteins). These food products can be effectively sterilized according to the process of this invention.

Furthermore, cooked foods containing the foregoing food products as additive components can be sterilized according to the process of this invention. As such cooked food. there can be mentioned, for example, stews such as cooked curry, cooked hash, borsch and beef stew, gravys such as meat sauce, and boiled and cooked vegetables, fishes, shellfishes and meats such as vinegared port, sukiyaki, Chinese kedgeree, Chinese kickshaw, cream-boiled chiken and cream-boiled tuna.

A packaged article formed by filling such food as mentioned above into the flexible container is subjected to degasiflcation according to optional means to thereby exclude non-condensable gases from the interior of the container. Degasification can be accomplished, for instance, by the following methods.

a. A method comprising reducing the pressure in the interior of the packaged article to a level lower by at least 70 cmHg (gauge) than the atmospheric pressure, to thereby exclude non-condensable gases, e.g., air.

b. A method comprising substituting non condensable gases, e.g., air, present in voids in the interior of the container by a condensable gas such as steam, to thereby accomplish removal of noncondensable gases.

For instance, when a food containing a large quantity of water, which is in the boiled or almost boiled state, is filled under heating, air contained in the interior of the container is readily substituted by stream.

Further, air present in the interior of the container can be substituted by steam by heating a food-filled container(exhausting).

Still further, when steam projected into a food-filled container, air present in the interior voids can be readily replaced by steam (steam flashing).

c. A method comprising applying a pressure from the outside to a food-filled flexible container to thereby deform the container and exclude non-condensable gases from the container.

d. A method in which non-condensable gases are removed by a combination of two or more of the foregoing techniques (a) to (c).

SEALING According to this invention, heat sealing is performed by applying heat sealing temperature and pressure necessary for melting and bonding the heat sealable resin film to an area to be heat sealed of the flexible container in which the content has been filled and from which non-condensable gases have been excluded. The heat sealing temperature and pressure to be applied vary greatly depending on the kind of the heat sealable resin of the flexible container, and it is impossible to define such temperature and pressure conditions sweepingly. in general, however, sufficient results can be obtained by conducting the heat sealing at a temperature higher than the softening or melting point of the heat scalable resin and under a pressure not causing substantial flow of the heat sealable resin at the temperature adopted for the heat sealing.

Suitable heat sealing temperatures and pressures are as shown in Table 1 given below.

Table l Seal Bar Seal Bar Heat Scalable Resin Pressure Temperature (Kg/cm) Polypropylene 2 5 I 280 Nylon-l2 2 7 200 300 Polytetramethylene 2 7 220 320 Terephthalate The time required for heat sealing varies depending on the kind of the container and the thickness of the heat scalable resin layer. In general, the heat sealing is conducted for a time sufficient to perform melting and bonding of the heat scalable resin, for instance, 0.] to 5 seconds.

The heat sealing operation can be carried out at one stage or at two or more stages. In the latter case, the same or different temperature and pressure conditions can be adopted at these stages.

The so formed sealed area is then cooled, if necessary, under application of a pressure by optional means, to thereby form a sealed area with good sealing credibility. For instance, immediately after completion of the heat sealing operation, the heat sealed area in which the resin is still in the softened or molten state is pressed by two positively cooled press bars, whereby the resin is solidified.

A heat sealing process especially suitable for practising this invention is described in the specification of our copending application Ser. No. 354,l2l.

In this invention, it is important that the flexible container is so selected and steps of content-filling. degasification and heat sealing are so conducted that the coefficient (Kn of flatness is maintained at a level not exceeding 0.25, preferably not exceeding 0.15, in the sealed packaged article. The criticality of this condition will now be described by reference to experimental results.

In the in-package heat sterilization, it is indispensable that the central portion of the sealed package should receive a heat history sufficient to annihilate spores of microorganisms with which the article to be sterilized is contaminated. Since heat is transferred from the outer wall of the container to the central portion of the package through the article to be sterilized, a temperature gradient should naturally formed in the container in correspondence to the distance from the wall surface of the container. As the sterilization temperature is high and as the heat conductivity of the article to be sterilized is small, this temperature gradient is great, and the temperature difference becomes greater as the distance between the container wall and the central portion is greater.

From results of experiments detailed hereinafter, we found that the in-package (post-packaging) hightemperature shot-time sterilization can be applied effectively while controlling the thermal deterioration of the content, only when the distance between the wall surface of the container and the central portion of the package does not exceed a certain limit. More specifically, it was found that only when the coefficient of flatness defined by the following formula I Ky in which I indicates a maximum thickness (cm) in the sealed packaged article, L designates a maximum distance (cm) across the surface of the container, K stands for a coefficient of flatness, does not exceed 0.25, intended effects can be obtained by the inpackage high-temperature short-time sterilization, and that if this value exceeds 0.25, the effects attained by conducting the high temperature short time sterilization are rather inferior to those attained by ordinary heat sterilization.

EXPERIMENT Commercially available starch powder (rice starch was sufficiently kneaded with a l 1 mixture of an aqueous solution containing l/50 mole per liter of glycine and an aqueous solution containing 1/50 mole per liter of glucose, to thereby form a relatively hard paste having a water content of about 35 to about 40%. Then, this paste was shaped into a plane plate, from which square samples having a thickness of l cm, 2 cm,

3 cm or 4 cm were prepared. The sample was filled in a flexible pouch (having a size of X 200 mm) formed by piling two laminate films, each of which was prepared by bonding an outer layer of polyethylene terephthalate (having a thickness of l2 t), an aluminum foil intermediate layer (having a thickness of9 u) and nylon-12 film inner layer (having a thickness of 40 p.) with use of an isocyanate type adhesive, so that the inner nylone-l2 films confronted each other, and heat sealing three sides of the piled laminate structure while leaving the remaining one side open.

In the physical central portion of the sample paste filled in the pouch there was positioned a thermocouple for determination of the sterilization value (F0 value) included in a measurement assembly attached to the side wall of the pouch. Then, the pouch was subjected to degasification and hermetic sealing under a pressure lower by 72 cmHg than the atmospheric pressure by means of a vacuum sealer.

The resulting packaged article was put into a retort (autoclave) and terminals of the thermocouple were connected to a sterilization value integrator (Fo value computor of model ZQCTF manufactured by Erab Compnay, Denmark). Then, high temperature steam and compressed air were introduced into the retort, and the temperature of the retort was elevated to l50C. over a period of 2 minutes. The heating was continued until the F0 value integrator indicated the value of 5.0, and immediately thereafter, the cooling operation was carried out. The foregoing operations were conducted with respect to each of the foregoing samples. In the case of packaged articles shown in Table 2 given below, the time required for the above heating treatment was within a range of from 3 to 20 minutes.

After the cooling operation, the package was opened, the spectral reflectance at each portion of the sample was determined at a wavelength of 450 mu by means of a spectrophotometer (model BPS-3T manufactured by Hitachi Electronics, Japan) by employing a standard plate of magnesium oxide as a control, and the difference of browning among the determined portions was examined.

The same test was conducted with respect to samples sterilized at l 15C. According to an ordinary heat sterilization method.

Results of the foregoing tests as well as data of the coefficient of flatness are shown in Table 2.

The sterilization value used herein is expressed in terms of the heating time (minutes) necessary for annihilating a certain concentration of bacterial spores. When this value is indicated as F or F0 value, it means that the value is one obtained when the heating was conducted at l2lC. (250F.).

TABLE 2 Relation Between Coefficient of Flatness of Sealed Packaged Article and Effects Attained by High-Temperature Short-Time Sterilization Coefficient Size of Packaged Article Degree of Browning logT, 450 m of Flatness (thickness X width X length) l/L) (cm) Process of This Invention Conventional Process Surface Central Difference Surface Central Difference Portion Portion Portion Portion 0.05 l X 10 X l8 0.0159 0.0092 0.0067 00742 0.0325 0.0417 0.l5 2 X 10 X 9 0.0410 0.0l46 0.0264 0.l I29 0.0467 0.0662 0.25 3 X 10 X 6 0.1493 0.0306 0.l I87 0.1302 0.050l 0.080l 0.36 4 X 10 X 4.5 0.2518 0.0550 0.l968 0.1844 0.0595 01249 Notes:

sterilized at C.

'sterili7ed at l 15C.

From the results shown in Table 2, it is seen that conspicuous effects are attained by the high-temperature short-time sterilization only when the coefficient of flatness is 0.15 or lower, and that when the coefficient of flatness of 0.25 or higher, better effects can be obtained by ordinary heat sterilization.

In the foregoing tests, the dgree of browning at the central portion of the packaged article was a little higher with increase of the coefficient of flatness and this fact is not in conformity with the concept that the same heat history should result in the same sterilization value. However, this is due to the fact that since the sterilization was conducted batchwise, the cooling rate could not be kept constant.

In view of the results obtained in the above experiment, it will readily be understood that in this invention it is specified that the coefficient of flatness is main tained at a level not exceeding 0.25, preferably not exceeding 0. l 5, in the contentfilled flexible container to be used in this invention.

In this invention, by employing a container having such heat resistance and flexibility and giving a packaged article having a coefficient of flatness not exceeding the specific limit and by conducting degasification under such conditions as giving such specific coefficient of flatness, it is made possible to apply the hightemperature short-time sterilization technique effectively, with the result that complete sterilization of a packaged article can be accomplished very effectively.

HIGH-TEMPERATURE SHORT-TIME STERILIZATION According to this invention, the above-mentioned sealed packaged article is maintained in a heating medium of a temperature of at least l30C, especially within a range of from 130 to 160C, for a short time, for instance. 0.5 to 15 minutes, especially 1 to 8 minutes, to thereby sterilize the filled food. Thus, the content food can be sterilized with good reliability without undesired thermal deterioration of the food quality.

In this invention, the foregoing high-temperature short-time sterilization is accomplished by the following procedures.

a. Sterilizer:

A heating pressure vessel called a retort (autoclave) is used for the sterilization, a batchprocess is adopted, and a so called sterilizing shelf on which packaged articles are arranged in a certain order is employed. As the sterilizer for use in the continuous sterilization, there can be mentioned, for instance, a continuous retort equipped with a hydro seal valve or a continuous retort equipped with a rottay pressure valve. In this invention, the kind of the sterilizer to be used is not particularly critical, and any of sterilizers that can provide the following temperature-elevating rate, sterilization temperature, sterilization pressure and cooling rate can be used in this invention.

b. Heating Medium:

Saturated steam, superheated steam, high temperature high pressure hot water and the like are used as the heating medium. In view of prevention of breakage of the flexible container, it is preferred that a heating medium comprising saturated steam and 10 to 30 /r of compressed air is employed. In this invention, it is unnecessary to be the temperature of the heating medium to a level same as the final sterilization temperature. and therefore. it is possible to employ saturated steam in the non-supercompressed state.

c. Sterilization Temperature:

Effects by the hightemperature short-time sterilization can be obtained when the high-temperature shorttime sterilization is conducted at temperatures ranging from l25 to 200C. However, temperatures within a range of from l30to 160C are preferably employed because (I complete sterilization can be attained while maintaining the thermal deterioration of the quality of the article to be sterilized at a minimum level, (2) uniform heat history can be obtained in lots of packaged articles and (3) the sterilization procedure can be performed most efficiently.

when the sterilization temperature is lower than 130C, the effects attained by the high-temperature short-time sterilization are not substantially different from those attained by the conventional sterilization conducted at a temperature of up to 121C. In case the sterilization temperature exceeds [60C, control of the sterilization time is very difficult, and a very small variation of the sterilization time (I to 10 seconds) results in a great change of the sterilization value (F0 value), with the result that it is difficult to obtain sterilized packaged articles uniform in the quality.

d. Preheating of Packaged Article:

In order to obtain uniform high-temperature shorttime sterilization history in sealed packaged articles, it is indispensable that the temperature difference among packaged articles forwarded to the sterilization step should be within a range oft l0C, preferably t 5C.

Further, in order to obtain sufficient effects by the high-temperature short-time sterilization, it is desired that the initial temperature is maintained above 40C., especially to l00C., in packaged articles forwarded to the sterilization step. Since the packaged article maintained at about lO0C under atmospheric pressure, it sometimes happens that the package is broken by the steam pressure generated in the packaged article. Therefore, it is especially preferred that the sealed packaged article to be sterilized is preheated at a temperature ranging from to 98C Of course, when the above-mentioned hot filling method or exhausting degasification method is adopted for exclusion of non-condensable gases, such pre-heating can be omitted. The degree of degradation of the quality of a packaged content such as a food brought about by such pre-heating conducted within the above temperature range is extremely low as far as the pre-heating is not conducted for too long a time, though the influence of the treating time in the high-temperature short-time sterilization and the heating time on the difference of the heat history among portions of the packaged article is very great. When the packaged article is pre-heated within the above temperature range, the sterilization temperature can be correspondingly shortened. For instance, when the sterilization is conducted at l50C., the sterilization time can be saved by about 70% by such preheating, as compared with the case where no pre-heating is conducted.

e. Temperature-Elevating Rate at Sterilization Step:

In the process of this invention, unlike the conventional sterilization process, it is indispensable that the time from the point of charging of a package article into the sterilizer to the point of elevation of the sterilizer temperature to be prescribed high temperature for sterilization should be as short as possible, preferably within 180 seconds, especially within to 30 seconds, if the sterilization temperature is 130 to 160C, which was confirmed from results of experiments made by us. More specifically, in this invention, even a batchwise retort can be used as far as the time required for the above temperature elevation is within 180 seconds, but in general, there is preferably employed a method in which packaged articles are directly introduced into high temperature atmosphere maintained at 130 to 160C. through a pressure-tight valve.

f. Sterilization Pressure and Cooling Pressure:

The flexible container of the sealed packaged article is not broken at the sterilization step as far as the foregoing conditions are satisfied. However, at the cooling step, breakage of the flexible container is sometimes caused to occur by the difference between the temperature in the container and the ambient temperature. In order to prevent such breakage of the flexible eontainer, it is necessary to apply a pressure higher by 0.1 to l Kg/cm than the saturated vapor pressure at the high temperature adopted at the high-temperature short-time sterilization by employing air or other noncondensable gas. A preferred pressure applied at the sterilization step is within a range of to Kg/cm if the sterilization is conducted at a temperature of 130 to 160C.

g. Cooling Rate:

The total heat history given to the packaged article is more influenced by the cooling rate than the temperature elevating rate at the sterilizing step. Accordingly, it is indispensable that when the temperature is lowered from the high temperature sterilization range to the ordinary sterilization range (l 10 to 121C), the cooling is accomplished within 120 seconds, preferably within 60 seconds, and that when the temperature is lowered from the high temperature sterilization range from the range approximating 100C, the cooling is accomplished within 250 seconds, preferably within 200 seconds. Such cooling is performed preferably by introducing the packaged article present in the hightemperature short-time sterilization atmosphere directly into cooling water through a pressure-tight valve.

As described above, in this invention the sterilization of the packaged article can be efficiently accomplished by maintaining the packaged article in an atmosphere of a heating medium of a temperature exceeding 130C. for a short time and then cooling the packaged article under application of a pressure.

UTILITY 1n the sterilized packaged article obtained according to this invention, each of 1 browning due to Mailard reaction of sugar-amino acid by high temperature heating, (2) loss and decrease of natural colors such as earotenoid and chlorophyl, (3) loss of flavor constituents by heating and (4) texture deterioration, thermal denaturation of proteins and change of the water holding capacity can be maintained at a much lower level than packaged articles sterilized by the conventional heat sterilization process (conducted at a temperature of up to 121C. Further, the packaged article obtained according to this invention is completely sterilized. and therefore, it can be preserved for a very long time at the room temperature.

Accordingly, foods, which have heretofore been formed into sterilized packaged articles obtained by the conventional retort sterilization process (conducted at a temperature of up to 121C.) or the out-package (pre-packing) high-temperature short-time sterilization process (aseptic packing process, can be effectively formed into sterilized packaged articles while maintaining the food quality at such a high level as not at all attainable by such conventional processes. Further, foods which are so sensitive to heat that they cannot be formed into sterilized packaged articles by such conventional processes can be conveniently formed into completely sterilized packaged articles without substantial degradation of the food quality.

Still in addition, according to this invention, articles which are difficult to apply to the conventional outpackage high-temperature short-time sterilization process, can be subjected to the high-temperature shorttime sterilization treatment in the stage packaged in a flexible container without substantial degradation of the food quality of the packaged article with the result that sterilized packaged articles, especially sterilized packaged foods, having a high preservability can be obtained. Accordingly, this invention makes great contribution to the art.

This invention will now be detailed by reference to Examples.

EXAMPLE 1 In this Example, a bentonite-water mixture was chosen as a model food and the relation between the sterilization temperature and the degree of browning due to Maillard reaction of sugar-amino acid as a criterion for determination of the quality retention.

A phosphate buffer solution containing 1/20 mole per liter of glycine and 1/20 mole per liter of glucose was added to bentonite of the chemical grade (manufactured by Kugita Chemicals, Japan) so that the bentonite concentration was 7% by weight, and the mixture was kneaded and allowed to stand still overnight to obtain a soup-like mixture. 180 g of this soup-like mixture was filled in a flexible container (size of X mm) formed by piling two laminate films, each being prepared by bonding an inner layer of unstretched polypropylene (having a thickness of 50 t), an intermediate resin layer of a polycapramide (Nylon 6,) having a thickness of 15 u), an intermediate layer of an aluminum foil (having a thickness of 7 u) and an outer layer of boaxially stretched polyethylene terephthalate (having a thickness of 12 a) with use of an isocyanate type adhesive, so that the polypropylene layers confronted each other, and heat sealing three sides of the resulting laminate structure while leaving the remaining one side open. Then, the container was degasified and sealed under a pressure lower by 74 cmHg than the atmospheric pressure by means of a vacuum sealer. The coefficient of flatness was below about 0.1 in the so obtained sealed packaged article.

The packaged article was pre-heated for 3 minutes in a hot water bath maintained at 95C., charged into a retort and subjected to the sterilization treatment under conditions indicated in Table 3.

At this sterilization step, the time required for the temperature elevation ws 120 to l80 seconds. Then, the sterilized packaged article was cooled below 90C. in 200 seconds. At each sterilization experiment the F value was within a range of from about 3.5 to about 4.5.

After the cooling treatment, the packaged article was opened, and the content was mixed with 100 ml of 90 ethanol. The mixture was homogenized, and a part of the homogenized mixture was passed through a filter. With respect to the filtrate, transmittance at 430 mp. was determined by means of a photoelectric spectrophotometer of model BPS-3T manufactured by Hitachi Electronics, Japan, and the obtained transmittance was expressed in terms of the absorbance so as to examine the degree of browning. Results are shown in Table 3.

Table 3 Comparison of Process of This invention and Conventional Process with Respect to Degree of Browning Sterilization Conditions Degree of Browning log T. 430 mm Temperature Time Pressure (C (min.) (Kg/cm gauge) Conventional Process 1 50 0.9 0.7077 120 22 1.5 0.43 l8 Process of This lnvention 130 8.4 2.5 0.2182 140 5.8 4.0 0.l68l 150 4.5 5.0 0.l6l2

EXAMPLE 2 g of milk concentrated to /5 of the original volume was hot filled at 85C., in a flexible pouch (having a size of 70 X 50 mm) formed by piling two laminate films, each being prepared by bonding an inner nylonl 2 layer (having a thickness of 40 pt), an intermediate aluminum foil layer (having a thickness of 9 a) and an outer layer of polyethylene terephthalate (having a thickness of 12 a), with use of an isocyanate type adhesive, so that the inner nylon-l2 layers confronted each other, and heat sealing three sides of the resulting laminate structure while leaving one side open. The coefficient of flatness was about 0.08 in the so obtained sealed packaged article. The sterilization was conducted according to the conventional process l 15C., [.2 Kg/cm gauge, minutes) and according to the process of this invention (l45C., 4.7 Kg/cm gauge, [.5 minutes), respectively. With respect to the flavor of the content taken out of the sterilized packaged article, the sensory test was conducted according to the comparison method with a panel of 25 men. As a result, a significant difference was observed at a significance level of l 7? and it was found that the sterilized packaged article according to the process of this invention was superior to the sterilized packaged article according to the conventional process with respect to either the taste or the color.

EXAMPLE 3 g of seasoned spitchcock was filled in a flexible pouch (having a size of l30 l70 mm) formed by piling two laminate films, each being prepared by bonding an inner layer of instretched polypropylene (having a thickness of 50 u). and intermediate layer of a biaxially stretched polypropylene film (having a thickness of 22 p.) and an aluminum foil (having a thickness of 9 p.) and an outer layer of a biaxially stretched polyethylene terephthalate film (having a thickness of 12 [.L) with use of an isocyanate type adhesive, so that the inner polypropylene layers confronted each other, and heat sealing three sides of the resulting laminate structure while leaving the remaining one side open. Then, the packaged article was degasified and heat sealed under a pressure lower by cmHg than the atmospheric pressure. The coefficient of flatness in the so obtained sealed packaged article was below 006 (maximum thickness being below l2 mm).

Then, the sealed packaged article was sterilized according to the method in which the sealed packaged article was introduced directly in a high temperature and high pressure chambef through a pressure-tight valve. ln this method, the come-up time (time required for temperature elevation) was 2 to 3 seconds. The cooling was similarly conducted according to the method in which the sterilized packaged article was directly from the high temperature and high pressure chamber into a, cooling atmosphere through a pressure-tight valve. The come-down time (time required for temperature reduction) was 20 to 30 seconds, and hence, the cooling was accomplished at a very high rate.

The sterilization was conducted under such conditions as giving the F0 value of about 3, 4 as measured by the same Fo value computor as described in the text of the specification at a Z value of 18F.

By the Z value is meant the change (F.) of the heating temperature corresponding to the change of the time for annihilation of bactrial spores by heating or the annihilation ratio to l/l0 or 10 times. In general, the Z value is defined to be a temperature (F.) required for the heating annihilation-time curve to cross one logarithmic cycle, and each bacterial spore has a specific inherent Z value.

The sterilization effects were evaluated by (l) the measurement of the texture by a texturometer (Zenken GTX-Z), which can physically express chewing movement in the mouth cavity, (2) the sensory test by a panel of 25 men and (3) the quantitative determination of Vitamin B (thiamine) according the the fluorescent thiochrome method. Results are shown in Tables 4 and 5.

Table 4 Texture Retention at High Temperature Short Time Sterilization of Seasoned spitchcock Sterilization Hardness Sensory Test Table 4-Contin ued Texture Retention at High Temperature Short Time Sterilization of Seasoned Spitchcock Vitamin Retention at High-Temperature Short- Time Sterilization of Seasoned Spitchcock EXAMPLE 3 120 g of beaf steak (medium treated) having a finished thickness of mm was filled in a flexible container (having a size of 1 10 X 160 mm) formed by piling two laminate films. each being prepared by bonding an inner layer of poly-w-aminododecanoic acid (nylon 12) (having a thickness of 40 t). an intermediate aluminum foil layer (having a thickness of 9 a) and an outer layer of biaxially stretched polyethylene terephthalate (having a thickness of 12 p.) with use of an isocyanate type adhesive. so that the inner nylon-12 layes confronted each other. and heat sealing three sides of the laminate structure while leaving the remaining one side open. The packaged article was degasified and sealed under a pressure lower by 74 cmHg than the atmospheric pressure by means of a vacuum sealer. The coefficient of flatness of the so obtained sealed packaged article was below 0.08.

According to the method described in Example 3, the sealed packaged article was subject to the hightemperature short-time sterilization under such conditions as giving the F0 value of about 3.5 at a Z value of 18F. The texture factor of the so sterilized beef steak was tested by means of the same texturometer as described in Example 3 and the sensory evaluation was conducted in the same manner as in Example 3, to thereby evaluate the effects by the high-temperature short-time sterilization. Results are shown in Table 6.

Table 6 Texture Retention at High Temperature Short Time Sterilization of Beef Steak 5.3 minutes Table o-Continued Texture Retention at High Temperature Short Time Sterilization of Beef Steak Sterilization Hardness Chewiness Gumminess Sensory Test Conditions (cm/v] (T. U.) (T.U.) (description) 135C. 13.4 11.2 10.4 fairly 6.2 minutes acceptable 130C. 13.8 1 1.0 10.1 acceptable 7.1 minutes C. 11.7 10.8 9.0 unacceptable 8.2 minutes 120C. 9.6 11.1% 7.4 no good 10.5 minutes 1 15C.. 8.4 6.6 6.0 no good 23.0 minutes EXAMPLE 5 Cream soup, potage soup and corn soup were prepared according to conventional procedures. With respect to each soup. 180 g of the sample was hot. packed at 85C. into a flexible container (having a size of X 170 mm) formed by piling two laminate films. each being prepared by bonding an inner layer of an unstretched polypropylene film (having a thickness of 40 1.1.). an intermediate layer of a biaxially stretched polycapramide (nylon-6) film (having a thickness of 15 u) and an aluminum foil (having a thickness of 9 p.) and an outer layer of a biaxially stretched polyethylene terephthalate film (having a thickness of 12 u) with use of an isocyanate type adhesive, so that the inner polypropylene film layers confronted each other, and heat sealing three sides of the resulting laminate structure while leaving the remaining one side open. Then. the package was sealed while excluding air contained in the voids in the upper portion of the interior of the container. The coefficient of flatness of the so obtained sealed packaged article was below 0.1.

The so obtained sealed packaged articles were subjected to the high-temperature short-time sterilization according to the same method as described in Example 3. The viscosity of the soup contained in the heat sterilized article was measured by means of Brookfield rotary viscometer, and the sensory test was conducted in the same manner as in Example 3. Results are shown in Table 7, from which it is apparent that the effect of preventing the change of the viscosity can be attained by the high-temperature short-time sterilization process according to this invention.

Table 7 Viscosity Retention at ln-Package High-Temperature Short- Time Sterilization of Soups (Vismetron VS-Al; shear rate=0.463 sec) Sterilization Viscosity. cps. Conditions cream soup potage soup corn soup unsterilized 14.8 (3) 161.0(3) 7.4 (3) 155C..5.1minutes 14.5(3) 16.2(3) 7.0(3) 150C. 5.8 minutes 14.8 (3) 15.8 (3) 7.2 (3) 145C. 6.3 minutes 15.0 (3) 15.9 (3) 7.0 (3) 140C. 7.0 minutes 17.9 (2) 18.8 (3) 8.8 (2) C. 8.0 minutes 17.3(2) 21.5(2) 9.8 (2) 130C. 9.4 minutes 17.7 (2) 20.7 (2) 8.5 (2) 125C. 11.8 minutes 20.2(1) 21.9(2) 11.0(1) 120C. 15.5 minutes 20.0 (1 24.2 I) 10.4 (1 115C.. 32.0 minutes 24.0 1) 24.0(1) 18.0111

Notes: Parenthesized values indicate results of the sensory test (3: good. 2: acceptable, 1: unacceptable).

EXAMPLE 6 140 g of 3 potato starch solution was hot packed at 87C into a flanged vessel (having a maximum size of 150 mm and a depth of 10 mm) obtained by press molding a laminate sheet comprising an inner layer of unstretched polypropylene (having a thickness of 50 a), an intermediate aluminum foil layer (having a thickness of 120 p.) and an outer layer of a baked coating of an epoxy-phenol resin (having a thickness of 3 u), the inner layer and intermediate layer being bonded to each other with use of an isocyanate type adhesive. Immediately, a lid composed of the same laminate sheet as mentioned above was fitted on the container so that the inner polypropylene layer of the lid confronted the inner polypropylene layer of the container, and the assembly was heat sealed. The coefficient of flatness of the so obtained sealed packaged article was below 0.07.

The so obtained sealed packaged article was subjected to the high-temperature shorttime sterilization according to the method described in Example 3 so as to control the F0 value to about 3.5 at a Z value of 18F. The viscosity of the content was determined by means of Brookfield rotary viscometer (Vismeteron model VS-Al) at a shear rate of 1.478 sec", to evaluate the effects by the high-temperature short-time sterilization. Results are shown in Table 8.

stretched polyethylene terephthalate film with use of an isocyanatc type adhesive, so that the inner polyestcr-ethcr layers confronted each other. and heat sealing three sides of the laminate structure while leaving the remaining one side open. Then. the container was degasified and sealed under a pressure lower by 73 cml-lg than the atmospheric pressure by means of a vacuum sealer. In each of the so obtained sealed packaged articles, the coefficient of flatness was below 0.05 (maximum thickness being below 6 mm).

Each sealed packaged article was subjected to the high'temperature short-time sterilization according to the method described in Example 3 under such conditions as giving the F0 value of from 3.3 to 3.5, and then it was cooled. With respect to each sterilized packaged article. the color (hue) was determined without opening of the package by employing a Hunter type photoelectric differential color meter (Color Machine of model CM- manufactured by Nippon Denshoku. .lapan) to evaluate the effects by the high-temperature short-time sterilization.

A white plate having an L value of 92.12, on a value of 0.17 and a b value of 4.62 was employed as a standard color platev Results are shown in Table 9. from which it is seen that a higher color retention effect can be attained by the high-temperature short-time sterilization process according to this invention than by the conventional sterilization process.

Table 9 Sterilization Conditions Natural Color Retention 1t ln-Package High-Temperature Short-Time Sterilization of Green Vegetables (Green Beanv Spanish Paprika 1nd Stone Leek) Hue (a/b) Green Bean Spanish Paprika Stone Leek Table 8 Viscosity Retention at High Temperature Short Time Sterilization of 3% Potato Starch Solution Sterilization Conditions Viscosity (cps) unsterilized 21.2 155C. 2.9 minutes 20.0 150C. 3.1 minutes 20.4 145C. 3.3 minutes 19.0 140C. 3.8 minutes 20.3 135C, 4.1 minutes 28.3 130C. 5.2 minutes 32.3 125"C 6.3 minutes 33.4 120C. 10.0 minutes 359 115C'., 21.7 minutes 374 EXAMPLE 7 What we claim is:

l. A process for the preparation of high-temperature short-time sterilized packaged articles which comprises the steps of providing a flexible container having a heat-scalable resin film at least on an area to be heat sealed of the inner surface thereof with the heat sealable resin being a crystalline thermoplastic resin having a softening or melting point of from to 250 C., filling an article to be sterilized in the flexible container, removing non-condensable gases present in interior voids of the flexible container, hermetically sealing the flexible container by application of heat in such a manner that the coefficient of flatness in the resulting sealed packaged article is maintained at a level not exceeding 025. said coefficient of flatness being defined by the following formula in which 1 indicates a maximum thickness (cm) in the sealed packaged article, L designates a maximum distance (cm) across the surface of the container, and K stands for the coefficient of flatness. maintaining the sealed packaged article for l to 8 minutes in a heating medium of a temperature of I30 to 160C. to thereby sterilize the article packaged in the container, and cooling the so heat-treated packaged article under a pressure higher than the saturated vapor pressure corresponding to the sterilization temperature.

2. A process according to claim 1 wherein when said flexible container is supplied it is assured that said flexible container has two inner surfaces confronting each other and is composed of one or two flexible sheets l0 with said container comprising a space for receiving the article to be sterilized between said two inner surfaces and an area to be heat sealed which is provided around the periphery of said space, and said inner surfaces having at least on said area a film of a heat sealable resin having a softening or melting point of 130 to 250C.

3. A process according to claim 1 wherein when said flexible container is supplied it is assured that said flexible container is a bag-like container formed by piling two flexible laminate sheets with each sheet including an inner layer of a heat sealable resin having a thickness of 5 to 200 u, an intermediate layer of a metal foil having a thickness of 5 to I00 p. and an outer layer of a heat resistant resin having a thickness of 2 to 100 u,

so that the heat sealable resin layers confront each other, and providing an area to be heat sealed around a space for receiving the article to be sterilized.

4. A process according to claim I wherein when said flexible container is supplied it is assured that said flexible container is a bag-like container formed by piling two flexible laminate sheets with each sheet including an inner layer of a heat scalable resin having 5 to 100 a, an intermediate layer of a heat resistant resin having a thickness of 5 to I00 1.1., a layer of a metal foil having a thickness of 2 to 100 p. and an outer layer of a heat 5. A process according to claim 1 wherein when said flexible container is supplied it is assured that said flexible container comprises a container proper which is formed by press forming a metal foil having a thickness of 25 to 150 p. and has a space for receiving the article to be sterilized and a flange portion, and a lid composed of a metal foil or a laminate of a metal foil and a resin film, a layer of a heat sealable resin being formed between said lid and said flange portion of the container proper.

6. A process according to claim 1 wherein it is assured that the heat sealable resin is poly-waminodecanoic acid.

7. A process according to claim 1 wherein it is assured that the heat sealable resin is polypropylene.

8. A process according to claim 1 wherein it is assured that the heat sealable resin is poly-4-methylpentene-l.

9. A process according to claim 1 wherein it is assured that the heat sealable resin is polytetramethylene 12. A process according to claim 1 wherein removal of noncondensable gases is accomplished by reducing the pressure in the interior of the container to a level lower by at least cmHg than the atmospheric pressure.

13. A process according to claim 1 wherein removal of non-condensable gases is accomplished by substituting non-condensable gases present in the interior voids of the container by steam.

14. A process according to claim 1 wherein removal of non-condensable gases is accomplished by applying a pressure from the outside to the article-filled flexible container to thereby change the shape of the container.

15. A process according to claim 1 wherein the hermetic sealing is accomplished by applying to the area to be heat sealed of the flexible container heat sealing temperature and pressure necessary for melt bonding the heat sealable resin film.

16. A process according to claim 1 wherein the coef ficient K,- of flatness of the sealed packaged article is maintained at a level not exceeding 0.l5.

17. A process according to claim 1 wherein the steril ization is accomplished by maintaining the sealed packaged article in a heating medium of a temperature of l30 to 160C. for l to 8 minutes under a pressure of L7 to 8 Kg/cm gauge.

18. A process according to claim I wherein the heating medium is selected from saturated steam and a mixture of saturated steam with 10 to 30 of compressed air.

19. A process according to claim 1 wherein the heating medium is compressed hot water maintained at a pressure of 1.7 to 8 Kg/cm gauge and a temperature of 130 to 160C.

20. A process according to claim 1 wherein the sealed packaged article is maintained at a temperature of to 98C. prior to the heat sterilization.

21. A process according to claim 1 wherein the heat sterilized sealed packaged article is cooled under a pressure higher by 0.1 to l Kg/cm than the saturated vapor pressure corresponding to the sterilization temperature.

22. A process according to claim 1 wherein the heat sterilized sealed packaged article is cooled by introducing it directly into cooling water from the heating me dium.

23. A process for the preparation of hightemperature short-time sterilized packaged articles which comprises the steps of providing a flexible container having a heatsealable resin film at least on an area to be heat sealed of the inner surface thereof with said heat sealable resin being a crystalline thermoplastic resin having a softening of melting point of from to 250C, filling an article to be sterilized in the flexible container, removing noncondensable gases present in interior voids of the flexible container, hermetically sealing the flexible container by application of heat in such a manner that the coefficient of flatness in the resulting sealed packaged article is maintained at a level not exceeding 0.25, said coefficient of flatness being defined by the following formula in which (indicates a maximum thickness (cm) in the sealed packaged article. I. designates a maximum distance (cm) across the surface of the container and K, stands for the coefficient of flatness, charging the sealed packaged article into a sterilizer, raising a temperature of a heating medium in said sterilizer to a sterilization temperature of l30 to l60C, within 180 seconds. maintaining the sealed packaged article for l to 8 minutes in said heating medium of said sterilization temperature to thereby sterilize the article packaged in the container, and cooling the so heattreated packaged article under a pressure higher than the saturated vapor pressure corresponding to the sterilization temperature.

24. A process for the preparation of hightemperature short-time sterilized packaged articles which comprises the steps of providing a flexible container having a heat'sealable resin film at least on an area to be heat sealed of the inner surface thereof with said heat sealable resin being a crystalline thermoplastic resin having a softening or melting point of from [30 to 250C, filling an article to be sterilized in the flexible container. removing non-condensable gases present in interior voids of the flexible container, hermetically sealing the flexible container by application of heat in such a manner that the coefficient of flatness 28 in the resulting sealed packaged article is maintained at a level not exceeding 0.25. said coefficient of flatness being defined by the following formula in which [indicates a maximum thickness (cm) in the sealed packaged article, L designates a maximum distance (cm) across the surface of the container and K stands for the coefficient of flatness, charging the sealed packaged article into a sterilizer in which a heating medium of a temperature of from l30 to C. is present, maintaining the sealed packaged article for l to 8 minutes in said heating medium to thereby sterilize the article packaged in the container. and cooling the so heat-treated packaged article under a pressure higher than the saturated vapor pressure corresponding to the sterilization temperature.

Claims

1. A process for the preparation of high-temperature short-time sterilized packaged articles which comprises the steps of providing a flexible container having a heat-sealable resin film at least on an area to be heat sealed of the inner surface thereof with the heat sealable resin being a crystalline thermoplastic resin having a softening or melting point of from 130* to 250* C., filling an article to be sterilized in the flexible container, removing non-condensable gases present in interior voids of the flexible container, hermetically sealing the flexible container by application of heat in such a manner that the coefficient of flatness in the resulting sealed packaged article is maintained at a level not exceeding 0.25, said coefficient of flatness being defined by the following formula

2. A process according to claim 1 wherein when said flexible container is supplied it is assured that said flexible container has two inner surfaces confronting each other and is composed of one or two flexible sheets with said container comprising a space for receiving the article to be sterilized between said two inner surfaces and an area to be heat sealed which is provided around the periphery of said space, and said inner surfaces having at least on said area a film of a heat sealable resin having a softening or melting point of 130* to 250*C.

3. A process according to claim 1 wherein when said flexible container is supplied it is assured that said flexible container is a bag-like container formed by piling two flexible laminate sheets with each sheet including an inner layer of a heat sealable resin having a thickness of 5 to 200 Mu , an intermediate layer of a metal foil having a thickness of 5 to 100 Mu and an outer layer of a heat resistant resin having a thickness of 2 to 100 Mu , so that the heat sealable resin layers confront each other, and providing an area to be heat sealed around a space for receiving the article to be sterilized.

4. A process according to claim 1 wherein when said flexible container is supplied it is assured that said flexible container is a bag-like container formed by piling two flexible laminate sheets with each sheet including an inner layer of a heat sealable resin having 5 to 100 Mu , an intermediate layer of a heat resistant resin having a thickness of 5 to 100 Mu , a layer of a metal foil having a thickness of 2 to 100 Mu and an outer layer of a heat resistant resin having a thickness of 2 to 100 Mu , so that the heat sealable resin layers confront each other, and providing an area to be heat sealed around the periphery of a space for receiving the article to be sterilized.

5. A process according to claim 1 wherein when said flexible container is supplied it is assured that said flexible container comprises a container proper which is formed by press forming a metal foil having a thickness of 25 to 150 Mu and has a space for receiving the article to be sterilized and a flange portion, and a lid compOsed of a metal foil or a laminate of a metal foil and a resin film, a layer of a heat sealable resin being formed between said lid and said flange portion of the container proper.

6. A process according to claim 1 wherein it is assured that the heat sealable resin is poly- omega -aminodecanoic acid.

8. A process according to claim 1 wherein it is assured that the heat sealable resin is poly-4-methylpentene-1.

9. A process according to claim 1 wherein it is assured that the heat sealable resin is polytetramethylene terephthalate including a polyalkylene ether structure in the molecular chain.

10. A process according to claim 1 wherein it is assured that the heat resistant resin is biaxially stretched polyethylene terephthalate.

11. A process according to claim 4 wherein it is assured that the intermediate layer-constituting heat resistant resin is biaxially stretched polycapramide.

12. A process according to claim 1 wherein removal of noncondensable gases is accomplished by reducing the pressure in the interior of the container to a level lower by at least 70 cmHg than the atmospheric pressure.

16. A process according to claim 1 wherein the coefficient KF of flatness of the sealed packaged article is maintained at a level not exceeding 0.15.

17. A process according to claim 1 wherein the sterilization is accomplished by maintaining the sealed packaged article in a heating medium of a temperature of 130* to 160*C. for 1 to 8 minutes under a pressure of 1.7 to 8 Kg/cm2 gauge.

18. A process according to claim 1 wherein the heating medium is selected from saturated steam and a mixture of saturated steam with 10 to 30 % of compressed air.

19. A process according to claim 1 wherein the heating medium is compressed hot water maintained at a pressure of 1.7 to 8 Kg/cm2 gauge and a temperature of 130* to 160*C.

20. A process according to claim 1 wherein the sealed packaged article is maintained at a temperature of 85* to 98*C. prior to the heat sterilization.

21. A process according to claim 1 wherein the heat sterilized sealed packaged article is cooled under a pressure higher by 0.1 to 1 Kg/cm2 than the saturated vapor pressure corresponding to the sterilization temperature.

22. A process according to claim 1 wherein the heat sterilized sealed packaged article is cooled by introducing it directly into cooling water from the heating medium.

23. A process for the preparation of high-temperature short-time sterilized packaged articles which comprises the steps of providing a flexible container having a heatsealable resin film at least on an area to be heat sealed of the inner surface thereof with said heat sealable resin being a crystalline thermoplastic resin having a softening of melting point of from 130* to 250*C., filling an article to be sterilized in the flexible container, removing noncondensable gases present in interior voids of the flexible container, hermetically sealing the flexible container by application of heat in such a manner that the coefficient of flatness in the resulting seaLed packaged article is maintained at a level not exceeding 0.25, said coefficient of flatness being defined by the following formula

24. A process for the preparation of high-temperature short-time sterilized packaged articles which comprises the steps of providing a flexible container having a heat-sealable resin film at least on an area to be heat sealed of the inner surface thereof with said heat sealable resin being a crystalline thermoplastic resin having a softening or melting point of from 130* to 250*C., filling an article to be sterilized in the flexible container, removing non-condensable gases present in interior voids of the flexible container, hermetically sealing the flexible container by application of heat in such a manner that the coefficient of flatness in the resulting sealed packaged article is maintained at a level not exceeding 0.25, said coefficient of flatness being defined by the following formula