EP0755190A1

EP0755190A1 - Method and apparatus for sterilization of seeds, herbs and spices

Info

Publication number: EP0755190A1
Application number: EP95944568A
Authority: EP
Inventors: Michael L. Siegmund; David V. Freeland; Gary B. Carman
Original assignee: Burns Philp Food Inc
Current assignee: Burns Philp Food Inc
Priority date: 1994-12-29
Filing date: 1995-12-29
Publication date: 1997-01-29
Also published as: CN1146137A; AU4691296A; BR9507120A; MX9603755A; WO1996020606A1; CA2184384A1; AR005165A1

Abstract

The present invention provides a method for sterilizing seeds, herbs and spices while minimizing the loss of volatile oils from the product. The seeds, herbs, and spices are fed from a hopper (116) to a sterilizer (112). Sterilization is carried out by quickly heating the surface of the seeds, herbs and spices with steam or other heating agent under greater than atmospheric pressure to reduce the microbial load substantially without volatilization of oils in the product. The product is then quickly cooled under greater than atmospheric pressure in a pressure vessel and cooling chamber (124). Carrying out the cooling under pressure reduces the volatile oil loss due to flashing and hence substantially retains the original aroma and flavor of the sterilized product. The cooled product may then be discharged from the cooling chamber (124) to a dryer (130).

Description

METHOD AND APPARATUS FOR STERILIZATION OF SEEDS, HERBS AND SPICES

BACKGROUND The present invention relates to a method and apparatus for sterilizing organic particulates. More particularly, the present invention relates to a method and apparatus for sterilizing seeds, herbs, spices and the like.

Sterilization treatments of seeds, herbs and spices ("SHS" or "organic particulates") as food products for consumer use must meet several conflicting requirements. For example, it is desirable to preserve the aroma, flavor and appearance of the sterilized product. Since the aroma and flavor are derived in large part from volatile oils contained within the SHS, it is desirable to minimize the loss of these volatile oils during processing. In addition, it is desirable to produce and maintain a reduced level of moisture in the sterilized product to ensure a sufficiently long shelf life. On the other hand, harmful bacteria and other microbes must be destroyed so that the food will be safe for human consumption. Another requirement is that the product be processed as efficiently as possible, i.e. continuous sterilization is preferred to batch processing.

Conventional sterilization methods rely on numerous well known mechanisms to achieve sterilization of SHS used in food products. In chemical sterilization methods, particulates are exposed to chemicals such as hydrogen peroxide or ethylene oxide to kill microbes. Disadvantages of such methods include undesirable changes in taste and chemical residues that may be harmful at some concentrations. Irradiation of food products has also been used for sterilization but is not a widely accepted method by the public.

Numerous sterilization methods rely on the application of heat to SHS to reduce the microbial load in the product. For example, it is known to heat SHS to high temperatures at superatmospheric pressures with steam (U.S. Patent No. 4,844,933). However, particularly for leafy herbs as opposed to seeds, prolonged exposure to high temperatures may cause the loss of desirable volatile oil components

("stripping"), as well as product degradation and discoloring. Furthermore, existing processing methods discharge the hot SHS directly from a high pressure sterilization step to an atmospheric or subatmospheric pressure cooling step. This rapid pressure change leads to further loss of volatile oils ("flashing") and therefore further reduces the volatile oil component in the sterilized product. Attempts have been made to minimize the loss of volatile oil components by capture and re- application of volatiles to the sterilized SHS (European patent application No. 0 556 101 Al ). However, this process has the drawback that volatile oils that are stripped and then reapplied to the surface of the SHS are less stable with respect to degradation and volatilization than those oils retained in their naturally occurring form. Consequently, SHS containing volatile oils that have been stripped and reapplied will have a shorter shelf life than SHS containing volatile oils in their original form.

Accordingly, there is a need for a sterilization process capable of continuously sterilizing seeds, herbs and spices while maintaining a desirable level of volatile oil content in the product, all without product degradation and discoloration.

SUMMARY The present invention fills these needs by providing a method and apparatus for rapidly and continuously sterilizing food products such as seeds, herbs and spices operating under unique processing conditions.

In one aspect, the present invention provides a continuous method for sterilizing organic particulates in which organic particulates are quickly passed through a steam atmosphere in a pressure vessel at superatmospheric pressure. The time taken for the organic particulates to pass through the pressure vessel will reduce the microbial load without either substantial volatilization of oils from within the particulates or substantial degradation of the organic particulates. The sterilized particulates are then quickly cooled while still under pressure to a temperature below the "flash point" of the volatile oils: that is, they are cooled to below the temperature at which the volatile oils will flash when the particulates are discharged. The product is then discharged for drying and further processing, if necessary.

In another aspect of the present invention, an apparatus capable of carrying out a continuous sterilization process includes a first pressure vessel having an inlet for organic particulates and an outlet for sterilized organic particulates, a means for heating the organic particulates within the vessel at a first pressure that is greater than atmospheric pressure, a second pressure vessel coupled to the outlet of the first vessel, and means for cooling the organic particulates within the second vessel while maintaining a superatmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood by reference to the appended figures wherein: Figure 1 is a block-type flow diagram setting forth a method of the present invention for sterilizing seeds, herbs and spices; and

Figure 2 is an apparatus according to the invention capable of performing the inventive method.

DETAILED DESCRIPTION The invention will now be described by reference to specific embodiments, keeping in mind that applicants' claims are not to be deemed limited to these particular embodiments. That is. those skilled in the art will quickly recognize that the process parameters and apparatus disclosed herein can be modified in many ways without departing from the fundamental principles of the invention, wherein volatile oils can be maintained within the SHS during sterilization. Thus, using the invention, a properly sterilized product is produced which nevertheless retains the natural flavors imparted to the product by the volatile oils contained therein. The need for chemical or radiative sterilization techniques are avoided, and no reapplication of collected volatiles is necessary.

It will be important that the terminology used in this patent be understood. In this regard, the term "organic particulates" or "SHS" will denote seeds, herbs, spices and other food products including, but not limited to, anise, caraway, cardamom, celery, dill, fennel, pepper, basil, parsley, oregano, dill, sage, cracked bay leaf, paprika and many others as are commonly processed in the spice and herb industry. More specifically, the term "particulates" is intended to encompass any of these plants and seeds in their as collected state where they are naturally found as small particles, as well as in their chopped, ground or crushed form.

The term "raw" is used to denote the state of organic particulates prior to sterilization according to the invention. Thus, for example, raw organic particulates used as feed to the present process may have previously undergone cleaning, chopping, sorting or other common processing steps prior to sterilization. The method of the present invention will now be generally described in connection with Figure 1. In this figure, the basic process steps of the invention are shown along with process parameters of the invention. The process is intended to be substantially continuous, whereby in step 1 , raw organic particulates are fed from a hopper 1 16 into a sterilizer 1 12. As will be discussed in greater detail with respect to Figure 2, the feed will necessarily pass through a pressure isolation device between the hopper 116 and sterilizer 112, such as a variable speed rotary valve capable of high differential pressure. Different feed rates will of course be necessary for different materials such as seeds versus powders. In step 2, the organic particulates are sterilized in sterilizer 1 12 by a means for heating. The means for heating is chosen to be capable of quickly heating the organic particulates to a high temperature at superatmospheric pressure. The means for heating may be steam, or other hot inert gases, such as air or nitrogen or mixtures thereof. In one embodiment, steam heat will be used. The steam may be saturated or superheated and will generally be limited to 285°F, thereby allowing product sterilization with minimal product degradation. Further, the drier the steam, the lower the microbial kill rate.

The sterilizer 1 12 may be a jacketed vessel in which the walls of the vessel can also be heated to thereby avoid condensation on the inside walls of the vessel.

The temperature, pressure, and dwell time in the sterilizer 112 are chosen to achieve sterilization of the organic particulates without significant volatile oil loss or product degradation. Exposure of the raw organic particulates to temperatures of about 215-285°F for less than one minute, e.g., 1-30 seconds, is suitable to achieve sterilization. In one embodiment, the necessary temperatures required are achieved by maintaining a pressure of about 20 psig in the sterilizer 1 12 (psig is the gauge pressure, i.e. the pressure measured in excess of atmospheric pressure). By minimizing the residence time in the sterilizer, the degree of volatilization of oils in the SHS is also minimized. Because of differences in the various organic particulates which may be processed, pressure within the sterilizer 1 12 may be controlled in a range between about 5 psig and about 40 psig while the temperature within the sterilizer 1 12 may be controlled in a range from about 215°F to about 285°F.

After sterilization, the SHS is transferred in step 3 to a separate pressure vessel 124 for cooling. The use of separate pressure vessels for the heating and cooling steps allows the process to be virtually continuous.

Under previous processing conditions (U.S. Patent No. 4,844,933 and European patent application No.O 556 101 Al), the hot sterilized organic particulates are transferred directly from the high pressure sterilizing unit to a cooling unit held at atmospheric or subatmospheric pressure. At the elevated temperatures necessary to achieve sterilization, this sudden pressure drop leads to flashing of the volatile oils contained in the organic particulates.

Without being bound by theory, we hypothesize that the organic particulates are less stable with respect to volatile oil flashing when they are hot because the membranes containing the volatile oils are stressed. When the hot organic particulates are subject to rapid pressure changes these membranes rupture, releasing the volatile oils and allowing their subsequent volatilization. The present invention overcomes this drawback by maintaining the organic particulates at a superatmospheric pressure during the cooling process. In this way, the hot product is not subject to the rapid pressure changes that lead to flashing of the volatile oils. In the present invention, the organic particulates are discharged for further processing only after they have been cooled. Therefore, only cooled SHS are subjected to rapid pressure changes and, since the cooled products are more stable with respect to volatile oil flashing, volatile oil loss is diminished.

The means for cooling is chosen to quickly cool the sterilized product at superatmospheric pressure. The means for cooling may be cooling gasses or fluids such as compressed air, gaseous nitrogen, compressed air/nitrogen mixtures, and liquid nitrogen.

The pressure during cooling may approximate that extant during the heating step or may be slightly less to facilitate passage of the sterilized organic particulates to the cooling vessel and to maintain temperature in the heating vessel. For example, when heating is carried out at about 20 psig, cooling may be carried out at about 18-19 psig.

After cooling, the sterilized product having desirable levels of volatile oils is recovered via passage of the SHS through a last pressure isolation device from the cooling chamber to the external environment that is at a given pressure. In one embodiment of the present invention the external environment is at atmospheric pressure. The moisture content of the finished sterilized particulates is desirably between about 5 to 10 wt%.

This moisture content may be achieved in step 4 in which the cooled product is discharged from the cooling chamber into a dryer 130. The dryer 130 uses mild drying conditions, thus drying the sterilized particulates to give the required moisture content without product degradation or volatile oil loss. The control of moisture levels in the product which can be achieved by the invention results in water activity levels below 0.58, i.e. the threshold at which growth of microorganisms will spontaneously occur. The process achieves a substantial reduction in "Standard Plate Count" ("SPC"), using standard tests for determining microbial load before and after the sterilization process. One form of the apparatus for carrying out a process according to the present invention will now be described in connection with Figure 2.

Generally, apparatus 10 includes a sealed, jacketed sterilization pressure vessel 12 having an inlet 14 for feeding raw organic particulates from hopper 16, and an outlet 18 for discharging sterilized organic particulates. The inlet 14 includes a pressure isolation valve 1 1 which is used to maintain a pressure difference between the feed hopper and the sterilizer. A conveyor such as a variable speed screw 13, is powered by a motor 20 and is positioned to transport the SHS along the length of the vessel 12 toward the outlet 18. Many other means for transporting the SHS within the vessel can be used, or the vessel may be rotated at an angle which moves the contents along the length thereof, or other conveyors. The means for transporting the SHS may also act to mix the SHS. Further, as is well known, it is possible to internally heat the screw or transport means to the same temperature as the walls of the vessel to thereby avoid condensation of moisture or volatiles thereon.

For heating, pressure vessel 12 includes an inlet 22 for directing a heating medium, such as steam, into the vessel for direct treatment of the SHS. The jacket of vessel 12 may also be heated either by steam or by an electrical coil. If necessary, an outlet (not shown) can be provided for draining condensate from the vessel.

As mentioned, in one embodiment the heating medium is super-heated or saturated steam under pressure conditions such that microbes in the organic particulates are reduced to acceptable levels without substantial loss of volatile oil. Generally, the residence time of the organic particulates in the heating region should be the minimum necessary to effect sterilization. For cooling, the particulates will pass out of vessel 12 through outlet 18, through pressure isolation valve 28, and through inlet 21 to a second pressure vessel 24. The organic particulates are then transported along the length of the vessel 24 towards an outlet 30 by a conveyor 25 powered by a motor 26. The means for transporting the organic particulates 25 may be the same as the conveyor 13 or may be different. This vessel will include an inlet 26 for introducing a cooling medium, such as air, nitrogen, or air/nitrogen mixtures, into the interior of the vessel 24, and may also include a cooling jacket/coil. As necessary, an appropriate outlet passage for used liquids and/or gasses will be included in the vessel.

To ensure continuous throughput of SHS, the dwell time in the cooler is equal to or less than the dwell time in the heater. Within this constraint, the dwell time in the cooler is chosen so that the sterilized organic particulates are cooled to a temperature at which the volatile oils in the product are stable with respect to the rapid pressure drop to atmospheric pressure experienced upon product discharge. The dwell time will depend on the product being sterilized and the cooling means employed. For example, using air, nitrogen, or air/nitrogen mixtures as the cooling means dwell times between 1 and 20 seconds are sufficient for cooling black pepper, cracked bay leaf, paprika, oregano, and basil. In one embodiment of the invention the dwell time in the cooling vessel is substantially equal to the dwell time in the heating vessel.

In both the heating and cooling vessels, the heating and cooling fluids will be food (culinary) grade.

Once the SHS is cooled to a temperature below that which will result in flashing of volatile oils at atmospheric pressure, the product is discharged through a last pressure isolation valve 29. The cooled product is then dried in dryer 31 , if necessary, and the dried sterilized product is then discharged for further processing and packaging.

We have performed testing on selected organic particulates under various process conditions and observed the superiority of the inventive pressure cooling process over the low pressure cooling process known in the prior art. Both processes result in a comparable increase in product moisture content and reduction in SPC. However, the volatile oil loss of the pressure cooled product is much less than the volatile oil loss of the low pressure cooled product. In fact, we have observed that SHS sterilized using the inventive pressure cooling method loses two to four times less volatile oils than SHS sterilized using the low pressure cooling method of the prior art.

Claims

We claim:

1. An apparatus for sterilizing organic particulates containing volatile oils, comprising: a first vessel having an inlet and an outlet; a first isolation valve coupled to the inlet of the first vessel; means for transporting the organic particulate from said first vessel inlet to said first vessel outlet in a first time period which is less than about 30 seconds; means for heating the organic particulate within the first vessel to a first temperature in the range of from about 215°F to about 285°F and at a first pressure in the range of from about 5 psig to about 40 psig; a second vessel having an inlet and an outlet; a valve coupling the outlet of the first vessel to the inlet of the second vessel; means for transporting the organic particulate from said second vessel inlet to said second vessel outlet; means for cooling the organic particulate within the second vessel at a second temperature and at a second pressure that is greater than atmospheric pressure; and a second isolation valve coupled to the outlet of the second vessel for discharging the sterilized, cooled organic particulate from the second vessel.

2. An apparatus for sterilizing organic particulate, comprising: a vessel having an inlet for organic particulate and an outlet for sterilized organic particulate; means for steam heating the organic particulate within the vessel at a first pressure that is greater than atmospheric pressure; and means for cooling the organic particulate within the vessel at a second pressure that is greater than atmospheric pressure.

3. The apparatus according to Claim 2, wherein the vessel further includes a first region for heating the organic particulate and a second region for cooling the organic particulate.

4. A method for sterilizing organic particulate containing volatile oils, comprising the steps of: a) introducing organic particulate into a vessel; b) heating the organic particulate in the vessel at a first pressure that is greater than atmospheric pressure; c) cooling the organic particulate in the vessel to a temperature below the flash point of the volatile oils at a second pressure that is greater than atmospheric pressure; and d) recovering the sterilized organic particulate from the vessel.

5. The method according to Claim 4, wherein the heating step and the cooling step are carried out in separate heating and cooling regions within the vessel.

6. The method according to Claim 5, wherein the second pressure is substantially equal to the first pressure.

7. The method according to Claim 5, wherein the second pressure is less than the first pressure.

8. The method according to Claim 4, wherein the first pressure is in the range of about from 5 psig to about 40 psig, and wherein the organic particulate is heated to a temperature in the range of from about 215°F to about 285°F.

9. The method according to Claim 8, wherein the second pressure is substantially equal to the first pressure.

10. The method according to Claim 4, wherein the organic particulate is heated for a heating time in the range of about 1 second to about 30 seconds.

1 1. The method according to Claim 10, wherein the organic particulate is cooled for a cooling time substantially equal to the heating time.

12. A method for sterilizing organic particulate containing volatile oils, comprising the steps of: a) introducing organic particulate into a heating vessel; b) heating the organic particulate in the heating vessel at a pressure of from about 5 psig to about 40 psig; c) transferring the organic particulate into a cooling vessel; d) cooling the organic particulate in the cooling vessel at a second pressure that is greater than atmospheric pressure and that is substantially equal to the pressure in the heating vessel; and e) discharging the sterilized organic particulate from the cooling vessel to a container when it has been cooled to a temperature that is below the flash point of volatile oils at the pressure of the container.

13. The method according to Claim 12, wherein the temperature in the heating vessel is in the range of from about 215°F to about 285^CF.

14. The method according to Claim 12, wherein the organic particulate is heated for a heating time in the range of from about 1 second to about 30 seconds.

15. The method according to Claim 14, wherein the organic particulate is cooled for a cooling time substantially equal to the heating time.