FR2716081A1 - Sterilisation of fruit juice - Google Patents

Abstract

Prodn. of storage-stable fruit juice comprises: (a) adding sufficient alcohol to inactivate bacteria; and (b) extracting the alcohol from the juice by dialysis against an alcohol-free aq. phase through a hydrophobic microporous membrane. Also claimed are: (i) fruit juice obtainable by the above process; and (ii) the dialysis unit for carrying out the above process which comprises a chamber (7) with one or more compartments (11) having an inlet (12) for the alcohol-contg. juice and an outlet (19) for the alcohol-free juice. The compartments are sepd. by a hydrophobic membrane in the form of tubes through which the juice is passed. .

Description

 The present invention relates to a process for preparing fruit juices capable of being preserved. It also relates to a device making it possible to implement said method and the long-life fruit juices, as they can be obtained by said method.

 The present invention also relates to a method for preserving fruit juices, aiming to considerably limit the presence of active germs, such as bacteria and more generally microorganisms.

 There are many methods of preparing long-life fruit juices. By the expression "fruit juice" is meant in the context of the present description the aqueous dispersions resulting from the grinding by any appropriate means of the material present inside the fruits.

 A list of the methods of preserving fruit juices is for example indicated in Encclopaedia Universalis, 1980 edition, volume l, pages 673-674, Encyclopaedia Universalis France edition.

 We can distinguish on the one hand the chemical processes and on the other hand the physical processes of preparation.

 Chemical processes consist in adding an additive with a specific action to the food. The disadvantage of these processes is their often difficult metabolic assimilation, and their use is more cn more regulated and restricted.

 Among the physical processes, a distinction is made between pasteurization, heat sterilization, cold storage or vacuum storage. and ionizing radiation.

 - Pasteurization consists of heating the juice for a few seconds to a few minutes to a temperature typically between ('(C and 95 "C. A large part of bacteria and microorganisms are thus destroyed, but there are still living germs, this which then requires permanent cold storage (typically about 4 (; pasteurization has the other disadvantage of degrading the organoleptic qullltvbs of the treated juices.

 - Sterilization by heat or appertization uses temperatures above 1 lOC, at times of the order of several di, ains of minutes and aims to obtain an almost total biological sterility. sl sterilization then allows a long conservation, it prtnte however two major drawbacks, namely a loss of 'food altur (vitamins, proteins, etc), and a very significant drop in organoleptic qualities.

 - Refrigeration, freezing and deep-freezing are commonly used processes. Storing food constantly in the cold, below 4 "C, and down to - 45 C for freezing, is however a heavy constraint.

 - Storage under vacuum is used to avoid the oxidizing action of the air which promotes the degradation of biological products. The main drawback of this process is that it has limited efficiency over time.

 - Ionizing radiation is a process that is still little used and limited to a limited number of foods, because their consequences on treated foods are still poorly understood.

 Also known from patent application EP-AO 539 ~ öO is a process for dehydration, at least partially, of an aqueous composition by means of a microporous hydrophobic membrane which separates said aqueous composition from a receptor phase, in particular liquid, comprising at least one solute, such as calcium chloride. The description of this document is incorporated by reference into the present description.

 The object of the invention is to overcome the drawbacks of the aforementioned hniqucs tee both in terms of the profitability of the process and in terms of the conservation and preservation properties of the organolcptic qualities of fruit juices.

 By the expression "fruit juice" is also meant citrus juices, citrus fruits including oranges, clementines, mandarins, lemons, pomelo and being de facto fruits in the strict sense. The term "fruit juice" also includes tomato juice.

 Consequently, an object of the present invention is to provide a process for preparing fruit juices capable of being stored at room temperature, said process allowing both an almost total destruction or inactivation of microorganisms, such as bat tt ' rlt '%, initially present, while preserving the organoleptic qualities and the nutritional value of said juices.

 The object of the invention is also to propose a process for the economical preparation of such juices, making its industrial use particularly attractive.

 Another object of the present invention is to provide fruit juices with long shelf life at room temperature which have organoleptic and food qualities substantially identical to those of freshly squeezed fruit juice, even after several weeks of storage.

 Finally, another object of the present invention is to propose a device making it possible to implement said method.

 Other advantages of the invention will appear during the description which follows.

The invention, firstly, relates to a process for preparing fruit juices suitable for being preserved, characterized in that it comprises the following steps
a) adding to a given volume of fruit juice a quantity
sufficient alcohol to substantially inactivate germs
bacterial,
b) extraction of the alcohol from the alcoholic fruit juice obtained in step
a) by bringing said juice into contact with a receiving phase
aqueous, substantially free from said alcohol, by
through a microporous hydrophobic membrane
for an appropriate period,
c) recovery of fruit juice substantially free of
active and dealcoholized germs.

 By the expression "capable of being preserved", it is meant that these fruit juices can be left at room temperature in closed packages according to the conditions commonly used for this type of preservation, for several weeks.

 By the term "dealcoholized" is meant that the fruit juice recovered contains an amount of alcohol of the order of magnitude of that naturally present in fruit juices.

 The starting fruit juices are generally freshly pressed and come from a fruit crushing or pressing unit, as is well known in the art considered.

 It is very clear that all the steps of the process according to the invention are carried out under sterile conditions required by the standards in force.

 In a known manner, therefore, these fruit juices have a solid content varying from 30 to 120 g per 1 liter of juice. These juices also include dissolved in the aqueous phase vitamins, organoleptic compounds and in general all the soluble compounds resulting from grinding.

 Alcohol is well known for inactivating germs that come into contact with it. Alcohol is preferably used pure so as not to add water or other substances which would modify the content and taste of fruit juice.

 By "alcohol" is meant any alcohol whose absorption in low doses by the human body does not present any toxicity problem. Therefore, preferably, ethyl alcohol will be used. This alcohol also has the advantage of being inexpensive. Finally, many fruit juices already contain in their natural state a low concentration of ethyl alcohol, and therefore the elimination of alcohol by means of the second phase of the process can possibly be stopped as soon as the alcohol concentration is back to the "natural" concentration.

 Adding alcohol to the juice can be done by simple pouring, but to ensure distribution of the alcohol in the juice, it is preferable industrially to use a mixer. A static mixer receiving on the one hand the juice to be treated and on the other hand the alcohol is thus quite suitable.

 The amount of alcohol to be added to ensure maximum efficiency obviously depends on the amount of germs, bacteria and microorganisms initially present and on the nature of the fruit juice.

 By the expression "substantially inactivate bacteria", it is meant that at least 90% of these will be definitively destroyed.

 One method of determining the amount of alcc, c, l required to inactivate most germs will be to test samples of fruit juice on a petri dish.

 The amount of alcohol normally required for such an inactivation is generally between 5 and 25% by volume relative to the volume of the fruit juice. It is obviously possible to add a greater quantity of alcohol, but it has been noted that additional quantities do not bring about a substantially greater destruction or inactivation of these germs. On the other hand, an addition of at least 5% by volume is generally necessary to ensure inactisa (sufficient izn.

 All fruit juices can be processed using the proe etl, object of the present invention.

 The invention has proved particularly suitable for most juices of economic importance; orange, grapefruit, grape, pineapple and tomato juice.

 Due to the contact between the alcoholic fruit juice and the receptor phase, the latter will enrich with extracted alcohol, especially ethanol. This alcohol concentration must however always remain lower than that existing in alcoholic fruit juice so as to maintain a high vapor pressure gradient in alcohol.

 The flow of alcohol, especially ethanol, through the membrane can vary depending on the nature of the membrane and the differences in ethanol concentration between the alcoholic fruit juice and the receptor phase. However, in order to avoid too low dealcoholization which would be detrimental to the industrial exploitation of the process, it is preferable that the receiving phase does not contain an amount of alcohol extracted, such that it can considerably reduce the extraction flow d 'alcohol. Therefore, advantageously, the flow will vary between 10-2 l / h.m2 and 10 l / h.mi, preferably between 10-1 l / h.m2 and 2 l / hm2.

 By the expression "aqueous receptor phase" is meant an aqueous solution, that is to say one which does not comprise substantially any dissolved organic substances, apart from the alcohol coming from alcoholic fruit juice. n is therefore generally water in which one or more mineral salts modifying the activity of water can be added. In general, in the present description, the aqueous phase will comprise at least 50% by weight of water, the remainder optionally consisting mainly of mineral salts.

 According to a first variant of the process of the invention, it will be necessary to ensure that this water does not comprise substantially any solute capable of appreciably increasing the osmotic pressure of the solution, such as an inorganic chloride salt for example, which could also cause the transfer of water molecules through the membrane, and thus dehydrate the fruit juice.

 In this case, the activity of the water must in fact be approximately equal on both sides of the membrane, so that there is no transfer of perceptible water through the membrane (the water could also pass as water vapor). Thus, the receiving phase must not significantly lower the activity of the water in order to precisely avoid this dehydration.

 According to a second variant of the process, at least one mineral salt, such as a chloride salt for example, can be added to the water voluntarily, making it possible to obtain an osmotic pressure of the receiving phase greater than that of the fruit juice, so as to dehydrate the fruit juice simultaneously with dealcoholization. This aqueous solution should not contain more than 50% by weight of the said solute. The mineral salt is preferably a chloride such as calcium chloride, but it can also be sodium chloride or magnesium chloride or another salt in the case where only minor dehydration is desired.

 By "hydrophobic microporous membrane" is meant here membranes comprising pores not visible to the naked eye but detectable by optical or electronic microscope. Several criteria can be used to choose this type of membrane. Indeed, if the average pore diameter is an essential parameter, the volume porosity, that is to say the percentage by volume of the pores relative to the total volume of the material must also be taken into account. Advantageously, the average pore diameter is between 0.01 and 5 microns, and even more advantageously between 0, () 5 and 1 micron. The volume porosity will preferably be greater than 40%, advantageously greater than 70%.

 In general, hydrophobic membranes are formed from polymeric materials which essentially do not have hydrophilic groups in their network. They therefore essentially consist of polymers obtained from hydrocarbons such as polyolefins. among these polyolefins, mention will advantageously be made of polyethylenes, polypropylenes, polyisopropylenes, polyvinylidenes, or a mixture of different polymers. These polyolefins may optionally be nuances such as polytetrafluoroethylenes or polyfluorovinylidenes. It is nevertheless an essential feature of the invention that the membrane has a hydrophobic character. These membranes are usually presented in the form of planes or hollow fibers.

 Due to the hydrophobicity of the membrane, alcoholic juice uhqu'a 25% alcohol does not wet the membrane, and therefore can not cross it. l.a difference in alcohol concentration between, on the one hand the juice to be treated and on the other hand the water, causes a vapor pressure gradient in al llt) such between the two faces of the membrane. Because of this gradient, the alcohol in the juice evaporates along the membrane, crosses the membrane, and dissolves in water on the other side of the membrane.

 The non-volatile particles in solution in the juice therefore remain entirely in solution in the juice, which allows an etelleiite preservation of its organoleptic qualities.

 The dealcoholized juice recovered can be immediately c) ns, mmé or conditioned without any additional operation and in particular without adding water.

 The preparation method according to an advantageous variant is characterized in that a stream of fruit juice is brought into contact with a mobile aqueous receptor phase formed of water, by means of a hydrophobic microporous membrane, as described below. -before.

 The water having thus been brought into contact with the fruit juice is advantageously treated so as to extract the alcohol therefrom, in particular by distillation, the alcohol possibly being recycled in step a).

 The water receiving alcohol from the juice after it has passed through the membrane is therefore enriched with alcohol over time. The alcohol concentration of the water increases, and causes a decrease in the vapor pressure gradient in alcohol between the two faces of the membrane.

In order to maintain this gradient within an acceptable value range, it has been found advantageous to use one of the following variants
- circulate water in an open loop,
- have a sufficient volume of water so that this gradient does not vanish until the alcohol concentration in the juice is very low. This volume is then either renewed or distilled for the elimination of alcohol,
- circulate in a closed loop, eliminating sit periodically or continuously alcohol in solution in water. By vsemplv, a bypass can be installed, which conducts part of the water to a distillation apparatus, the water released from the alcohol leaving this laughing apparatus cooled then reinjected into the circulation loop. The reprocessing of the water to extract the alcohol from it makes it possible to recover the alcohol, which can be reused for the first step of the process, and thus avoid almost any consumption of alcohol.

 Very generally, the fruit juice most often is not dealcoholized in one pass. Closed circuit traffic is appropriate.

 The process can be carried out at any temperature above 0 C. A temperature above about 50 "C is however not advisable, because the prior heating of the juice to this temperature pr <utr.ut a degradation of its qualities The simplest implementation, which is quite satisfactory with regard to the performance of alcohol extraction, is to proceed at room temperature. A possible difference in temperature between the juice to be treated and the water used the extraction of alcohol does not disturb the proper functioning of the process, as long as it remains of the order of a few degrees.

 The subject of the invention is also a fruit juice substantially free from germs, capable of being stored at room temperature, as it can be obtained by the process described above.

 The invention also relates to a device for implementing the method described above, characterized in that it consists of a chamber comprising one or more compartments provided with an inlet for alcoholic fruit juice and an outlet fruit juice, said compartments being separated, by a hydrophobic membrane, from one or more conduits provided with an inlet of an aqueous receiving phase, in particular of water, and an outlet of alcoholic water.

 According to an advantageous variant, said inlet of alcoholic fruit juice is connected to a mixer provided with an inlet of fruit juice to be treated and an inlet of alcohol. A static mixer receiving on the one hand the juice to be treated and on the other hand the alcohol is thus quite suitable.

 According to another advantageous variant, the outlet of alcoholic water is connected to the inlet of water via a bypass comprising on a branch, in series an apparatus for distilling alcohol and a refrigerant, the evacuation alcohol being optionally connected to the alcohol inlet of the mixer.

 In the latter case, it is a device for recycling water as well as alcohol.

 The device according to the invention will now be described according to a particular non-limiting variant, illustrated by Figures 1 and 2, in the appendix.

 - Figure 1 is a schematic view of a device according to the invention provided with a recycling circuit.

 - Figure 2 is a sectional view of the alcohol extraction device. This extractor is identical to the module described in FIG. 2 of patent application EP-A-0 539280.

 According to FIG. 1, a mixer 1 has an inlet for fruit juice 2, an inlet for alcohol 3 and an outlet 5, this mixer being provided with an agitator 4.

 The outlet 5 of the mixer is connected to the inlet 12 of the extractor 6 which will be described in connection with FIG. 2.

 The extractor 6 is formed of a tubular structure 7 closed near these two ends by two plugs 8 delimiting on the one hand an internal tube 9 and on either side of this internal tube, two tutular ends 10. A hollow fiber module 1 1 is placed co-axially in said internal tube. This module made up of a multiplicity of hollow fibers joined together 17 is fixed at its ends to the plugs 8, in such a way that the interior of the fibers 18 can, by means of cavities formed in said plugs, communicate with the external ends of the tubular structure. Said tubular ends are connected to tubes 12, 19 in a sealed manner, by means of seals 13, one of the tubes making it possible to supply the fibers with alcoholic juice, and the other tube making it possible to recover the dealcoholized juice. The volume outside the fibers is filled with an aqueous receiving phase 14, preferably water. Advantageously, this receiving phase is mobile and in this case, the fibers are fed by means of an inlet 15 located at one end of the internal tube, and recovered at the other end by an outlet 16.

 The receiving phase entering through input 15 is evacuated through output 16 to a three-way valve 20 which allows either return to input 15 via connection 25, or passage to input 21 of a distiller 22. This distiller 22 makes it possible to separate, on the one hand the alcohol which is evacuated by the outlet 23 and, on the other hand the water which is recycled by exiting by the evacuation 24 connected to the inlet 15 via connection 25. The alcohol discharged through outlet 23 is cooled in an exchanger 26 and reintroduced into the mixer via inlet 3.

 According to a variant, the fruit juice circulates in a closed circuit, the outlet 19 being connected by means of a three-way valve 27 to the inlet 12. Pumps 28 ensure the circulation of the fruit juice and the water.

 The invention is now illustrated by an exemplary embodiment.

 This example concerned the processing of grape juice. In the experiment described below, clear black grape juice was used. I.a sugar concentration (mainly sucrose) was 147 g l, the total acidity of 4.6 g / l (mainly sulfuric acid), and the p11 of 3.6. The initial density was 1043 g / l.

 The first step of the process consists in adding to this juice, () 4 g of ethyl alcohol up to 16% by volume, so as to form a final volume of 500 milliliters. The addition was made by exposing the grape juice to the air as little as possible, so as to avoid any oxidation of the juice.

 The mixture placed in a beaker was then stirred for fifteen minutes by means of a rotating magnetic bar, then left to stand for two hours.

 For the second step of the process, a microfiltration module of the "Microdyn-Enka" brand was used, composed of 40 capillary tubes in microporous membrane, in polypropylene, with an internal diameter of 1.8 mm, having a total membrane surface. 0.1 m2. The thickness of the membrane walls is 400 microns, and the average pore diameter is 0.2 microns.

 By means of a centrifugal pump, the 500 ml of grape juice were circulated inside the tubes, at a speed of the order of 0.3 m / s. Outside the tubes, tap water was circulated by means of a centrifugal pump from an initial volume equal to 25 liters.

 The juice circulating towards the module from a graduated cylinder of 10 in 10 ml, the decrease in volume of the juice was recorded as a function of time.

 Again, all contact between the juice and the air has been minimized to avoid any oxidation of the grape juice.

The following kinetics have been recorded
CUMULATIVE VOLUME DECREASE TIME
t = 0 Oml
t 1h 30ml
t = 2h 60ml
t = 3h 80ml
t = 4h 80ml
After 4 hours, the second stage was stopped. The residual quantity of alcohol was then measured and was found to be less than 0.2% by volume, a value which is entirely acceptable for future consumption of the juice.

Claims (14)

 1. Method for preparing fruit juices suitable for being preserved, characterized in that it comprises the following stages  a) adding to a given volume of fruit juice a quantity  sufficient alcohol to substantially inactivate  bacterial germs,  b) extraction of the alcohol from the alcoholic fruit juice obtained in step  a) by bringing said juice into contact with a receiving phase  aqueous, substantially free from said alcohol, by  through a microporous hydrophobic membrane  for an appropriate period,  c) recovery of fruit juice substantially free of  active and dealcoholized germs.  2. Preparation process according to claim 1, characterized in that the alcohol is ethyl alcohol.  3. Preparation process according to one of claims 1 or 2, characterized in that the amount of alcohol is greater than 5% by volume.  4. Preparation process according to one of claims 1 ì 3, characterized in that the microporous membrane has a volume porosity greater than 40%, advantageously greater than 70%, and in that the average pore size is between 0 , 01 and 5 microns.  5. Preparation process according to claim 4, characterized in that the hydrophobic membrane is chosen from those of optionally fluorinated polyolfinvs.  6. Preparation process according to claim 1, characterized in that the aqueous receiving phase is substantially formed of water.  7. Preparation process according to claim 1, characterized in that the receiving phase is an aqueous solution of at least one ore salt making it possible to lower the activity of the water, so as to concentrate the fruit juice by dehydration simultaneously with his dealcoholization.  8. Preparation process according to claim 7, characterized in that the mineral salt is chosen from calcium chloride, sodium chloride, magnesium chloride.  9. Preparation process according to claim 1, caractvsrls. in that a stream of fruit juice is brought into contact with a mobile aqueous phase, via a hydr) phz, he microporous membrane.  10. Preparation process according to claim 9, characterized in that the aqueous receiving phase, after it has been brought into contact with the fruit juice, is treated so as to extract the alcohol, in particular by distillation, l alcohol being optionally recycled in step a).  11. Fruit juice substantially free from germs, capable of being stored at room temperature, as it can be obtained by the process according to one of claims 1 to 10.  12. Device for implementing the method according to one of claims 1 to 10, characterized in that it consists of a chamber (7) comprising one or more compartments (11) provided with an inlet (12 ) of alcoholic fruit juice and an outlet (19) of fruit juice, said compartments being separated, by a hydrophobic membrane of about several conduits (18) provided with an inlet (15) of a receiving aqueous phase , in particular water, and an outlet (16) for alcoholic water.  13. Device according to claim 12, characterized in that said inlet (12) of alcoholic fruit juice is connected to a mixer (1) p <, unu of an inlet of fruit juice to be treated and an inlet d 'alcohol.  14. Device according to claim 12 or 13, characterized in zv quc the outlet (16) of alcoholic water is connected to the inlet (15) of the receiving phase via an alcohol distillation apparatus ( 22), the evacuation '3) of alcohol possibly being connected to the alcohol inlet (3) of the mixer.