METHOD FOR FOOD PASTEURIZATION

Abstract

A method for treating food where inside a packaging, made of a material configured for containing a gas-mixture, a food product and a gas mixture including at least carbon dioxide are inserted. Then, on the sealed packaging a uniform pressure, between 4 MPa and 20 MPa, is applied to compress the food. During application of the pressure, the packaging is maintained at a temperature between 25 C. and 50 C.

Claims

1-12. (canceled)

13. A method for treating food comprising: inserting a food product and a gas mixture at least comprising carbon dioxide into a packaging, said packaging made of a material configured for containing said gas mixture; sealing the packaging; uniformly applying a pressure to the packaging to compress the packaging, the gas mixture and the food product inside of it; wherein the pressure applied to the packaging is between 4 MPa and 20 MPa and, during application of the pressure, the packaging is maintained at a temperature between 25 C. and 50 C.

14. The method according to claim 13, wherein a pressure is applied and a temperature is maintained during operation, such as to maintain the carbon dioxide in a supercritical state.

15. The method according to claim 13, wherein the amount of carbon dioxide in the gas mixture is between 5% and 100% by volume or mass.

16. The method according to claim 14, wherein the amount of carbon dioxide in the gas mixture is between 5% and 100% by volume or mass.

17. The method according to claim 13, wherein the gas mixture further comprises one or more of the gases included in the group consisting of air, nitrogen, oxygen, carbon monoxide, and nitrogen dioxide.

18. The method according to claim 14, wherein the gas mixture further comprises one or more of the gases included in the group consisting of air, nitrogen, oxygen, carbon monoxide, and nitrogen dioxide.

19. The method according to claim 15, wherein the gas mixture further comprises one or more of the gases included in the group consisting of air, nitrogen, oxygen, carbon monoxide, and nitrogen dioxide.

20. The method according to claim 16, wherein the gas mixture further comprises one or more of the gases included in the group consisting of air, nitrogen, oxygen, carbon monoxide, and nitrogen dioxide.

21. The method according to claim 13, wherein the pressure is applied in a variable manner over time.

22. The method according to claim 14, wherein the pressure is applied in a variable manner over time.

23. The method according to claim 13, wherein said pressure is applied to the packaging for a time between 5 minutes and 3 hours.

24. The method according to claim 14, wherein said pressure is applied to the packaging for a time between 5 minutes and 3 hours.

25. The method according to claim 13, wherein the temperature is varied during application of the pressure to the packaging.

26. The method according to claim 14, wherein the temperature is varied during application of the pressure to the packaging.

27. The method according to claim 13, wherein the packaging is inserted into a watertight reactor provided with a liquid loading and unloading system, and wherein the method provides for charging a liquid in the reactor up to reaching said pressure.

28. The method according to claim 27, wherein the liquid contained in the reactor is heated by an electrical resistance, or by applying an electromagnetic field or by applying ultrasound.

29. The method according to claim 27, wherein the reactor is provided with a heating jacket, and wherein the liquid contained in the reactor is heated by flowing a heating liquid inside the heating jacket.

30. The method according to claim 13, wherein a plurality of pasteurization cycles are performed, each pasteurization cycle having different pressure and temperature curves that are applied.

31. The method according to claim 14, wherein a plurality of pasteurization cycles are performed, each pasteurization cycle being having different pressure and temperature curves that are applied.

32. The method according to claim 13, wherein the packaging comprises ascorbic acid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Further characteristics and advantages of the present invention will be more clear from the following detailed description of some preferred embodiments thereof, with reference to annexed drawings.

[0056] The different characteristics in the individual arrangements can be combined with one another as one desires according to the above description, if advantages specifically resulting from one particular combination should be used.

[0057] In these drawings,

[0058] FIGS. 1a to 1f are different steps of the pasteurization process according to the invention;

[0059] FIG. 2 is a flow chart of the process shown in FIGS. 1a-1f;

[0060] FIG. 3 is a chart showing data about microbial inactivation for mesophilic bacteria (right) and yeasts and molds (left) on cut carrot samples treated by the method of FIG. 2, and in samples treated in different manner or untreated samples;

[0061] FIG. 4 is the results of shelf-life studies for mesophilic bacteria (chart on the left) and for yeasts and molds (chart on the right);

[0062] FIG. 5 is a chart showing data about microbial inactivation for yeasts and molds (left), mesophilic bacteria (center) and mesophilic spores (right) on coriander leaves treated by the method of FIG. 2, and in samples treated in different manner;

[0063] FIG. 6 is a chart showing data of the reduction of Lysteria monocytogens in samples of coriander treated by the method of FIG. 2, and in samples treated in different manner or untreated samples;

[0064] FIG. 7 is a chart showing data about microbial inactivation for mesophilic bacteria on pear samples treated by the method of FIG. 2 at different temperature and treatment time;

[0065] FIG. 8 is a chart showing data about microbial inactivation for yeasts and molds on pear samples treated by the method of FIG. 2 at different temperature and treatment time;

[0066] FIG. 9 is a chart showing data about microbial inactivation for mesophilic bacteria (left), mesophilic spores (center) and yeasts and molds (right) on pear samples treated by the method of FIG. 2 at different concentrations of CO.sub.2 in a mixture with nitrogen.

DETAILED DESCRIPTION OF THE INVENTION

[0067] In the following description, to disclose the figures like reference numerals or symbols are used to denote constructional elements with the same function. Moreover, for purposes of clarity, some references may not be repeated in all the figures.

[0068] While the invention is susceptible of various modifications and alternative constructions, some preferred embodiments are shown in the drawings and will be described in details herein below. It should be understood, however, that there is no intention to limit the invention to the specific disclosed embodiment but, on the contrary, the invention intends to cover all the modifications, alternative constructions and equivalents that fall within the scope of the invention as defined in the claims.

[0069] The use of for example, etc., or denotes non-exclusive alternatives without limitation, unless otherwise noted. The use of comprises and includes means comprises or includes, but not limited to, unless otherwise noted.

[0070] With reference to FIGS. 1a-1f and 2, a pasteurization process according to a preferred embodiment of the invention is described herein below.

[0071] The process begins at step 100, FIG. 1a, where food 1 is taken for being packaged. Food can be previously subjected to cut processes for excluding some parts or for providing a shape more suitable for use thereof (for instance cubes, rhombus, spheres, sticks etc).

[0072] Then, step 101, food is inserted into a packaging 2 composed, partially or completely, of a flexible film. The packaging is made of a material configured for containing a gas mixture that is able to form a barrier substantially impermeable to gases and vapors of the mixture, and it can have various dimensions and volumes ranging from 0.1 mL (milliliters) to 100 L (liters) depending on the amount of food to be treated. As the material suitable for containing the gas mixture it is known to use, individually or coupled as a multilayer, for instance plastic polymer films (polyethylene-PE, polypropylene-PPE, polyethylene terephthalate-PET), aluminum, paper.

[0073] Once food is inserted in the packaging, the latter is filled with (step 102) carbon dioxide in a mixture ranging from 5% to 100% (by volume or by mass) with other gases such as air, nitrogen, oxygen, carbon monoxide, nitrogen dioxide, etc.

[0074] Packaging process preferably occurs at room temperature or anyway at such a temperature and pressure to maintain gases, that have to be inserted in the packaging, in the gaseous state.

[0075] In one embodiment, an antioxidant agent, preferably natural, is added to the gas mixture. For instance ascorbic acid (vitamin C or the like) in liquid or solid form can be possibly inserted in the packaging.

[0076] Then packaging 2 is sealed (step 103, FIG. 1b) such to hold food 1 and gas mixture 3 therein.

[0077] The sealed packaging 2 is inserted (step 104, FIG. 1c) in a reactor 4that is a container provided with a reaction chamber 40 where chemical reaction processes take placeable to withstand pressures of 30 Mpa. To this end, the reactor can be made partially or completely of metal (steel or other alloy) or other organic or inorganic material able to withstand employed pressures.

[0078] In the preferred embodiment, the reactor 4 is equipped with a heating system 5 comprising a heating jacket, namely a gap formed along one or more of the walls of the reaction chamber, wherein heating means 6 are placed to heat the interior of the reactor. By way of example, heating means can comprise a thermal fluid or an electrical resistance that, being placed inside the heating jacket, heat one of the walls of the reaction chamber, such to heat food placed inside the reactor. As an alternative, heating means can comprise means intended to generate an electromagnetic field or ultrasounds. These means radiate the interior of the reactor while heating food therein.

[0079] By means of the heating system the temperature inside the reactor is controlled depending on process needs. For instance, the heating system can be configured to maintain temperature as constant or to change it depending on other process parameters, such as time or pressure inside the reactor. Preferably for the pasteurization process described herein, temperature is preferably kept below 50 C., such to prevent thermosensitive molecules of food from being altered, such as vitamins or proteins.

[0080] In order to regulate the temperature inside the reaction chamber 40, the reactor 4 is equipped with a pump and a pipe system (not shown in the figure) that allow a incompressible working fluid 41 to be loaded and unloaded, for example water, used for the treatment step. Suitable on-off and throttling valves (not shown in figures) allow loading and unloading operations to be controlled. Advantageously such valves are electronically controlled by a control unit of the reactor, however they can be manually controlled by the use of pressure gauges showing the operator the pressure inside the reaction chamber.

[0081] Once sealed packaging that contains food 1 and gas mixture 3 is inserted, the reaction chamber 40 is closed and sealed. To this end the reactor is equipped with members for tightly closing the reaction chamber, that can comprise flanged members, threaded members etc.

[0082] Now the reaction chamber 40 is filled (step 105) with the working fluid and food pasteurization cycle begins (step 106, FIG. 1d). In details, the pasteurization cycle provides to set a constant or variable hydrostatic pressure, from 4 to 20 MPa while the temperature inside the reaction chamber 40 is kept at a temperature from 25 C. to 50 C. Preferably the pasteurization cycle provides to maintain, inside the reaction chamber, such temperature and pressure conditions to maintain carbon dioxide, present inside the packaging, in a supercritical state. Therefore, while observing the maximum values of pressure and temperature mentioned above, the reaction chamber is maintained at a temperature higher than 31 C. and at a pressure higher than 7.38 Mpa.

[0083] The duration of the pasteurization cycle changes depending on food to be treated, and generally it is from 5 minutes to 3 hours. As regards vegetable products the duration of the pasteurization cycle preferably is from 5 to 60 minutes.

[0084] In one embodiment, the increase of the pressure in the reaction chamber 40 occurs by using the loading pump, or by hydraulic force of one or more of the walls of the reaction chamber.

[0085] At the end of the pasteurization cycle the reactor is depressurized (step 107, FIG. 1e) for example by opening a throttling valve, till reaching room pressure or an intermediate pressure between the room pressure and the final treatment pressure.

[0086] At the end of the treatment the reactor is opened and the packaging 2 is removed (step 108 FIG. 1f) and subjected to drying for being later preserved at suitable temperature.

[0087] In the light of the above it is clear how the pasteurization process described above allows an efficacious food pasteurization to be obtained by a reactor simple to be manufactured and that can be made as semi-continuous. The results of experimental tests, that prove the efficacy of the pasteurization process described above, are shown in the examples of the experimental tests below.

[0088] It is also clear that many variants can be made to the embodiments described above by way of example of the invention defined in the annexed claims.

[0089] For example in one embodiment instead of providing heating means to control the temperature inside the reaction chamber it is possible to provide a system heating the working fluid. In this embodiment, the working fluid that is supplied in the reaction chamber is heated before being loaded in the reaction chamber.

[0090] Again in one embodiment the pasteurization method can provide several pasteurization cycles, each pasteurization cycle being characterized by different pressure and temperature curves that are applied to the packaging/packages present in the reactor.

Experimental Tests

EXAMPLE 1

Carrots

[0091] Experimental tests were carried out on cut carrot samples that were inserted in a packaging made of a material configured for containing a gas mixture together with a gas mixture comprising 100% of CO.sub.2. For each test about 3 grams of sample were packaged with about 100 mL of CO.sub.2. Closed packaging was maintained in the reaction chamber at 120 bar (about 12 Mpa), 40 C. for 15 minutes.

[0092] FIG. 3 illustrates a chart showing the microbial inactivation of mesophilic bacteria and yeasts and molds on cut carrot samples to compare inactivation obtained during the conventional process such as shown in the study published by Spilimbergo et al., 2013. In details, bars ctrlTemp show population of Yeasts and Molds (left) and of mesophilic bacteria (right) respectively in a control sample kept at the same temperature conditions for the all duration of the treatment. Central bars imp are the population of Yeasts and Molds (left) and mesophilic bacteria (right) respectively in a sample treated by the pasteurization process according to the invention. The bars ctrlCO2 are the population of Yeasts and Molds (left) and mesophilic bacteria (right) respectively in a sample treated by the process of Spilimbergo et al., 2013, [33].

[0093] As seen in FIG. 3, the pasteurization process described herein is able to inactivate microorganisms in a manner similar to conventional process of Spilimbergo (that provides the direct contact of food with CO.sub.2 at supercritical state). Unlike the latter, however, the process of the invention avoids contamination risk due to the packaging step that, in Spilimbergo process, has to follow pasteurization process. Moreover the use of the amount of CO.sub.2 is considerably reduced that, for the same amount of product, is reduced from about 9.45 g for the reactor of the process of Spilimbergo et al., 2013 to about 0.18 g by the method of FIG. 2, corresponding to a reduction higher than 98% CO.sub.2.

[0094] On the contrary FIG. 4 shows results of shelf-life studies at 7 days. On the left the shelf-life for mesophilic bacteria is shown, while on the right for yeasts and molds. The figure shows, in logarithmic scale, the values of the ratio N/N0, where N is the number of colonies after the treatment, and N0 the number of colonies of the fresh sample before the treatment. Data are normalized with respect to the untreated fresh sample. FIG. 4 shows data obtained for four types of treatments: trCO2 refers to a sample treated in CO.sub.2 atmosphere and packaging kept at 120 bar, 40 C. for 15 minutes of treatment. trAIR refers to a sample treated under ambient air atmosphere at 120 bar, 40 C. for 15 minutes. nntr AIR refers to a untreated sample preserved under ambient air atmosphere. nntrCO.sub.2 refers to untreated sample preserved under atmosphere at 100% of CO.sub.2 at atmospheric pressure.

[0095] The figure shows that, after 7 days, the samples treated with the pasteurization method described above have a bacterial load still lower than the one of the product before the treatment. The same figure further shows that mere pressure and temperature do not have any effects on microbial reduction and they show a behavior similar to the several samples preserved without being treated. Likewise, the mere atmosphere at 100% of CO.sub.2 at atmospheric pressure does not have any effect on inactivation of mesophilic bacteria and on molds.

[0096] Finally carrot samples treated in these experimental tests exhibited, at the end of the treatment, an aspect and a texture very similar to that of untreated samples.

EXAMPLE 2

Coriander Leaves

[0097] Further experimental tests were carried out on coriander leaves that were inserted in a packaging made of a material configured for containing a gas mixture together with a gas mixture comprising 100% of CO.sub.2. For each test about 1 gram of sample was packaged with about 100 mL of gas. Closed packaging was maintained in the reaction chamber at 100 bar (about 10 Mpa), 40 C. for 10 minutes. FIG. 5 illustrates a chart showing the microbial inactivation for mesophilic bacteria and yeasts and molds on coriander samples to compare inactivation obtained during the conventional process where supercritical CO.sub.2 was placed in direct contact with the sample likewise the case of carrot in the study of Spilimbergo et al., 2013, [33].

[0098] Experimental tests carried out on coriander samples, further show the efficacy of the method on the reduction of pathogenic microorganisms. Particularly FIG. 6 shows data of the reduction of Lysteria monocytogens composed of a cocktail composed, ratio 1:1:1, of three strains LMG23192, LMG23194 and LMG2648 respectively. The sample was inoculated such to obtain a starting contamination of 5.850.33 log. Such as in FIG. 3, also in this case the reference imp denotes the results of measurements in a sample inserted in a sealed packaging with a mixture of 100% CO.sub.2 at 100 bar 40 C. for 10 minutes, according to the method of FIG. 2. The reference ctrlCO2 shows the data of measurements taken on a control sample inserted in the reactor without the packaging and treated according to conventional procedure that provides to insert supercritical CO.sub.2 directly in the pasteurization reactor likewise the study about carrot by Spilimbergo et al. 2013 [33], under the same conditions (100 bar 40 C. for 10 minutes). The reference ctrlTemp shows the results of measurements taken on a control sample maintained at atmospheric pressure under the same temperature conditions of the process (40 C.) for all the duration of the treatment.

EXAMPLE 3

Pear Pieces

[0099] Additional experimental confirmations were carried out on pear pieces inserted in a packaging made of a material suitable for containing a gas mixture together with a gas mixture comprising 100% of CO.sub.2. For each experiment about 1 gram of sample was packaged with about 100 mL of gas. Closed packaging was maintained inside the reaction chamber at 100 bar (about 10 MPa). Different temperatures and treatment time were analyzed. FIGS. 7 and 8 show inactivation of mesophilic bacteria and yeasts and molds respectively at different treatment time (10, 30 and 60 minutes), and for two different temperatures (25 C. and 35 C.) below and above the critical point of CO.sub.2 respectively. From this study it results that for both the microorganisms the inactivation occurs substantially only upon exceeding critical conditions of CO.sub.2. Moreover it shows that over 30 minutes of treatment under the described conditions, there is no substantial increase in inactivation for mesophilic bacteria.

[0100] Further experiments were carried out with different mixtures of nitrogen and carbon dioxide. FIG. 7 shows a chart indicating the microbial inactivation for mesophilic bacteria, mesophilic spores and yeasts and molds on cut pear samples treated after being inserted in packaging made of a material configured for containing a gas mixture together with a gas mixture composed of N.sub.2 and CO.sub.2 at 0.50 and 100% of CO.sub.2 respectively after a treatment at 100 bar (about 10 MPa), 35 C. for 30 minutes. From this study it results that CO.sub.2 is fundamental for inactivation of microorganisms and if another gas is used the mere pressure and temperature do not have any effects on microorganism inactivation. Moreover it results that inactivation occurs also for gas mixtures having CO.sub.2 in a percentage lower than 100%, but such to guarantee a bactericidal action of CO.sub.2.

EXAMPLE 4

Other Foods

[0101] Other experimental tests, like those carried out for carrots, coriander and pear, were performed on apple pieces, coconut pieces, strawberry pieces, entire French beans, avocado pieces, entire grapefruit, entire currant, kiwi pieces, chicken, cooked ham, Parma ham, codfish and shrimp. Results demonstrated the efficacy of the provided pasteurization process as regards microbial inactivation and preservation of organoleptic properties and texture/color characteristics of the treated food.