HPP PROCESS FOR DAIRY FOOD

Abstract

The invention relates to a high hydrostatic pressure process for reducing the level of micro-organisms in commercial dairy products.

Claims

1. A process for reducing the level of active spoilage and pathogenic micro-organisms in an untreated dairy product, the process comprising the steps of: a. applying a source of high hydrostatic pressure of at least 5200 Bar to the untreated dairy product for a first period of time; b. removing the source of pressure from the dairy product; c. reapplying the source of pressure to the dairy product for a second period of time; and d. optionally repeating steps (a) to (c) to produce a treated dairy product, wherein there is no initial heat pasteurisation step of said untreated dairy product.

2. The process of claim 1 wherein the maximum hydrostatic pressure applied is 5500 Bar or greater.

3. The process of claim 1 wherein the maximum hydrostatic pressure applied is 5800 Bar or greater.

4. The process of claim 1 wherein the maximum hydrostatic pressure applied is 6000 Bar or greater.

5. The process of claim 1, wherein said first period of time is between 60 and 120 seconds.

6. The process of claim 1, wherein said first period of time is about 90 seconds.

7. The process of claim 1, wherein said second period of time is between 60 and 150 seconds.

8. The process of claim 1, wherein said second period of time is about 120 seconds.

9. The process of claim 1, wherein the source of pressure is removed for a time period of between 1 to 10 seconds.

10. The process of claim 1, wherein the source of pressure is removed for about 5 seconds.

11. The process of claim 1, wherein the untreated dairy product is raw milk.

12. The process of claim 1, wherein the treated dairy product has a shelf life of greater than 40 days at 5 C.

13. The process of claim 1, wherein the treated dairy product has a >6 log.sub.10 reduction of both E. coli and L. Monocytogenes.

14. The process of claim 1, wherein the treated dairy product has a >4.3 log.sub.10 reduction of S. Typhimurium.

15. The process according to claim 1, wherein the process comprises repeating steps (a) to (c) to produce a treated dairy product.

16-20. (canceled)

21. The process according to claim 1, wherein the process further comprises producing cream, skim milk, low fat milk, kefir, yoghurt, buttermilk, or cheese from the dairy product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0020] The invention is embodied in a high pressure process that has been developed for the treatment of raw milk, particularly for bovine milk, to render it microbiologically safe and stable for a commercially viable time period under refrigeration. It will be appreciated that this embodiment is by way of example only and the inventive process could be used to treat a wide range of other dairy products, and food products generally.

[0021] Food safety authorities in some jurisdictions mandate a specific log.sub.10 reduction in particular types of spoilage organisms that must be achieved in order for the food to be considered commercially sterile and saleable. For example, the New South Wales Food Authority (NSWFA) require a treatment process to achieve a log.sub.10 reduction of 5 (i.e. a 100,000 reduction) in pathogenic microorganisms.

[0022] In high pressure processing (HPP), there are two key variables that define the treatment process. Every different food type requires testing to ascertain at what point the process has been effective in inactivating the target pathogens. The variables are: time spent under pressure; and the magnitude of pressure applied.

[0023] With typical HPP equipment, pressure can be applied up to about 6000 Bar. The time that a food item is placed under this level of pressure must be consistent with commercial food production process requirements and result in elimination or inactivation of a sufficient proportion of the target micro-organisms while maintaining the quality, texture and taste properties of the food.

High Pressure Process Testing

[0024] The following test conditions were applied to five replicates of pre-inoculated milk feedstock:

i. Three pathogens: (Salmonella typhimurium, Listeria monocytogenes, and Staphylococcus aureus).
ii. Two pressure hold times at 6000 Bar: 3 minutes and 4 minutes, as it was postulated that each additional minute of hold time should produce an extra log reduction.

[0025] The results at 3 minutes showed a kill of pathogenic bacteria, with log.sub.10 reductions of between 2 and 3 for Salmonella and Staphylococcus at four minutes, and 3 to 4 log.sub.10 reduction for Listeria. Results at four minutes were slightly better than at three minutes treatment (approximately 1 log.sub.10). Taken together, these results were not sufficient to demonstrate equivalence to heat pasteurisation, in which a 5 log.sub.10 reduction is achieved.

[0026] On this occasion, the raw milk used was incidentally contaminated with >1,100 coliforms and E. coli. These bacteria were not detected in the non-inoculated HP processed control sample, demonstrating at least a log.sub.10 reduction of 3.

Extended Treatment and Cycled Pressure Testing

[0027] A further pathogen challenge test was conducted on five replicates using two new test processes:

i. An extended treatment of 6000 Bar/90 seconds for 15 minutes; and
ii. A cycled treatment process at 6000 Bar for 90 seconds, repeated once immediately.

[0028] To date, there is no known reference to the commercial use of either of these treatments in the processing of commercial dairy products. The rationale for testing the cycled process was that the first cycle would induce sub-lethal injury of the cell walls of the microorganisms and that the second cycle would complete the lethal effect of the high pressure on the damaged cell. The extended treatment was tested to measure the effect of a longer period of high pressure on cell death. Of the two processes tested, only the cycled process is likely to be commercially viable, as the extended treatment reduces overall the maximum product throughput.

[0029] In the extended treatment trial, pathogens tested were Salmonella typhimurium and Staphylococcus aureus.

[0030] The results for the treatment of both bacteria showed a log.sub.10 reduction of 5 for Salmonella and a log.sub.10 reduction of 2 to 3 for Staphylococcus. Therefore, the required log.sub.10 reduction of 5 was only demonstrated for one of the target pathogens in this instance.

[0031] The cycled pressure testing was designed with the objective of confirming the impact of the cycled process on reduction of Salmonella and testing it on Listeria, and E. coli. Five replicates were tested.

[0032] Log reductions of greater than 6 were demonstrated for E. coli and Listeria. In the case of E. coli and Listeria, this was higher than the equivalent log reductions under process conditions of 6000 Bar for 3 minutes. The Salmonella challenge showed inconsistent results initially between replicates so that log reductions of 3 and >6 were demonstrated. Low log reduction counts of Staphylococcus were reproduced from previous trials.

[0033] Shelf life testing yielded a potential shelf life of greater than 42 days at 5 C., and a longer shelf life than that achieved using the 3 minute standard cycle, an superior to those obtained at 4000 Bar and at 5000 Bar, both of which indicated microbiological spoilage at approximately 23 days.

[0034] A further trial was conducted, with the objective to test for the first time the impact on Campylobacter jejuni. Under these test conditions, Campylobacter demonstrated a degree of resistance to high pressure with a log reduction of 1.2.

[0035] The results of the shelf life and challenge testing for the raw milk product are shown in Table 1.

[0036] In most food products containing E. coli, Listeria, Salmonella, Campylobacter or Staphylococcus aureus, holding the product at pressures up to 6000 Bar for a period of 3 minutes would be sufficient to achieve a log.sub.10 reduction of 5 in the pathogen level. However, in this trial with raw milk, these conditions were found to be insufficient to achieve a log.sub.10 reduction of 5 in Listeria, Salmonella, Campylobacter and Staphylococcus due to the protection of the bacterial cells afforded by the food matrix typical of raw milk. A 4-minute hold at 6000 Bar did achieve a log.sub.10 reduction of 5 for Listeria, but not for Salmonella.

[0037] Testing was then done using a cyclic approach, as shown in Table 1. The cyclic approach held the raw milk product at 6000 Bar for two time periods of 90 seconds, one immediately following the other. It was surprisingly discovered that this shorter, cyclic approach at 6000 Bar was successful in achieving a superior log reduction of E. coli and Listeria monocytogenes compared with a more standard 3 minute pressure treatment at the same pressure, and produced a longer shelf life. The required log reduction of 5 (equivalent to heat pasteurisation) was achieved using the cyclic approach for Listeria monocytogenes and E. coli.

[0038] It is proposed that those bacterial pathogens that were not reduced by 5 log using any of the tested high pressure process conditions (Salmonella, Staphylococcus aureus and Campylobacter jejuni) can be controlled by applying hygienic raw milk production techniques and animal health strategies in combination with raw milk compliance testing prior to high pressure processing, to produce a commercially viable, safe unheated milk product with a longer shelf life.

[0039] The inventors have found that a cycled HPP has a unique, significant impact on the reduction in numbers of Salmonella Listeria, and E. coli) in raw milk. Such results may also be applicable to other dairy products, particularly those using raw milk as an ingredient.

[0040] It will be appreciated by those skilled in the art that the above described embodiment is merely one example of how the inventive concept can be implemented. It will be understood that other embodiments may be conceived that, while differing in their detail, nevertheless fall within the same inventive concept and represent the same invention.