AU7326398A - Method and apparatus for preserving food - Google Patents

Description

WO 98/52421 PCT/AU98/00357 1 METHOD AND APPARATUS FOR PRESERVING FOOD The present invention relates to a method of preserving food, particularly meat, vegetables, fruits and products based on meat, vegetables and fruit and 5 apparatus used in this method. More particularly the present application is directed to a method of pre-processing the food which can then be subjected to a main preserving process which can be carried out at much lower temperatures and for shorter time intervals than many other preserving processes and produces food more organoleptically acceptable to a consumer. 10 Although the present invention will be described with particular reference to the preparation of shelf stable meat, vegetable and fruit and products based on these food groups, it will be readily appreciated by the persons skilled in the relevant technology that the scope of the present invention is not limited to meat, 15 vegetable and fruit and products based on these food groups but rather the scope is more extensive to include food generally, including home replacement meals comprising meats and vegetable, bulkfood service portions and including unprocessed food such as nuts and pulses, and processed foods such as salamis, cheeses, bread, pastries and the like. The scope of the present 20 invention also extends to preservation of food for short term as well as long term storage. Food preservation methods applied to prevent or delay the deterioration of food have been used for centuries. Early hunter-gatherers prepared dried meats such 25 as pemmican and used caves and other cool places to provide refrigeration of their food. Cheese and yoghurt are the products of fermentation, a food preservation technique known from early times. Fruits, vegetables and meat have been preserved by pickling, a process in which food is salted to selectively control microorganisms such as bacteria then fermented to stabilise the treated 30 tissues. Preservation of fruit has also been practiced for centuries by concentrating soluble solids as jams, marmalades and other preserves. The natural and/or added sugar in these foods also acts as a preservative.

WO 98/52421 PCT/AU98/00357 2 Early efforts at food preservation were often effective at delaying food deterioration, but the texture and colour of the food often suffered and the food was often either tasteless or alternatively comprised an overwhelming taste of 5 salts or spices used to preserve the food. The development by Pasteur in 1846 of the food sterilisation process now known as pasteurisation was a significant step forward in food processing technology. The rise of the consumer society and advances in food processing technology have radically improved all aspects of food preservation during the twentieth century. Methods of food preservation 10 based on the pasteurisation process such as canning, freeze-drying and irradiation have made enormous progress. Vast numbers of chemicals are also now used in food preservation not only to preserve the food but to improve the colour, taste and texture. 15 Consumer expectations of preserved foods have risen to a very high level. Consumers quite reasonably expect that they can eat a preserved food at any time before its "use by" or "best before" date without running the risk of infection and sickness caused by harmful micro-organisms including certain bacteria, spores, fungi and enzymes. Consumers also expect that preserved food will 20 remain unspoiled and not change in appearance, at least until the "use by date" is reached. The "use by date" is usually displayed on the packaging of preserved foods and indicates the date until which the foodstuff should not start to exhibit any 25 significant decrease in quality. Foods which have a use by date at least 2 years after their date of manufacture are referred to as "shelf stable". Shelf stable products are not only in demand from ordinary consumers but are also used as part of army rations, campers' supplies, rescue and relief packages and so forth. 30 In recent time, consumers have also become very aware of potential health risks associated with the use of unacceptable chemical additives and certain methods of preservation such as irradiation.

WO 98/52421 PCT/AU98/00357 3 Accordingly one of the most popular methods of preservation of food is pasteurisation or sterilisation using retort technology because this method does not generally require the use of additives such as chemicals or techniques such 5 as irradiation. Retort technology is based on sterilisation of food using heat, for example by heating a product at elevated temperature to destroy vegetative cells and various forms of micro-organisms such as bacteria that cause spoilage. A typical process for preserving food using retort technology may comprise 10 placing sealed packages of food in a retort and then pressurising the retort while the food packages are submerged in steam heated hot water for a period of time sufficient to raise the internal temperature of the food to a predetermined level One of the problems associated with this type of food preservation is that 15 application of heat for a minimum amount of time suitable to kill bacteria may cause changes in the food that detract from its appearance. For example, sweet corn has a relatively high natural sugar content, and the application of heat during sterilisation by retort technology tends to caramelise the sugar, thus altering the corn from its natural yellow colour to a caramel colour. Consumers prefer 20 preserved food to have the same appearance as the corresponding fresh food and often associate such a colour change with poor quality. It has now been found that preservation of foodstuffs can be greatly improved by a method of pre-processing carried out before the main food preservation process 25 such as pasteurisation or sterilisation by retort technology. The use of the pre processing method provides foods on which detrimental micro-organisms and enzymes have been stabilised and when such foods are subjected to a main food preservation process, the final food products are of superior appearance and superior organoleptic qualities compared to foods preserved by preservation 30 techniques of the prior art. Furthermore use of the pre-processing method can reduce the processing temperature and/or time spent in the main food WO 98/52421 PCT/AU98/00357 4 preservation process, thus reducing use of energy and reducing the cost of the food preservation process. In one aspect the present invention provides a method of pre-processing food 5 comprising subjecting the food to an environment for a time sufficient to stabilise any unwanted micro-organisms and enzymes present on the food. Foods usually comprise numerous types of micro-organisms and enzymes, some of which may be detrimental, and some of which are harmless or even useful. 10 For example the cheeses (such as blue vein cheeses), salami and sauerkraut owe their taste and long shelf life to useful, naturally occurring micro-organisms and enzymes. The method of the first aspect of the present invention is directed to stabilising 15 unwanted micro-organisms present on foods, and does not necessarily affect the harmless or useful micro-organisms present. However, the method may affect all types of micro-organisms and enzymes. Throughout this specification, reference to stabilisation of a micro-organism shall 20 mean that propagation and/or growth of the micro-organism is inhibited or completely stopped and/or the micro-organism is rendered more sensitive to being killed during subsequent processing. Throughout this specification, reference to stabilisation of an enzyme shall mean that the enzyme is affected so that it cannot chemically react with or cause detriment to the food or its ability to 25 do so is reduced. The types of micro-organisms intended to be stabilised by the method of the present invention include micro-flora and micro-fauna such as bacteria, moulds, fungi, yeast and spores. 30 Most micro-organisms are present at or adjacent the surface or skin of foodstuffs. Accordingly it is often unnecessary for the conditions and the pre-processing WO 98/52421 PCT/AU98/00357 5 method to penetrate into the foodstuff far beyond the surface or skin of the foodstuff. The types of micro-organism present and the degree of detriment caused will vary 5 from foodstuff to foodstuff. Accordingly the method of pre-processing and in particular the environment used with respect to the present invention will vary with the type of food. The pre-processing takes into account the known growth and survival limits for 10 the micro-organisms present on the type of food being processed. The following table (Table 1) lists various species of micro-organisms and approximate growth and survival limits where various other parameters are optimal. For example, the minimum growth temperatures in Table 1 are for growth in optimal, neutral pH, high a w (water activity) microbiological media. 15 TABLE 1 Type pH for Mina for Anaerobic micro-organism growth growth g rowth growth in (eg n vacuum temp pack) (C) Aeromonas 4.0 4% Yes 0 hydrophilla salt Bacillus cereus 4.4 0.91 Yes 4 Clostridium botulinum 4.8 0.94 Yes 10 (proteolytic A, B and F) Clostridium botulinum 4.8 0.97 Yes 3.3 (non-proteolytic E) Clostridum botulinum 4.6 0.94 Yes 3.3 (non-proteolytic B and

F)

WO 98/52421 PCT/AU98/00357 6 Clostridium 5.5 0.93 Yes 5 perfringens Enterobacter 4.4 0.94 Yes 2 aerogeries Escherichia Coli 4.4 0.9 Yes 4 Lactobacilli 3.8 0.94 Yes 4 Listeria 4.4 0.92 Yes 0.1 monocytogenes Micrococci 5.6 0.9 No 4 Moulds <2.0 0.9 No <0 Pseudomonas species 5.5 0.97 No <0 Salmonella species 3.8 0.92 Yes 4 Staphylococcus 4.0 0.83 Yes 7.7 aureus Vibrio 4.8 0.94 Yes 5 paraheamolyticus Yeasts 1.50 0.8 Yes .5 Yersinia 4.5 7% Yes -1.3 enterocolitica salt Interactions between factors are likely to considerably alter these values Source: Campden & Chorleywood Food Research Association; from the Freshline m Guide to Modified Atmosphere Packaging, p.26 5 The environment to which the micro-organisms and enzymes are subjected can be liquid, vapour or gas or mixtures thereof. Dissolved solutes may be present in the liquid or vapour. 10 Preferably the pre-processing method of the present invention comprises acidification of the food. For example the pre-processing method may comprise bringing the foodstuff in contact with an acidulant.

WO 98/52421 PCT/AU98/00357 7 Preferably the acidulant is an organic food acid such as citric acid, tartaric acid, phosphoric acid or the like. Its is further preferred that the acidulant is an aqueous solution of an organic food acid. For example it may be formed by 5 adding to water 1-5% of said acid, more preferably .5-1% of said acid, based on the total volume of the solution. It is also preferred that the acidic solution not contain any added salts. That is the acidic solution is not a brine. 10 Typically the acidic solution may be used for fruits, such as apples. Apples have a naturally high acid content and many of the bacteria associated with apples are adapted to tolerate this acid content. However if the level of acid in the environment surrounding the apple is raised during the pre-processing method of 15 the present invention the remaining bacteria will not propagate. Alternatively, the acidulant may be a solution containing glucono delta lactone. It is preferable that the solution is water to which is added .1-5% glucono delta lactone more preferably 1-2% glucono delta lactone, based on the total volume of 20 the solution. It is also preferred that the solution containing glucono delta lactone also not contain any added salts. That is the solution is not a brine. The acidulant may be brought into contact with the acidulant in a number of ways. In a preferred embodiment, where the acidulant is a solution, the food is blanched 25 in the solution. The blanching may be carrying out by bringing the solution to the boil and for a period of 5 seconds to 10 minutes, more preferably 1-4 minutes. After blanching, the food may be removed from the solution. In another embodiment, the acidulant solution is added to the food during a pre 30 manufacture stage and becomes incorporated as part of the food. For example, in the manufacture of hamburgers, an acidulant solution to added to the raw WO 98/52421 PCT/AU98/00357 8 ingredients combined to form the hamburger. It is preferred to package this product in the absence of any additional acidulant solution. The method of the present invention for pre-processing food will typically be 5 carried out using a processing apparatus comprising a processing tank into which the food is placed, a reservoir for storage of a processing liquid which can be added to the tank and optionally a pump for circulating the liquid in the tank, a heater for heating the liquid and detectors/controllers for monitoring and changing physical parameters associated with the environment created in the tank for 10 processing the food. The tank may be able to be pressurised with liquid or gas. The pre-processing method is not sufficient on its own to provide a shelf-stable product hence further processing is also required. 15 In another aspect the present invention provides a method of preserving food comprising subjecting the food to the aforementioned pre-processing method, and then subjecting the food to a preserving process. Preferably, the method is used to produce a shelf stable food product as earlier 20 defined. In a preferred embodiment, the food is packaged before undergoing the further processing. Typically the packaging step comprises hermetically sealing the pre processed food in a polymeric bag or other suitable polymeric container. Other 25 containers suitable for processing and storage of the shelf-stable product will be readily apparent to those skilled in the relevant technology. The container may be evacuated or filled with air or alternatively the air may be replaced by another gas such as nitrogen. 30 In a preferred embodiment, the food is placed in a polymeric bag in the absence of a brine solution or substantially in the absence of any acidulant solution. It is WO 98/52421 PCT/AU98/00357 9 preferred to partially evacuate the air in the bag. For example vacuum packaging to about 30% can be undertaken. The food preserving process may be of the type typically used in the food 5 preparation industry. For example, it may comprise a sterilisation process using heat such as in a retort process or by heating at ambient pressure. Preferably the food is heated to a temperature between 70'C to 115'C. For food to achieve a certain temperature it is usual that the surrounding environment must be raised to above 5°C above the desired food temperature. 10 The sterilisation process may be quite simple but the processing parameters will vary from foodstuff to foodstuff. For example food that is not dense may be heated by exposing it to hot water or steam. Food that is dense may require heating at a higher temperature such as in a retort under pressure. The food, 15 placed in packaging in the retort, may be heated by full emersion in water or steam. Where a retort system is being used for sterilisation, it is noted that some foodstuffs need full retort processing while other foodstuffs do not require full 20 retort processing. Typically, the packaged food is heated in the retort apparatus to a temperature of between 1000C to 115'C for a period of 10-35 minutes at a pressure of 120 kPa to 145 kPa. Alternatively the packaged pre-processed food may be heated using an ambient 25 pressure system such as a bath of boiling water, or heating via a spiral steam cooker. In a preferred embodiment, the food is heated to a first temperature and then maintained at a second temperature. More preferably the food is heated to a first temperature of about 800C to 950C for around 5-15 minutes and then maintained at a second temperature of around 700C to 950C for around 5-25 30 minutes, the whole sterilisation process being carried out at ambient pressure.

WO 98/52421 PCT/AU98/00357 10 As noted above in one embodiment the pre-processing method is followed by retort processing. What follows is a description of a typical retort process applicable to the present invention. 5 The food is subjected to the pre-processing method of the present invention and then the food is placed in retort quality barrier bags such as those comprising a film of nylon laminated between layers of polypropylene. The bags are then laid out on trays, allowing for bag expansion during processing. The trays are then placed in a retort and the retort secured. The retort is filled with water to a level 10 near a sensor at the top of the inside of the retort. A vapour space is left for condensation of the heated water. The blowing of steam into the water is then commenced. A circulation pump is started, sucking water form two inlets at the lowest point of the retort and spraying the water back through an opening at the top of the retort. The recycle time is 5 minutes. The steam blowing is continued 15 until the core of the foodstuff reaches the desired temperature. The hot water is then pumped out and immediately replaced with cold water, reducing the foodstuff temperature to below 55 OC, the temperature at which the cooking process stops. 20 Typically the apparatus for retort processing comprises a retort in which the food is placed, hot and cold water reservoirs from which hot and cold water respectively can be pumped into the retort, a boiler for supplying steam to the retort, an air compressor for supplying air to the retort and appropriate sensors and controllers fro controlling the supply of water, steam and compressed air to 25 the retort. In a less rigorous sterilising process the packaged food is placed on a conveyor belt which travels slowly through a long closet. In the mentioned closet the packaged food is exposed to heat through the spraying of hot water or steam at a 30 temperature of 950 (such that the temperature of the packaged food reaches around 900C) for a certain time period. Later, as the package travels on the conveyer belt the external temperature is reduced to around 90 0 C (so that the WO 98/52421 PCT/AU98/00357 11 temperature of the packaged food is 850C) for a certain time period depending upon the food being processed. At the end of the conveyor belt the bag drops onto a cooling plate where its temperature is quickly reduced to ambient. 5 One of the advantages of the present invention is that the pre-processing may reduce the severity required of the conditions of the main preserving process. This leads to savings in time and energy expended on the main processing step, thus contributing to the economy of the process. 10 It should be noted that the severity of the main preserving process may be reduced to a level where the main preserving process (or the pre-processing) alone would not provide a shelf stable product, but the combination of the pre processing method of the present invention plus the main preserving process is sufficient to provide a shelf stable product. 15 Typically each processing run using the pre-processing method of the present invention will be used for one particular food or type of food. For example, the pre-processing method may be used to process a batch consisting of a single vegetable such as corn or several different types of vegetables such as corn and 20 peas. The pre-processed vegetables may then be packaged and sent for further processing or they may be mixed with other food such as meat, lentils, cereal, flour, rice, pasta or the like, and the mixture is then packaged and subjected to further processing. 25 The process may be used in a typically canning process such that the canning times and temperatures can be reduced due to the pre-processing stabilisation stage. In another embodiment the present invention is directed to food preserved by the 30 method of this invention and to such food in packaged form. Preferably this food product is a vegetable, fruit, meat or cereal or is formed from a combination of foods ie pasta.

WO 98/52421 PCT/AU98/00357 12 The invention will now be further described by the following non-limiting Examples: 5 Example 1 The method of the present invention was applied to a food manufactured from a recipe which comprised prime sliced meat, soy sauce, egg, starch, wine, sodium bicarbonate, chilli powder, Chinese pepper, five spice powder, mono-sodium glutamate and sugar. The recipe was prepared by separating the ingredients into 10 dry ingredients and wet ingredients. The wet ingredients were combined and thoroughly mixed and the pH of the mixture measured at 6.7. At this pH most micro-organisms will grow prolifically if given sufficient nutrients, moisture, temperature and air. 15 Pre-Processing To stabilise the micro-organisms, fungus, mould etc on the food, the wet ingredients were steamed for two minutes. Such steaming is sufficient to kill most of the surface organisms mentioned before. At this point the proliferation of micro-organisms had been halted and a significant number of micro-organisms 20 had been killed. The pre-processed wet ingredients were then combined with the dry ingredients At this point the pH of the ingredients was lowered by the addition of 1.5% Glucono Delta lactone diluted in an amount of pure water sufficient to lower the 25 pH of the total ingredients to 4.3. The ingredients were then portioned and placed in retort barrier bags and hermetically sealed. Sterilisation Process 30 The plastic retort bags containing the recipe mixture were placed into a retort which was then filled with water. ( It is noted that the same sterilisation can be carried out by filling the retort with hot water). The food was exposed to a WO 98/52421 PCT/AU98/00357 13 temperature of 100 Celsius for 10 minutes at then 90 Celsius for 20 minutes at ambient pressure. The water was then pumped out of the retort and the retort bags containing the 5 recipe mixture were left to cool over a 5 minute period in the retort before being removed. The food thus prepared was shelf stable and required no refrigeration. No micro-organism growth could be detected and the food maintained most of the organoleptic properties of the freshly cooked ingredients. 10 The food recipe prepared by the process of the present invention was compared with the results of processing the same food recipe using a process of the prior art. The differences between the process parameters for the two processes are summarised in Table 2; 15 TABLE 2 Process of this Invention Prior Art Process Acidification; Yes No Blanching; Yes Sometimes Retort 1000C for 10 mins 121 0 C 20 Temperature; then 90 0 C for 20 mins Time; 35-45 minutes 70-90 minutes Pressure; Ambient 90-95 kPa 25 Comparison of the values in Table 2 show that the current process subjects the food to a lower temperature for a far shorter time compared to the process of the prior art. Accordingly the process of the current invention is not as harsh on the food and is therefore less likely to damage or change the physical or chemical structure of the ingredients. The process of the current invention requires less 30 energy input and is therefore more economical than the process of the prior art. Example 2 Red Kidney Bean WO 98/52421 PCT/AU98/00357 14 Pre processing Red Kidney Beans are soaked in hot water for 1Hr then blanched in boiling water with a solution of .5% Citric Acid for a period of 4 Minutes. The beans are 5 removed from the blanching mixture and all liquid allowed to drain off. Packing The Red kidney Beans are then packed in retort quality barrier bags or other appropriate packaging. The package is heat sealed. The packaging may be 10 vacuum packed if desired however it is recommended that any vacuum packing should be limited to 30% to minimise damage and to give a fresh appearance. Sterilisation The packages are placed in a retort. The retort is filled with hot water and the 15 temperature is increased to 110 OC over 7 minutes. Pressure in the retort is kept at 140 kpa. The water in the retort stays at 110C for 30 minutes before being quickly cooled by evacuating the hot water and replacing with cold water. At this stage the product is shelf stable 20 Example 3 Sweet Corn The sweet corn is de husked and cleaned 25 Pre-Processing A blanching solution is prepared by adding to water 1 % citric acid. The blanching solution is brought to the boil and the sweet corn is then blanched for 1 minute at boil. The sweet corn is removed from the blanching mixture 30 Packaging WO 98/52421 PCT/AU98/00357 15 The sweet corn is then packed in retort quality barrier bags or other appropriate packaging. The package is heat sealed. The packaging may be vacuum packed if desired however it is recommended that any vacuum packing should be limited to 30% to minimise damage and to give a fresh appearance. 5 Sterilisation Because the sweet corn is a dense product requiring a higher degree of heat penetration it requires the sterilisation process to be carried out in a retort. 10 The packages are placed in a retort. The retort is filled with hot water and after 7 minutes reaches 115C at 140 kpa. The water in the retort is kept at 115C for 30 minutes before being quickly cooled by evacuating the hot water and replacing with chilled water. 15 At this stage the product is shelf stable Example 4 Chicken and Curry Dish 20 The above example involved the purchase of a chilled home replacement meal available from a retailer. The meal was tested for its organoleptic qualities and then for its chemical characteristics. The ingredients were found to have a high pH and hence required adjustment to comply with the present process. 25 Pre-Processing A solution of 2% by weight of Glucono Delta Lactone was added to the ingredients sufficient to lower the ingredients pH to 4.3 pH. The addition of Glucono Delta Lactone did not effect basic organoleptic qualities 30 Packaging WO 98/52421 PCT/AU98/00357 16 The chicken and curry meal is then packed in retort quality barrier bags or other appropriate packaging. The package is heat sealed. The packaging may be vacuum packed if desired however it is recommended that any vacuum packing should be limited to 30% to minimise damage and to give a fresh appearance. 5 Sterilisation The packaged food is immersed in boiling water (100C) for 10 minutes and then left to simmer (90C) for a further 20 minutes. The heated packaging is then immediately flushed with chilled water sufficient to cool the contents of the 10 package. At this stage the product is shelf stable Example 5 15 Cauliflower The cauliflower is cleaned thoroughly and the florets are separated to adequate serving size. 20 Pre-Processing A blanching solution is prepared containing 1% citric acid. The blanching solution is brought to boil and the cauliflower is blanched for 1 minute. The cauliflower is removed from the blanching solution and then immersed in a bath of 1% sodium 25 meta bisulphite at 45C for 5 minutes. Packaging The cauliflower is removed from the bath and then packed in retort quality barrier bags or other appropriate packaging. The package is heat sealed. The packaging 30 may be vacuum packed if desired however it is recommended that any vacuum packing should be limited to 30% to minimise damage and to give a fresh appearance.

WO 98/52421 PCT/AU98/00357 17 Sterilisation The packaged food is immersed in boiling water for 10 minutes and then left to simmer for a further 10 minutes. The heated packaging is then immediately 5 flushed with chilled water sufficient to cool the contents of the package. At this stage the product is shelf stable Example 6 10 Hamburger Ingredients for the manufacture of hamburgers were combined. Ingredients may include beef, lamb, chicken or any other meat. These are combined with egg, flour, garlic, diced onion and other minor ingredients such as spices. A chemical 15 analysis was then completed to find the ingredients pH level. Pre-Processing To the hamburger ingredients a solution of Glucono delta lactone was added 20 sufficient to decrease the acid level to a 4.3. The hamburgers were then formed and fried in boiling oil until cooked The hamburgers were taken from the fryer and immediately packed. Packaging 25 The hamburgers were then packed in retort quality barrier bags or other appropriate packaging. The package is heat sealed. The packaging may be vacuum packed if desired however it is recommended that any vacuum packing should be limited to 30% to minimise damage and to give a fresh appearance. 30 Sterilisation WO 98/52421 PCT/AU98/00357 18 The packaged food is immersed in boiling water for 10 minutes and then left to simmer for a further 20 minutes. The heated packaging is then immediately flushed with chilled water sufficient to cool the contents of the package. 5 At this stage the product is shelf stable Example 7 Carrot 10 The carrot is cleaned and the skin peeled away. The carrot is then sliced julienne style. Pre-Processing A blanching solution is prepared containing 1% Glucono delta Lactone. The 15 blanching solution is brought to the boil and the julienne carrot is then blanched for 1 minute at 100C. Packaging The julienne carrots were removed from the blanching solution and then packed 20 in retort quality barrier bags or other appropriate packaging. The package is heat sealed. The packaging may be vacuum packed if desired however it is recommended that any vacuum packing should be limited to 30% to minimise damage and to give a fresh appearance. 25 Sterilisation The packaged food is immersed in boiling water for 10 minutes and then left to simmer for a further 10 minutes. The heated packaging is then immediately flushed with chilled water sufficient to cool the contents of the package. 30 At this stage the product is shelf stable WO 98/52421 PCT/AU98/00357 19 Throughout the description and claims of this specification, the word "comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives, components, integers or steps. 5 It will be appreciated that various modifications can be made to the method and apparatus of this invention without departing from the spirit and ambit of the invention.

Claims (22)

1. A method of pre-processing food comprising subjecting the food to an environment for a time sufficient to stabilise any unwanted micro 5 organisms and enzymes present on the food.

2. The method according to claim 1 wherein the step of subjecting the food to an environment comprises bringing the food in contact with an acidulant to lower the pH of the food to around 4.5 or lower. 10

3. The method according to claim 2 wherein the acidulant is an aqueous solution of an organic food acid. 0

4. The method according to claim 3 wherein the organic food acid is selected 15 from citric acid, tartaric acid or phosphoric acid.

5. The method according to claim 2 wherein the acidulant is an aqueous solution containing glucono delta lactone. 20

6. The method according to any one of claims 3-5 wherein the solution substantially free of any added salts.

7. The method according to any one of claims 3-6 wherein the food is blanched with said solution. 25

8. The method of any one of claims 2-6 wherein the acidulant is added as a raw ingredient of the food during a step of manufacturing the food.

9. A method of preserving food comprising pre-processing the food according 30 to the method of any one of claims 1-6 and 8 and then subjecting the food to a preserving process. WO 98/52421 PCT/AU98/00357 21

10. The method according to claim 9 wherein prior to said preserving process the food is packaged in the absence of a brine solution.

11. The method of claims 9 or 10 wherein the preserving process comprises 5 heating the food to a sufficient temperature and for a sufficient time to sterilise the food.

12. The method of claims 10 or 11 wherein during the sterilising step the packaged food is heated to a temperature of around 70 0 C-1150C. 10

13. The method of claim 12 wherein the packaged food is heated to a first temperature of around 800C to 950C for around 5-15 minutes and then maintained at a second temperature of around 700C to 950C for around 5 25 minute, said sterilisation process being carried out at ambient pressure. 15

14. The method of claim 12 wherein during the sterilisation step the packaged food is heated to a temperature of 1000C to 115oC for a period of 10-35 minutes at a pressure of 120 kPa to 145 kPa. 20

15. A method of preserving food comprising pre-processing the food according to the method of claim 7 and then subjecting the food to a preserving process.

16. The method according to claim 15 wherein prior to said preserving process 25 the food is removed from the acidulant solution and is packaged in the absence of a brine solution.

17. The method of claims 15 or 16 wherein the preserving process comprises heating the food to a sufficient temperature and for a sufficient time to 30 sterilise the food. WO 98/52421 PCT/AU98/00357 22

18. The method of claim 18 wherein during the sterilising step the packaged food is heated to a temperature of around 70'C-1151C.

19. The method of claim 18 wherein the packaged food is heated to a first 5 temperature of around 800C to 950C for around 5-15 minutes and then maintained at a second temperature of around 700C to 950C for around 5 25 minute, said sterilisation process being carried out at ambient pressure.

20. The method of claim 18 wherein during the sterilisation step the packaged 10 food is heated to a temperature of 1000C to 115 0 C for a period of 10-35 minutes at a pressure of 120 kPa to 145 kPa.

21. Food produced by the method of claims 9 or 15. 15

22. Packaged food produced by the method of any one of claims 10-14 or 16 20.