FIELD OF THE INVENTION

The invention relates to a process for preparing a modified commercial dairy protein concentrate. In particular, the invention relates to the preparation of a dairy protein concentrate which is suitable for use as a replacer or extender of rennet casein in the production of food products, in particular analog mozzarella cheese, processed cheese and imitation cheese. BACKGROUND OF THE INVENTION

Many consumer food products, such as frozen pizzas, require the presence of cheese for aesthetic and flavour reasons. However, due to the relative expense of real cheese, and due to the relatively careful handling required for real cheese, there have been developed 'analog cheeses' which fulfil the aesthetic and flavour requirements, but which are more robust and which can be manufactured at a lower cost than real cheese.

Due to its functionality, it is usual to use rennet casein as the source of protein in the preparation of analog cheeses. The rennet casein has a critical functional role in the analog cheese: forming a structural network in order to encase the fat and to give the analog cheese the characteristic texture of real cheese.

However, due to the limited supply and high price of rennet casein, it is desired to find lower cost alternatives for this material, which nevertheless will perform in a manner which would allow them to replace rennet casein in analog and other cheese preparations.

In order to address this, attempts have been made to use other high protein milk powders to replace rennet casein, one example being 'MPC-85', which is a commercial milk protein concentrate supplied by Murray Goulbum Cooperative Co Limited, of 140 Dawson St, Brunswick, Victoria 3056, Australia. However, in general, these powders have not exhibited sufficient functionality as a rennet casein replacer for anything more than partial replacement of the rennet casein to be made in these analog cheese applications.

Therefore, it is an object of the present invention to provide a method for preparing a milk protein concentrate, milk protein isolate or micellar casein, said method imparting sufficient functionality to said product to allow it to be used as a rennet casein replacer or extender in the manufacture of food products, particularly analog cheese products. SUMMARY OF THE INVENTION

According to the invention, there is provided a method for preparing a dairy protein concentrate, isolate or micellar casein, said method including the steps of: preparing a pasteurised liquid skim milk, whole milk, milk protein concentrate or reconstituted milk feedstock; subjecting the feedstock prepared above to membrane filtration thereby to obtain a retentate having a protein content of between 50% and 95% by weight (dry matter basis), as desired; reacting said retentate with a proteolytic enzyme to modify the protein, for example to cleave the glycomacropeptide (GMP) from the kappa-casein in the protein structure.

A dairy protein product prepared according to the above process is anticipated to successfully act as a complete or partial replacement for rennet casein. Further, it is anticipated that protein products manufactured according to the invention will perform as well or better than rennet casein in a range of food products.

The advantage of the invention is thought to derive from the inventive realisation that hydrolysing the dairy protein, in the manner described above, results in a product with a protein structure similar to that found in rennet casein. The structural similarity of the protein thus created is thought to allow the modified protein concentrate to mimic the action and functionality of rennet casein.

Preferably, the proteolytic enzyme is chymosin, as best results have been obtained with this enzyme. Where chymosin is used, it is preferred to keep the reaction temperature between about 2°C and about 40°C, in order to ensure efficacy of the enzyme, and optimally at about 15°C.

Preferably, the protein content of the retentate is about 85% (dry matter basis).

Advantageously, the retentate prepared according to the above method can be spray dried to form a dispersible powder, for ease of storage, transport and handling.

Preferably, where the feedstock is milk, after the membrane filtration step and prior to the addition of the enzyme, a chelating agent (such as sodium hexametaphosphate) may be added to the retentate. Preferably, the sodium hexametaphosphate is added to the retentate at a level of about 0.05% by weight. Such chelating agents may be added at levels between about 0.02% and about 1.0% by weight.

The advantage of adding a chelating agent is that this acts to sequester calcium in the feedstock, preventing the reaction of calcium with the kappa- casein, which would cause coagulation of the remaining feedstock into curd, which would both reduce the overall conversion of feedstock into the desired product and would create difficulties in drying the protein concentrate.

Alternatively, careful control of temperature of the enzyme reaction will also act to manipulate protein solubility, and may be applied to this effect, either with or without the addition of the chelating agent. However, use of the chelating agent will allow for superior control of the coagulating reaction.

According to another aspect of the invention, there is provided a dairy protein concentrate, isolate or micellar casein manufactured according to the method as described above.

According to another aspect of the invention, there is provided an analog cheese product prepared using a protein concentrate, isolate or micellar casein manufactured according to the method as described above.

According to another aspect of the invention, there is provided the use of a protein concentrate, isolate or micellar casein manufactured according to the method as described above in the manufacture of an analog cheese product.

Now will be described, via specific, non-limiting examples, a preferred embodiment of the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Example 1 - Preparation from skim milk

As a feedstock, 100,000 litres of skim milk, containing 3.70% protein, 0.07% fat and 9.15% non-fat solids, was pasteurised at 72°C for 15 seconds and subsequently cooled to 8 ⁰ C. The skim milk was then concentrated by ultrafiltration to produce 22,957 litres of retentate, having 15.36% protein, 0.30% fat and 18.28% non-fat solids.

To the retentate was added 8.4 kg of sodium hexametaphosphate, injected as a 3.5% solution in water.

The temperature of the retentate was then adjusted to 15°C and 5.3 litres of chymosin (quadruple strength, obtained from CHR Hansen Pty Ltd, of Greenacres, South Australia) was added to the retentate as a 2.5% solution in water.

After a reaction time with the enzyme of 20 minutes, the retentate thus modified was then spray dried to produce 4,394 kg of modified milk protein concentrate powder containing 80.26% protein, 1.59% fat and 4.50% moisture. The powder was cooled and packed.

Example 2 - Enzymic modification of commercial milk powder.

A feedstock was prepared by combining 100 kg of milk protein concentrate having 85% protein in dry matter (MPC-85, obtained from Murray Goulburn Co-Operative Co Limited, of 140 Dawson St, Brunswick, Victoria 3056, Australia) with 200 kg water at 55 ⁹ C, using an Ultraturrax mixer to minimise aeration.

The solution was cooled to 12 ^Q C and 0.25 kg of hexametaphosphate was added to the solution.

Enzyme (120 mL of chymosin as per Example 1), diluted 10-fold with water, was added with gentle agitation. After 20 minutes of reaction time, the material was transferred to the analog cheese-making process discussed below.

Example 3 - Analog cheese production 1.

The material obtained in Example 1 would be anticipated to be successful in producing analog cheese via the following indicative method: mix 25kg of

Example 1 dried powder with 25 kg vegetable fat, 45 kg water, 2.1 kg emulsifying salt (Joha PZ7, obtained from B K Giulini GmbH, of Dr.-Albert-Reimann-Straβe 2, D-68526 Ladenburg, Germany), 1 kg sodium chloride and 0.01 kg citric acid. Adjust the pH of the mixture to between 5.5 - 5.8. Heat the mixture to 75 ^Q C and hold for one minute using a steam jacketed kettle, or similar. Then mould and cool the analog cheese.

Example 4 - Analog cheese production 2.

The material obtained in Example 2 would be anticipated to be successful in producing analog cheese via the following indicative method: heat the material obtained in Example 2 to 40 ⁹ C then mix with 100 kg vegetable fat, 8.4 kg emulsifying salt (Joha PZ7, obtained from B K Giulini GmbH, of Dr.-Albert- Reimann-Straβe 2, D-68526 Ladenburg, Germany), 4 kg sodium chloride and 0.04 kg citric acid. Adjust the pH of the mixture to between 5.5 and 5.8. Heat the mixture to 75 ^Q C and hold for one minute using a steam jacketed kettle, of similar. Then mould and cool the analog cheese so produced.

It will be understood by those skilled in the art that the exemplary embodiments of the invention described above are not the only ways in which the invention may be put into effect. There will be numerous ways of putting the invention into effect, whilst remaining within the spirit and scope of the invention. For example, while the above examples relate to the manufacture and use of a dairy protein concentrate, it will be appreciated by those skilled in the art that selection of well known different filtration conditions will result in the manufacture of protein isolates or micellar caseins, to which the inventive method is equally applicable without significant modification.