Food or edible material: processes – compositions – and products – Fermentation processes – Of milk or milk product
Reexamination Certificate
1997-10-13
2001-01-16
Wong, Leslie (Department: 1761)
Food or edible material: processes, compositions, and products
Fermentation processes
Of milk or milk product
C426S036000, C426S042000, C426S580000, C426S583000, C435S041000, C435S071100, C435S252900, C435S253400
Reexamination Certificate
active
06174550
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods and reagents useful in maintaining the quality of frozen food products during frozen storage, particularly enhanced storage life and the maintenance of consumer accepted quality of dairy products.
BACKGROUND OF THE INVENTION
Refrigeration, particularly freezing, is a common and preferred means for storing biological materials. Frozen storage generally arrests or considerably slows the deterioration of the biological product.
Frozen or refrigerated foods are now a mainstay of the human diet in developed nations. Thus extensive research has and is being carried out by food scientists to ensure high quality products for the consumers. This is particularly true with regard to frozen vegetables and frozen deserts such as ice cream and yogurt.
Frozen deserts such as ice cream or yogurt are generally eaten in the frozen state. Thus, the texture of the frozen product as well as its flavor is important to consumers. Texture is to a large extent governed by the size of the ice crystals. Producers of these frozen deserts have gone to considerable effort and expense to ensure smooth textured products. However, during frozen storage the ice crystals can grow and thus roughen and spoil this texture. The growth of ice crystals during frozen storage is known as recrystallization. This problem is particularly common when the frozen storage conditions are less than ideal, such as during transportation or storage in modern frost-free home freezers. After a relatively short period of time at above-zero temperatures (i.e., above 0° C.), or even at sustained freezing temperatures, frozen foods can become less desirable or even unsuitable for human consumption due to the ice recrystallization process.
Although manufacturers use a variety of techniques to reduce the damage associated with recrystallization success has been limited and significant problems remain. Thus there is a need for new techniques to reduce or prevent the recrystallization process and improve the characteristics of frozen foods. These techniques and compositions should be inexpensive and completely safe and suitable for human consumption.
It has been clearly demonstrated that antifreeze polypeptides (AFP) can effectively inhibit ice recrystallization at low (&mgr;g/ml) concentrations in aqueous solutions and frozen food products (see, e.g., Knight et al., 1984,
Nature
308:295-296; Knight et al., 1986,
Cryobiology,
23:256-262; Knight et al., 1988,
Cryobiology,
25:55-60; Warren et al., U.S. Pat. No. 5,118,792). Warren et al, supra, have suggested adding purified antifreeze polypeptides directly to food products prior to freezing to improve preservation characteristics during frozen storage.
At the present time antifreeze proteins are available for commercial use from two sources; the blood serum from a small number of fish species found in cold water, and recombinant DNA techniques such as those described by (but not restricted to) Warren et al., supra. Other sources of antifreeze proteins, such as transgenic plants and animals, are currently being explored. Regardless of the source, the antifreeze polypeptides must be isolated from the medium in which they are found or produced, and subject to extensive purification. These purification procedures are expensive to the point where the cost of the antifreeze polypeptide additions could exceed the value of the frozen product. Moreover, the purification protocol may introduce contaminants unsafe for consumption.
In the view of the inherent value to producers and consumers of inhibiting ice recrystallization in frozen fermented dairy products, and the fact that antifreeze polypeptides are very effective in this regard, it is desirable to develop methods to incorporate the antifreeze polypeptides into the food products in the most efficient and cost effective method possible.
An ideal method of incorporating antifreeze polypeptides into frozen fermented food products is to have the organism responsible for the fermentation process produce the antifreeze proteins while fermenting the food. A number of antifreeze polypeptides and their genes have been well characterized and sequenced (see, e.g. Anathanarayanan, 1989,
Life Chem. Rep.
7:1-32 and Davies et al., 1990,
FASEB Journal
4:2460-2467). Several of these genes have been expressed in bacteria, transgenic plants, fish and Drosophila (see, e.g., Fletcher et al., 1988,
Can. J. Fish. Aquat. Sci.
45:352-357; Rancourt et al., 1987,
Mol. Cell. Biol.
7:2188-2195; Kenward et al., 1993,
Plant Mol.Biol.
23:377-385; Li et al., 1991,
Protein Engineering
4:995-1012; and Sönnichsen et al., 1993,
Science
259:1154-1157).
In view of the widespread popularity of frozen fermented dairy products such as yogurt it would be desirable to develop methods for producing such products more efficiently at lower cost and with better flavor and texture. The present invention provides methods for achieving this goal.
SUMMARY OF THE INVENTION
The present invention provides methods for preparing a frozen fermented food product. This method comprises the steps of (a) contacting a food product with a microorganism that is capable of secreting a fish antifreeze polypeptide, wherein the microorganism is capable of fermenting the food product to produce the fermented food product, (b) incubating the food product with the microorganism under conditions in which fermentation takes place so that a fermented food product is produced having the antifreeze polypeptide present in an amount effective at inhibiting recrystallization of the product; and (c) freezing the fermented food product at a temperature below −5° C., so as to produce a frozen fermented food product.
In one embodiment the food product is a dairy product (e.g., milk) which can be fermented to produce yogurt, buttermilk or cheese.
The microorganism of the invention is usually a bacterium (e.g.,
Lactobacillus bulgaricus; Streptococcus cremoris, Streptococcus lactis; Bifidobacterium bifidum, Bifidobacterium longum
) but may also be a fungus such as a yeast (e.g.,
Saccharomyces fragilis, Saccharomyces cerevisiae, Saccharomyces lactis,
and others). According to the invention these microorganisms are genetically engineered so that they are capable of secreting a fish antifreeze polypeptide (or a peptide with substantial sequence similarity to a fish antifreeze polypeptide and with antifreeze properties similar to a fish antifreeze polypeptide). In a preferred embodiment, the antifreeze polypeptide is an animal antifreeze polypeptide, with a fish antifreeze polypeptide preferred. Most preferred is microorganism capable of expressing an ocean pout type III antifreeze polypeptide (see, e.g., Hew et al., 1984,
J. Comp. Physiol. B
155:81-85; Li et al., 1985,
J. Biol. Chem.
260:12904-12909).
In a most preferred embodiment the invention comprises incubating milk with bacterial species
Lactobacillus balgaricus
and
Streptococcus lactis
that are capable of fermenting milk to produce yogurt and capable of secreting an ocean pout type III antifreeze polypeptide; incubating the bacteria and milk under conditions that produce yogurt; and freezing the yogurt at a temperature below −5° C., so as to produce frozen yogurt.
The invention also provides a composition comprising yogurt and a microorganism wherein the microorganism comprises a gene encoding a fish antifreeze polypeptide.
DETAILED DESCRIPTION
Definitions
As used herein, “fermentation” refers to the chemical conversion of carbohydrates or proteins in foods through the use of microorganisms. In this process carbohydrates are often converted to lactic acid.
As used herein, “food product” refers to a foodstuff (a substance that can be used, or prepared for use, as food) that can be transformed by the action of a fermenting microorganism to a fermented food product.
As used herein “fermented food product” refers to an edible food prepared by a process that includes fermentation by a microorganism.
As used herein “yogurt” refers to a dairy product produced by the lac
Fletcher Garth L.
Hew Choy L.
Joshi Shashikant B.
Wu Yaling
Seabright Corporation Limited
Townsend and Townsend / and Crew LLP
Wong Leslie
LandOfFree
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