Physicians and health organizations currently agree that the lipid phase of a diet should provide an optimal balance between polyunsaturated and saturated fats. There has been shown to be a correlation between heart and circulatory diseases and diets containing higher amounts of cholesterol and saturated fats. It is therefore desirable to reduce whenever possible, the amount of cholesterol and saturated fat in foods and in raw materials which are used in food production.
Egg yolk has a large application in foods and as it is an efficient emulsifying agent, it is an essential ingredient in mayonnaises, cake batters containing fats, cream puffs, bakery goods and candies.
Egg yolk contains a high level of cholesterol and saturated fats and is itself an emulsion comprising a dispersion of oil droplets in a continuous phase of aqueous components. It has a total solid content of approximately 50% to 52% composed of 15.5% to 16.5% protein, 31.5% to 34.5% lipid, 0.5% to 1.5% carbohydrate and 0.9% to 1.2% ash.
The egg yolk lipids comprise as their main components approximately 65% triglyceride, 29% phospholipid and 5% cholesterol. The high amount of self emulsifying -phospholipids, wherein the highest hydrophilic component is phosphatidylcholine representing 75% of the total, makes egg yolk a very stable emulsion in addition to being an emulsifying agent.
Substantial research effort has been directed to removal of cholesterol from egg yolks as well as food products which include these materials as ingredients. A variety of approaches to remove cholesterol from egg yolks have been tried. One approach utilizes microorganisms to enzymatically oxidize and degrade cholesterol [Japanese Patent 60-18375]. This method produces cholesterol oxidation products which may be undesirable. Organic solvents have also been used to extract cholesterol [Japanese 48/44458, U.S. Pat. Nos. 4,104,286, 3,881,034, 3,563,765, 4,234,619 and Tokarska, et al., Can. Inst. Food Sci. Tech. J., 18:256-258 (1985)]. Such methods remove a substantial portion of the triglyceride oils, and may involve significant processing steps to remove solvents. These solvents are used to extract the cholesterol from the egg yolk. Even with supercritical carbon dioxide as the solvent, selectivity of cholesterol over triglycerides may be limited [Prepared Foods, 157:186 (1988); Japanese 59-135847]. Edible vegetable oils have also been used to extract cholesterol from egg yolks, as described in U.S. Pat. Nos. 3,717,414, 4,103,040 and 4,333,959. However, each of the processes described in these vegetable oil patents requires the use of high shear mixing treatment to attain adequate extraction transfer of the cholesterol from the egg yolk to the vegetable oil.
U.S. Pat. No. 4,804,555 discloses a process for the simultaneous deodorization and cholesterol level reduction of fish oils. The fish oil is deaerated, mixed with steam, heated, flash vaporized, thin film-stripped with a countercurrent stream and cooled. U.S. Pat. No. 2,234,619 discloses a method for cholesterol removal from eggs by dehydrating the eggs, extracting the cholesterol with liquid dimethyl ether under anhydrous conditions and removing the dimethyl ether by treatment under reduced pressure at low temperatures. U.S. Pat. No. 4,104,286 describes the isolation of cholesterol from eggs through extraction with ethanol, saponification in an aqueous ethanolic alkali metal hydroxide and concentration and purification with a hydrocarbon solvent and methanol.
Thus, it would be desirable to provide egg products having the desirable functional characteristics of egg yolk products (e.g., protein and phospholipids), while reducing the cholesterol level and increasing the polyunsaturated fat to saturated fat ratio. It would further be desirable to do this while retaining the functionality, appearance and taste of natural eggs which would yield good texture upon being cooked.
It is therefore a principal object of this invention to produce egg yolks and egg products therefrom which are substantially lower in cholesterol than normal egg. It is a further object of the invention to produce egg yolk and egg products therefrom which have a polyunsaturated fat to saturated fat ratio of 1 or greater, i.e., the polyunsaturated fat content is equal to or greater than the saturated fat content. In achieving the above objects, it is an overall object of this invention to obtain egg products having the functionality of natural eggs.