Composition and Flavor of Milk and Cheddar Cheese from Cows Fed Unsaturated Dietary Fat

Cheese is one of five products in the dairy industry that increased in per capita sales in 1990 (Milk Industry Foundation, 1991). In the past decade, cheese sales increased by 25.8% (Milk Industry Foundation, 1991). In 1980, 23.5% of the United States milk supply was utilized by the cheese industry, that has increased to 31.9% of the total supply in 1990 (Milk Industry Foundation, 1991). Per capita consumption of all cheeses other than cottage cheese increased from 7.94 kg in 1980 to 11.12 kg in 1990 (USDA, 1991). Today an increasing share of new food products introduced into the marketplace are low-fat or no-fat. Many health professionals are recommending diets lower in fats, particularly diets lower in saturated fatty acids. For consumption of hard cheeses to increase at previous levels, dairy processors may have to offer cheeses to consumers that are lower in fat and/or saturated fatty acids. Fatty acid composition of milk fat can be influenced by several factors. Composition of the ration fed to a cow is one method that can be used to alter the fatty acid composition of milk fat (Christie, 1980). Ample research has been reported on the feeding of unprotected fats, oils, and oilseeds to dairy cows (Palmquist and Jenkins, 1980). Sources of fat added to diets of dairy cows are heat-treated soybeans (Mielke and Schingoethe, 1981), rolled sunflowers (Finn et al., 1985; Middaugh et al.-, 1988), whole sunflowers (McGuffey and Schingoethe, 1982; Rafalowski and Park, 1982), cottonseed oil (Steele and Moore, 1968), safflower seeds (Stegeman et al., 1992), hydrogenated marine oils (Astrup et al., 1981), canola seeds (Ashes et al., 1992), and oleic acid (C18:1) (Selner and Schultz, 1980). In most experiments where cows were fed fats high in long-chain unsaturated fatty acids, the milk fat had reduced amounts of medium-chain fatty acids and increased amounts of stearic (C18:0) and oleic acids (Christie, 1980). Considerable research has been conducted on feeding protected fats to dairy cows (Astrup et al., 1976; Mattos and Palmquist, 1974; Scott et al., 1971; Wrenn et al., 1976). Polyunsaturated fats were coated with a protein and treated with formaldehyde to protect the lipid from hydrogenation by rumen microorganisms. This allowed larger amounts of fatty acids to be absorbed by the intestines. Incorporation of protected lipid sources into the diet changed the fatty acid composition of the milk fat by increasing, the concentration of polyunsaturated fatty acids, while increasing milk production (Bitman et .al., 1973; Cook et al., 1972; Dunkley et al., 1977). Residual formaldehyde is transferred .to the milk (Wrenn et al., 1976) when using formaldehyde for protecting fat. · Formaldehyde protected lipid supplements -have not been approved by the Food and Drug Administration for use in lactating dairy cows due to the formaldehyde residues that are transferred to milk. Research into the processing and sensory properties of milk and dairy products produced by cows fed unprotected lipids that are high in unsaturated fatty acids has been limited. The objective of this research was to evaluate the effect of feeding two sources of unprotected added dietary fat, extruded soybeans and rolled sunflowers, to lactating dairy cows to evaluate the effects on composition, flavor, and physical properties of milk and Cheddar cheese