Whey protein gel composites of soybean and linseed oils as a dietary method to modify the unsaturated fatty acid composition of milk lipids

Abstract

Dairy products are an important source of nutrients in diets of many persons in developed countries. One criticism of milk fat is its low content of polyunsaturated fatty acids (PUFA), in particular the omega-3 fatty acids (FA). Various methods to protect unsaturated FA from rumen biohydrogenation have been developed. The most promising method employs formaldehyde, a carcinogen, and thus of limited application in many parts of the world due to regulatory exclusion. A novel gel based on whey protein, water, and oil [US Patent Application 20040058003 A1 (Pending); US Patent Application 20050089550 A1 (Pending)] was developed at the University of California in Davis. The objective of this study was to determine the efficacy of this whey protein gel composite as a dietary delivery method to modify the FA composition of triacylglycerol (TG) and phospholipid (PL) fractions, as well as TG sn-2 composition of milk lipids, compared to feeding either unprotected or calcium salts of the oils. Four primiparous Holstein cows were used in a 4 × 4 Latin square design. The supplemental lipid was a 1:1 (w/w) mixture of soybean oil/linseed oil (S/L) added to a total mixed ration. Soybean oil was selected as a source of n6 and linseed as a source of n3 FA. The S/L supplement was fed in one of four physical forms including: (1) oil (Oil) where S/L was added directly to the diet unmodified, (2) calcium salts (CaS) of S/L, (3) whey protein concentrate (WPC) gel complex of S/L, and (4) whey protein isolate (WPI) gel complex of S/L. Each diet provided a similar amount of total FA. Dietary treatment had no effect on dry matter intake, milk yield, or milk fat proportion. Unsaturated FA composition of the TG and PL increased with WPI. Linoleic acid (C18:2) concentration in TG averaged 2.77, 3.53, 3.59 and 6.35 g/100 g FA and linolenic acid (C18:3) averaged 0.97, 1.33, 1.73 and 4.09 g/100 g FA for Oil, CaS, WPC and WPI, respectively. Total C18:1 trans FA decreased from 4.01 g/100 g FA for Oil to 2.50 g/100 g FA for WPI. Similar changes in PUFA content of PL and sn-2 of TG occurred. The lower trans FA, and higher PUFA, in milk fat are a result of reduced rumen biohydrogenation of PUFA in WPI. Feeding whey protein isolate gel complex successfully increased the PUFA of milk lipids without affecting productive performance. This protein gel offers a practical dietary method to modify the PUFA composition of milk lipids, by the type of FA protected, to allow changes in both the nutritional value of milk fat as well as potential changes in its manufacturing properties.