Bioavailability of Oil-Based and β-Lactoglobulin-Complexed Vitamin A in a Rat Model

β-Lactoglobulin is capable of binding fat-soluble compounds including vitamin A palmitate and is suggested to specifically enhance intestinal uptake of retinol. In this study, bioavailability of a vitamin-A-retinyl palmitate complex in skim milk and in water-based liquids was investigated in vitamin-A-depleted rats. First, rats were fed a vitamin-A-free pellet diet for 6？wk and were thereafter gavage-fed with vitamin A in oil, vitamin-A-β-lactoglobulin complex, vitamin A in oil + skim milk, and vitamin-A-β-lactoglobulin + skim milk for 2？wk and 42？wk. Vitamin A repletion, as judged by vitamin A accumulation in serum and liver, occurred in all the treatments. Vitamin-A-β-lactoglobulin complex treatments had statistical equivalence with oil-based vitamin A treatments. In a second experiment, vitamin-A-depleted rats were fed UHT-processed skim milk fortified with either oil-based or freeze-dried β-lactoglobulin-complexed retinyl palmitate. Liver and serum vitamin A were analyzed by HPLC to indicate vitamin A status in the rats. Results showed no significant difference in bioavailability of retinyl palmitate from milk made with either regular oil-based or β-lactoglobulin-complexed fortifiers. The vitamin-A-β-lactoglobulin complex, being water soluble, may be useful for fortification of nonfat products. 1. Introduction Vitamin A has long been known to be crucial to normal vision and control of differentiation of epithelial cells in the digestive tract, respiratory system, skin, and bone [1]. It is also important in cell replication, growth, and maturation of the nervous and immune systems. Because of the important role of vitamin A, fluid milk products have been fortified with vitamin A (along with vitamin D) since the 1930s to reduce the incidence of disorders caused by vitamin deficiency in the USA. Vitamin A addition to whole milk is optional, but low fat and nonfat milk must be fortified with vitamin A so that each quart contains >2000？IU [2]. Vitamin-A-fortified skim milk is either prepared with oil-based carriers or water-based emulsions. Currently, the acceptable deviation range of vitamin A is 100% to 150% of the FDA-specified concentration [3]. However, nonfat or low-fat milk products often do not comply with nutrition labeling requirements over their entire shelf life. This may be due to analytical methods and loss of vitamin during processing and storage [4, 5]. Furthermore, the degradation of vitamin A generally parallels the oxidative degradation of unsaturated lipids. β-Lactoglobulin is a major whey protein (7 to 12% of skim milk total