Beta-lactoglobulin Complexed Vitamins A and D in Skim Milk: Shelf Life and Bioavailability

Abstract

As reduced fat dairy products became popular in the U.S., the reduction of vitamins A and D in these products rendered a nutritional concern. Beta-lactoglobulin has been reported capable of binding fat-soluble vitamins. In order to justify the potential of beta-lactoglobulin as a stable and protective carrier for the vitamins, stability and bioavailability of beta-lactoglobulin complexed vitamins A and D in skim milk were investigated in this study.

The first objective of this research was to observe the stability of vitamin A palmitate and vitamin D₃ in fortified skim milk during storage. The fortifiers included regular oil-based vitamins, Roche dry vitamins, and spray-dried and freeze-dried protein-based vitamins. Milk was stored in different packaging materials including glass test tubes, plastic bottles, and paperboard cartons. The effect of High Temperature Short Time (HTST) and Ultra High Temperature (UHT) pasteurizations on shelf life was also studied. Vitamin A palmitate and vitamin D₃ were extracted by organic solvents and assayed by High Performance Liquid Chromatography (HPLC). Results showed that vitamin D₃ was relatively stable in all milks during the 4 weeks of shelf life. Vitamin A concentrations remained stable in most HTST milk except for those fortified with Roche dry vitamin A. A significant decrease in retinyl palmitate was detected in UHT protein-based vitamin-fortified skim milk. The second objective was to test the ability of different forms of fortified skim milk to boost vitamin levels in vitamin-depleted rats. Serum, liver and bone tissues were assayed for both vitamins and calcium. Data indicated that oil-based vitamin A-fortified skim milk was as efficient as positive AIN-93G pelleted rodent diet in raising the vitamin A levels in the tissues and protein-based vitamin D₃ fortified skim milk most effectively boosted the serum 25-OH D level.

In conclusion, beta-lactoglobulin complexed vitamin A palmitate is not an appropriate fortifier for UHT skim milk while beta-lactoglobulin complexed vitamin D₃ is a more stable and effective fortifier than the regular oil-based fortifier.