1032
Stability of Vitamin A Palmitate in Raw Skim Milk and Apple Juice on Exposure to Ultraviolet Light
Vitamin A palmitate is commercially fortified in milk. Earlier studies have indicated that the vitamin A fortified in milk is associated with the casein micelles in milk. Our objective was to study whether casein micelles protect vitamin A palmitate from degradation on exposure to ultraviolet (UV) radiation. For this purpose raw skim milk and apple juice was fortified with vitamin A palmitate (1.4 mM) after dispersing in ethanol (2.44% v/v ethanol in sample) with rotary homogenization at 10, 000 rpm for 3 min. The vitamin A milk and juice samples were then subjected to strong UV radiation (365 nm, intensity at the surface of transilluminator 5300µW/cm2) for 0, 5, 10, 15 and 20 min. The vitamin A was extracted with hexane and quantified by using a normal phase HPLC at 325 nm. Vitamin A milk samples were subjected to size exclusion chromatography (SEC) and the fractions pertaining to the same peak at 280nm were pooled, then freeze dried and analyzed for vitamin A content. There was rapid degradation of vitamin A palmitate in juice samples, with a reduction of 59% of vitamin A of the initial amount added, on exposure to 20 min of UV light. The vitamin A content was 100%, 97%, 88%, 67% and 41% (± 4%) of the initial amount added, on subjecting to UV exposure for 0, 5, 10, 15 and 20 min, respectively. While the vitamin A in milk samples degraded only 6% over 20 min of UV exposure, with a degradation pattern 100%, 100%, 99%, 97% and 94% (± 4%) of the initial amount added, on subjecting to UV exposure for 0, 5, 10, 15 and 20 min, respectively. The difference in the percentage of vitamin A between milk and juice was especially significant after 15 and 20 min of UV light exposure (P < 0.01). The quantification of vitamin A in the SEC fractions indicated that vitamin A palmitate associated only to casein micelles in milk with a recovery of 42% of the initial amount added within the casein section. The results indicate that the association of vitamin A palmitate and casein micelles in raw skim milk samples provide a protective effect to vitamin A palmitate against degradation on exposure to UV light.
Keywords: vitamin A palmitate, ultraviolet, casein, milk