Effect of processing conditions on the stability of native vitamin A and fortified retinol acetate in milk.

The objective of this investigation was to evaluate the stability of vitamin A in fortified milk which was exposed to different processing conditions viz. heat treatments (pasteurization, boiling and sterilization), light exposure treatments (1485, 2970 and 4455 lux for 2, 4, 8, 16 and 32 h) and different packaging materials (polyethylene pouches and glass bottles) and also to evaluate the effect of fortified iron (ferric pyrophosphate soluble (FPP) and ferrous gluconate hydrate (FG) on vitamin A stability during processing and storage. Toned milk was fortified with 25 ppm iron and vitamin A acetate 2500 IU/L, singly and also in combination. The vitamin A analysis method was optimized and accuracy and precision were below ± 5%. The results indicated that vitamin A was heat-labile and its degradation increased with the increase in the intensity of heat treatments. Pasteurized milk (318.11 IU/L) showed non-significant (p > 0.05) decrease, however, boiling (250.21 IU/L) and sterilization (205.65 IU/L) showed a significant difference (p < 0.05) in vitamin A content in comparison to control (324.71 IU/L). Similarly, vitamin A was light sensitive and its degradation significantly increased (p < 0.05) with an increase in the intensity of light exposure (34.82 to 92.53%). Loss of vitamin A (%) was significantly greater (p < 0.05) in iron-fortified milk suggesting that iron might have played a role in accelerating the degradation of vitamin A. Extent of losses were significantly higher (p < 0.05) in FG compared to FPP fortified milk. Vitamin A (microencapsulated form) which was added externally was more stable than the inherent vitamin A present in milk.