EFFECTS of GAMMA-IRRADIATION ON THE CONTENTS of THIAMIN, RIBOFLAVIN, AND VITAMIN B-12 IN DAIRY PRODUCTS FOR LOW MICROBIAL DIETS

Frozen dairy products were exposed to 40 kGy (4 Mrad) of cobalt-60 irradiation to sterilize them for the low microbial diets of immunosuppressed patients. In this study, the levels of thiamin, riboflavin, and vitamin B-12 were measured in Cheddar cheese, mozzarella cheese, yogurt bars, ice cream, and nonfat dry milk before and after irradiation at −78°C. There was no significant change in the levels of thiamin, riboflavin, or vitamin B-12 after irradiation. Samples of nonfat dry milk irradiated at three different temperatures (22°, 0 to 5°, or −78°C) sustained no significant loss of thiamin compared to levels in the nonirradiated fresh product. However, in irradiated mozzarella cheese, more thiamin was retained in products irradiated at −78°C than at 0 to 5°C. Irradiation of cheese, yogurt, ice cream, and nonfat dry milk at −78°C appeared to preserve the content of these three B vitamins.