VALIDATION OF CHEMICAL MEASURES OF CALCIUM WITH BIOASSAY OF CALCIUM-FORTIFIED COTTAGE CHEESE

Chemically measured calcium was correlated with bioavailability of calcium by rat bioassay. Calcium-fortified cottage cheese was evaluated by both chemical and bioassay tests. Cheese was fortified at four levels of calcium with or without added guar to increase acceptability. Chemical tests on laboratory digests and non-digested samples were by two different methods: (1) dialyzed and ionic dialyzed calcium, and (2) soluble and ionic soluble calcium. Calcium added to cheese significantly increased % calcium availability. Calcium availability from rat diets containing the same cheese with and without guar correlated well with bioassay results. Ionic dialyzed, ionic soluble and soluble calcium correlated with bioassay measures. Ionic dialyzed calcium in non-digested diets was the best chemical test for bioavailability. Digestion did not improve accuracy. These chemical tests accurately measured bioavailability from a calcium-fortified cheese.