Bioaccessibility of calcium in freeze-dried yogurt based snacks

A variety of yogurt based calcium-rich snacks were formulated with pectin, whey protein or casein ingredients and combinations hereof to provide a crisp food matrix after freeze-drying. The calcium content ranged from 0.28 g to 0.74 g/100 g snacks. Pectin and heating prior to freeze drying were found important to provide snacks with a suitable texture, in terms of crispness and hardness. A three step in vitro static digestion simulating oral, gastric and intestinal conditions showed that the snacks with high calcium content had the largest difference between soluble calcium at the beginning and at the end of the intestinal phase. The soluble calcium at the end of the intestinal phase corresponds to calcium bioaccessibility, while the difference between soluble calcium at the beginning and at end of the intestinal phase shows a competition between absorption and precipitation during transport through the intestine. Enzymatic hydrolysis during the intestinal phase is suggested to liberate calcium from proteins but not from pectin. Heat treatment at 90 °C prior to drying and addition of pectin had little or no effect on the calcium bioaccessibility from any of the snacks.