Kinetics of calcium release in the GIT influenced by whey protein structures: an in-vitro digestion study using a dynamic model

Calcium (Ca), primary consumed through diet, is essential for skeletal health and various other biological functions in humans. While the mechanisms of Ca absorption are well-understood, little is known about the role of food structure properties on Ca release kinetics into the GIT, which may have important implications in Ca uptake. Therefore, the aim of this study was to investigate calcium release kinetics from whey protein matrices with varying structures during gastrointestinal digestion. Whey protein structures (Liquid: storage modulus G′ = 0.18 Pa at 1 Hz; soft gel: 1791 Pa; hard gel: 4103 Pa) with 8% (w/w) protein an equal Ca concentration (25 mM CaCl2) were subjected to dynamic in vitro gastric digestion using the Human Gastric Simulator, followed by intestinal digestion of emptied chyme fractions using a static model. Results revealed that both soluble and ionic Ca release from whey protein gels were significantly delayed, compared with the liquid counterpart. Slower Ca release patterns from protein gels in the gastric phase led to a higher soluble Ca content release in the intestinal phase, especially at early stages of digestion. These findings demonstrated that the physical structure of whey protein gels modulates soluble Ca release rates into the gastrointestinal environment. Further research is required to understand the implications of calcium release modulation in absorption efficiency.