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

Calcium (Ca), primarily 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 in 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 and 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 the release of both soluble and ionic Ca from whey protein gels was significantly delayed, compared with their liquid counterpart. Slower Ca release patterns from protein gels in the gastric phase led to the release of a higher soluble Ca content 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.