Kinetics of calcium release in the GIT influenced by whey protein structures: an <i>in-vitro</i> 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.钙（Calcium, Ca）主要经膳食摄入，对人体骨骼健康及多种其他生理功能不可或缺。尽管钙的吸收机制已被充分阐明，但食品结构特性对钙释放进入胃肠道（gastrointestinal tract, GIT）的动力学过程所起的作用仍鲜为人知，而这或许对钙的摄取具有重要意义。因此，本研究旨在探究不同结构乳清蛋白基质在胃肠消化过程中的钙释放动力学特性。本研究采用蛋白含量为8%（质量分数，w/w）且钙浓度一致（25 mM氯化钙，CaCl₂）的乳清蛋白体系，其结构分为三类：液态（1 Hz下储能模量G′=0.18 Pa）、软凝胶（1791 Pa）及硬凝胶（4103 Pa）。所有样本均通过人体胃模拟器（Human Gastric Simulator）进行动态体外胃消化，随后采用静态模型对排空的食糜组分进行肠内消化。结果显示，与液态体系相比，乳清蛋白凝胶的可溶性钙与离子钙释放过程均显著延迟。胃消化阶段蛋白凝胶的钙释放速率较慢，使得肠消化阶段的可溶性钙释放量更高，尤其在消化早期阶段更为显著。上述研究结果表明，乳清蛋白凝胶的物理结构可调控可溶性钙向胃肠道环境的释放速率。未来仍需开展进一步研究，以阐明钙释放调控对钙吸收效率的影响机制。