In vitro bioaccessibility of calcium in whey protein matrices depends on calcium sources, gastro-intestinal pH but not on the matrix structure

Calciumis an essential mineral for the organism. Numerous calciumsources are available to enrich food products, but only calciumcarbonate has been well studied. Calciumbioaccessibility depends mainly on solubility. Furthermore in vitro digestion allows to determine bioaccessibility and to identify the key parameters affecting it. The purpose of this study was to focus on the influence of gastro-intestinal pH variation, the effect of the food matrix structure and the calciumsources on calciumbioaccessibility. Four calciumsources ( calciumcarbonate, calciumcitrate malate, dairy calciumphosphate and calciumbisglycinate) were added at 0.5% (w/w) in water (control), and in whey proteinmatrices liquid or heat-induced gel. These matrices were digested under static conditions in duplicate, with the harmonized INFOGEST protocol (Minekus et al. 2014). Soluble and ionic calcium, and pH kinetics were followed during in vitro digestion. The kinetics were analyzed by nonparametric tests with repeated measurements. Results showed that all calciumsources were soluble in the matrices, mainly as ionic form (Ca2+), during the gastric phase at pH 3, but that calciuminsolubilisation occurred in the intestinal compartment at pH 7. Dairy calciumphosphate insolubilisation was quicker and more intense than for other calciumsources; its concentration of soluble calciumis 17+/-3%, instead of more than 60% for the three other calciumsources (p 0.1). These results provide new insights to better understand bioavailability differences between calciumsources and matrices. Further in vivo digestion experiments on a pig model will be achieved in order to confirm bioaccessibility and to measure the bioavailability of those different sources of calcium. It will finally provide a relation between the results from in vitro and in vivo models of digestion.