Which factors impact calcium bioaccessibility in dairy and plant-based products during static in vitro digestion?

Calcium deficiency is widespread worldwide. In western countries, the main source of dietary calcium are dairy products, although some plant foods can also contribute. This work aimed to determine the solubility and the bioaccessibility of calcium from various food sources and to investigate how food components impact these two properties. A static in vitro gastrointestinal digestion model (INFOGEST) was used for two types of samples: (1) model solutions consisting in calcium solutions to which a compound present in dairy or plant products presumed to interact with calcium was added and (2) plant and dairy products. Calcium bioaccessibility was determined by measuring the soluble calcium concentration relative to total calcium concentration in the samples. The soluble calcium content was measured at different times during gastric and intestinal digestion using inductively coupled plasma-optical emission spectrometry. In vitro digestion indicated that the low pH during the gastric phase promoted the calcium solubilization. During the intestinal phase, however, calcium solubility decreased due to the pH increase to about 7. Phosphate, palmitic acid, micellar casein and phytate appear to interact with calcium, decreasing its solubility in the intestinal phase, probably through the formation of insoluble complexes. The calcium bioaccessibility of dairy matrices (yogurt, cheese, milk) was particularly high (between 19 and 34 %). However, calcium bioaccessibility was more disparate for plant-based dairy alternatives (between 5 and 20 %) and whole plant foods (between 1 and 27 %). In terms of the quantity of bioaccessible calcium per serving, dairy products (yogurt, cheese, milk) were the best sources.