Previous studies of our group demonstrated bitter-tasting food constituents, such as caffeine to stimulate mechanisms of gastric acid secretion as key process of gastric protein digestion via activation of bitter taste receptors (TAS2Rs). Here, we aimed to elucidate whether dietary casein, not tasting bitter and being the predominant protein in dairy products, is intra-gastrically degraded into peptides that target TAS2Rs and, thereby, stimulate mechanisms of gastric acid secretion. In a first step, dietary casein was subjected an in vitro model of gastric digestion. After respective hydrolization, the resulting peptides were identified by untargeted LC-ToF/MS, resulting in a library of 238 peptides. The in vivo release of these peptides was verified and quantitated in casein-fed pigs (n = 6). From these 238 peptides identified, five casein-derived, potentially bitter-tasting peptides were selected by means of bitter predicting software tools. Afterwards, their bitterness was validated by sensory analyses and an in vitro screening method based on human gastric parietal (HGT-1), with non-digested casein being validated as non-bitter. On a mechanistic level, an upregulation of gene expression of the bitter receptors TAS2R16 and TAS2R38 of up to 400% was observed in HGT-1 cells after treatment with three of the bitter peptides (YFYPEL, VAPFPEVF, YQEPVLGPVRGPFPIIV). Functional involvement of TAS2R16 was verified in knock-down experiments by means of siRNA targeted at TAS2R16 in HGT-1. In conclusion, we demonstrate gastric digestion of non-bitter tasting casein to result in bitter tasting peptides which stimulate mechanisms of gastric acid secretion via activation of bitter taste receptor TAS2R16.

Bitter peptides released during digestion of non-bitter tasting casein stimulate mechanisms of gastric acid secretion via activation of bitter taste receptor TAS2R16

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