Water-Soluble Coffee Melanoidins Inhibit Digestive Proteases

Abstract

Coffee is one of the most popular beverages around the world and its consumption contributes to the daily intake of dietary melanoidins. Despite the emerging physiological role of food melanoidins, their effect on digestive processes has not been studied so far. In this study, the activity of the gastrointestinal enzymes pepsin and trypsin was investigated in the presence of water-soluble coffee melanoidins. The gastric enzyme pepsin is only slightly affected, whereas the intestinal enzyme trypsin is severely inhibited by coffee melanoidins. The intestinal digestibility of casein was significantly inhibited by coffee melanoidins at a concentration achievable by regular coffee consumption. The inhibition of proteolytic enzymes by coffee melanoidins might decrease the nutritional value of dietary proteins.

Keywords: coffee; digestion; melanoidins; pepsin; trypsin.

Figure 1

Inhibition of pepsin with water-soluble coffee melanoidins. The dose–response curve of pepsin and water-soluble coffee melanoidins. The dotted line marks the concentration present in the simulated gastric digestion experiment (0.25 mg/mL). Data are mean ± S.D., n = 3.

Figure 2

Inhibition of trypsin with water-soluble coffee melanoidins. (A) Dose–response curve of trypsin and water-soluble coffee melanoidins. The dotted line marks the concentration present in the simulated intestinal digestion experiment (0.125 mg/mL). (B) Michaelis–Menten kinetics in the absence (−M) or presence of 0.08 mg/mL water-soluble coffee melanoidins (+M). Data are mean ± S.D., n = 3.

Figure 3

Release of amino compounds during simulated digestion in the presence or absence of water-soluble coffee melanoidins. The concentration of water-soluble coffee melanoidins at t₀ is 0.5 mg/mL, in the gastric phase is 0.25 mg/mL, and in the intestinal phase is 0.125 mg/mL. Data are mean ± S.D., n = 3.

Figure 4

Release of amino acids after simulated intestinal digestion. (A) Absolute concentrations of amino acids after intestinal digestion of casein in the absence or presence of coffee melanoidins, measured according to analytical performances reported in Table 1 through pure analytical reference standards. (B) Release (%) of amino acids in the presence of coffee melanoidins. Data are mean ± S.D., n = 3, n.d. not detectable.