Inhibition of digestive enzyme activities by pectic polysaccharides in model solutions

• Digestive enzyme activities were evaluated after incubation with pectin.
• Studied citrus pectin behaved as a non-competitive inhibitor of digestive enzymes.
• The enzymatic activities were markedly reduced by high methylated pectin.
• Enzyme–pectin surface interactions are mediated by hydrophobic interactions.
• Citrus pectin might be able to slow down digestion rate by inhibiting enzymes.

The presence of dietary fiber (e.g., pectic polysaccharides, PPs) in the gastrointestinal tract may decrease the caloric intake and reduce the risk of developing cardiovascular diseases. These phenomena are governed by several mechanisms, such as the regulation of the rate of nutrient absorption and the alteration of the normal activity of the gastrointestinal tract enzymes. In this study, we evaluated the effect of PPs with five methylation degrees (MD) on the activities of lipase, α-amylase, alkaline phosphatase, and protease. The MD of the PPs ranged (in mol/mol) from 87.4% (high-methylated PP, HMPP) to 7.1% (low-methylated PP, LMPP). The enzymatic activities were evaluated in model solutions after incubation with PPs. The Michaelis–Menten constant remained unmodified whereas the apparent maximum velocity (Vmaxapp) decreased with increasing PP concentrations. The Vmaxapp represented 13.3%, 38.6%, 41.9%, and 44.4% of the Vmax (without PPs) for lipase, α-amylase, alkaline phosphatase, and protease, respectively, when they were inhibited with 100 μg mL−1 HMPP. Kinetic analyses showed that all of the tested PPs behaved as non-competitive inhibitors of digestive enzymes. Increasing both the concentration and MD of the PPs reduced the enzymatic activities by decreasing the non-competitive inhibition constant (Ki). In plotting Ki versus MD, a straight line was obtained, with slopes of 1.943, 1.558, 1.344, and 1.165 μg mL−1%−1 for lipase, α-amylase, alkaline phosphatase, and protease, respectively. Among them, lipase was most likely to be inhibited by the PPs. Our results suggested that PPs might be able to suppress digestion by inhibiting digestive enzymes.

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