Epsilon-polylysine (epsilon-PL) has been used as a food additive in Japan for many years. In this study, it inhibited human and porcine pancreatic lipase activity in substrate emulsions containing bile salts and phosphatidylcholine, in the concentration range of 10-1000 mg/L. At the same concentrations, it also destroyed the emulsifying activity, suggesting that lipase inhibitory activity and emulsion breakdown activity were associated. Epsilon-PL inhibited porcine pancreatic lipase activity and destroyed emulsion breakdown activity at 1000 mg/L in the substrate containing bile salts and phosphatidylcholine alone. Epsilon-PL did not inhibit lipase activity or affect emulsifying activity at 1000 mg/L in the substrates containing arabic gum and polyvinyl alcohol. A comparison of lipase inhibitory activity between epsilon-PL and three types of alpha-PL with differing polymerization rates was performed. The lipase inhibitory activity of epsilon-PL was not different from that of alpha-PL (44 lysine residues). Epsilon-PL maintained its inhibitory activity after incubation with trypsin, alpha-chymotrypsin and pepsin, whereas alpha-PL did not. The effect of epsilon-PL on postprandial hypertriacylglyceridemia was investigated in rats. The plasma triacylglycerol concentration in rats intragastrically administered > or =15 mg/kg of both fat emulsion and epsilon-PL was significantly lower at 2 and 3 h after administration than that in rats administered fat emulsion alone (P < 0.05). These results strongly suggest that epsilon-PL is able to suppress dietary fat absorption from the small intestine by inhibiting pancreatic lipase activity.