Catalyzes the hydrolysis of triacylglycerols to yield free fatty acids, diacylglycerol, monoacylglycerol, and glycerol (PubMed:1568562, PubMed:1935982, PubMed:11689574). Shows a preferential hydrolysis at the sn-3 position of triacylglycerol (By similarity). a triacylglycerol + H2O = a diacylglycerol + a fatty acid + H(+) 1,2,3-tri-(9Z-octadecenoyl)-glycerol + H2O = (9Z)-octadecenoate + 1,2-di-(9Z-octadecenoyl)-sn-glycerol + H(+) 1,2,3-trioctanoylglycerol + H2O = 1,2-dioctanoyl-sn-glycerol + H(+) + octanoate Inactivated by thiol reagents 5,5'- dithiobis(2-nitrobenzoic acid) and 4,4'-dithiopyridine. Optimum pH is 6 for short chain and medium-chain triacylglycerol and 4 for long-chain triacylglycerol (PubMed:1935982). Inactivated when pH is below 1.5 (PubMed:1568562). Expressed in the mucous pit cells of gastric glands (at protein level) (PubMed:1568562). Expressed in the fundic and pyloric mucosa (PubMed:1935982). Belongs to the AB hydrolase superfamily. Lipase family.