Hydrolyzes all ester bonds in triglyceride and displays a high affinity for triolein. For unsaturated substrates having long fatty acyl chains (C18:2 cis-9, cis-12 and C18:3 cis-9, cis-12, cis-15) GCL I shows higher specific activity than GCL II, whereas GCL II shows higher specific activity against saturated substrates having short fatty acid chains (C8, C10, C12 and C14). a triacylglycerol + H2O = a diacylglycerol + a fatty acid + H(+) Monomer. Belongs to the type-B carboxylesterase/lipase family.