SUBSTRATE PREFERENCES FOR LIPASE-MEDIATED ACYL-EXCHANGE REACTIONS WITH BUTTEROIL ARE CONCENTRATION-DEPENDENT

Substrate preferences for pancreatic lipase-mediated acyl-exchange reactions with butteroil were concentration-dependent for the series of acyl donors and alcohol acceptors evaluated. For acidolysis reactions, the initial reaction rates and percent reaction yields after 18 h at 50 mumol acyl donor per gram substrate mixture were similar for n-fatty acids and their methyl and glycerol esters. At 400-500 mumol g-1 (and greater), order of initial reaction rates and percent reaction yield was fatty acid glycerol esters > fatty acid methyl esters > fatty acids. At concentrations above 300-500 mumol g-1, reaction inhibition was observed for fatty acid substrates, and inhibition took place at lower concentrations for the shorter-chainlength fatty acids of those evaluated (5-17 carbons). Inhibition was primarily attributed to acidification of the microaqueous environment of the lipase. Desorption of water by the fatty acid substrate may be a secondary mode of inhibition. The concentration dependence of initial reaction rates and percent reaction yield was similar for the n-alcohol substrates evaluated (2-15 carbons) for alcoholysis reactions with butteroil. Optimum alcohol concentration was 375-500 mumol g-1 (except for butanol, which was 1 mmol g-1), above which reaction inhibition was observed. Inhibition was attributed to desorption of water from the enzyme by the alcohol substrate. Relative reactivity of classes of alcohols for this reaction system was primary alcohols > secondary alcohols > tertiary alcohols. Generally, alcoholysis reactions were faster than acidolysis reactions, and triacylglycerols were the best substrates for acidolysis reactions with butteroil at high levels (up to 2 mmol g-1) of acyl donor substrate.