Substrate preferences for lipase-mediated acyl-exchange reactions with butteroil are concentration-dependent |
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Authors: | Shu-Jung Kuo Kirk L Parkin |
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Affiliation: | (1) Department of Food Science, University of Wisconsin, 53706 Madison, Wisconsin |
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Abstract: | 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 μmol acyl donor per gram substrate mixture were similar forn-fatty acids and their methyl and glycerol esters. At 400–500 μmol 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 μmol 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 then-alcohol substrates evaluated (2–15 carbons) for alcoholysis reactions with butteroil. Optimum alcohol concentration was 375–500
μmol 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. |
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Keywords: | Acidolysis acyl exchange alcoholysis anhydrous butteroil lipase modification substrate preferences |
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