Abstract: MLM-type (medium-long-medium carbon chain) structured lipids were synthesized by the reaction between lauric acid (C12:0) and refined soybean oil using Lipozyme RM IM lipase as a catalyst. The effects of molar ratio of between soybean oil and lauric acid, reaction temperature, reaction time and lipase dosage on the insertion rate of lauric acid were studied. The physicochemical properties of the MLM-type structured lipids prepared under optimized reaction conditions were determined. The optimal conditions for the synthesis of MLM-type structured lipids were as follows: molar ratio of soybean oil to lauric acid 6:1, reaction temperature was 45 ℃, reaction time was 24 h, and enzyme/substrate ratio 13%. Under these conditions, the insertion rate of lauric acid was 29.26%. The iodine value (97.38 g/100 g) and viscosity (70.39 cP) of the structurzed lipids were lower than those of soybean oil, and the saponification value (calculated as KOH equivalent) (229.58 mg/g), crystallization starting temperature (4.89 ℃) and melting starting temperature (?19.87 ℃) were significantly higher than those of soybean oil (P < 0.05), while no significant different (P > 0.05) in smoke point (231.24 ℃) was found. The MLM-type structured lipids synthesized in this study had higher nutritional value than soybean oil and could be developed as anti-obesity and lipid-reducing high-quality oils.

Key words: soybean oil, lauric acid, structured lipid, lipase catalysis, physicochemical properties