Chemical and enzymatic interesterification of a beef tallow and rapeseed oil equal-weight blend

A mixture of beef tallow and rapeseed oil (1:1, wt/wt) was interesterified using sodium methoxide or immobilized lipases from Rhizomucor miehei (Lipozyme IM) and Candida antarctica (Novozym 435) as catalysts. Chemical interesterifications were carried out at 60 and 90 degreesC for 0.5 and 1.5 h using 0.4, 0.6 and 1.0 wt-% CH3ONa. Enzymatic interesterifications were carried out at 60 degreesC for 8 h with Lipozyme IM or at 80 degreesC for 4 h with Novozym 435. The biocatalyst doses were kept constant (8 wt-%), but the water content was varied from 2 to 10 wt-%. The starting mixture and the interesterified products were separated by column chromatography into a pure triacylglycerol fraction and a nontriacylglycerol fraction, which contained free fatty acids, mono-, and diacylglycerols. It was found that the concentration of free fatty acids and partial acylglycerols increased after interesterification. The slip melting points and solid fat contents of the triacylglycerol fractions isolated from interesterified fats were lower compared with the nonesterified blends. The sn-2 and sn-1,3 distribution of fatty acids in the TAG fractions before and after interesterification were determined. These distributions were random after chemical interesterification and near random when Novozym 435 was used. When Lipozyme IM was used, the fatty acid composition at the sn-2 position remained practically unchanged, compared with the starting blend. The interesterified fats and isolated triacylglycerols had reduced oxidative stabilities, as assessed by Rancimat induction times. Addition of 0.02% BHA and BHT to the interesterified fats improved their stabilities.