Enzymatic interesterification of a lard and rapeseed oil equal-weight blend

A mixture of lard and rapeseed oil (1:1, wt/wt) was interesterified using immobilized lipases from Rhizomucor miehei (Lipozyme RM IM) and Candida antarctica (Novozym 435) as catalysts. Enzymatic interesterifications were carried out at 60°C for 8 h with Lipozyme RM IM or at 80°C for 4 h with Novozym 435. The biocatalyst doses were kept constant (8 wt-%). The starting blend was quantitatively separated by column chromatography into pure triacylglycerol fraction (98.5%), and a nontriacylglycerol fraction containing free fatty acids (0.3%) and of mono- and diacylglycerols (1.2%). It was found that after interesterification the contents of free fatty acids and of mono- and diacylglycerols increased to 3.5% and 6.3% or to 1.5% and 4.5% when Lipozyme RM IM and Novozym 435 were used, respectively.The slip melting temperatures and solid fat contents of the triacylglycerol fractions separated from interesterified samples were lower compared with the nonesterified blend. The sn-2 and sn-1,3 distribution of fatty acids in the triacylglycerol fractions before and after interesterification were determined. The compositions of fatty acids at sn-2 were near statistical (33.3%) when Novozym 435 was used. When Lipozyme RM IM was used, the fatty acid compositions at the sn-2 position remained practically unchanged, compared with the starting blend. The changes in molecular structures of fat components due to interesterification have greatly influenced on the melting profiles of products as illustrated by the DSC melting scans. The interesterified fats and isolated triacylglycerols had reduced oxidative stabilities, as assessed by Dynamic DSC and Isothermal PDSC measurements. The Arrhenius kinetic parameters for fats oxidation based on DSC and PDSC measurements were calculated.