The effect of enzymatic interesterification on the physico-chemical properties and thermo-oxidative stabilities of beef tallow stearin and rapeseed oil blends
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Beef tallow stearin (BTS) was blended with rapeseed oil (RSO) and the blends: 40 % BTS + 60 % RSO, 30 % BTS + 70 % RSO, 20 % BTS + 80 % RSO were interesterified using immobilized lipases from Rhizomucor miehei (Lipozyme IM) and Candida antarctica (Novozym 435) as the catalysts. The starting blends and the products of interesterifications were quantitatively separated into the triacylglycerol and non-triacylglycerol fractions containing free fatty acids (FFA) and of mono- and di-acylglycerols. It has been found that after interesterification the contents of the FFA and of MAG and DAG increased. The slip melting temperatures and solid fat contents of triacylglycerols separated from interesterified samples decreased if compared with non-esterified blends. The DSC melting profiles of the blends before and after interesterification were substantially different. The total fatty acid compositions of fats before and after interesterifications remained unchanged. Their distributions into sn-2 and sn-1,3 positions were close to random when Novozym 435 was used. When Lipozyme IM was used, the fatty acid composition at sn-2 position remained practically unchanged compared with the starting blend. Using the DSC and PDSC techniques, the oxidative stabilities of the fats before and after interesterification were also characterized. The interesterified blends were less resistant on thermo-oxidative degradation than the non-esterified ones.
KeywordsBeef tallow stearin DSC Enzymatic interesterification Pressure differential scanning calorimetry (PDSC) Rapeseed oil
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