Abstract
The mixture of beef tallow with rapeseed oil (1:3, w/w) was interesterified using sodium metoxide or immobilized lipases from Rhizomucor miehei (Lipozyme IM) and from Candida antarctica (Novozym 435) as the catalysts. The chemical interesterifications were carried out at 60 and 90°C for 0.5 and 1.5 h using 0.4, 0.6 and 1.0% of CH3ONa. Depend on the catalyst used the enzymatic interesterifications were carried out at 60°C for 8 h (Lipozyme IM) or at 80°C for 4 h (Novozym 435). The catalyst doses were kept constant (8%) but the water content in catalysts was changed in the range of 2 to 10%. The starting mixture and the products of interesterifications were quantitatively separated into pure triacylglycerols and non-triacylglycerols fraction containing free fatty acids and mono- and diacylglycerols. It has been found that after interesterification the concentrations of free fatty acids and partial acylglycerols increased. On the other hand the slip melting temperatures and solid fat contents in triacylglycerols isolated from interesterified fats and their oxidative stability were lower if compared with noninteresterified, initial blend. It was interpreted on the base of alteration on molecular structure of triacylglycerols as confirmed by their sn-2 and sn-1,3 distribution of fatty acids before and after interesterification. These distributions were practically random after chemical interesterification and close to random when Novozym 435 was applied. When Lipozyme IM was used the fatty acids composition at sn-2 position remained practically unchanged if compared with starting blend.
