INTERESTERIFICATION OF MILK-FAT WITH OLEIC-ACID CATALYZED BY IMMOBILIZED RHIZOPUS-ORYZAE LIPASE

Milk fat was interesterified with oleic acid by catalysis of an immobi lized lipase in a microaqueous two-phase system. A commercial lipase f rom Rhizopus oryzae and a controlled pore glass carrier were selected for preparation of an immobilized lipase. The prepared immobilized lip ase showed a Michaelis constant of 77 mM and a maximum velocity of 40 U/g of carrier on the hydrolysis of triolein. Conditions for intereste rification catalyzed by the immobilized lipase were optimized by the r eaction between trimyristin and oleic acid under various conditions. T he interesterification of milk fat with oleic acid was performed in is ooctane with .3% (vol/vol) water content. The fatty acid composition a nd thermal characteristics of the triglycerides of the interesterified milk fat were investigated. The interesterified milk fat had about 50 % more oleic acid and a significantly lower palmitic acid content than those of the original milk fat. The crystallization and melting curve s obtained by differential scanning calorimetry analysis showed that t he transition temperature of the major milk fat peaks decreased by 7.6 and 5.4-degrees-C, respectively. The results suggest that the prepare d immobilized lipase can induce rather specific interesterification be tween oleic acid and palmitic acid in the milk fat triglycerides, whic h produces a lower melting milk fat, without losses of the short-chain fatty acid composition.