Interesterification of Milk Fat with Oleic Acid Catalyzed by Immobilized Rhizopus oryzae Lipase

Milk fat was interesterified with oleic acid by catalysis of an immobilized lipase in a microaqueous two-phase system. A commercial lipase from Rhizopus oryzae and a controlled pore glass carrier were selected for preparation of an immobilized lipase. The prepared immobilized lipase showed a Michaelis constant of 77 mM and a maximum velocity of 40 U/g of carrier on the hydrolysis of triolein. Conditions for interesterification catalyzed by the immobilized lipase were optimized by the reaction between trimyristin and oleic acid under various conditions. The interesterification of milk fat with oleic acid was performed in isooctane with .3% (vol/vol) water content. The fatty acid composition and 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 curves obtained by differential scanning calorimetry analysis showed that the transition temperature of the major milk fat peaks decreased by 7.6 and 5.4-degrees-C, respectively. The results suggest that the prepared immobilized lipase can induce rather specific interesterification between oleic acid and palmitic acid in the milk fat triglycerides, which produces a lower melting milk fat, without losses of the short-chain fatty acid composition.