INTERESTERIFICATION OF BUTTER FAT BY PARTIALLY PURIFIED EXTRACELLULARLIPASES FROM PSEUDOMONAS-PUTIDA, ASPERGILLUS-NIGER AND RHIZOPUS-ORYZAE

Three extracellular lipases were produced by batch fermentation of Pse udomonas putida ATCC 795, Aspergillus niger CBS 131.52 and Rhizopus or yzae ATCC 34612 during the late phase of growth, at 72, 96 and 96 h, r espectively. The lipases were partially purified by (NH4)(2)SO4 fracti onation. The lipase of P. putida was optimal at pH 8.0 whereas those f rom A, niger and R. oryzae were optimal at pH 7.5. The A. niger lipase had the lowest V-max value (0.51 X 10(-3) U/min) and R, oryzae the hi ghest (1.86 X 10(-3) U/min). The K-m values for P. putida, A. niger an d R. oryzae lipases were 1.18, 0.97, and 0.98 mg/ml, respectively. Nat ive PAGE of the partially-purified lipase extracts showed two to four major bands. The interesterification of butter fat by A. niger lipase decreased the water activity as well as the hydrolytic activity. The A . niger lipase had the highest interesterification yield value (26%) a nd the R. oryzae lipase the lowest (4%). In addition, A. niger lipase exhibited the highest decrease (17%) in long-chain hypercholesterolemi c fatty acids (C12:0, C14:0 and C16:0) at the sn-2-position; the P. pu tida lipase demonstrated the least favourable changes in specificity a t the same position.