Modification of milkfat physical properties by immobilized Pseudomonas fluorescens lipase.

摘要

A bifunctional fusion protein was constructed by fusion of the streptavidin gene from Streptomyces avidinii to the lipase gene from P. fluorescens, and the resulting streptavidin-lipase was expressed in Escherichia coli. Immobilized streptavidin-lipase was prepared by direct bio-selective adsorption from crude cell lysates on biotinylated controlled-pore glass and used to catalyse interesterification of anhydrous butter oil. Changes in the triacylglycerol composition indicated that those with equivalent carbon numbers (ECN) ranging from 36 to 42 decreased, while those with ECN values from 48 to 50 increased following inter-esterification for 120 h in hexane at 42deg C. Both the melting temperatures and the solid fat content at various temperatures were lower compared with those of the unmodified butter oil. Addition of unsaturated fatty acids, linoleic and linolenic, yielded modified butter oils with lower melting points and solid fat content, whereas addition of saturated fatty acids, palmitic andstearic, increased the solid fat content of the modified butter oil. The liquid butter oil could function as a solvent as well as the substrate; however, the inter-esterification reaction rate was much slower than in hexane.