MODIFICATION OF MILKFAT PHYSICAL-PROPERTIES BY IMMOBILIZED PSEUDOMONAS-FLUORESCENS LIPASE

A bifunctional fusion protein was constructed by fusion of the strepta vidin gene from Streptomyces avidinii to the lipase gene from Pseudomo nas fluorescens, and the resulting streptavidin-lipase was expressed i n Escherichia coli. Immobilized streptavidin-lipase was prepared by di rect bioselective adsorption from crude cell lysates on biotinylated c ontrolled-pore glass and used to catalyze interesterification of anhyd rous butteroil. Changes in the triacylglycerol composition indicated t hat those with equivalent carbon numbers (ECN) ranging from 36 to 42 d ecreased, while those with ECN values from 48 to 50 increased followin g interesterification for 120 h in hexane at 42 degrees C. Both the me lting temperatures and the solid fat content at various temperatures w ere lower as compared to those of the unmodified butteroil. Addition o f unsaturated fatty acids, linoleic and linolenic, yielded modified bu tteroils with lower melting points and solid fat content, whereas addi tion of saturated fatty acids, palmitic and stearic, increased the sol id fat content of the modified butteroil. The liquid butteroil could f unction as a solvent as well as the substrate; however, the interester ification reaction rate was much slower than in hexane.