Characterization and evaluation of Aspergillus oryzae lactase coupled to a regenerable support

A derivative of crosslinked Sepharose, p-(N-acetyl-L-tyrosine azo) benzamidoethyl-CL-Sepharose 4B, was synthesized and used for the selective immobilization of thermostable lactase from Aspergillus oryzae.Preparations of soluble and immobilized lactase were evaluated under initial velocity conditions in a batch process. Immobilization had no significant effect on the pH optimum at 50 degrees C or kinetic parameters at pH 4.5 or pH 6.5 and 50 degrees C. At pH 4.5, the soluble enzyme possessed maximum activity at 60 degrees C and the immobilized at 55 degrees C; at pH 6.5 both showed maximum activity at 55 degrees C. The activation energy, entropy, and enthalpy decreased significantly with immobilization at pH 4.5 but not at pH 6.5. When the immobilized enzyme was placed in a packed-bed reactor, the effect of temperature on activity was altered as reflected by a marked decrease in the thermodynamic parameters of activation at both pH levels. Upon immobilization there was also a dramatic increase in the apparent thermal stability of the lactase, and the mean half-life at 50 degrees C was increased from 7.2 to 13 days at pH 4.5 and from 3.8 to 16 days at pH 6.5.