Abstract
To study lactose hydrolysis by β-galactosidase, this enzyme was produced from Streptococcus thermophilus strain 11F and partially purified by acetone and ammonium sulphate fractionation, and ion exchange chromatography on a Q Sepharose FF column. Lactose hydrolysis by the enzyme was affected by lactose concentrations, sugars and milk proteins. The maximum extent of lactose hydrolysis in buffer was obtained with a 15% lactose concentration. Addition of 2% of lactose, glucose, galactose or sucrose in milk inhibited the enzymatic hydrolysis. The enzyme was activated by bovine serum albumin and a combination of αs-casein and β-casein. Of the casein fractions, the principal fraction, αs-casein, was less effective than β-casein and κ-casein. The fibre entrapped enzyme had a temperature optimum of 57°C, and a pH optimum from 7.5 to at least 9.0 with O-nitrophenyl-β-D-galactopyranoside as substrate. By recycling with whey and skim milk through a jacketed glass column (1.6 cm x 30 cm) loaded with fibre-entrapped enzyme at 55°C, a lactose hydrolysis of 49.5% and 47.9% was achieved in 11 h and 7 h respectively.
Highlights
Hydrolysis of lactose in milk and milk products by
Attention has recently been shifted to finding a heat-stable, neutral-pH
The research on the immobilization of the enzyme is still lacking and certain factors influencing the enzymatic hydrolysis of lactose need to be determined in more detail
Summary
Hydrolysis of lactose in milk and milk products by The present study was carried out to assay the hydrolysis of lactose in milk and buffer by the
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