Stabilization of Lactase (Escherichia coli) by Milk Components and Related Compounds

Abstract

Thermal stability of lactase was I70-fold greater in milk than in phosphate buffer at 60°C. Enhanced stability was due primarily to casein, whose cffcct was largely substrate dependent. Casein or lactose alone had little or no effect, but together they stabilized the enzyme more than 400-fold at 60°C. The relative effectiveness of other proteins, as stabilizers, was: bovine serum albumin >caseinate>ovatbumin>soy isolate > u-lactalbumin > lysozyme. Galactose was much less effective than lactose in promoting stability; sucrose and glucose were ineffective. Stability was dependent upon both lactose concentration and casein concentration, and decreased with increasing enzyme concentration. Dithioerythritol increased stability in buffer but had relatively little effect in milk.

A Dynamic Light Scattering Study of β‐Galactosidase: Environmental Effects on Protein Conformation and Enzyme Activity

“…There is a shift of about 2 pH units when comparing the particle size curve with the activity curve. However, this inconsistency can be attributed to the stabilization effect of enzyme substrate (Mahoney et al, 1988;Mahoney and Wilder, 1989;Izutsu et al, 1991). Lactose was present in all enzyme solutions used for the activity assay, but not in this size study.…”

Biochemical and thermal properties of β-galactosidase enzymes produced by artisanal yoghurt cultures

“…However, yeast b-galactosidases, recognised for their higher activities, are characterised by their neutral pH optima (Cortes et al, 2005;Jurado et al, 2002). In fact, the major drawback of these enzymes is their low optimum temperatures (30-37°C) and low heat stabilities; inactivation is observed at temperatures above 48°C (Mahoney & Wilder, 1989;Voget et al, 1994).…”

Retention of β‐galactosidase activity in crude cellular extracts from Lactobacillus delbrueckii ssp. bulgaricus 11842 upon drying

“…Bioactive materials such as enzymes, bioactive proteins and peptides are unstable in aqueous solutions in the absence of stabilizers 4,9 and are often preserved by drying. Freeze‐drying has been the method of choice for long‐term preservation of bioactive materials.…”