Cultural conditions for production of glucoamylase from Lactobacillus amylovorus ATCC 33621

Abstract

Lactobacillus amylovorus ATCC 33621 is an actively amylolytic bacterial strain which produces a cell-bound glucoamylase (EC 3.2.1.3). Conditions of growth and glucoamylase production were investigated using dextrose-free de Man-Rogosa-Sharpe (MRS) medium in a 1.5 l fermenter, with varying dextrin concentration (0.1-1.5% (w/v)), pH (4.5-6.5) and temperature (25-55 degrees C). Cell extracts were prepared by subjecting cells to treatment with a French Pressure cell in order to release intracellular proteins. Glucoamylase activity was then assayed. The effects of pH (4.0-9.0), temperature (15-85 degrees C) and substrate (dextrin and starch, 0-2% w/v) concentration on crude enzyme activity were investigated. Optimal growth was obtained in MRS medium containing 1% (w/v) dextrin, at pH 5.5 and 37 degrees C. Glucoamylase production was maximal at the late logarithmic phase of growth, during 16-18 h. Crude enzyme had a pH optimum of 6.0 and temperature optimum of 60 degrees C. With starch as the substrate, maximal activity was obtained at a concentration of 1.5% (w/v). The effects of ions and inhibitors on glucoamylase activity were also investigated. Enzyme activity was not significantly influenced by Ca2+ and EDTA at 1 mmol l-1 concentration; however Pb2+ and Co2+ were found to inhibit the activity at concentrations of 1 mmol l-1. The crude enzyme was found to be thermolabile when glucoamylase activity decreased after about 10 min exposure at 60 degrees C. This property can be exploited in the brewing of low calorie beers where only mild pasteurization treatments are used to inactivate enzymes. The elimination of residual enzyme effect would prevent further maltodextrin degradation and sweetening during long-term storage, thus helping to stabilize the flavour of beer.

Characterization of glucoamylase from Lactobacillus amylovorus ATCC 33621

“…This enzyme was also similar to glucoamylase from Lb. amy/ovorus, in that it was active in the pH range of 5.5 to 6.5 and was heat sensitive above 55'C (Fogarty, 1983;James and Lee, 1995). Glucose was revealed as the main end product of enzyme action after hydrolysis of starch and dextrin at 45°C overnight.…”

“…at 37'C. The preparation of crude cell-free extracts was performed as previously described (James and Lee, 1995). Glucoamylase from Lb.…”

“…An intracellular, thermolabile glucoamylase was identified in Lactobacillus amylovorus (James and Lee, 1995). The objective of this study was to characterize this glucoamylase by investigating its reaction with oligosaccharides of varying chain length.…”

Cloning and expression of a glucoamylase gene from Lactobacillus amylovorus ATCC 33621 in Escherichia coli

“…To date, there has been no report of a thermolabile glucoamylase gene being cloned from a food grade bacteria. Lactobacillus amylovorus was discovered growing on waste corn (Nakamura, 1981), and this amylolytic bacteria is known to secrete large amounts of tr-amylase (Burgess-Cassler and Imam, 1991) and to produce glucoamylase intracellularly (James and Lee, 1995). The objectives of this study were to clone the glucoamylase gene from Lacfobacillus arny/ovorus in fscherichia co/i, and to characterize the recombinant enzyme in terms of its thermostability and effect of pH on enzyme activity.…”