CULTURAL CONDITIONS FOR PRODUCTION OF GLUCOAMYLASE FROM LACTOBACILLUS-AMYLOVORUS ATCC-33621

Lactobacillus amylovorus ATCC 33621 is an actively amylolytic bacteria l strain which produces a cell-bound glucoamylase (EC 3.2.1.3). Condit ions of growth and glucoamylase production were investigated using dex trose-free de Man-Rogosa-Sharpe (MRS) medium in a 1.51 fermenter, with varying dextrin concentration (0.1-1.5% (w/v)), pH (4.5-6.5) and temp erature (25-55 degrees C). Cell extracts were prepared by subjecting c ells to treatment with a French Pressure cell in order to release intr acellular proteins. Glucoamylase activity was then assayed. The effect s of pH (4.0-9.0), temperature (15-85 degrees C) and substrate (dextri n and starch, 0-2% w/v) concentration on crude enzyme activity were in vestigated. Optimal growth was obtained in MRS medium containing 1% (w /v) dextrin, at pH 5.5 and 37 degrees C. Glucoamylase production was m aximal 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 con centration of 1.5% (w/v). The effects of ions and inhibitors on glucoa mylase activity were also investigated. Enzyme activity was not signif icantly influenced by Ca2+ and EDTA at 1 mmol l(-1) concentration; how ever Pb2+ and Co2+ were found to inhibit the activity at concentration s of 1 mmol l(-1). The crude enzyme was found to be thermolabile when glucoamylase activity decreased after about 10 min exposure at 60 degr ees C. This property can be exploited in the brewing of low calorie be ers where only mild pasteurization treatments are used to inactivate e nzymes. The elimination of residual enzyme effect would prevent furthe r maltodextrin degradation and sweetening during long-term storage, th us helping to stabilize the flavour of beer.