Optimization Of Conditions For Producing Glucomannanase And Its Effect On The Quality Of Steamed Bread

Based on the single factor experiment,the optimum conditions for the production of glucomannanase by Bacillus amyloliquefaciens were optimized by the response surface method,and the high activity glucomannanase was obtained.And then the properties of glucomannanase were preliminarily studied.Furthermore,the effects of glucomannanase on dough characteristics and the quality of steamed bread were studied by adding glucomannanase into the making of steamed bread,which provided reference basis for industrial production of glucomannanase and application of glucomannanase.(1)With Bacillus amyloliquefaciens as the initial strain,the enzyme production conditions of the flask fermentation were studied.The effects of some factors,such as fermentation time,inoculum size,liquid volume,carbon source,nitrogen source and so on,on the production of glucomannanase from Bacillus amyloliquefaciens were investigated by single factor experiment.To further optimize enzyme production conditions,a three-factor and three-level quadratic regression analysis experiments were designed to perform response surface analysis,with inoculation amount,liquid loading amount and fermentation time selected as independent variables,and the activity of glucomannanase taken as response value.By solving the regression equation with Design-Expert software,the optimal culture conditions for the production of glucomannanase from Bacillus amyloliquefaciens were determined as follows:inoculum size,8%;fermentation time,80 h;liquid volume,100 mL/250mL.Under the circumstances,the glucomannanase activity was measured as 2509 U/mL,which was close to the predicted value of the regression equation,2535 U/mL.(2)The properties of glucomannanase were preliminarily studied.The results showed that the optimum reaction temperature and pH of glucomannanase were 50?and 7.0,respectively.And the glucomannanase was stable in the range of 30-40?and pH 3.0-7.0.Al3+,Fe3+and Cu2+had inhibitory effects on glucomannanase,while Mn2+ had activation effects.The glucomannanase activity was higher when the substrate concentration was in the range of 3-5 mg/mL.When konjac was used as a substrate,the Km value of glucomannanase was 1.05 mg/mL.(3)In the process of making steamed bread,1%,2%and 3%glucomannanase were added to analyze the effects of glucomannanase on dough properties and quality of steamed bread.The results showed that proper amount of glucomannanase had significant effects on stretching and other properties of dough and texture of steamed bread(p<0.05).The dough became softer and the network structure was stable.The quality,volume,texture and structure of steamed bread were improved.At the same time,in addition to inhibiting the increase of hardness and the decrease of elasticity during storage,glucomannanase could also reduce the melting enthalpy of steamed bread and inhibit the regeneration of steamed bread.