Alkaline Pectinase Production By Submerged Fermentation With Rhizopus Sp. And Its Application

In textile industry, bioscouring of cotton fabrics has replaced traditional alkaline scouring duing to its environmental protection and energy saving. The alkaline pectinase is the main enzyme preparation in bioscouring. At present, the alkaline pectinase is produced by bacteria and actinomyces mostly. It has not reported that Rhizopus sp. produces alkaline pectinase. Rhizopus GZ-11 producing alkaline pectinase had been found. The culture conditions and enzymatic properties were studied. Its application was tested in textile industry for bioscouring of the cotton fabric.With the enzymatic activity, biomass and residul sugar as indexes, 4 days was chosen as the fermentation period. The optimal culture conditions were as follows: seed age 20 h, the initial pH of PG and PGL 4.0 and 5.0 separately, the culture temperature 28℃, the inoculum size 6%, volume of medium 50 mL/250 mL, the speed of shaker 160 r/min, culturing 96 h. Under these conditions, the optimal medium ingredients of this strain were studied by single factor test and L18(35) orthogonal experiment. The optimal fermentation medium was determined(g/L): orange peel power 20.0, soluble starch 10.0, (NH4)2SO4 20.0, wheat bran 45.0, Ca2+ 0.33, Tween-80 2.5, K2HPO4 4.0, KH2PO4 4.0. Under the optimized fermentation conditions, the highest yields of PG and PGL reached 1.593 million IU/mL and 20.65 IU/mL, which increased by 34.98% and 62.21% respectively.The crude alkaline pectinase properties were investigated. The optimum pH, the optimum temperature and the stable pH range of PG were 8.6, 50℃and 4.0~9.4 respectively. The optimum pH, the optimum temperature and the stable pH range of PGL were 9.4, 45℃, and 5.0~11.0 respectively. The thermal stability was studied, when the temperature was under 50℃for PG and under 45℃for PGL, they could stay steady. Influences on enzymatic activity of many kinds of ions were also studied. Na+ and Ca2+ could promoted their catalytic activity significantly, while K+, Zn2+, Mg2+ and Hg2+ restrained their activity.The optimal stabilizer recipe of PGL was studied by single factor test and L9(34) orthogonal experiment: dextrin 5%, EDTA 2%, ethylene glycol 3%, sodium acetate 2%. The residual rate of PGL activity with stabilizer was 67.35% higher than control group.The optimal conditions that refined the cotton fabric using crude pectinase were studied by single factor test: the time of boiling water pretreatment 10 min, enzyme concentration 1200 IU/L, pH of scouring bath 8.6, scouring time 40 min, scouring temperature 60℃. The capillary effect and weight-loss ratio improved 110.95% and 129.66% respectively when the stabilizer was added.Comparing to the Scourzyme 301L of Novozymes, the weight-loss ratio and capillary effect of the cotton fabric were close and could reach the conventional standard of alkaline scouring craft. These cotton fabric which were refined by crude alkaline pectinase made in our lab had softer handle and smooth surface.