Production of an alkali-stable xylanase from Bacillus pumilus K22 and its application in tomato juice clarification

A xylanase-producing bacterium Bacillus pumilus K22 was isolated from hot spring located in Manghopir area, Karachi, Pakistan. The enzyme was purified to homogeneity by acetone precipitation and size exclusion chromatography. The molecular weight was determined to be approximately 24 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified xylanase retained its activity at wide range of temperature (20-70?C) and pH (5.0?10.0) with maximum stability at 50?C and pH 8.0. Xylanase activity was inhibited by Zn2+, Cu2+, and Hg2+ metal ions while it remained stable in the presence of Mn2+, Ca2+ and Mg2+. The activity was also inhibited by chemical reagents such as EDTA, PMSF, and ?-mercaptoethanol. The enzyme was stable in the presence of all organic solvents (20%) except formaldehyde and glycerol, which inhibited its activity. Treatment of tomato pulp with purified xylanase-increased juice yield (30%), clarity (9%), and reducing sugars (69%), indicating an improvement in physico-chemical characteristics of the tomato pulp.