Silk Degumming Solution as Substrate for Microbial Protease Production

Abstract

As waste solution from the silk degumming process contains high nitrogen levels, wastewater must be treated prior to discharge. In this study, waste solution was prepared and tested as a nutrient substrate for microbial growth and protease production by Bacillus licheniformis TISTR 1010 and Aspergillus flavus TISTR 3130, TISTR 3366, TISTR 3135 and TISTR 3041. All strains were preliminarily screened for their protease activity by growing on casein-agar plates with B. licheniformis TISTR 1010 being chosen as the best producer of protease. Cultivation in a silk degumming solution as the nutrient source demonstrated that the highest protease activity was achieved at an optimum pH of 10 for 36 h. Among the culture media used, the specific activity of released protease was best with a medium containing 6% protein from the silk degumming waste, 1% malt extract, 1% polypeptone and 1% Na₂CO₃. This study was the first to report the use of silk degumming waste as a nitrogen source for microorganism
growth and protease production. As such it could suggest an alternative way to convert wastes into more valuable and marketable products.