Screening And Identification Of Degumming Bacteria And Degumming Of Silk By Microbiological Process

Today silk product is still popular in the world due to its soft,perfect luster,hygroscopic and comfortable dressing,even though chemical fibers have been developed very well.In silk industry, degumming is a key process during which sericin is partly removed and silk fibers gain the typical shiny aspect and soft handle.Degumming by chemical method causes water pollution and fiber damage.Degumming by natural fermentation leads to unstable quality.Degumming by enzyme is expensive.In this study,the degumming bacteria was isolated from natural fermentation liquor of silk and a pure fermentation process was developed to improve the efficiency of degumming and the quality of silk fibers.Nine degumming strains were isolated from two types of natural fermentation liquors basing on the plating assay.The strain D7 was selected due to its high efficiency degumming.This strain was identified as Bacillus cereus based on its morphological,physiological and biochemical characteristics and 16S rDNA sequence analysis.The suitable condition for the growth of the strain included 37。C,pH 7.0,and the time of the exponential phase in LB medium was 2¹2 hours.A pure fermentation process by strain D7 was used in degumming of silk.Some parameters such as inoculum size,temperature,pH,treatment time,rotating speed and components of medium on degumming and protease productivity were investigated.The optimum conditions for degumming were as follows:0.05%Mg²⁺,5%inoculum size,37°C,pH 7.0,150r/min,incubate time for 3d.The residual sericin content was 4.46%.The high degumming ability of strain D7 corresponded to its high enzyme productivity.The strength and elongation of degummed fiber by pure fermentation was better than that of degummed fibers by chemical method and enzyme method.Scanning electron microscope showed that the surface of the fibers treated by fermentation were smooth and clean.Results showed that it is feasible to remove excessive sericin by pure culture fermentation.