The Study On The Functional Effect Of Acetyl Xylan Esterase In Ramie Bast Fiber Microbial Degumming Process

Boehmeria nivea(L.) Gaudich is Chinese specific fibrous crops for spinning. The filament of ramie is excellent in breathability and hygroscopicity. The 30% non-fibrous compositions in bast fiber of ramie, which was called gums, was consisted of pectin, hemicellulose, and lignin and so on. Microbial degumming, with the advantages of high degumming efficiency, low cost, and low pollution, was becoming the main research field in ramie degumming. Bacillus sp. HG-28 was applied in ramie degumming in our previous study with high degumming efficiency, only leaving little hemicellulose and lignin to be removed. According to the literatures, hemicellulose and lignin was linked with covalent linkage. After the degradation of hemicellulose, lignin structure was loosed and possibly partially removed. In order to improve the degumming efficiency, the hemicellulose was the main substances to be removed. Many acetylated structure was existed in ramie hemicellulose and hindered the ramie hemicellulose to be degraded by degumming enzymes from microorganisms. Based on above, mixed microbial degumming was applied to improve the removing efficiency of acetyl side chains in this study. After that, it was expected that the hemicellulose degradation efficiency was improved and then the degumming efficiency was improved. The research results were as follows.Firstly, in single strain degumming with Bacillus sp. HG-28, adding acetyl xylan esterase(AXE) inducer(ethyl acetate) could induce the strain to secret the AXE with improved activity, increased by 3.79% and 5.60% respectively. And the promoting effect for microbial degumming was determined, so the removing ratio of hemicellulose and total gums could be improved by removing the acetyl side chains via being induced to improve the AXE activity. The best concentration of inducer and the best time point for adding inducer were determined for 1%(v/v) and 8 h after degumming starting time respectively. After adding inducer, the AXE activity increased.Secondly, Bacillus pumilus HG-56, which was able to secret acetyl xylan esterase with high efficiency, was selected as the synergetic degumming strain with Bacillus sp. HG-28. It was discovered that the AXE activity of Bacillus pumilus HG-56 was relatively high and Bacillus pumilus HG-56 was synergetic with Bacillus sp. HG-28. The best mixed microbial degumming pattern was determined as follows: At first, Bacillus sp. HG-28 was inoculated, after 2 h degumming process, 4 h-age Bacillus pumilus HG-56 was inoculated for mixed degumming, the total degumming process lasted for 40 h. With the best mixed degumming conditions determined above, compared with single strain degumming, the hemicellulose and total gums removing ratio increased by 15.80% and 7.03% respectively.Thirdly, DNS method, X-ray diffraction, fourier transform infrared spectrum(FTIR) and scanning electron microscope(SEM) were utilized to analyze the enzymes activity changes during the mixed degumming progress, the ramie composition content changes and fiber structure changes before and after degumming process. The two strains were determined with complementary degumming ability and good synergistic effect and the acetyl side chains were nearly removed. Most of hemicellulose and pectin exposed outside were further degraded so that the crystallinity of ramie filament increased and the surface was smoother. The mixed microbial degumming was more advantageous than single strain degumming.The study above laid a solid theoretical and experimental foundation for future microbial degumming optimization and industrialization.