Application of two Bacillus sp. strains in composite degumming of ramie fibers

Abstract:

[Background] Ramie fiber is known as the "king of natural fiber" and used in many fields due to its excellent properties such as slender, strong, white, and shiny. However, the fiber is wrapped by the gum materials with hemicellulose and pectin as the main components, and degumming is the pivotal process for obtaining the refined ramie fibers. Using a single strain for ramie degumming, the gum removal rate is always low due to its incomplete degumming enzyme system. As a result, lots of alkalis and bleachers have to be used to remove the residual gum materials in the later stage. [Objective] Enriching the key enzyme systems in the degumming process of ramie fibers, improving the gum removal rate, reducing the usage of chemical reagents in the later stage, and promoting the industrial application of ramie biological degumming. [Methods] One strain Bacillus sp. HG-9 with highly activities of pectinase and mannanase and another Bacillus sp. HG-25 with highly activities of xylanase were selected to establish a mixed microbial degumming technology. Besides, the related parameters of the degumming process were optimized.[Results] When the inoculation amount of the two strains, the ratio of water to material, the initial pH value, the temperature, and the degumming time were 6%, 16:1, 5.9, 37.6℃, and 14 h, respectively, the effect was best. Compared with strain HG-9 alone, the degumming time was reduced by 2 h, and the removal rate of gums, hemicellulose, and lignin were increased by 9.32%, 21.24%, and 17.93%, respectively. The amount of sodium hypochlorite was reduced by 20%. The results of scanning electron microscopy showed that the fibers obtained by composite degumming was smoother, without obvious distortion and damage. Meanwhile, the fiber dispersion was high. [Conclusion] With the synergistic action of composite microorganisms, the key enzymes in the degumming process was enriched, the gum removal rate was improved, the degumming time and the amount of bleacher in the later stage was reduced. This study provided meaningful guidance for the further industrial application of ramie biological degumming.