Visual degumming process of ramie fiber using a microbial consortium RAMCD407

Abstract

Morphological changes and biochemical process of ramie retting by RAMCD407 was investigated using microscopy techniques, including OM, PLM, FLSM and SEM coupled with enzyme activity analysis. Results showed that retting was completed within 56 h followed by 0.2% NaOH treatment. Residual gum content and breaking strength of the final fiber was 2.84% and 5.2 cN/dtex, respectively. This fulfills the requirement for ramie spinning. Retting included four main processes: water absorption and CCCO formation; cortex removal; removal of gum in the middle lamella; and removal of gum on the surface of fiber. The first two processes were completed under low enzyme activity condition, while the third process was related to higher pectinase enzyme activity and the last process was related to higher enzyme activities of pectinase and xylanase. In fact, only a small fraction of hemicellulose and pectin is required to be hydrolyzed to ensure fiber separation. In this process, pectinase played a key role supported by xylanase. Valuable retting residues, such as pectinase crystals, pectin blocks, xylan chips and microcrystalline cellulose was recovered from residual liquor by filtration and/or centrifugation. Reuse of these waste residues can help increase the overall economic benefit for ramie industries. The occurrence of spherical balls with double shell structure was found in retting process, and FLSM showed that the outer shell was composed of xylan-rich material. Compared to traditional chemical degumming methods, ramie retting by RAMCD407 is an eco-friendly degumming technique.