Retting of Mitsumata Bast by Alkalophilic Bacillus in Papermaking

Abstract

An alkalophilic bacterium isolated from soil and designated as strain GIR-277 was found to efficiently macerate bast fibers of mitsumata (Edgeworthia papyrifera Sieb. et Zucc.). The organism identified as a Bacillus sp. was successfully applied to alkaline retting in papermaking. The optimum concentration of alkali (Na₂CO₃) for this process was 1.0-1.5%, which corresponded to an initial pH of 10.1-10.3. The retting was accomplished within a few days at 30°C. Substantial maceration was ascribed primarily to pectate lyase (EC 4.2.2.2) secreted by the bacterium, and to a lesser extent to the β-eliminative splitting of pectic substances. The overall yield of pulp was about 70%. The strength of the unbeaten pulp resulting from bacterial retting was as higher than that by the conventional soda ash-cooking method. Paper sheets were quite uniform and very soft to touch. It is concluded that bacterial retting under alkaline conditions is a potentially useful process to produce pulp of excellent quality from non-woody pectocellulosic fibers.