A simplified and efficient preparation process of pineapple leaf fibers via in-situ retting and degumming by Bacillus subtilis XW-18

Pineapple leaves are agricultural waste but rich in the pineapple leaf fiber (PALF) with superior mechanical properties. The conventional PALF preparation usually include two steps of manual/mechanical extraction and chemical degumming, resulting in adverse issues such as fiber loss, inferior fiber quality, and environmental pollution. In the present study, a simplified and efficient preparation process of PALF, without any pretreatment and subsequent bleaching, was successfully achieved through in-situ inoculation of Bacillus subtilis XW-18 to fresh pineapple leaves. Results showed that B. subtilis XW-18 was rich in the diversified degumming-related enzymes, which could exert an direct retting and degumming action on the fresh pineapple leaves by simultaneously secreting high-activity pectinase, mannanase, and xylanase but low-activity cellulase. Due to the ideal combination of degumming-related enzymes in B. subtilis XW-18, the prepared PALF reached 2.29% of fiber yield and 3.50% of residual gum content, displaying a dispersed fibrous structure and white appearance. Structural characterizations and chemical compositions of PALF further confirmed that B. subtilis XW-18 had an effective action on removal of the non-cellulosic macromolecules such as gummy substances, hemicelluloses, and lignin, thus acquiring a high cellulose content up to 79.36 wt%. Furthermore, the method using in-situ inoculation of B. subtilis XW-18 achieved the prepared PALF with ideal physical and mechanical properties. In summary, B. subtilis XW-18 offered a promising alternative option for the green and efficient preparation of PALF, not only due to its one-step process for PALF preparation, but also due to its ideal combination of the degumming-related enzymes.