Synthesis of nanocrystalline cellulose via microwave-assisted acetic acid pretreatment and endoglucanase-xylanase-mediated enzymatic hydrolysis.

The tangerine (Citrus unshiu) peel-derived cellulose nanofibrils (TP-CNFs) were synthesized via an integrated microwave-assisted acetic acid pretreatment and enzymatic hydrolysis using a cocktail of endoglucanase and xylanase. The resulting TP-CNFs were characterized in terms of morphology, dimensions, chemical composition, yield, crystallinity, functional properties, thermal stability and surface charge. The biosynthesized nanofibrils formed an interwoven, elongated network, with diameters of 2.89-17.12 nm (mean 9.23 nm) and lengths of 340.10-898.93 nm (mean 603.48 nm). Benefiting from the selective and protective actions of the enzyme mixture, which limited excessive hydrolysis, the CNF yield reached 70.80%, while crystalline domains and amphiphilic properties were well-preserved. The process efficacy was further evidenced by a clear cellulose signature and removal of amorphous components, notably hemicellulose, lignin and pectin, accompanied by enhanced accessibility of hydroxyl groups. These structural modifications resulted in a crystallinity index of 64.35%, thermal stability of 338.90 °C and stable colloidal behaviour, with a zeta potential of -30.2 mV. This proposed research framework demonstrates a green and effective strategy for valorizing citrus waste into high-quality nanocellulose, providing a sustainable pathway compatible with future biorefinery applications.