Evaluation of growth age for the diverse conversion of Ficus carica L. cut branches using steam explosion

•Evaluation of growth age on the conversions of fig cut branches was first studied.•1-year-old branch gave higher sugar conversion compared with 0.5- and 3-year-old.•Steam explosion decreased number- and weight-average molecular weight of lignin.•Mechanism for the age-related diverse conversion was proposed by plant auxanology.

Growth age determines the composition and structure of woody biomass and hence its conversion performance. Effects of growth age of seasonal Ficus carica L. cut branches (FCBs) on the diverse conversion efficiency by steam explosion (SE) were evaluated. Results showed that sugar contents increased with the growth age of FCBs (0.5-, 1- and 3-year-old). Sugar conversions increased dramatically after SE for all FCBs, and the highest sugar conversion was observed at 1-year-old FCB, reaching 48.4% for glucan. SE decreased number- and weight-average molecular weight and increased polydispersity of lignin. 1-year-old FCB obtained the highest specific surface area value (0.439 m2/g) after SE, 64.0% and 28.8% higher than that of 0.5- and 3-year-old FCBs. Morphology observation of single fibers showed the homogeneous fiber size distribution for 1-year-old FCB after SE, which should be helpful to increase the adsorptivity of enzymes during hydrolysis. Through SE, 1-year-old FCB obtained higher sugar contents, bigger specific surface area, homogeneous fiber size distribution, and hence higher sugar conversion during enzymatic hydrolysis. Therefore, the analysis of physicochemical property and the hydrolysis performance suggested that 1-year-old FCB would be a desirable substrate for the conversion process using SE.

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