Two-step isolation of hemicelluloses from Chinese quince fruit: Effect of hydrothermal treatment on structural features

Abstract

Two-step isolation of hemicelluloses from Chinese quince fruit was carried out in this investigation. At the first treatment stage, hydrothermal treatment was developed to enhance the xylose amount in the solid residue remaining after pectin extraction. Second, the alkali-extractable hemicelluloses were isolated from the solid residue obtained from hydrothermal treatment and were successively sub-fractionated by precipitation at graded ethanol concentrations of 30%, 50%, 70% and 90%. The structural properties of the isolated hemicelluloses from raw fruits and fruits treated with the hydrothermal process were characterized by sugar analysis, FT-IR, molecular weights, thermo-gravimetric analysis, morphological analysis, and NMR. Results showed that the xylose amount in the solid residue increased from 58.2% to 62.2% when the hydrothermal treatment temperature was increased from 120°C to 150°C. Arabinose and mannose were found to be hydrolyzed by hydrothermal treatment, while the crystalline cellulose and lignin were not affected. Compared with the raw Chinese quince, the treatment had an important effect on the sugar composition distributions and average molecular weights of hemicelluloses obtained at various ethanol concentrations. Structural characterization revealed that the isolated hemicellulosic sub-fractions precipitated at a final ethanol concentration of 30% had a backbone of d-xylose residues with a β-(1→4)-linkage. This work reveals a novel hemicelluloses isolation route from Chinese quince fruit, which was important in the development of biomass refining industry. This work reveals a novel hemicelluloses isolation route from Chinese quince fruit, which was important in the development of biomass refining industry.