An integrated process based on hydrothermal pretreatment (HTP) and alkaline post-treatment was proposed to treat sweet sorghum stem. The structural features of the alkali-soluble hemicelluloses (ASHs) obtained from the un-pretreated and hydrothermally pretreated materials were comprehensively investigated by HPAEC, GPC, NMR, FT-IR, and TGA techniques. The ASH with the highest yield (60.6%) was obtained from the HTP residue performed at 130 °C for 1.0 h. All the results indicated that the ASHs had a more linear structure with increasing the pretreatment temperature (110-170 °C). The molecular weights of the ASHs were decreased with increasing the pretreatment temperature, suggesting that C-O bonds in the ASHs were gradually cleaved, especially at the higher temperatures (≥ 170 °C). Interestingly, the integrated process yielded more homogeneous ASHs than hemicelluloses obtained from the un-pretreated material. Based on the spectral analyses, the structure of the ASHs was assumed to be L-arabino-4-O-methyl-D-glucurono-D-xylan.
Keywords: Alkaline treatment; Hemicelluloses; Hydrothermal pretreatment; Nuclear magnetic resonance (NMR); Structural feature; Sweet sorghum stem.
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