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Journal of Zhejiang University SCIENCE B
ISSN 1673-1581(Print), 1862-1783(Online), Monthly
2017 Vol.18 No.2 P.138-151
Isolation, chemical characterization, and immunomodulatory activity of naturally acetylated hemicelluloses from bamboo shavings
Abstract: Bamboo shavings, the outer or intermediate layer of bamboo stems, are the bulk of by-products produced in bamboo processing. In this study we investigated the isolation, chemical characterization, and immunostimulatory activity in vitro of the hemicelluloses from bamboo shavings. Shavings were first pretreated by steam explosion. The optimal pretreatment was found to be steam explosion at 2.2 MPa for 1 min. Following this pretreatment, the yield of hemicelluloses reached (2.05±0.22)% (based on the dry dewaxed raw materials), which was 5.7-fold higher than that of untreated samples. Bamboo-shavings hemicellulose (BSH) was then prepared by hot water extraction and ethanol precipitation from the steam-exploded shavings. Purification of BSH by anion-exchange chromatography of diethylaminoethanol (DEAE)-sepharose Fast Flow resulted in a neutral fraction (BSH-1, purity of 95.3%, yield of 1.06%) and an acidic fraction (BSH-2, purity of 92.5%, yield of 0.79%). The weight-average molecular weights (Mw) of BSH-1 and BSH-2 were 12 800 and 11 300 g/mol, respectively. Chemical and structural analyses by Fourier transform infrared spectroscopy (FT-IR), 1D (1H and 13C) and 2D (heteronuclear single quantum correlation (HSQC)) nuclear magnetic resonance (NMR) spectra revealed that BSH-1 was O-acetylated-arabinoxylan and BSH-2 was O-acetylated-(4-O-methylglucurono)-arabinoxylan. BSH-1 had a higher content of acetyl groups than BSH-2. For the immunomodulatory activity in vitro, BSH and BSH-2 significantly stimulated mouse splenocyte proliferation while BSH-1 had no effect; BSH, BSH-1, and BSH-2 markedly enhanced the phagocytosis activity and nitric oxide production of the murine macrophage RAW264.7 in a dose-dependent manner. Our results suggest that the water-extractable hemicelluloses from steam-exploded bamboo shavings are naturally acetylated and have immunostimulatory activity.
Key words: Bamboo shavings; Steam explosion pretreatment; Naturally acetylated hemicelluloses; Isolation; Chemical characterization; Immunomodulatory activity
创新点：首次采用蒸汽爆破预处理联合热水提取法从竹茹中获得有免疫调节活性的天然乙酰化半纤维素。
方法：采用蒸汽爆破预处理联合热水抽提法从竹茹中提取半纤维素；通过阴离子交换柱层析法对优化条件下制得的BSH进行分离；利用化学法和波谱法对分离得到的两个半纤维素组分（BSH-1和BSH-2）进行化学结构解析；采用小鼠脾脏淋巴细胞转化增殖试验、小鼠巨噬细胞RAW264.7吞噬中性红以及分泌NO试验评价BSH、BSH-1和BSH-2的体外免疫调节活性。
结论：当蒸汽爆破压力为2.2 MPa和维压时间为1 min时，BSH的得率达到最大，为(2.05±0.22)%（以脱蜡样品干重计），高于未经处理对照样品5.7倍。通过DEAE-Sepharose Fast Flow阴离子交换柱对BSH进行分离，获得一个中性组分BSH-1（得率0.79%，纯度95.3%）和一个酸性组分BSH-2（得率1.06%，纯度92.5%）。化学结构解析结果表明BSH-1为乙酰化的阿拉伯木聚糖（分子量：12 800），而BSH-2为乙酰化的4-甲氧基-葡萄糖醛酸阿拉伯木聚糖（分子量：11 300）。体外免疫试验结果表明BSH和BSH-2能够显著刺激小鼠脾脏淋巴细胞增殖，而BSH-1无此活性；BSH、BSH-1和BSH-2三者均能显著促进巨噬细胞RAW264.7吞噬中性红及分泌释放NO，且呈现明显的剂量依赖性。综上所述，采用蒸汽爆破预处理联合热水提取法从竹茹中获得的半纤维素含天然乙酰基，并具有体外免疫刺激活性。
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DOI:
10.1631/jzus.B1500274
CLC number:
O636.1; R392.12
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On-line Access:
2017-01-26
Received:
2015-11-09
Revision Accepted:
2016-05-07
Crosschecked:
2017-01-05