乙酰化蛋黄果多糖及其抗氧化活性研究

Acetylated Lucuma nervosa Polysaccharide and Its Antioxidant Activity

蛋黄果(Lucuma nervosa A.DC)乙酰化修饰多糖的抗氧活性优于未修饰多糖,通过分析乙酰化蛋黄果多糖的乙酰化度、红外光谱和形貌特征,阐明引起抗氧活性提升的原因。试验采用超声波辅助法提取蛋黄果果肉粗多糖,用三氯乙酸法除去蛋白质得到多糖。选取3份0.50 g多糖加入20%NaOH溶液溶解,分别加入1、3、5 mL乙酸酐,得到3种取代度(0.237±0.05、0.275±0.07、0.228±0.04)的乙酰化蛋黄果果肉多糖,评价其清除DPPH自由基、OH自由基和ABTS自由基的能力。结果表明,乙酸酐添加量由少到多时,蛋黄果多糖乙酰基取代度先显著升高,后趋于平缓下降。乙酰化蛋黄果多糖的红外光谱显示了3417 cm^(-1)(-OH)、2950 cm^(-1)(-CH)处的伸缩振动和1636 cm^(-1)处的(-OH)转动振动,1738 cm^(-1)处出现酯基C=O的伸缩振动吸收峰,表明乙酰化已经成功接入。扫描电镜结果显示,未经乙酰化的蛋黄果多糖表面相对光滑平整,呈片状结构;乙酰化修饰多糖分子间交联增强,构象发生了变化,变为表面形状不规则,出现很多空隙且表面粗糙。3种乙酰化蛋黄果多糖中DHG-Ac2(3 mL醋酐)清除效果最好,在浓度1.0 mg/mL时,DPPH清除能力、ABTS自由基清除率、OH自由基清除率分别为91.37%、58.73%、56.36%,分别高于蛋黄果多糖10.0%、43.7%、25.3%。这是引入的乙酰基能活化多糖链中的异头碳,使多糖的供氢能力提升,继而提升乙酰化蛋黄果多糖的抗氧化作用。本研究为海南产蛋黄果多糖的深入开发与抗氧化应用提供了基础研究数据。

The antioxidant activity of the acetylated polysaccharides of Lucuma nervosa is better than that of unmodified polysaccharide.The reasons for the improvement of antioxidant activity of acetylated polysaccharides of L.nervosa were analyzed by degrees of acetyl substitution,infrared spectra and morphological characterization.The polysaccharide was extracted using the ultrasonic-assisted method,and the protein was removed by the trichloroacetic acid method.0.50 g of the polysaccharide was dissolved in 20%NaOH solution,then 1 mL,3 mL and 5 mL of acetic anhydride were added respectively to obtain three degrees of substitution(0.237±0.014,0.275±0.011 and 0.228±0.012)of acetylated polysaccharides.The scavenging effects were evaluated by DPPH free radical,OH radical and ABTS radical.The degree of acetyl substitution of polysaccharides increased significantly at first,then decreased gently with addition of acetic anhydride.The infrared spectra of the acetylated polysaccharides showed a stretching vibration of 3417 cm^(-1) hydroxyl(-OH),2950 cm^(-1) methylene(-CH),1636 cm^(-1) hydroxyl(-OH)rotational vibration,and 1738 cm^(-1) C=O stretching vibration,indicating that acetylation was successfully connected.The results of scanning electron microscope showed that the surface of the original polysaccharides was relatively smooth and flat.As for acetylated polysaccharides,the intermolecular crosslinking was enhanced,the conformation was changed,and the surface shape became irregular and rough.Among the three acetylated polysaccharides,DHG-Ac2(3 mL acetic anhydride)had the best scavenging effect.At the concentration of 1.0 mg/mL,the DPPH scavenging capacity,ABTS radical scavenging rate and OH radical scavenging rate was 91.37%,58.73%and 56.36%respectively,which was higher than 10.0%,43.7%and 25.3%of the original polysaccharides.The introduced acetyl group could activate the heterocephalic carbon in the polysaccharide chain to improve the hydrogen supply capacity of the polysaccharides,and then to enhance the antioxidant effect.This study would provide basic research data for further development and application of the polysaccharides of L.nervosa.