结构单元构成及相互作用对麦麸阿魏酰低聚糖酯抗氧化活性调控机制研究

Feruloylated oligosaccharides（FOs）were derived from various cereal cortex and show the effective activity of antioxidation based on the special ester structure. But so far, the mechanism(s) of that was not well understood. Therefore, the main points of this project on antioxidant activity mechanism(s) of FOs are as the follows. Firstly, the structure of diffident FOs obtained from wheat bran were characterized by using high performance liquid chromatography (HPLC), mass spectrometry (MS) and nuclear magnetic resonance (NMR). Meanwhile, the content and ratio of FA and oligosaccharides were determinated with spectroscopy and chromatographic detection technology. Secondly, the antioxidant capacity of those FOs were measured with the 2,2-diphenyl-l-picrylhydrazyl (DPPH), oxygen radical absorbance capacity (ORAC) and ferric reducing antioxidant power (FRAP) assays. to investigate the possible structure site with antioxidation of FOs,the structure-activity relationship of FOs was determined with relativity analysis and theoretical calculation of quantum chemistry. Thirdly, the interaction effect of oligosaccharides on O-methoxyphenol was measured with the DPPH assay by using uv-vis spectrophotometry (UV), cyclic voltammetry (CV) and MS. It is expected to clarify the antioxidant activity mechanism(s) of FOs in the study. Then it would provide theoretical basis for practical applications of FOs and promote the development and utilization of cereal.

阿魏酰低聚糖酯（FOs）广泛存在于谷物皮层。基于低聚糖与阿魏酸（FA）的羧基酯化结构，FOs具强抗氧化活性。这一活性是由结构单元单一起效，还是由相互间协同作用，即其抗氧化活性机制尚未见阐明。为此，本项目在纯化富集麦麸FOs组分基础上，拟进行以下几个方面的工作：（1）采用HPLC、质谱与核磁共振法，进行麦麸FOs结构中FA和低聚糖的组成、数目和连接方式的表征与结构单元含量和比例的测定；（2）采用ORAC法、FRAP法和DPPH法评价麦麸FOs的抗氧化活性。经活性与结构单元相关性分析，结合量化理论参数，研究麦麸FOs结构中抗氧化活性部位；（3）采用分光光度法、循环伏安法和质谱法，检测计算麦麸FOs与DPPH反应动力学参数，研究麦麸FOs结构中低聚糖对阿魏酰基酚活性的影响作用及机制。通过研究，以期阐明FOs的抗氧化活性机制，为天然高效抗氧化剂的筛选与应用提供理论依据，并促进谷物资源的开发利用。

全谷物的健康效应与其酚类物质的抗氧化活性密切相关。阿魏酰低聚糖酯（FOs）是谷物酚的主要存在形式，广泛存在于谷物皮层。项目分离制备不同聚合度FOs组分表征其结构特征可见各组分具糖酯结构，表现为阿魏酸通过酯键交联到以β(1-4)吡喃糖糖苷键连接的阿拉伯木聚糖；不同聚合度麦麸FOs组分在抗氧化评价模型与其浓度之间存在量效关系。低聚合度FOs组分（FO低）对DPPH•的EC50为0.05 mg/mL，优于FA的1.229 mg/mL（p<0.01）；麦麸FOs组分影响美拉德反应中间产物乙二醛、丙酮醛和2,3-丁二酮的生成，与聚合度呈负相关。在50 mg/mL时FO低对其抑制率分别为76.46%、62.41%和88.35%，均优于FA的57.18%、33.49%和64.85%（p<0.05）。同时，浓度依赖性的抑制食品模拟体系中糖基化终末产物的生成。FO低在10mg/mL时的抑制率达97.52%，显著优于FA的77.36%（p<0.05）。. 组分中阿魏酰基和低聚糖基均具有抗氧化活性。阿魏酰基为主要活性单元，前线分子轨道电子云主要分布在苯环(-H)、羧基(-H)、甲氧基及C=C上；阿魏酰基酚（OHA）为主要活性部位，其电荷数大于其他位置，以FO低为例0.286A> 0.063B> 0.037C> 0.040D；FOs低聚糖基团的引入基于单电子转移机制增强OHA的活性，给单子能力（EHOMO）排序为：FO中>FO低>FO高>FA，电离能与聚合度负相关；低聚糖结构引入使得自由能下降，组分键解离能（70.76 kcal/mol）<FA（71.84 kcal/mol）；组分中糖基的远端羟基由于空间位阻效应影响其活性。. 本项目通过麦麸FOs组分结构与活性规律分析，揭示了结构中抗氧化活性部位及结构单元间的相互作用，阐明麦麸FOs结合型糖酯结构对其抗氧化活性的调控机制，为谷物资源的合理加工与开发利用提供参考。