【作者】 王毕妮；

【导师】 樊明涛；

【作者基本信息】 西北农林科技大学 ， 食品科学， 2011， 博士

【摘要】 我国是世界上红枣资源最丰富的国家,红枣的栽培和食用历史悠久,长期以来,红枣已广泛用于食品、中药和保健品中。关于红枣的功能,一般认为主要来自两个方面,一是红枣多糖,二是红枣多酚。红枣多糖在我国已经研究的很多,也基本搞清了红枣多糖的功能机理,但关于红枣多酚,尽管已经开展了部分研究工作,但主要集中于粗提物抗氧化活性的研究,对其中酚类化合物的组成了解甚少,也未见有关红枣加工处理对其多酚种类及抗氧化活性影响方面的研究报道。本文分析了红枣不同部位(枣皮、枣肉和枣核)中酚类化合物的组成,采用不同的抗氧化活性评价体系评价了其抗氧化能力,分析各多酚种类与抗氧化活性间的相关性;建立了一种同时测定几种酚类化合物的HPLC-ECD分析测定方法;分析了红枣不同部位中酚酸的组成及分布;探讨了干制和烹饪处理对红枣中酚类化合物的组成和抗氧化活性的影响。取得的主要研究结果如下:1.新鲜红枣三个部位(枣肉、枣核和枣皮)的甲醇提取液均具一定的抗氧化能力,也有清除DPPH·和·OH的能力。红枣枣皮中总酚含量和总黄酮含量均较枣肉和枣核高,且具有最强的总抗氧化能力和清除DPPH·和·OH的能力。鲜枣中总黄酮对总酚有一定的贡献,二者均对其抗氧化活性有很大的贡献,三种抗氧化活性评价方法间也存在较高的相关性。2.通过对分离条件和检测条件的选择和优化,建立了一种可快速同时测定六种酚类化合物的HPLC-ECD方法。ECD检测这六种酚类化合物较DAD灵敏度高。在选定的液相色谱条件下,六种酚类化合物在25min内得到了很好的分离,检出限在8.7×10-3μg/mL以下,平均回收率在98%以上,具有较高的准确度和精密度。该法已成功用于五种红枣样品中的此六种酚类化合物的同时测定,也为其他天然产物中酚类化合物的测定提供参考。3.游离态、酯键合态、糖苷键合态及甲醇不溶性键合态酚酸部分的总酚含量、酚酸的分布及抗氧化活性在红枣各部位中均存在差异。测定了红枣中四种形式存在的八种酚酸的含量,其中对羟基苯甲酸和肉桂酸在所测几种酚酸中的含量最高,而阿魏酸含量最低。各测定酚酸主要分布在枣皮中。枣核和枣皮中的酚酸主要以甲醇不溶性键合态形式存在,而枣肉中则主要以糖苷键合态形式存在。各部分酚酸的抗氧化活性均与其总酚含量相关,枣肉和枣皮中糖苷键合态和甲醇不溶性键合态酚酸部分的总酚含量最高,其DPPH·清除能力和FRAP值也最高,表现出最强的抗氧化活性。4.红枣经干制后,其酚类化合物组成和抗氧化活性变化很大。干制后红枣中酚酸类化合物含量显著下降,总黄酮含量变化不明显,而热风干制后其原花青素含量显著升高。红枣的抗氧化活性与其中总黄酮和原花青素含量关系不大,而与酚酸类化合物有很大关系。经热风干制和自然干制的红枣抗氧化活性间无显著性差异,但热风干制红枣中酚酸类化合物含量显著低于自然干制的红枣。5.高压蒸煮较常压处理红枣中的总酚含量较高,尤其是枣肉,但高压处理的红枣口感偏苦。常压煮制红枣的枣皮和枣肉中酚酸类化合物的总酚含量均最高,而高压煮制的枣皮和蒸制的枣肉中酚酸类化合物均最少。高压蒸制红枣的总黄酮含量最高,常压蒸制红枣的枣皮中总黄酮含量最高,而高压处理的枣肉中总黄酮含量最高。但是,不管哪种烹饪方式处理红枣,其枣皮中均未测出原花青素的含量,枣肉中以高压蒸制处理的原花青素含量最高。6.常压蒸制处理的红枣枣皮清除DPPH·的能力和总抗氧化能力均较强,而高压蒸制处理的红枣枣肉的DPPH·清除能力较强,常压煮制的红枣枣肉总抗氧化能力较强。红枣中总黄酮对其抗氧化活性贡献不大,而总酚尤其是原花青素、酚酸类化合物对其抗氧化活性起了很大的作用。7.红枣若采用高压烹饪方式,蒸制处理能较好地保存红枣中的酚类化合物及抗氧化活性;若采用常压烹饪方式,则采用煮制较好。更多还原

【Abstract】 China is the largest producer of jujube in the world. There has been a long history in cultivating and feeding jujube, the fruit of Zizyphus jujube Miller in China. Jujube has been widely used as food, a functional food additive, and a traditional Chinese medicine for many years. Studies on the functions of jujube are mostly on the polysaccharide and polyphenols in jujube. There have been many studies on the polysaccharide, which mechanism has been clarified. Although there has been some published research on the phenolic compounds and antioxidant activity of jujube, they are mostly concentrated on the antioxidant activity of jujube extracts. As far as we know, little has been reported on the distribution of phenolic compounds in jujube and effects of processing on the phenolic compounds and their antioxidant activity.In this study, the composition of phenolic compounds in different tissues of jujube and the correlation analysis of kinds of phenolic compounds and their antioxidant activity evaluated by different methods were analyzed; a simple, sensitive and accurate high performance liquid chromatography with electrochemical detection (HPLC-ECD) method for simultaneous separation and determination of some phenolic compounds has been established; the composition and distribution of phenolic acids in jujube were analyzed; effects of drying and cooking treatment on the composition of phenolic compounds in jujube and their antioxidant activity were discussed.The main results are as follows.1. The methanolic extracts from different tissues of fresh jujube (pulp, seed and peel) all exhibits antioxidant activity, 1,1-diphenyl-2-picrylhydrazyl radical (DPPH·) and hydroxyl radical (·OH) scavenging activity. The extracts of jujube peel show the higher total phenolic and flavanoid contents and the stronger total antioxidant power and DPPH·and·OH scavenging activity than those of pulp and seed. Furthermore, the antioxidant activities are significantly correlated with total phenolic and flavanoid contents, and there is high correlation in the evaluation methods of antioxidant activity. 2. A simple, sensitive and accurate high performance liquid chromatography with electrochemical detection (HPLC-ECD) method for simultaneous separation and determination of six phenolic compounds in jujube has been established by optimizing the separation conditions and selecting the detection conditions. ECD is more sensitive than diode-array detection (DAD) for the detection of the six phenolic compounds. On the HPLC conditions the six phenolic compounds are well separated within 25 min. The limits of detection (LOD) are lower than 8.7×10-3μg/mL and the recoveries are higher than 98 %. This approach has been applied for the simultaneous determination of the six phenolic compounds in jujube, and can provide a reference to determine phenolic compounds in other products.3. The total phenolic contents of free, esterified, glycosided, and insoluble-bound phenolic acids, and the distribution of phenolic acids and their antioxidant activity are different in different tissues (pulp, seed, and peel) of fresh jujube. The free, esterified, glycosided, and insoluble-bound forms of eight phenolic acids in pulp, seed, and peel of jujube are separated and quantified by high performance liquid chromatography with electrochemical detection (HPLC-ECD). In the whole jujube, p-hydroxybenzoic and cinnamic acids are the most abundant phenolic acids. All quantified phenolic acids are mainly present in jujube peel. Phenolic acids in seed and peel are present in the insoluble-bound form, while, in pulp in the glycosided form. The glycosided and insoluble-bound phenolic acid fractions in jujube pulp represent the highest total phenolic content and the strongest antioxidant activity determined by DPPH and FRAP assays. Our results show that most phenolic compounds with antioxidant activity in different tissues of jujube are present as the glycosided and insoluble-bound forms.4. The composition of phenolic compounds in jujube and their antioxidant activity has greatly changed after jujube is dried. The phenolic content significantly decreased after jujube is dried, the total flavonoids contents did not change significantly, but the procyanidin contents increased significantly. The antioxidant activity of jujube is not correlated with the total flavonoids and procyanidin contents, but with the phenolic acids. There is no significant difference in the antioxidant activity of jujube between the hot-air drying and natural drying, but the phenolic acid content in jujube by hot-air drying is lower than that by natural drying.5. The total phenolic content in jujube treated by high-pressure cooking and steam is higher than that by pressure treatments, especially in pulp of jujube. But the jujube treated by high-pressure treatments is a little bitter. The total phenolic acids contents in the peel and pulp of jujube treated by pressure cooking are both the highest, and those in the peel of jujube sufferring from high-pressure cooking and in the pulp sufferring from high-pressure steam are both the lowest. The total flavanoid content in the jujube treated by high-pressure steam is the highest, and that in jujube peel sufferring from pressure cooking and in jujube pulp sufferring from high-pressure treatments is the highest in the jujube peel and pulp, respectively. However, the procyanidin contents in the jujube peel sufferring from any treatments are not detected, and the content in jujube pulp treated by high-pressure steam is the highest.6. The peel of jujube treated by pressure steam exhibits the highest DPPH·scavenging activity and total antioxidant activity. The DPPH·scavenging activity of jujube pulp sufferring from high-pressure steam is greater, and the total antioxidant activity of pulp sufferring from pressure cooking is greater. The total flavanoids in jujube contributes little to its antioxidant activity, but the total phenolics especially the procyanidin and the phenolic acids play an important role in the antioxidant activity.7. If jujube is treated by high-pressure treatments, steam treatment can better preserve the phenolic compounds in jujube and their antioxidant activity. If the pressure treatments are used, cooking treatment is better.更多还原