【作者】 曾庆帅；

【导师】 张名位；

【作者基本信息】 华中农业大学 ， 食品科学， 2011， 硕士

【摘要】 近年来,自由基学说与疾病预防和延缓衰老的研究上受到广泛的关注。现代流行病学调查研究表明富含水果和蔬菜的膳食可减少心血管病和癌症等慢性疾病的发生,其作用主要源于果蔬中含量丰富的酚类物质等天然抗氧化活性物质。探寻和研究果蔬及其加工制品的酚类物质和抗氧化能力已成为食品、医药等多个学科领域共同关注的课题。荔枝是我国华南地区特色水果,其种植资源丰富,但目前对荔枝酚类物质的研究主要集中在果皮果核等副产物上,而对不同荔枝品种果肉抗氧化活性和酚类化合物含量的研究则鲜有报道；加工和贮藏过程中荔枝果汁抗氧化能力及酚类物质的变化规律尚不明晰。为此,本文通过研究不同品种荔枝果肉抗氧化能力及酚类物质含量,筛选出抗氧化活性强、酚类物质含量高的品种：分析荔枝果汁在不同加工单元操作和贮藏过程中理化性质,抗氧化能力和酚类物质的变化规律,为加工高品质荔枝果汁提供科学依据。主要研究结果如下：1不同荔枝品种酚类物质特性和抗氧化能力比较：比较和分析了13个不同荔枝品种果肉提取物的总酚含量、总黄酮含量、酚类组成、DPPH自由基清除能力和FRAP抗氧化能力及其之间相关性。结果表明不同荔枝品种果肉提取物的总酚含量、总黄酮含量、酚类组成、DPPH自由基清除能力和FRAP抗氧化能力存在显著的差异性(p<0.05),其中不同荔枝品种果肉游离酚、结合酚和总酚含量变幅分别为66.17-226.03、11.18-40.54和101.51-259.18 mg GAE/100 g,游离酚占总酚比例变幅为63.1%-91.4%,总酚含量变异系数为29.1%；不同荔枝品种果肉游离黄酮、结合黄酮和总黄酮含量变幅分别为16.68-110.33、10.48-22.75和39.43129.86 mg CE/100 g,游离黄酮占总黄酮比例变幅为42.3%-87.4%,总黄酮含量变异系数为34.5%；HPLC分析表明荔枝果肉中单体酚类物质包括没食子酸、绿原酸、儿茶素、咖啡酸、表儿茶素和芦丁,其中没食子酸和绿原酸以游离形式存在,儿茶素存在于结合酚中,咖啡酸、表儿茶素和芦丁则以游离态和结合态两种形式存在,表儿茶素和芦丁是主要的单体酚类物质。不同荔枝品种果肉游离部和结合部DPPH自由基清除能力变幅分别为23.02-58.03和29.13-44.75μg GAE/mL;不同荔枝品种果肉游离部、结合部和总的FRAP抗氧化能力变幅分别为61.99439.54、18.97-68.7和121.53-495.96 mg TE/100 g；不同品种荔枝果肉DPPH自由基清除能力和FRAP抗氧化能力与果肉中总酚含量和黄酮含量有显著相关性.表明酚类物质含量是荔枝果肉抗氧化能力重要的物质基础之一。2不同加工单元操作对荔枝果汁抗氧化能力及酚类物质影响的研究：研究在烫漂钝酶、榨汁、离心、精滤和UHT杀菌等加工单元操作中荔枝果汁的理化性质、抗氧化能力及酚类物质含量的变化。结果表明,酚类物质和抗氧化能力的损失主要集中在烫漂、榨汁粗滤和UHT处理单元。结果显示加工过程总酚含量、黄酮含量、表儿茶素、芦丁和绿原酸含量分别减少57.7%、81.4%、57.9%、58.7%和46.0%,FRAP抗氧化能力和ABTS抗氧化能力分别下降69.0%和64.2%,清除DPPH自由基能力的IC50从8.15上升为12.85μg GAE/g。研究普通热处理、UHT处理以及HPCD处理等杀菌方式对荔枝果汁理化性质、抗氧化能力及酚类物质含量的影响,结果表明,HPCD处理能较好的保持果汁的理化性质,而普通热处理、UHT处理会使荔枝果汁的褐变度显著增大：对比不同杀菌处理发现热杀菌处理造成果汁抗氧化能力及酚类物质有较大损失,而HPCD处理则相对较好的保持果汁的酚类物质含量及抗氧化能力,有助于保持果汁活性成分,提高其营养价值。3不同贮藏条件对荔枝果汁抗氧化能力及酚类物质影响的分析：以经UHT杀菌的荔枝果汁为原料,分析5周内在4℃、25℃和37℃3个不同贮藏温度下荔枝果汁中理化性质、抗氧化能力及酚类物质含量的变化。结果显示,5周内,在4℃、25℃和37℃等不同贮藏温度下荔枝果汁中总酚含量,黄酮含量,单体酚类物质与抗氧化能力均呈现显著下降趋势(p<0.05),总酚含量分别下降37.0%、25.8%和23.5%,黄酮含量分别改变2.9%、15.6%和9.7%,表儿茶素分别下降45.7%、54.0%和65.1%。,芦丁分别下降16.9%、45.5%和46.1%,绿原酸分别降低9.7%,16.9%,20.5%；FRAP抗氧化能力分别下降54.0%、64.7%和64.5%,ABTS抗氧化能力分别降低44.7%、29.1%和30.0%；双因素方差分析表明总酚含量受贮藏时间影响显著(p<0.05),总黄酮含量受温度影响显著(p<0.05),贮藏温度和时间均对对单体酚类物质和抗氧化能力影响显著(p<0.05)。不同贮藏条件对荔枝果汁中酚类物质含量和抗氧化能力存在显著影响,低温和短时贮藏有利于保持荔枝果汁中理化品质和酚类物质含量。更多还原

【Abstract】 Recently, research about free radical theories and the prevention of disease and anti-aging are getting more and more attentions. Epidemiological studies have shown that diets rich in fruits and vegetables could reduce chronic diseases, such as cardiovascular disease and cancer, which is mostly due to the natural active substances with strong antioxidative activities, such as phenolics. Explore and research of phenolics and antioxidant activity in fruits and vegetables and their processed products has become a common concern in food and medicine. Litchi is a typical fruit and has diverse cultivars in southern China. Previous studies about phenolics and their antioxidant activity of litchi fruit mainly focused on litchi by-products which are usually discarded as a waste, including litchi pericarp, litchi seeds. However, antioxidant activity and phenolics profile of large groups of cultivars of litchi pulp is rarely reported; changes of phenolics and antioxidant activity of litchi juice during processing are not yet clear. In the current study. antioxidant properties and phenolics of different litchi cultivars were compared in order to select the outstanding cultivars that owned the relatively stronger antioxidant activity and higher phenolics contents; the changes of physicochemical properties, phenolics and antioxidant activity of litchi juice were analyzed during different processing units and storage conditions. The major results are as follows:1 Comparison of antioxidant properties and phenolic profiles of different litchi cultivars. Samples of 13 different litchi cultivars were evaluated for total phenolics, total flavonoids and phenolic compositions and tested for their antioxidant potential by DPPH and FRAP assays. The results show that DPPH and FRAP antioxidant activity, total phenolics contents, total flavonoids contents and phenolic compositions had significant different (p<0.05). The free, bound and total phenolic contents of 13 litchi cultivars ranged from 66.17 to 226.03, from 11.18 to 40.54, and from 101.51 to 259.18 mg of GAE per 100g, respectively. The percentage contribution of free fractions to the total was from 63.1% to 91.4%. The coefficient of variation of total phenolic content in 13 litchi cultivars was 29.1%. The free, bound and total flavonoid contents varied from 16.68 to 110.33,10.48 to 22.75, and 39.43 to 129.86 mg of CE per 100g, respectively. The percentage contribution of free fractions to the total was from 42.3% to 87.4%. The coefficient of variation of total flavonoid content in 13 litchi cultivars was 34.5%. The phenolic compositions through HPLC analysis included gallic acid, chlorogenic acid, (+)-catechin, caffeic acid, (-)-epicatechin and rutin. Gallic acid and chlorogenic acid were only in free fractions; (+)-Catechin was only found in the bound fractions; Caffeic acid, (-)-epicatechin and rutin were found in both free and bound fractions, (-)-epicatechin and rutin were the main phenolics in litchi pulp. The free and bound IC50 values of 13 litchi cultivars determined by DPPH assay varied from 23.02 to 58.03 and from 29.13 to 44.75μg GAE/ml. And the free, bound and total FRAP values ranged from 61.99 to 439.54. from 18.97 to 68.7, and from 121.53 to 495.96 mg TE/100g. respectively. Total antioxidant activities determined by DPPH and FRAP assays were significantly correlated to the contents of total phenolics,total flavonoids,respectively. All the findings suggested that phenolics was one of active substance contributing for the antioxidant activity of litchi fruit.2 Analysis of physicochemical properties, phenolics and antioxidant activity of litchi juice during different processing units. Changes of physicochemical properties, phenolics and antioxidant activity of litchi juice were studied after blanching(enzyme inactivation),squeeze(rough filtration), centrifugation, diatomite filtration and UHT sterilization. The loss of phenolics and antioxidant activity mainly focused on blanching, sterilization and squeeze. The results showed that the loss of total phenolics. total flavonoids. (-)-epicatechin, rutin and chlorogenic acid contents during processing were 57.7%,81.4%,57.9%,58.7% and 46.0%, respectively. The FRAP and ABTS antioxidant activities lost 69.0 % and 64.2% in processing, and the IC50 value of DPPH antioxidant activities became from 8.15 to 12.85μg GAE/g during processing. Comparison of physicochemical properties, phenolics and antioxidant activity of litchi juice with common thermal sterilization, UHT sterilization and HPCD processing. The study showed that HPCD could keep unremarkable differences on the physicochemical properties, but both common thermal sterilization and UHT sterilization caused a increase of browning index. Moreover, HPCD had fewer effects on phenolics and antioxidant activity of litchi juice, maintaining and improving the active substances and nutritional values of litchi juice.3 Analysis of physicochemical properties, phenolics and antioxidant activity of litchi juice during three different temperature storage conditions. The changes of total phenolics content, total flavonoids content, FRAP and ABTS antioxidant activity present in litchi juice treated with UHT were investigated during 5 weeks’ storage times at 4℃,25℃, and 37℃. The results showed that during 5 weeks’ storage times at 4℃,25℃. and 37℃,the decease of total phenolics contents were 37.0%、25.8% and 23.5%; the changes of total flavonoids were 2.9%、15.6% and 9.7%; the decrease of (-)-epicatechin contents were 45.7%、54.0% and 65.1%; the decrease of rutin contents were 16.9%、45.5% and 46.1%; the decrease of chlorogenic acid contents were 9.1%、16.9% and 20.5%; the losses of FRAP were 54.0%、64.7% and 64.5%; the losses of ABTS antioxidant activities were 44.7%、29.1% and 30.0%. The results of Two-factor ANOVA showed that total phenolics content and antioxidant capacity were significant decreased (p <0.05) with the extension of storage time; in contrast, total phenolics content was influenced mainly by time (p<0.05), total flavonoid content was influenced mainly by temperature (p<0.05); phenolics compositions and antioxidant capacity was influenced by both time (p<0.05) and temperature (p<0.05).The study indicated that different storage conditions had significant impact on phenolic compounds; low temperature and short storage time could help keep physicochemical properties and phenolics contents.更多还原