【作者】 丁胜华；

【导师】 汪政富；

【作者基本信息】 中国农业大学 ， 农产品加工及贮藏工程， 2014， 博士

【摘要】 本文首先系统评价六个品种枣果的品质特性和果胶多糖特性,然后以品质特性佳、既适鲜食又适干制的‘金丝小枣’为材料,研究其在生长成熟过程中品质特性和果胶多糖特性变化,同时结合关键内源酶的变化,阐释其品质特性形成规律和果胶多糖降解机制；针对枣果被大量干制的现状,本文还比较研究不同干制方式对枣果品质特性及对果胶多糖降解的影响。经分析归纳,主要结论如下：(1)枣果营养成分丰富,其主要可溶性糖为蔗糖、葡萄糖、果糖,蔗糖含量最高,是蔗糖积累性果实;枣果有机酸组成为苹果酸、柠檬酸和琥珀酸,除‘灰枣’外,其余枣果为苹果酸积累型果实：枣果中富含游离氨基酸,脯氨酸和天冬氨酸是枣果中最主要的游离氨基酸,其中脯氨酸含量占游离氨基酸总量的68%以上；枣果主要酚类物质是儿茶素、香豆酸、表儿茶素和芦丁；‘金丝小枣’与‘木枣’的抗氧化特性显著高于其余品种枣果(p<0.05);枣果富含3’,5’-环腺苷酸(Cyclic adenosine monophosphate, cAMP)和3’,5’-环鸟苷酸(Cyclic guanosine monophosphate, cGMP),六种枣果中3’,5’-环腺苷酸含量最高的为‘哈密大枣’,3’,5’-环鸟苷酸含量最高的为‘金丝小枣’；鲜枣中挥发性芳香物质以小分子直链醛类和酸类为主,呈现枣香的物质为苯甲酸乙酯。(2)枣果细胞壁物质(Cell wall material, CWM)、水溶性果胶(Water solute pectin, WSP)、螯合性果胶(Chelate-solute pectin, CSP)和碱溶性果胶(Sodium carbonate solute pectin, SSP)含量及其中性单糖受品种来源影响；枣果中水溶性果胶含量高于螯合性果胶和碱溶性果胶含量；WSP和SSP主要性单糖为阿拉伯糖、鼠李糖、半乳糖和葡萄糖,而CSP的主要中性单糖为阿拉伯糖、葡萄糖和岩藻糖;果胶的分子量分布受枣果品种来源和果胶类型两方面影响,其中‘金丝小枣,与‘木枣’WSP的分子量分布明显宽于其余四种枣果,‘金丝小枣’和‘灰枣’中CSP分子量分布比其余四个品种枣果的分子量分布更加集中,且主要集中在高分子量端；‘金丝小枣’、‘灰枣’和‘哈密大枣’SSP组分比‘梨枣’、‘木枣’和‘相枣’的SSP组分分子量分布更宽；枣果过氧化物酶(Peroxidase, POD)、果胶甲酯酶(Pectin methylesterase, PME)口多聚半乳糖醛酸酶(Polygalacturonase, PG)受品种来源影响,且PG活性越高,枣果WSP低分子量端的分布越宽。(3)‘金丝小枣’成熟过程中,果型膨大,可滴定酸和总可溶性固形物升高,pH、水分、叶绿素含量降低,果实变黄变红；枣果中叶绿素a含量始终高于叶绿素b,是幼果呈现绿色的主要物质,叶绿素的降解主要发生在生长发育前期；葡萄糖、果糖被逐步积累,而山梨醇含量降低,蔗糖则在生长发育初期未被检出,其积累主要发生在枣果成熟后期,且其含量最高,‘金丝小枣’为蔗糖积累性果实,蔗糖磷酸合成酶(Sucrose phosphate synthase, SPS)和蔗糖合成酶(Sucrose phophate synthase, SS)是蔗糖积累的关键酶；脯氨酸和天冬氨酸被大量合成,是成熟枣果最主要的游离氨基酸；总酚(Total phenolics, TPs)、总黄酮(Total flavonoids, TFs)、维生素C(Ascorbic acid,Vc)、α-生育酚、β-胡萝卜素、儿茶素、咖啡酸、丁香酸和芦丁含量降低,枣果抗氧化特性呈现下降趋势；儿茶素和表儿茶素是枣果在成熟过程中代谢最为活跃的两种酚类物质；cAMP和cGMP含量增加,而三萜酸含量在枣果的S3-S4期最高;枣果的挥发性成分主要在成熟后期合成。(4)‘金丝小枣’生长成熟过程中,硬度、CWM和SSP的含量下降,WSP含量上升,CSP含量则先上升后下降；果胶多糖发生了一系列变化导致枣果质构的软变;其中,WSP其鼠李半乳糖醛酸聚糖-I(Rhamngalacturonan-I,RG-I)主链骨架由于鼠李糖的损失而逐渐被降解；CSP和SSP其RG-I主链骨架几乎不发生降解；WSP、CSP和CSP的RG-1支链降解发生在成熟后期；果胶支链的降解主要是由于其支链中阿拉伯糖和半乳糖含量的降低；WSP和SSP在其RG-1支链被降解时,阿拉伯糖比半乳糖被释放更多；WSP中高分子量端组分逐渐降解为低分子量组分；CSP和SSP中高分子量端组分经历先快速合成后降解两个过程；PME活性逐渐降低,PG活性上升,尤其在成熟后期尤为显著,参与多聚半乳糖醛酸链的降解。(5)除冷冻干燥(Freeze drying, FD)外,枣果干制处理均导致山梨醇和蔗糖含量的显著下降p<0.05),其中微波干制(Microwave drying, MD)口太阳晾晒(Sun drying, SD)处理其蔗糖保留率比热风干制(Air drying, AD)处理高,但其果糖与葡萄糖含量低于AD处理；干制处理引起枣果褐变,产生HMF,其中MD处理褐变最严重,产生的HMF显著高于其余干制处理组(p<0.05),干燥温度越高,枣果褐变越严重；FD处理能很好的保留枣果中的cAMP和cGMP,而其余干制处理均导致cAMP和cGMP含量的显著下降p<0.05)；除FD处理外,AD50处理其cAMP和cGMP保留率同时达到最高,高温或者低温均导致cAMP和cGMP含量更为严重的下降；干制引起枣果的抗氧化性成分的变化,并导致枣果抗氧化特性的下降；枣果抗氧化能力的下降与Vc含量显著相关p<0.05)FRAP和清除ABTS自由能力的下降与TPs含量显著相关(p<0.05);FD与MD处理导致表儿茶素和儿茶素含量显著增加(p<0.05)。(6)干制处理导致枣果CWM、WSP和SSP含量显著下降p<0.05),而其CSP含量显著增加p<0.05)；高温或低温处理均导致CWM、WSP和SSP含量更严重的降低；干制导致枣果果胶分子量显现不同趋势的变化；WSP组分：高温或低温处理均导致高分子量端组分的减少,AD50处理其分子量分布最为集中：SSP组分：干制导致高分子量端果胶组分的增加,低分子量端则发生降解,且高温或者低温都导致低分子量端果胶组分更为严重的降解。更多还原

【Abstract】 The physico-chemical properties change of jujube fruits from various cultivars, different growth stages or dehydrated by diverse drying methods were evaluated. At the same time, the effects of ripening process and dehydration methods on the pectic polysaccharide properties and its related enzyme activities of jujube fruits were assessed. The main results were shown as follows:(1) Jujube fruits were rich in nutrients and sucrose was the dominant sugar in the six different cultivars jujube fruits, followed by fructose and glucose, while malic acid and succinic aid were the principal organic acids in jujube fruits. Jujube fruits contained plenty of free amino acids and the primary free amino acids of the six various cultivars jujube fruits were proline and aspartic acid, in the mean while, proline accounted for more the68%of total free amino acids. The main phenolic compounds in the six cultivars jujube fruits were (+)-catechin, vanillic acid, coumaric acid,(-)-epicatechin, and rutin, while small amounts of caffeic acid and syringic aicd were also detected. Among the six various cultivars jujube fruits, the antioxidant capacities of ’jinsixiaozao’ and ’muzao’ were higher than those of the rest. All of six different jujube fruits had a high level of cAMP and cGMP, and ’hamidazao’ contained the highest level of cAMP among these jujube fruits, while ’jinsixiaozao’occupied the maximum level of cGMP among the above jujube fruits. The main volatiles of fresh maturated jujube fruits were consisted of micro-molecule aldehydes and organic acid with straight chains.(2) The contents of CWM, WSP, CSP, and SSP and the neutral monosaccharides of pectic polysaccharides (WSP, CSP, and SSP) were affected by the source of jujube fruits. The main neutral monosaccharides of WSP and SSP were the same, including arabinose, rhamnose, galactose, and glucose, which differed from those of CSP, which was consisted of arabinose, glucose, and fucose. The molecular weight distribution of pectins was not only influenced by the source of jujube fruit but also by the type of pectins. The activities of PG, PME or POD were dependant on the cultivars of jujube fruits and the higher PG activities the cultivars jujube fruits occupied, the wider molecular weight distribution of WSP in the low molecular weight segment showed.(3) During the ripening process of jujube fruits cv ’jinsixiaozao’, a series of physico-chemical changes had happened, including its appearance, pH value, moisture, colorness, chlorophyll, nutrients, bioactive compounds, antioxidant capacities and its related compounds, volatiles, enzyme activities. Sucrose, TSS, totol free amino acids, proline, aspartic acid, cAMP and cGMP were accumulated during the growth stages of jujube fruits. SPS and SS were the critical enzymes when accumulating sucrose during the ripening of jujube fruits. However, the green of jujube fruits disappeared due to the degradation of chlorophylls, at the same time, the antioxidant capacities, total phenolics, total flavonoids, L-ascorbic acid, a-tocopherol,β-carotene contents of jujube fruits decreased during the various growth stages. The volatiles of jujube fruits were synthesized at the later periods of ripening.(4) Softening phenomenon in jujube fruits cv ’jinsixiaozao’was observed during the process of ripening due to the degradation of cell wall pectic polysaccharide and its related degradation enzymes. The contents of CWM, WSP, SSP in jujube fruits showed a decrease tendency during the softening process, while the CSP content exhibited an increase trend in the earlier softening periods of jujube and showed a decrease tendency in the following softening periods. The backbone of RG-I in WSP was depolymerized gradually during the softening process while the backbones of RG-1in CSP or SSP were not depolymerized. In the mean while, all of the branches of RG-I in WSP, CSP or SSP were depolymerized at the later softening stages duo to the loss of arabinose and galactose. What’s more, higher ratio of arabinose was released during the growth stages of jujube fruits. The activity of PME jujube fruits decreased as the fruits became softened, while the PG activity increased, especially in the later softening periods, which played an important role in the depolymerization of pectin polysaccharides.(5) With the exception of FD, dehydration of jujube fruits led to a significant decrease of sorbitol and sucrose content (p<0.05). The retention rate of sucrose treated by MD or SD was higher than treated by AD, while the contents of glucose or fructose treated by MD or SD was lower than treated by AD. Drying of jujube fruits also generated browning of jujube pulp, introducing a different level of HMF content and MD caused the most significant increase of HMF content among the various drying treatments of jujube fruits. The higher of drying temperature was applied, the more serious browning index of jujube fruits generated. A fine retention rate of cAMP and cGMP was achieved by FD of jujube fruits, while a significant decrease of cAMP and cGMP occurred when employed AD, MD or SD. A higher retention rate of cAMP and cGMP was obtained at the same time by AD50treatment when compared to AD60, AD70, SD, and MD treatments. Too high or too low drying temperatures could result in a bad retention of cAMP and cGMP. Dehydration of jujube fruits by different drying methods posed different effects on the various antioxidant compounds but all dehydration of jujube fruits result in a significant decrease of antioxidant capacities in jujube fruits (p<0.05). The antioxidant capacities of jujube fruits, including the ability of scavenging DPPH free radical, ABTS free radical and FRAP showed a significant correlation with L-ascorbic acid (p<0.05) and the capacity of scavenging ABTS free radical or FRAP also exhibited a significant correlation with total phenolics (p<0.05). FD or MD treatment of jujube fruits could lead to a significant increase of (+)-catechin or (-)-epicatechin.(6) Dehydration of jujube fruits by various drying methods could led to a significant of CWM, WSP, SSP contents (p<0.05), while introduced a significant increase of CSP content. Too high or too low drying temperature could cause a more decrease of CWM, WSP, and SSP contents. Dehydration of jujube fruits also influenced the structure of pectic polysaccharides. Too high drying temperature or too low temperature could led to a more serious depolymerization of high molecular weight segment in WSP and AD50treatment of jujube fruit introduced a more centralized molecular weight distribution of WSP. However, Dehydration of jujube fruits could led to a increase of high molecular weight segment in SSP while introduced a decrease of low molecular weight segment in SSP. In the mean while, too high or low drying temperature could introduce a more serious depolymerizaion of low molecular weight segment in SSP.更多还原