【作者】 金鹏；

【导师】 郑永华；

【作者基本信息】 南京农业大学 ， 食品科学， 2009， 博士

【摘要】 桃果实柔软多汁,风味芳香,营养丰富,鲜食易于消化吸收,是深受广大人民喜爱的水果之一。桃果实成熟于盛夏,正值高温多雨季节,采后呼吸旺盛,常温下2-3d即达到后熟软化,容易受到机械伤从而易受病原菌侵染,引起大量腐烂。扩展青霉(Penicillium expansum)、灰霉(Botrytis cinerea)和匍枝根霉(Rhizopus stolonifer)是导致桃果实采后青霉病、灰霉病和软腐病发生的主要病原菌。化学防腐剂可有效控制桃果实采后腐烂病害的发生,但随着人们对食品安全和环保的重视,化学杀菌剂的使用日益受到限制。低温冷藏可有效抑制桃果实采后腐烂,并且可以延缓果实后熟,在一定程度上抑制桃果实品质下降。然而桃果实属于冷敏性果实,对低温环境较敏感,在低温下贮藏较长时间易引起冷害,出现果心褐变和果肉粉质化等冷害症状。果心褐变表现为果心周围以及果肉组织出现棕褐色或黑褐色,粉质化表现为果肉发绵,呈沙粒状,果汁减少,丧失原有风味。因此,桃果实不耐贮藏与运输,采后损失十分严重。目前虽已有研究气调、热处理、低温预贮和紫外线照射等处理减轻桃果实采后病害或冷害的报道,但由于各种处理方法的效果受到果实品种、成熟度、处理时间等因素的影响,其结果不尽一致,另外对桃果实采后病害和冷害调控的机理也不十分清楚,在生产实际中仍缺乏有效的保鲜方法。因此,研究桃果实采后病害和冷害调控技术及其机理,已成为解决桃果实贮运保鲜问题的关键。本论文以“白凤”桃(Prunus persica Batsch cv Baifeng)果实为试材,研究茉莉酸甲酯(methyl jasmonate, MeJA)和1-甲基环丙烯(1-methylcyclopropene,1-MCP)单独处理对桃果实采后主要病害和冷害的影响及其机理,研究MeJA复合低温预贮(low temperature conditioning, LTC)或复合热空气(hot air, HA)处理对减轻桃果实冷害的作用及其机理,以期为桃果实保鲜新技术的开发提供依据。研究结果分述如下：1. MeJA处理对桃果实采后病害的影响及其机理采用果实接种试验,研究了不同浓度(1,10和100μmol/L) MeJA处理对桃果实采后青霉病、灰霉病和软腐病的影响。发现1、10μmol/L MeJA可以显著抑制桃果实采后病害的发生,其中以1μmol/L MeJA处理效果较好,而100μmol/L MeJA处理没有明显效果。此外,研究了不同浓度(1、10和100μmol/L)MeJA对P. expansum, B. cinerea和R. stolonifer离体生长的影响。发现MeJA能显著抑制P. expansum, B. cinerea和R.stolonifer的孢子萌发、芽管生长和菌丝扩展,且MeJA浓度越高,抑制效果越显著。在此基础上研究了1μmol/L MeJA对桃果实抗病相关酶活性和活性氧代谢的影响,以揭示MeJA控制桃腐烂病害的机理。结果显示,MeJA处理可诱导提高桃果实中几丁质酶、β-1,3葡聚糖酶、苯丙氨酸解氨酶(PAL)、过氧化物酶(POD)和多酚氧化酶(PPO)等抗病相关酶类活性,提高总酚含量,说明MeJA减少桃腐烂病害发生与提高抗病相关酶活性和总酚含量有关。此外,MeJA处理提高桃果实中超氧化物歧化酶(SOD)活性,抑制了过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性,并且促进了H2O2的积累,说明MeJA通过调节桃果实中活性氧代谢,提高对病原菌的抵抗能力。这些结果表明,MeJA处理抑制桃果实采后病害的发生可能与其直接抑制病原菌的生长和间接诱导提高果实的抗病性有关。2. MeJA复合LTC处理减轻桃果实冷害的作用及其机理首先研究了不同浓度(1,10、100和500μmol/L) MeJA处理对桃果实冷害和品质的影响,发现1和10μmol/L MeJA可以显著抑制桃果肉褐变和粉质化的发生,保持较高的TSS、TA含量和出汁率,其中以1μmol/LMeJA处理效果较好,而100和500μmol/L MeJA处理对桃果实品质没有明显影响,甚至促进了果肉褐变和粉质化的发生。因此,在此基础上选用1μmol/LMeJA与LTC复合,探索复合处理对减轻桃果实冷害的作用,通过研究复合处理对桃果实活性氧代谢和果胶代谢的影响,以揭示MeJA复合LTC处理减轻桃果实冷害的机理。结果显示MeJA复合LTC处理显著抑制了桃果肉褐变和粉质化的冷害症状,其中以10℃下预贮2d的复合处理(LTC2+MJ)效果最好。MeJA复合LTC处理抑制了桃果实中PPO和POD活性,保持果实中较高的PAL、SOD、CAT和APX活性,使得O2ˉ和H2O2得以及时清除,减轻膜脂过氧化程度,从而降低了果心褐变的发生。MeJA复合LTC处理能维持冷藏桃果实中果胶甲酯酶(PME)和多聚半乳糖醛酸酶(PG)活性变化的平衡,保持较高的PG/PME比率,使果胶代谢趋于正常,维持果肉较高的出汁率,减少粉质化症状的发生。这些结果说明,MeJA复合LTC处理可维持桃果实活性氧和果胶物质代谢的平衡,从而减轻桃果实冷害的发生。3. MeJA复合HA处理减轻桃果实冷害的作用及其机理选用1μmol/L MeJA与38℃热空气(HA)复合,探索两者复合处理对减轻桃果实冷害的作用,并通过研究复合处理对桃果实活性氧代谢和果胶代谢的影响,揭示MeJA复合HA处理减轻桃果实冷害的机理。结果显示HA单独处理可显著抑制桃果肉褐变,却表现出较为严重的果肉粉质化症状。MeJA复合HA处理可减轻HA处理的不良效果,MeJA复合HA处理抑制了桃果实中PPO和POD活性,保持果实中较高的PAL、SOD、CAT和APX活性,使得O2ˉ和H2O2得以及时清除,减轻膜脂过氧化程度,从而降低了果心褐变的发生。MeJA复合HA处理提高了桃果实冷藏期间PG的活性,保持较高的PG/PME比率,能维持果胶物质代谢平衡,减少粉质化症状的发生。这些结果说明,MeJA复合HA处理减轻桃果实冷害的发生,与其保持桃果实中较高的抗氧化酶活性和较高的PG/PME比率有关。4.1-MCP处理对桃果实采后病害的影响及其机理采用果实接种试验,研究了不同浓度(0.1、0.5、5μl/L) 1-MCP处理对桃果实采后由扩展青霉(P. expansum)引起的青霉病、由灰霉葡萄孢(B. cinerea)引起的灰霉病和由匍枝根霉(R. stolonifer)引起的软腐病的影响。发现0.5μl/L1-MCP处理显著抑制桃果实青霉病、灰霉病和软腐病的发生,而0.1、5μl/L1-MCP处理没有明显效果。因此,在此基础上研究了0.5μl/L1-MCP对桃果实抗病相关酶活性和活性氧代谢的影响,以揭示1-MCP减少桃果实腐烂病害的机理。结果显示,1-MCP处理提高了桃果实中PAL活性,且诱导总酚含量的积累,说明1-MCP通过增强酚类等植保素的积累,抑制病原菌的侵染和扩展。1-MCP处理提高了桃果实中POD、CAT和APX等抗氧化酶活性,降低了H2O2的含量,说明1-MCP不能够诱导H2O2信号分子的积累。此外,1-MCP处理对桃果实中几丁质酶和β-1,3葡聚糖酶活性没有明显影响,说明1-MCP对桃果实抗病相关酶活性也没有诱导作用。这些结果说明,1-MCP处理并不是通过提高抗病相关酶活性和增强H2O2信号分子积累的途径,提高桃果实对病原菌的抵抗能力,而是通过加强酚类物质等植保素的积累,提高抗氧化酶活性,延缓桃果实衰老,从而增强果实的抗病性。5.1-MCP处理对桃果实冷害的影响及其机理研究了不同浓度(0.1、0.5、5、10μl/L) 1-MCP处理对桃果实冷害和品质的影响,发现0.5μl/L1-MCP处理可显著抑制桃果肉褐变和粉质化的冷害症状,保持较高的TSS和TA含量,延长了桃果实的贮藏期,而高浓度(5、10μl/L) 1-MCP处理对桃果实冷害的发生没有显著影响。因此,在此基础上研究了作用效果不同的两个1-MCP浓度(0.5和10μl/L)处理对冷藏桃果实活性氧代谢和果胶代谢的的影响,以揭示不同浓度1-MCP处理对桃果实冷害调控的机理。结果显示两个浓度的1-MCP处理都可显著抑制冷藏桃果实的呼吸速率、乙烯释放和果肉软化,保持果实较高的TSS、TA和维生素C含量,说明1-MCP可延缓桃果实的后熟作用,且10μl/L1-MCP处理的效果比0.5μl/L1-MCP显著。0.5μl/L1-MCP处理显著抑制了桃果实中PPO和POD活性,降低了桃果实中相对电导率和MDA含量,延缓果实衰老。此外,0.5μl/L1-MCP处理保持果实中较高的SOD、CAT和APX等抗氧化酶活性,抑制了H2O2的积累,减轻膜脂过氧化程度,从而降低果肉褐变的发生。10μl／L1-MCP处理对PPO、POD以及抗氧化酶活性均无明显影响。0.5μl／L1-MCP处理提高了冷藏桃果实中PG活性,保持较高的PG／PME比率,能维持冷藏桃果实中PME和PG活性变化的平衡,促进了原果胶的降解,保持果实中较高的水溶性果胶含量,减少粉质化症状的发生。而10μl/L1-MCP处理却显著抑制了桃果实中PME和PG活性,使果胶物质不能正常降解,导致果肉粉质化发生。这些结果说明,1-MCP通过抑制桃果实采后呼吸速率和乙烯释放量,来延缓果实后熟进程,保持桃果实贮藏期间较高的品质。低浓度1-MCP处理减轻桃果实冷害发生,与其维持果实活性氧和果胶物质代谢的平衡有关；而高浓度1-MCP处理促进桃果实冷害发生与其抑制果胶物质正常降解的作用有关。更多还原

【Abstract】 Peach fruit is an important fruit in China, and is very popular for its juiceful texture, delicious flavor and rich in nutrient. Peaches are matured in mid-summer, and are highly susceptible to pathogenic infection and physiological deterioration during ambient temperature storage and ripening. Low temperature storage is effectively used to control postharvest disease and inhibited ripening of peach fruit. However, chilling injury, such as internal browning and flesh mealiness, is usually found in peach fruit stored at low temperature for long time. Thus, it is crucial to study the regulation and mechanism of disease resistant and chilling injury of peach fruit after harvest for transportation and storage.In this paper, the effect of MeJA and 1-MCP on the major fungal disease, such as blue mold, gray mold and soft rot caused by Penicillium expansum, Botrytis cinerea and Rhizopus stolonifer respectively, and chilling injury in peach fruit and the possible mechanisms involved were investigated. In addition, the effects of MeJA combined with low temperature conditioning (LTC) or with hot air (HA) treatment on alleviating chilling injury in peach fruit and the possible mechanisms involved were investigated. The results were as follows:1 Effects of MeJA treatment on postharvest disease in peach fruit and possible mechanisms involvedPeaches were treated with different concentrations of MeJA (1,10 or 100μmol/L) to investigate the effect of MeJA treatment on blue mold, gray mold and soft rot. We found that treatment with 1μmol/L MeJA was most effective in reducing fruit decay caused by P. expansum, B. cinerea and R. stolonifer infection, however,100μmol/L MeJA treatment had little effect. In addition, the in vitro experiment showed that MeJA inhibited mycelial growth, spore germination and germ tube length of P. expansum, B. cinerea and R. stolonifer. Thus,1μmol/L MeJA was chosen to investigate the effects of MeJA on reducing blue mold and the possible mechanisms involved in postharvest peach fruit. The MeJA-treatment enhanced the activities of chitinase,β-1,3-glucanase, phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO), and maintained the higher level of total phenolic content in peach fruit, which is considered to play important roles in disease resistance. Moreover, MeJA-treatment induced accumulation of H2O2 content due to increased superoxide dismutase (SOD) activity, decreased catalase (CAT) and ascorbate peroxidase (APX) activities in peach fruit. The level of H2O2 induced by the treatment might also be related to the higher resistance of the MeJA-treated fruit to infection by the pathogen. These results indicated that MeJA inhibited postharvest disease probably due to suppressed pathogen growth directly and enhanced the disease resistance of fruit tissues by increasing anti-pathogenic proteins and antimicrobial phenolic compounds.2 MeJA combined with LTC treatment alleviates chilling injury in peach fruit and possible mechanisms involvedPeach fruits were treated with different concentrations of MeJA (1,10 or 100μmol/L) to investigate the effect of MeJA treatment on chilling injury and fruit quality. We found that treatment with 1μmol/L MeJA was most effective in reducing internal browning (IB) and flesh mealiness (FM) while maintaining higher level of TSS, TA and extractable juice in peach fruit, however,100 and 500μmol/L MeJA treatments had little effect. Thus,1μmol/L MeJA was chosen to combine with LTC treatment to investigate the effects of combination treatment on chilling tolerance and the influence on H2O2 and pectin metabolism. MeJA combined with LTC treatment alleviated chilling injury, maintained higher fruit quality in peach fruit during cold storage. The activities of PPO and POD were significantly inhibited, while the activities of antioxidant enzymes such as SOD, CAT, and APX were induced by MeJA combined with LTC treatment. In addition, the activities of PAL, polygalacturonase (PG) and the level of total phenolic content were enhanced by MeJA combined with LTC treatment. These results suggested that the effect of MeJA combined with LTC treatment on alleviating chilling injury of peaches during cold storage may be attributed to it ability to enhance defense system against cold stress, induce antioxidant system and affect the activities of pectin metabolism enzymes.3 MeJA combined with HA treatment alleviate chilling injury in peach fruit and possible mechanisms involved Peach fruits were treated with 1μmol/L MeJA combined with 38℃hot air treatment to investigate the effects of combination treatment on chilling tolerance and the influence on H2O2 and pectin metabolism. The results showed that the fruit treated with combined treatment showed the high quality and low percent of chilling injury symptom. HA treatment alone significantly inhibited IB, however, it showed more severe FM than other treatments, this side effect was counteracted by MeJA. In addition, MeJA combined with HA treatments exhibited the higher activities in PAL, SOD, CAT and PG, and showed the lower activities in PPO and POD. These results suggested that effect of MeJA combined with HA treatment on alleviating chilling injury of peaches during cold storage may be attributed to it ability to induce antioxidant system and affect the activities of pectin metabolism enzymes. The combination of MeJA and HA treatment could be a useful technique to alleviate the chilling injury and maintain fruit quality during cold storage.4 Effects of 1-MCP treatment on postharvest disease in peach fruit and possible mechanisms involvedPeaches were treated with different concentrations of 1-MCP (0.1,0.5 or 5μl/L) to investigate the effect of 1-MCP treatment on blue mold, gray mold and soft rot. We found that treatment with 0.5μl/L 1-MCP was most effective in reducing fruit decay caused by P. expansum, B. cinerea and R. stolonifer infection, however,0.1 or 5μl/L 1-MCP treatments had little effect. Thus,0.5μl/L 1-MCP was chosen to investigate the effects of 1-MCP on reducing blue mold and the possible mechanisms involved in postharvest peach fruit. The results shown that 1-MCP enhanced the activities of PAL and maintained the higher level of total phenolic content, which indicated that 1-MCP reduced postharvest disease probably due to increase antimicrobial phenolic compounds. In addition,1-MCP decreased accumulation of H2O2 content due to increased CAT and APX activities in peach fruit. However, little effect was found on chitinase andβ-1,3-glucanase activities in 1-MCP treated fruits. These results indicated that 1-MCP was not enhanced disease resistance of fruit tissues by increasing anti-pathogenic proteins or regulating H2O2 signal pathway. The effect of inhibiting fruit decay was probably due to maintaining higher level of antimicrobial phenolic compounds and delaying fruit ripening and senescence. 5 Effects of 1-MCP treatment on chilling injury in peach fruit and possible mechanisms involvedPeaches were treated with different concentrations of 1-MCP (0.1,0.5,5 or 10μl/L) to investigate the effect of 1-MCP treatment on chilling injury and fruit quality. We found that 0.5μl L-l 1-MCP was the optimal concentration to alleviate chilling injury and maintain higher quality of peach. However, higher concentration of 1-MCP treatment had little effect. The activities of PPO and POD were significantly inhibited, while the activities of antioxidant enzymes such as SOD, CAT, and APX were induced by 0.5μl L-1 1-MCP treatment.0.5μl L-1 1-MCP enhanced the activity of PG, which made the higher ratio of PG/PME and kept the balance of pectin metabolism. These results suggested that 0.5μl L-1 1-MCP treatment had considerable effect to alleviate the chilling injury rather than high concentration of 1-MCP applied in peach fruit during cold storage. The effect of low concentration of 1-MCP treatment on alleviating chilling injury of peaches during cold storage may be attributed to it ability to induce antioxidant system and affect the activities of pectin metabolism enzymes.更多还原