【作者】 闫师杰；

【导师】 胡小松； 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， 2005， 博士

【摘要】 鸭梨（Pyrus bretschneideri Rehd）,作为原产于我国、白梨品系优良主栽品种之一,采后贮藏中很重要的一种生理病害是果心褐变。国内外对鸭梨这种病害发生的原冈有多种说法,大多数注重了酚类物质在PPO作用下的生化反应和膜脂过氧化作用,同时也注意到成熟度、温度、高CO₂、乙烯、低Ca等指标的影响,但对于这些指标间的联系,以及它们在鸭梨褐变发生中的相互作用,还没有较为系统全面的阐述。 本研究确定了鸭梨采后褐变的主要影响因素为采收成熟度和降温方法,在此基础上,选用两种不同采收成熟度（9月上旬和9月下旬采摘）的鸭梨,结合不同的降温方法,即急速降温（从常温直接降到0℃）和缓慢降温（从12℃入库,每5d降低2℃,用30d时间降到0℃）,着重研究了不同降温方法对不同采收成熟度鸭梨采后的抗逆性、酚类物质、膜脂过氧化、膜脂脂肪酸、CO₂溶解量及种子生理的影响,以及与鸭梨果实衰老及褐变的关系。得到如下结论: 1.延迟采收提高了果肉和果心的可溶性固形物、还原糖、Vc、GSH、可溶性蛋白、亚麻酸、亚油酸含量和U/S值,降低了果肉和果心的相变温度,提高了鸭梨果实的抗冷性。但采后果实呼吸、乙烯代谢旺盛,使得果实硬度、可滴定酸、可溶性固形物、还原糖、Vc、GSH、可溶性蛋白含量下降较快,SOD活性下降和LOX活性升高较快,H₂O₂、O₂^-·自由基积累,果实膜脂过氧化严重,丙二醛含量升高,细胞膜透性增强,引起PPO和PPO同工酶活性增强,酚类物质降低,最终导致晚采果更容易褐变,而其中果心较果肉变化更为剧烈,所以果心较果肉褐变严重。 2.急降温处理造成了对早采果实特别是果心的低温伤害。与急降温相比,缓慢降温明显提高了早采果果肉和果心的可溶性蛋白、亚油酸、亚麻酸含量和U/S值,降低了鸭梨果心的相变温度,提高了鸭梨果实的抗性。缓慢降温降低了呼吸、乙烯代谢,提高了SOD活性,延缓了果实硬度、可滴定酸、可溶性固形物、还原糖、可溶性蛋白,以及贮藏后期Vc和GSH含量下降,延缓了果实LOX、PPO活性的升高,脯氨酸、H₂O₂、O₂^-·自由基的积累和膜脂过氧化,从而很好抑制了早采果实的褐变。其中缓慢降温对早采果果心的影响更明显。 3.果皮部位占到整个鸭梨果实呼吸总量的90%以上,CO₂在果实由内到外的组织中的溶解量是递减的。CO₂在组织中的溶解量与温度、外界CO₂浓度及组织生理状态有关,温度越低、CO₂浓度越高、组织越衰老,组织内溶解的CO₂越多,而组织内大量CO₂降低了组织内水溶性Ca含量。 4.鸭梨种子属于采后呼吸高峰型,与果实同时出现呼吸和乙烯高峰,乙烯在子房室内逐渐积累。贮藏中鸭梨种子激素代谢旺盛,后期部分种子萌发,种子呼吸、乙烯、子房室乙烯积累量、及电导率都有所升高,升高程度与果实褐变的规律相似,表明种子生理代谢与果心成熟衰老及褐变存在一定联系。 综上所述,不同降温方法和不同采收成熟度造成了鸭梨果实果肉和果心相变温度、内溶物、抗逆性、呼吸乙烯代谢、膜脂过氧化、种子生理、组织内部CO₂溶解量及水溶性Ca含量的差异,最终导致对膜的损伤不同,对PPO和酚类物质的区域性分隔破坏程度的不同,从而影响了果实褐变的发生。鸭梨褐变与采收成熟度有很大关系,晚采果容易褐变,提前采收并结合缓降温对控制鸭梨果实的褐变有良好的效果。更多还原

【Abstract】 Yali pear (Pyrus bretschneideri Rehd) originated in our country is one of the major varieties of white pear lines. Browning heart has been one of the most severe postharvest physiological injury in storage. Although there are many reports about the reason why this kind of physiological injury happened, and yet most opinions only stressed the biochemical reactions of phenol catalyzed by PPO, the lipid peroxidation of cell membrane and the physiological affecting factors such as maturity, temperature, high CO2, ethylene, low Ca, and etc. Presently, the relationship between these indexes and their interactions during browning of Yali pear have not been comprehensively elucidated yet.The harvest maturity and cooling methods were the main influence factors of browning of Yali pear fruit. In this paper, both early harvested Yali pear (picked in the first ten days of September) and the late harvested Yali pear ( picked in the last ten days of September) were treated with slow cooling treatment (cooling from room temperature directly to 0 ℃) or rapid cooling treatment ( storage at 12 ℃ and cooling them to 0 ℃ over 30 d by reducing temperature by 2 ℃ every 5 d). The effects of the two cooling treatment on the pear’s ability against stress, polyphenol content, membrane lipid’s peroxidation, membrane fatty acids’ composition, dissolved CO2 amount and pear seed physiology were systematic--ally studied. So did the relationship between ripening and browning. The obtained main results are as follows.1. Late harvest increased the content of soluble solid, reduced sugar, vitamin C, GSH, and soluble protein, linoleic acid, linolenic acid content and U/S value of flesh and core of Yali pear. The phase transition temperature was reduced. The pear’s ability against stress was improved. However, the late harvested fruit had vigorous respiration and ethylene metabolism so that the fruit hardness, titrated acid content, soluble solid content, reduced sugar content, soluble protein content, vitamin C content and GSH content decreased very quickly. Moreover, the decrease of SOD activity and increase of LOX activity caused the accumulation of hydrogen peroxide and superoxide radical, increase of MDA content and severe oxidation of fruit membrane lipids. Resultantly, the permeability of cell membrane was enhanced, which lead to the enzymatic activity increase of PPO and PPO isoenzyme and content decrease of phenols. All these changes mentioned above finally made the late harvested fruits much easier to get browning. Moreover, the more severe browning was found in pear’s core than in its flesh because of the more acute changes in its core.2. Rapid cooling induced cold injury to early harvested pears and especially to their cores. Compared with rapid cooling treatment, slow cooling treatment obviously increased the pear flesh and core’s soluble protein content, linoleic acid content, linolenic acid content, and U/S value, reduced its phase transition temperature and resultantly enhanced the Yali pear’s ability against stress. Additionally, slow cooling slowered the metabolism of respiration and ethylene, enhanced the SOD activity, delayed the decrease of fruit hardness, titrated acid content, soluble solid content, reduced sugarcontent, soluble protein content, vitamin C content and GSH content in late stage of storage. The increase of enzymatic activity of LOX, PPO and PPO isoenzyme, the accumulation of proline, hydrogen peroxide and superoxide radical and cell membrane lipid peroxidation was reduced or attenuated. Resultantly, slow cooling well restrained the browning of early harvested pear and especially exerted better protective effect on pear core browning.3. Fruit peel contributed to more than 90% of the total respiration of the whole fruit. Dissolve of CO2 decreased from inner to outer tissue of the fruit. Results showed that dissolve of CO2 in tissue was correlated with temperature, CO2 concentration in environment and physiological status of the tissue. As temperature decreased, CO2 concentration increased, and se更多还原