低温打蜡对贮藏菠萝黑心病控制的作用

研究了常温、低温、低温加打蜡 3种贮藏条件下菠萝果实硬度、可溶性固形物 (TSS)、可溶性糖醛酸、多聚半乳糖醛酸酶 (PG)和多酚氧化酶 (PPO)等因素的变化 ,及它们对黑心病发生及发展情况的影响。结果表明 ,低温加打蜡可以延缓果肉硬度、可溶性固形物和可溶性糖醛酸含量的下降 ,降低 PG和 PPO的活性 ,降低黑心病的发病率 ,较好的保持果实品质     

串番茄果实货架期间与耐贮性有关的生理特性的变化

串番茄品种随着货架期延长,果实硬度、果肉硬度、原果胶含量逐渐下降;可溶性果胶含量逐渐上升;多聚半乳糖醛酸酶(PG)活性呈峰值变化,变化幅度小于普通番茄.     

枇杷冷藏过程中果肉木质化与细胞壁物质变化的关系

“大红袍”和“解放钟”枇杷果实在 1℃下贮藏时 ,细胞壁物质代谢异常 ,果肉硬度持续升高而出汁率逐渐降低 ,果胶酯酶 (PE)和多聚半乳糖醛酸酶 (PG)活性和水溶性果胶含量下降 ,原果胶含量、苯丙氨酸解氨酶(PAL)活性及木质素和纤维素含量不断增加。约经 3周贮藏后 ,果实出现果皮难剥、果肉质地变硬、粗糙少汁的异常劣变现象。在 12℃下贮藏的枇杷果实 ,细胞壁物质代谢正常 ,果肉硬度增加少 ,PE和PG活性及水溶性果胶含量较高 ,无原果胶增加现象 ,PAL活性呈下降趋势 ,木质素和纤维素含量变化不大 ,果实不出现木质化败坏。这些结果表明冷藏枇杷的木质化败坏可能是一种低温失调现象     

不同贮藏温度对枇杷果肉木质化及相关酶活性的影响

将“解放钟”枇杷(Eriobotrya japonicaL ind l.cv.Jiefangzhong)果实于4℃和12℃下贮藏,研究了不同贮藏温度对采后枇杷果肉木质化及相关酶活性的影响。结果表明,4℃贮藏的枇杷果肉苯丙氨酸解氨酶(phenylalan ineammon ia lyase,PAL)、4-香豆酸辅酶A连接酶(4-coum arate coenzym e A ligase,4-CL)、肉桂醇脱氢酶(c innamyl alco-hol dehydrogenase,CAD)和过氧化物酶(peroxidase,POD)活性高于12℃贮果,而多酚氧化酶(polyphenol oxidase,PPO)活性低于12℃贮果。4℃贮藏的枇杷果肉硬度和木质素含量不断增加,果肉木质化较为严重;12℃贮藏的枇杷果肉硬度和木质素含量低于4℃贮果,果肉木质化程度较低。低温诱导PAL和POD活性的上升是导致枇杷果肉发生木质化的主要原因。     

多聚半乳糖醛酸酶(PG)在苹果成熟过程中的作用

在未成熟的绿果内,多聚半乳糖醛酸酶(PG)的活性几乎难以察觉。盛花后130天果实还很硬时,PG 活性只有0.58—0.64酶单位(每克果肉)。呼吸高峰后果实硬度开始下降时,PG活性急剧增加。在盛花后165天硬度下降到10.5(每磅/平方厘米)时,酶活性达到最大值。果实变绵后,PG 活性下降。与此同时果胶酸的组分也有明显变化:盛花后120—150天,总果胶酸含量稳定,以后则不断下降;而醇溶性的半乳糖醛酸含量迅速上升,在盛花后120天到165天内增加10多倍。说明果胶酸的分解引起了果实的软化。     

柿果实采后胞壁多糖代谢及其降解酶活性的变化

以富平尖柿为试验材料,研究了室温下柿果实硬度和细胞壁组分及其降解酶活性变化。结果表明,柿采后后熟期间果肉硬度持续下降,平均日下降3．1％,其中第7天到第16天下降最快,平均日下降6．9％。碳酸钠可溶果胶(SSP)和24％KOH可溶组分含量持续下降,与果肉硬度变化呈极显著正相关(r分别为0．9698和0．8084);而水溶性果胶(WSP)和4％KOH可溶组分含量不断上升,与果肉硬度变化呈极显著负相关(r分别为0．9566和-0．9392),螯合剂可溶果胶(CSP)与24％KOH不溶组分含量变化缓慢。多聚半乳糖醛酸酶(PG)和纤维素酶(Cx)活性均在采后第16天达最高值。相关性分析表明,PG活性上升可能是导致柿SSP含量下降和WSP含量上升的主要原因;而Cx活性则可能引起纤维素以及难溶性的半纤维素(24％KOH可溶组分)向易溶的半纤维素(4％KOH可溶组分)转化,从而导致了柿果肉硬度的下降。     

香蕉果实后熟过程中果肉软化差异的研究

对香蕉果实贮藏过程中内、外果肉相关生理生化指标及细胞结构的变化进行系统的观察分析,结果显示:(1)在贮藏初期香蕉果实内果肉的硬度小于外果肉,在贮藏过程中的同一时期,均表现出内果肉硬度小于外果肉,且内果肉硬度较外果肉先降到零;(2)在贮藏初期内果肉中多聚乳糖醛酸酶(PG)和淀粉酶的活性均高于外果肉,随着贮藏时间的延长,酶活性在内、外果肉均表现出不断增加,且这两种酶活性在内果肉中早于外果肉达到最高值,但其在内果肉中的最高值均略低于外果肉的最高值;而淀粉含量却相反,在贮藏初期内果肉中淀粉含量低于外果肉,且在贮藏过程中的降解速率高于外果肉;(3)超微结构显示,香蕉果实内果肉中淀粉粒和细胞壁结构的降解均早于外果肉.研究表明,香蕉果实的软化首先由内果肉细胞降解开始,并呈放射状向外逐步延伸.     

谷胱甘肽对采后石刁柏木质化和食用品质的影响

在(24±1)℃条件下,谷胱甘肽(GSH)可显著抑制采后石刁柏木质素合成前体总酚的含量及与木质素合成相关的苯丙氨酸解氨酶(PAL)和过氧化物酶(POD)活性上升,延缓叶绿素、可溶性糖、可溶性蛋白和核酸的降解,降低活性氧和木质素含量,从而保持石刁柏的鲜嫩品质.     

三个脐橙品种果实主要细胞壁酶动态变化研究

以罗伯逊脐橙、丰脐、纽荷尔脐橙果实为试材,对其果皮和果肉的果胶甲酯酶(PE)、多聚半乳糖醛酸酶(PG)、β-葡萄糖苷酶和纤维素酶(CX)的动态变化进行研究。结果表明,三个品种PE活性均为果肉明显高于果皮,其中纽荷尔和罗脐分别在果实膨大期、转色期和成熟期出现三个峰值;PE活性变幅纽荷尔大于罗脐,丰脐变化较平稳。PG活性果肉略高果皮,且皆在转色期开始快速升高。首次对脐橙果实β-葡萄糖苷酶研究表明,该酶活性微弱,成熟期活性最高,纽荷尔高于丰脐和罗脐;动态变化中果皮和果肉无明显差异。酶活性高峰出现的时间为PE早于PG和β-葡萄糖苷酶;PE和PG是影响脐橙果实发育的主要酶,β-葡萄糖苷酶可能是PE和PG的补充。     

PG与番茄果实成熟的关系

系统比较了转多聚半乳糖醛酸酶(PG)反义基因和对照番茄果实成熟过程中绿熟、转色、粉顶、粉红、全红5个时期的PG活性和与其相关的生理、生化组分的动态变化.实验表明,转基因果与对照果相比,PG活性始终处于较低水平,PG活性强烈被抑制是在全红期;果实的硬度、贮藏寿命指数都高于对照果;番茄红素合成积累进程被延缓;可溶性果胶含量、电解质外渗百分率均低于对照果.外源乙烯刺激引起对照果PG活性剧增,而转基因果表现钝化.讨论了PG活性与果实成熟、耐贮性及软化的关系,及对外源乙烯刺激的敏感性.首次明确提出PG活性在对照果中极大地表达,在转基因果中强烈被抑制是在全红期,而不是在整个成熟期;PG活性在果实软化中起直接和重要作用;PG活性的高低与番茄红素的合成与积累有关.     

Polyuronides in Avocado (Persea americana) and Tomato (Lycopersicon esculentum) Fruits Exhibit Markedly Different Patterns of Molecular Weight Downshifts during Ripening

Avocado (Persea americana) fruit experience a rapid and extensive loss of firmness during ripening. In this study, we examined whether the chelator solubility and molecular weight of avocado polyuronides paralleled the accumulation of polygalacturonase (PG) activity and loss in fruit firmness. Polyuronides were derived from ethanolic precipitates of avocado mesocarp prepared using a procedure to rapidly inactivate endogenous enzymes. During ripening, chelator (cyclohexane-trans-1,2-diamine tetraacetic acid [CDTA])-soluble polyuronides increased from approximately 30 to 40 [mu]g of galacturonic acid equivalents (mg alcohol-insoluble solids)-1 in preripe fruit to 150 to 170 [mu]g mg-1 in postclimacteric fruit. In preripe fruit, chelator-extractable polyuronides were of high molecular weight and were partially excluded from Sepharose CL- 2B-300 gel filtration media. Avocado polyuronides exhibited marked downshifts in molecular weight during ripening. At the postclimacteric stage, nearly all chelator-extractable polyuronides, which constituted from 75 to 90% of total cell wall uronic acid content, eluted near the total volume of the filtration media. Rechromatography of low molecular weight polyuronides on Bio-Gel P-4 disclosed that oligomeric uronic acids are produced in vivo during avocado ripening. The gel filtration behavior and pattern of depolymerization of avocado polyuronides were not influenced by the polyuronide extraction protocol (imidazole versus CDTA) or by chromatographic conditions designed to minimize interpolymeric aggregation. Polyuronides from ripening tomato (Lycopersicon esculentum) fruit extracted and chromatographed under conditions identical with those used for avocado polyuronides exhibited markedly less rapid and less extensive downshifts in molecular weight during the transition from mature-green to fully ripe. Even during a 9-d period beyond the fully ripe stage, tomato fruit polyuronides exhibited limited additional depolymerization and did not include oligomeric species. A comparison of the data for the avocado and tomato fruit indicates that downshifts in polyuronide molecular weight are a prominent feature of avocado ripening and may also explain why molecular down-regulation of PG (EC 3.2.1.15) in tomato fruit has resulted in minimal effects on fruit performance until the terminal stages of ripening.     

Extensive solubilization and depolymerization of cell wall polysaccharides during avocado (Perseaamericana) ripening involves concerted action of polygalacturonase and pectinmethylesterase

During the ripening of avocado ( Persea americana Mill.) fruit, water-soluble polyuronides increased dramatically, concomitant with marked downshifts in molecular mass. Treatment of cell walls from pre-ripe fruit with purified avocado polygalacturonase (PG, EC 3.2.1.15) promoted the release and molecular mass downshift of polyuronides. The polyuronides released by PG were similar in size distribution to water-soluble polyuronides from fruit at intermediate stages of ripening. Polyuronides released from pre-ripe fruit by PG, although of relatively high molecular mass, were not further degraded upon additional incubation with fresh enzyme. Similarly, water-soluble polyuronides prepared from fruit at intermediate stages of ripening were largely resistant to the action of purified PG in vitro. When polyuronides derived from fruit at intermediate stages of ripening were treated with weak alkali or pectinmethylesterase (PME, EC 3.1.1.11), extensive molecular mass downshifts occurred in response to incubation with PG. These results suggest that PG plays the central role in polyuronide degradation in ripening avocado fruit cell walls and that partial de-esterification is necessary for the increase in the susceptibility of polyuronides to PG. Differences in the patterns of polyuronide depolymerization in avocado fruit compared with the more thoroughly characterized tomato fruit are discussed.     

Cell wall-degrading enzymes and pectin solubility and depolymerization in immature and ripe watermelon (Citrullus lanatus) fruit in response to exogenous ethylene

Watermelon fruit have been shown to be extremely sensitive to exogenous ethylene, exhibiting acute symptoms of whole-fruit softening and placental-tissue water-soaking following short periods of exposure to the gas. This study addressed the firmness, specific activities of cell wall hydrolases, and solubility and molecular mass properties of polyuronides in placental tissue in response to treatment of intact fruit with ethylene. Watermelon fruit were harvested at the immature and full-ripe stages and exposed to 50 µl l⁻¹ ethylene for 6 days at 20°C. The firmness of placental tissue from ethylene-treated ripe and immature fruit decreased nearly 80% during 6 days of ethylene exposure, whereas the firmness of placental tissue from fruit maintained in air remained relatively constant up to day 3 and then decreased slightly (12%) during the following 3 days of storage. Although ethylene treatment in some cases influenced the levels of extractable placental-tissue polygalacturonase (EC 3.2.1.15), pectinmethylesterase (EC 3.2.1.11), and α -(EC 3.2.1.22) and β -galactosidase (EC 3.2.1.23) specific activities, these effects were not observed for fruit of both developmental stages and appeared not to be directly involved in the water–soaking syndrome. Symptoms of water-soaking were accompanied by increases in the levels of water- and CDTA ( trans -1,2-cyclohexanediamine- N,N,N',N' -tetraacetic acid)-soluble polyuronides and significant molecular mass downshifts in polyuronides in both immature and ripe watermelon fruit. Polyuronide depolymerization in ethylene-treated ripe fruit was extensive. The parallel trends of enzyme changes in ethylene- compared with air-treated fruit indicate that extractable enzyme levels are not associated with development of the water-soaking disorder. The potential involvement of membrane dysfunction in the water-soaking phenomenon is discussed.     

采后钙处理对梨果实钙的形态和果胶及相关代谢酶类影响的研究

研究了黄花梨经浸钙处理后,果实钙形态转变及果胶含量、多聚半乳糖醛酸酶（PG）和果胶甲酯酶（PME）活力的变化,以及果实硬度的变化。结果表明：浸钙处理的果实总钙含量显著提高,其硬度明显高于对照,且有利于细胞膜透性的保持;梨果实中的NaCl溶性钙最多,其次是水溶性钙,醋酸溶性钙和HCl溶性钙含量较少。在果实贮藏21d时,水溶性钙含量有一个上升的过程,而NaCl溶性钙则有一个下降的过程。浸钙处理后,除醋酸溶性钙外,果实中的水、NaCl和HCl溶性钙含量均有显著的提高。浸钙处理明显抑制了果胶的降解进程与PG的活力,但对PME抑制作用不明显。浸钙处理能提高果实硬度可能与浸钙处理抑制了PG活力有关。     

Comparative content of total polyphenols and dietary fiber in tropical fruits and persimmon

Recent studies have shown that dietary fiber and polyphenols of vegetables and fruits improve lipid metabolism and prevent the oxidation of low density lipoprotein cholesterol (LDL-C), which hinder the development of atherosclerosis. The goal of this study was to measure the total polyphenol and dietary fiber contents of some tropical fruits (i.e., pineapple, wax apple, rambutan, lichi, guava, and mango) and compare the results to the content of these substances in the better characterized persimmon. It was found that lichi, guava, and ripe mango (cv. Keaw) have 3.35, 4.95, and 6.25 mg of total polyphenols in 100 g fresh fruit, respectively. This is significantly higher than in persimmon, pineapple, wax apple, mature green mango, and rambutan [P < 0.0005 for pineapple (Smooth Cayene variant), wax apple, persimmon, rambutan, mature green mango (cv. Keaw); the value of P < 0.001 is found only for pineapple (Phuket, Queen variant)]. The same relationship was observed for the contents of gallic acid and of dietary fiber. It can be supposed that among the studied fruit, lichi, guava, and ripe mango may be preferable for dietary prevention of atherosclerosis.     

Pectin esterase, polygalacturonase and gel formation in peach pectin fractions

Peaches (Prunus persica cv. Hermoza) were stored at 0C in regular air (RA) or in controlled atmosphere (CA 10% CO2, 3% O2) for 4 weeks and then ripened for 4 days at 20 degrees C. Woolliness developed in the regular air stored fruit while the controlled atmosphere stored fruit ripened normally. In the woolly fruit symptoms of the disorder were greater in the inner mesocarp than in the outer. Polygalacturonase (PG) and pectin esterase (PE) activities differed in the outer and inner mesocarp of the affected fruit. PG activity was low and PE activity was high in the inner mesocarp of the woolly fruit during ripening relative to the outer mesocarp, while in the healthy fruit, activities were similar in both areas. Cell wall fractions of water-soluble, CDTA-soluble and carbonate-soluble pectins were prepared from freshly harvested peaches and incubated with PE and PG from ripe peaches at different ratios. Only the CDTA-soluble fraction formed a gel with peach enzymes, and the rate of gelation increased with increasing amounts of PE relative to PG. Both water-soluble and CDTA-soluble pectin fractions formed gels with commercial PE (extracted from orange peel). The PE extracted from peaches was stable when stored at 0 degrees C for 9 days, while PG activity was stable only for 1 day. We suggest that PE, acting on pectins in the cell wall in vivo may cause gel formation and that the CDTA-soluble polymers have the capacity to bind apoplastic water and create the dry appearance observed in woolly fruit.     

Cell wall modification in 1-methylcyclopropene-treated post-climacteric fresh-cut and intact papaya fruit

Papaya is a climacteric fruit in which ripening is greatly regulated by ethylene often associated with stress responses such as wounding. The changes in cell wall compositions in papaya fruit at an advanced stage of ripening under stress conditions including chilling temperature of 5°C and wounding employed as fresh-cut and how these changes were affected by an ethylene action inhibitor of 1-methylcyclopropopene (1-MCP) were examined in the study. The recovery of ethanol-insoluble solids, total soluble sugars, water-soluble polyuronides, neutral hemicelluloses, and neutral sugars of rhamnose, arabinose, mannose and glucose were not affected by 1-MCP or fresh-cut processing. The fresh-cut processing, however, caused a higher loss of total polyuronides and the neutral sugar galactose while increasing the recovery of chelator-soluble polyuronides. Few significant differences due to 1-MCP application were recorded in the recoveries of alkali-soluble polyuronides, hemicellulosic polyuronides extracted with 4% KOH, and the neutral sugar xylose. Modifications of cell wall polyuronides and hemicelluloses in ripe fresh-cut papaya fruit exhibited mostly similar patterns to those in intact ripe papaya fruit under the chilling temperature of 5°C while minimally affected by 1-MCP.     

Compositional and enzymatic changes in guava (Psidium guajava L.) fruits during ripening

Changes in chemical composition and hydrolytic enzyme activities in guava fruits cv. Lucknow-49 have been reported at four different stages of maturity, viz., mature green (MG), color turning (CT), ripe (R) and over ripe (OR). Chlorophyll content decreased, while carotenoid content increased with advancement of ripening. Starch content decreased with concomitant increase in alcohol soluble sugars. The cell wall constituents viz., cellulose, hemicellulose, and lignin decreased up to R stage, while the pectin content decreased throughout up to OR stage. Among the cell wall hydrolyzing enzymes, polygalacturonase (PG) and cellulase exhibited progressive increase in activity throughout ripening, while pectin methyl esterase (PME) activity increased up to CT stage and then decreased up to OR stage. The maximum increase in the activities of cell wall hydrolysing enzymes was observed between MG and CT stages. The activities of starch hydrolyzing enzymes, α-amylase and β-amylase decreased significantly with advancement of ripening. These changes in the activities of hydrolyzing enzymes could be considered good indicators of ripening in guava.