石榴PAL基因的克隆与表达分析

为探究石榴PAL基因的功能及表达特性,解析石榴呈色和褐变机理,以石榴品种泰山红和泰山三白甜为试材,利用RT-PCR和RACE技术克隆PAL基因全长,分析其在不同发育期的表达情况。结果表明,从泰山红果皮c DNA中克隆得到石榴PAL基因(Gen Bank登录号为KY094504)。PAL基因ORF序列长2 205 bp,编码734个氨基酸,含有典型的苯丙氨酸和组氨酸解氨酶保守结构域、PLN02457结合位点和PLN02457超家族保守结构域;石榴PAL编码蛋白的预测分子质量为79 693.87 Da,为稳定蛋白和亲水性蛋白,存在丝氨酸、苏氨酸和酪氨酸3个磷酸化位点,二级结构中含有丰富的α-螺旋(47.55%)和无规则卷曲(30.52%);实时荧光定量PCR分析表明,泰山红和泰山三白甜果实发育过程中,PAL表达水平呈先降低后升高的变化趋势,泰山红果实发育各时期果皮中PAL表达水平均高于泰山三白甜;2个品种发育期果皮褐变度逐渐降低,且泰山三白甜褐变度明显高于泰山红;泰山红果实发育期果皮花青苷含量逐渐升高,泰山三白甜变化较平缓,且泰山红花青苷含量明显高于泰山三白甜。2个品种PAL基因表达量与褐变度呈显著正相关,泰山红PAL基因表达量与花青苷含量呈极显著负相关。本研究结果为揭示石榴果实呈色和褐变机理提供了理论依据。     

不同石榴品种果实酚类物质及抗氧化活性研究

为探明石榴不同栽培地区和不同品种间酚类物质含量分布特征,筛选抗氧化能力强的功能型优良品种,以山东、云南、新疆和四川地区8个主栽石榴品种的成熟期果实为试材,利用常规品质分析方法和高效液相色谱技术,对其果实品质、酚类物质和抗氧化能力进行分析。结果表明,石榴品种间果实各品质指标存在显著差异,其中,喀什甜单果质量、可溶性糖和维生素C含量最高,甜绿籽固酸比最高,泰山红可溶性固形物含量最高,红玛瑙可滴定酸含量最高。不同石榴品种果皮中酚类物质含量与抗氧化能力均最高;果汁次之,种子最低。喀什甜果皮和红玛瑙种子中酚类物质含量和DPPH自由基清除率均最高;果汁中花青苷含量和DPPH自由基清除率分别在千籽红和大青皮甜中最高,安石榴苷、没食子酸、鞣花酸、总黄酮和总酚含量在红玛瑙中最高;果皮中安石榴苷含量(平均为135.00 mg·g-1)占总酚的48.94%,是石榴果实中最主要的酚类物质。果实品质指标间、果实品质与酚类物质间存在一定的相关性,安石榴苷、没食子酸、鞣花酸、花青苷、总黄酮和总酚间互为正相关,各指标与DPPH自由基清除率均正相关。红玛瑙、喀什红和千籽红果实的综合品质佳,富含酚类物质,是值得推广和开发利用的优良品种。研究结果为石榴加工产品的研发和新品种选育提供了理论依据。     

外源甘氨酸甜菜碱处理对西葫芦果实冷害和品质的影响

为探讨甘氨酸甜菜碱(GB)处理对西葫芦果实贮藏期间冷害和品质的影响,以亚历山大西葫芦为材料,采用外源甜菜碱浸泡的方法,比较分析了冷害指数、相对电导率、叶绿素含量、抗氧化酶类活性、1,1-二苯基-2-三硝基苯肼(DPPH)自由基清除力等指标的变化。结果表明,10 mmol·L-1GB处理能有效抑制西葫芦果实低温贮藏过程中冷害的发生和相对电导率的上升,保持较高的叶绿素、总酚含量;同时,GB处理抑制了褐变相关的多酚氧化酶(PPO)和过氧化物酶(POD)活性,促进了抗氧化相关的过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性,减少了活性氧的产生和积累,从而使西葫芦果实保持较高的抗氧化活性。综上所述,GB处理能有效减轻西葫芦果实的冷害症状,维持西葫芦果实在低温贮藏期间的品质,本研究为西葫芦果实采后贮藏保鲜提供了理论依据。     

气调处理对绿芦笋抗氧化及抗病酶活性的影响

为探讨气调处理对绿芦笋抗氧化和抗病性相关酶活性的影响,以空气为对照(CK),在15±1℃和相对湿度为90%~95%的贮藏条件下,研究5种不同比例气体成分[CA1(5%CO_2+1.5%O_2)、CA2(7%CO_2+0%O_2)、CA3(7%CO_2+1.5%O_2)、CA4(7%CO_2+3.5%O_2)、CA5(9%CO_2+1.5%O_2)]对达宝利绿芦笋采后感官品质、菌落总数、相对电导率、丙二醛(MDA)含量、总酚含量、二苯基苦基苯肼(DPPH)清除率、羟自由基(·OH)清除率以及超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)、多酚氧化酶(PPO)、苯丙氨酸解氨酶(PAL)活性的影响。结果表明,气调处理不同程度抑制了芦笋根部的腐烂,延缓了其菌落总数、相对电导率和MDA含量的上升,维持其较高的总酚含量、DPPH清除率、·OH清除率以及SOD、CAT、PPO活性,减缓了其POD活性上升,并保持了组织较低的PAL活性,所有气调处理中以CA3效果较好。此外,以绿芦笋根部开始出现腐烂为标准,CK、CA1、CA2、CA4、CA5和CA3的贮藏期分别为1、2、2、2、4和5 d。因此,CA3(7%CO_2+1.5%O_2)的气调处理可维持达宝利绿芦笋采后较好品质。本研究结果为绿芦笋的贮藏保鲜提供了理论依据及技术支持。     

短波紫外线处理对采后香菇褐变的影响

为了控制采后香菇在贮藏过程中的褐变并提高其贮藏品质,本试验采用不同剂量(2、4、6和8 kJ·m^-2) 短波紫外线(UV-C)对新鲜香菇进行预处理,研究不同剂量UV-C处理对香菇色泽、总酚含量、多酚氧化酶(PPO)活性、过氧化物酶(POD)活性、超氧化物歧化酶(SOD)活性、过氧化氢酶(CAT)活性、苯丙氨酸解氨酶(PAL)活性、可溶性蛋白含量、还原糖含量、游离氨基酸含量以及香菇表面微生物的影响。结果表明,UV-C处理延缓了香菇色泽的下降,保持了较高的总酚含量,并且有利于POD、SOD、CAT和PAL活性维持在较高水平,抑制了PPO活性,同时可以保持较高的还原糖和可溶性蛋白含量,在一定程度上延缓了蛋白质的降解,而且可以有效抑制微生物的生长,其中4 kJ·m^-2 UV-C处理效果最佳。综上所述,UV-C处理可以有效地抑制香菇褐变,延长其贮藏期。本研究结果为香菇的贮藏保鲜提供了理论依据。     

快速脱水抑制葡萄干制过程中膜脂过氧化及褐变

为探索脱水速度对无核白葡萄干制过程中膜脂过氧化作用及褐变的影响,以新疆无核白葡萄为试验材料,经过葡萄促干剂处理后,采用快速脱水和缓慢脱水2种处理,质量每减轻10%进行取样,测定脱水过程中果实干基含水率、干燥速率、褐变度、细胞膜透性、丙二醛(malonaldehyde,MDA)含量、脂氧合酶(lipoxygenase,LOX)、超氧化物歧化酶(superoxide dismutase,SOD)、过氧化氢酶(catalase,CAT)、过氧化物酶(peroxidase,POD)、多酚氧化酶(polyphenol oxidase,PPO)活性以及总酚含量的变化。结果表明:与缓慢脱水相比,快速脱水处理显著(P0.05)降低了无核白葡萄褐变度的上升,减少MDA生成量以及膜透性的增加,抑制LOX活性的升高,保持较高的活性氧清除酶SOD、CAT及POD活性及较高的总酚含量,且使PPO活性保持在一个较低的水平。因此认为,快速脱水可以有效地抑制无核白葡萄的膜脂过氧化作用对细胞膜的破坏,保持细胞的完整性,且PPO活性较低,从而减少无核白葡萄脱水褐变的发生。研究结果为快速脱水在无核白葡萄干制中的应用提供参考。     

红熟番茄果实多酚氧化酶酶学特性

多酚氧化酶（Polyphenol oxidase,PPO,EC 1.14.18.1 or 1.10.3.2）与果蔬加工制品的色泽、抗氧化能力关系密切。果蔬PPO酶学特性分析和活性控制越来越受到关注,为设计、开发番茄加工技术和工艺提供理论依据,该文采用光谱法,研究了红熟番茄（Lycopersicum esculentum Mill. cv 918）果实PPO的酶学特性。研究结果表明红熟番茄果实PPO的最适反应pH值是6.0,反应温度是40℃,耐热性较好,50℃加热10 min仍保有88%的活性。红熟番茄果实PPO对一元酚、二元酚和三元酚均有催化氧化能力,最适底物是儿茶酚,其最大反应速率和米氏常数分别是226.30 U/min和 6.00 mmol/L。抗坏血酸、β-巯基乙醇或L-半胱氨酸可抑番茄PPO活性,十二烷基硫酸钠可显著增强其活性。     

He-Ne激光和增强UV-B辐射对小麦幼苗多酚代谢3种酶活性的影响

为探讨He-Ne激光和增强UV-B辐射对小麦幼苗多酚代谢相关酶活性的影响,利用5 mW·mm-2的He-Ne激光和增强UV-B(10.08 kJ·m-2·d-2)辐射处理"晋麦8号"小麦幼苗,分别在不同时段测定苯丙氨酸解氨酶(PAL)、多酚氧化酶(PPO)及过氧化物酶(POD)的活性.结果表明,增强UV-B辐射使小麦幼苗叶片PAL活性升高,PPO与POD活性降低,且随处理天数的增加,不同处理组小麦幼苗叶片PAL、PPO、POD活性间具有一定相关性.长期增强UV-B辐射,导致多酚类物质的代谢速度降低甚至停止,自由基不能被及时清除,生物膜破坏:经过一定剂量的He-Ne激光辐照可修复增强UV-B辐射对小麦幼苗叶片多酚类物质代谢的损伤.     

保鲜剂对百合鳞片常温贮藏期间品质及抗氧化活性的影响

以兰州地产鲜百合为试材,采用0.5 mmol/L水杨酸和6 mg/L二氧化氯两种保鲜剂分别浸泡鲜百合鳞片5 min和10 min,并常温下贮藏的处理方法,研究不同保鲜剂处理对百合鳞片贮藏过程中褐变度、抗坏血酸(Vc)含量、总酚、黄酮以及抗氧化活性等指标的影响,通过品质与抗氧化活性之间的相关性分析,确定水杨酸和二氧化氯的保鲜效果及其最佳使用浓度。结果表明,水杨酸和二氧化氯均可有效保持百合的感官品质,延缓营养物质的流失。其中以0.5 mmol/L的水杨酸浸泡10 min的处理效果最好,能够更好地延缓百合鳞片的褐变,抑制Vc、总黄酮、总酚含量的下降,降低多酚氧化酶活性,提高了DPPH自由基、羟基自由基清除能力和总抗氧化能力。     

贵州不同生态区蓝莓果实抗氧化特性研究

为了探讨贵州省不同生态区不同蓝莓品种果实抗氧化能力的差异,对不同生态区蓝莓品种选育及栽种配置做出合理规划。选择贵州省3个不同海拔生态区内种植5年生的4个蓝莓品种,并分别对供试蓝莓果实样品的总抗氧化能力、羟自由基清除能力和DPPH自由基清除能力进行测定,并结合测定蓝莓果实中总酚、类黄酮和原花色素含量,对蓝莓果实的抗氧化能力进行评价,结果表明,在高海拔地区蓝莓果实抗氧化能力强于低海拔地区,4个品种中"园蓝"的综合抗氧化能力最强;兔眼蓝莓中"园蓝"抗氧化能力强于"灿烂",高丛类蓝莓中"蓝雨"的抗氧化能力强于"莱克西"。蓝莓果实中原花青素含量、类黄酮含量、总酚含量与植株抗氧化活性显著相关(p0.01)。     

Effect of wounding on phenolic enzymes in six minimally processed lettuce cultivars upon storage

The effect of wounding on polyphenol oxidase (PPO), peroxidase (POD), and phenylalanine ammonia-lyase (PAL) was studied in six minimally processed lettuce (Lactuca sativa L.) cultivars upon storage for 7 days at 5 degrees C (Iceberg Mikonos (IM), I. Green Queen (IGQ), I. Asdrúbal (IA), Little Gem Sandra (LGS), Romaine Cazorla (RC), and R. Modelo (RM)). Wounding of lettuce tissue midribs (because of minimal processing) caused an exponential increase in PPO activity due to the activation process from latent to fully active PPO by following first order kinetics in the time range from 3.7 days (LGS) to 6.3 days (RC). However, total PPO activity (active plus latent) remained constant. Isoform pattern of PPO changed upon storage probably because of posttranslational processes. POD activity linearly increased with induction of new POD isoenzymes. PAL activity presented a typical bell-shaped induction pattern in four cultivars. Only IM and IGQ showed a second induction response which has not been previously described in the literature. IM was the cultivar most susceptible to browning and RC was the cultivar least susceptible. However, no clear correlation was observed between browning and any of the biochemical and physiological attributes investigated (PPO, PAL, and POD activities, total and individual phenols accumulation, and ascorbic acid content).     

Phenolic compounds and related enzymes are not rate-limiting in browning development of fresh-cut potatoes

The effect of minimal processing on polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL), and phenolic compounds was studied in five potato cultivars (Agria, Cara, Liseta, Monalisa, and Spunta). Minimal processing caused an overall increase in PPO, POD, and PAL activities. The isoform pattern of PPO was the same for all of the cultivars before and after processing. No latent PPO was detected. The isoperoxidase pattern was approximately the same among cultivars. An increase in POD activity was related to the specific induction of an acidic isoperoxidase. PAL showed an induction pattern characterized by the presence of a maximum peak of activity after 4 days of processing for all of the cultivars. The sequence of browning susceptibility of potato cultivars was as follows: Monalisa > Spunta > Liseta > Cara > Agria. Browning development was only partially correlated to PAL activity (only during the first 4 days after wounding). However, this correlation could not explain the above sequence of browning susceptibility. Minimal processing caused an increase of chlorogenic acid, whereas tyrosine content remained unchanged. In summary, no significant correlation was found between either rate or degree of browning and any other biochemical and physiological attribute investigated (PPO, POD, hydrogen peroxide, ascorbic acid content, and initial phenolics content as well as total and individual phenolics accumulation).     

湿度对甘薯愈伤的影响

为探索湿度对甘薯愈伤的影响,本试验以普薯32号甘薯为原料,人工模拟机械损伤后于25℃、不同相对湿度(RH50%和RH80%)条件下愈伤,通过比较甘薯木质素生成、失重率、呼吸强度、愈伤过程关键酶活性、总酚和类黄酮含量的差异,评价湿度对甘薯愈伤的影响。结果表明,RH80%条件下较RH50%更有利于甘薯愈伤木栓组织的形成,在愈伤4 d时甘薯木质素积累达到最高。与RH50%组相比,RH80%条件处理能显著提高甘薯愈伤组织苯丙氨酸解氨酶(PAL)、过氧化物酶(POD)和多酚氧化酶(PPO)活性(P<0.05),提升总酚、类黄酮含量,促进呼吸高峰提前,降低甘薯重量损失。相关性分析表明,RH80%条件下愈伤,甘薯木质素含量与PAL、POD、PPO活性及总酚、类黄酮含量呈显著正相关(P<0.05)。本研究结果为甘薯采后愈伤提供了一定的理论依据。     

外源NO对采后绿芦笋木质化和抗氧化能力的影响

为探讨NO处理对采后绿芦笋木质化合成的调控机理。以0.2mmol/L的硝普钠为一氧化氮供体,以蒸馏水处理为对照,研究了NO对采后绿芦笋总酚、木质素含量;木质素合成关键酶(苯丙氨酸解氨酶、肉桂醇脱氢酶、过氧化物酶、多酚氧化酶);抗氧化能力(1,1-二苯基-2-三硝基苯肼自由基清除率、超氧阴离子自由基(O2.-)清除率、羟基自由基(·OH)清除率)及膜透性的影响,结果表明,与对照相比,NO处理可延缓采后绿芦笋木质素含量和膜透性的增加,抑制肉桂醇脱氢酶和多酚氧化酶活性,增强抗氧化能力,诱导过氧化物酶活性增强,但对苯丙氨酸解氨酶活性和总酚含量的影响不显著。说明NO处理是通过抑制肉桂醇脱氢酶和多酚氧化酶活性、提高抗氧化能力而延缓采后绿芦笋的木质化进程。研究结果可为NO在绿芦笋保鲜中的应用提供理论依据和技术方法。     

Effect of wash water temperature and chlorination on phenolic metabolism and browning of stored iceberg lettuce photosynthetic and vascular tissues

Cut tissues from distinct anatomical locations in iceberg lettuce (Lactuca sativa L.) were subjected to washing in cold (4 degrees C) and warm (47 degrees C) water with or without chlorine to assess their propensity to discoloration during storage. Total protein (Bradford method) and phenolic (TPH; Folin-Ciocalteu method) contents and polyphenol oxidase (PPO; spectrophotometric method using catechol as a substrate), peroxidase (POD; guaiacol substrate), and phenylalanine ammonia-lyase (PAL; phenylalanine substrate) activities were determined in photosynthetic and vascular tissue from outer and inner leaves. Unprocessed photosynthetic and inner leaf tissues had significantly higher (P < 0.05) levels of protein and TPH and PPO and POD activities than vascular and outer leaf tissues. PAL activities (on a fresh weight basis) were similar in all tissues. Changes in browning (light reflectance measurement) and phenolic metabolism in all four tissue types were observed during aerobic storage at 5 degrees C over 10 days. PAL activity increased in all tissues after 1-2 days of storage and then gradually decreased. POD activity also increased steadily for the storage duration. Protein content and PPO activity remained constant. Edge browning (measured with a Minolta Chroma Meter) and TPH increased in all tissues, especially in outer vascular tissue. Cut photosynthetic and vascular tissues washed at 4 and 47 degrees C with and without 100 microg mL(-1) chlorine for 3 min were analyzed during 7 days in storage at 5 degrees C. Enzyme activities and accumulation of phenolics in all tissues washed at 47 degrees C were significantly (P < 0.05) lower compared to controls or tissues washed at 4 degrees C. Chlorine had no additional effect at 47 degrees C but significantly (P < 0.05) reduced browning and accumulation of phenolics in lettuce washed at 4 degrees C. These results showed that inherent differences between tissues affect phenolic metabolism and browning in stored, fresh-cut lettuce.     

减压贮藏对冷藏枇杷果实品质和木质化败坏的影响

为阐明低温减压贮藏对枇杷果实品质和木质化败坏的影响,该研究应用40～50 kPa压力于(0±0.5)℃下贮藏果实49 d,并每隔7 d测定果实的营养品质、出汁率、硬度、褐变指数、呼吸速率、乙烯产生速率、过氧化物酶(POD)和苯丙氨酸解氨酶(PAL)等木质化相关酶活性及木质素含量的变化.结果表明,减压处理可明显抑制冷藏枇杷果实的呼吸强度、乙烯产生和果实褐变,并保持较高的果实可溶性固形物、可滴定酸度和维生素C含量,抑制贮藏21 d后果实硬度的增加,减轻出汁率的下降,降低POD和PAL酶活性的上升趋势,抑制木质素含量的增加.另外,减压贮藏减轻冷藏枇杷果实的木质化败坏,可能与抑制POD和PAL酶活性有关.低温减压贮藏可有效保持果实食用品质,延长贮藏期,是适合枇杷果实贮藏的有效方法.     

Effect of natamycin in combination with pure oxygen treatment on postharvest quality and selected enzyme activities of button mushroom (Agaricus bisporus)

The combined effects of natamycin (NA) and pure oxygen (PO) treatment on microbial and physicochemical characteristics of button mushroom ( Agaricus bisporus ) stored at 4 ± 1 °C for 16 days was investigated. Mushroom respiration rate, weight loss, firmness, color, percent open caps, total soluble solids, microbial and activities of polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and peroxidase (POD) were measured. The results indicate that treatment with natamycin + pure oxygen (NAPO) maintained tissue firmness, inhibited increase of respiration rate, delayed browning and cap opening, and reduced microorganism counts of yeasts and molds compared to control treatment. The efficiency was better than that of NA or PO treatment. Furthermore, NAPO inhibited the activities of PPO, PAL, and POD throughout the storage period. Our study suggests that NAPO treatment has the potential to improve the quality of button mushroom and extend the shelf life.     

Biochemical study of leaf browning in minimally processed leaves of lettuce (Lactuca sativa L. var. acephala)

A series of biochemical parameters, including the concentration of total ascorbic acid (ASA(tot)) and the activities of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and peroxidases (PODs), was investigated during cold storage (72 h at 4 degrees C in the dark) in fresh-cut (minimally processed) leaves of two lettuce (Lactuca sativa L. var. acephala) cultivars differing in the susceptibility to tissue browning: Green Salade Bowl (GSB), susceptible, and Red Salade Bowl (RSB), resistant. The two cultivars showed differences also at the biochemical level. The content in ASA(tot) increased in RSB, as a consequence of increased DHA concentration; conversely, ASA(tot) diminished in GSB, in which ASA was not detectable after 72 h of storage, thus suggesting a disappearance of ascorbate (both ASA and DHA) into nonactive forms. The antioxidant capacity (as determined by using FRAP analysis) decreased significantly during storage in RSB, while a strong increase was observed in GSB. PAL activity increased soon after processing reaching a maximum by 3 h, then it declined to a relatively constant value in RSB, while in GSB it showed a tendency to decrease in the first few hours from harvest and processing. POD activity, at least for chlorogenic acid, increased significantly during storage only in GSB.