鲜切竹笋冷藏过程中生理和生化变化的研究

研究了最少化加工(MP)对竹笋呼吸强度的影响及MP竹笋贮藏期间呼吸强度的变化。测定了4℃下不同部位的竹笋的总糖、还原糖、总酚、木质素、纤维素、丙二醛(MDA)含量及苯丙氨酸解氨酶(PAL)和多酚氧化酶(PPO)活性的变化。结果表明:加工造成的机械损伤导致了竹笋呼吸强度的迅速增加,在随后的贮藏过程中又逐步减弱。竹笋尖部和中部的总糖和还原糖的含量贮藏前期下降、后期增加,而基部的总糖呈上升趋势。竹笋尖部和中部的总酚含量先减少后上升,之后再减少,而基部的总酚含量没有大的变化。纤维素和木质素含量贮藏前期从尖部的到基部的逐渐增加,贮藏中期从尖部的到基部的有不同程度的下降,贮藏后期有不同程度的增加。各部位MP竹笋的MDA含量在贮藏初期急剧上升,随后维持在高水平状态。尖部的PAL和PPO的活性高于中部和基部的。各部位的PAL活性贮藏前期上升,中期下降,后期又上升。尖、中部的PPO活性贮藏前期上升,后期下降,但仍维持在较高水平,而基部的PPO活性一直下降。     

壳聚糖-乳清分离蛋白复合膜对鲜切雷竹笋木质化和品质的影响

采用壳聚糖-乳清分离蛋白复合膜（chitosan-whey protein isolate composite film,CWF）涂膜1、2、3 次及去离子水、乙酸处理鲜切雷竹笋,于4 ℃冷藏15 d,以贮藏过程雷竹笋的苯丙氨酸解氨酶（PAL）、过氧化物酶（POD）活力、丙二醛（MDA）、多酚、木质素含量、菌落总数等为指标,研究CWF对鲜切雷竹笋木质化和品质劣变以及涂膜次数对保鲜效果的影响。结果显示,乙酸对鲜切雷竹笋的木质化和微生物有一定的抑制作用,但影响不显著;CWF涂膜可以显著降低鲜切雷竹笋表面的微生物数量,抑制PAL和POD活力,降低木质素、MDA含量,延长鲜切雷竹笋的货架期。随着CWF涂膜次数的增加,保鲜效果更好,考虑到生产成本选择涂膜2 次。     

马齿苋提取物对鲜切苹果褐变的影响

酶促褐变是影响鲜切果蔬品质及商业价值的关键问题之一。为探究马齿苋提取物在果蔬保鲜方面的应用价值,以鲜切苹果为研究材料,采用质量分数0.05%马齿苋提取物溶液浸泡鲜切苹果5min,在(4±1)℃存放8d。以鲜切苹果的褐变指数、多酚氧化酶(polyphenol oxidase,PPO)活力、苯丙氨酸解氨酶(phenylalanine ammonia-lyase,PAL)活力、过氧化氢酶(catalase,CAT)活力、过氧化物酶(peroxidase,POD)活力、丙二醛(malondiadehyde,MDA)含量、抗坏血酸含量以及DPPH自由基清除能力为评价指标,分析马齿苋提取物对鲜切苹果褐变及贮藏品质的影响。结果表明:与蒸馏水对照组相比,马齿苋提取物溶液处理能有效抑制鲜切苹果的褐变程度,在降低POD、PPO和PAL活力方面也有明显效果,能够在保证膜完整性的基础上减少细胞膜出现的损伤。相关性分析表明:鲜切苹果的褐变指数与CAT活力、抗坏血酸含量、DPPH自由基清除能力呈现极显著负相关(P<0.01),与MDA含量、PPO活力、POD活力、总酚含量呈极显著正相关(P<0.01)。马齿苋提取物溶液处理的鲜切苹果抗褐变效果较好,同时贮藏后鲜切苹果的抗氧化能力也有一定提高。     

UV-C辐照处理对高节笋冷藏品质的影响

为研究UV-C辐照处理对采后剥壳后的高节笋的品质、木质化和褐变的控制效果,本文将UV-C 4.0 kJ·m-2强度辐照处理剥壳后的高节笋于(6±1) ℃、85%~90% RH环境下贮藏15 d,分析硬度、呼吸速率、失重率、腐烂率、纤维素和木质素含量以及4-香豆酸辅酶A连接酶(4CL)、过氧化物酶(POD)、肉桂醇脱氢酶(CAD)、苯丙氨酸解氨酶(PAL)和多酚氧化酶(PPO)的活性等指标的变化。结果表明:UV-C处理对抑制高节笋切面的褐变,延缓高节笋的硬度、呼吸速率、失重率、腐烂率、纤维素和木质素含量的上升,抑制4-香豆酸辅酶A连接酶(4CL)、过氧化物酶(POD)、肉桂醇脱氢酶(CAD)、苯丙氨酸解氨酶(PAL)和多酚氧化酶(PPO)的活性均有显著性作用(p<0.05)。研究发现,UV-C辐照处理能够通过降低木质素合成代谢的相关酶活以抑制采后去壳竹笋木质素的累积,从而延缓采后冷藏竹笋的木质化进程,使其保持良好的食用品质。     

超高压处理对鲜切莴苣酶促褐变及相关基因表达的影响

鲜切莴苣在贮藏销售过程中极易褐变,严重影响鲜切莴苣的商品价值。为探究超高压(high pressure process, HPP)处理对鲜切莴苣褐变的影响,以鲜切莴苣为原料,采用不同压力(100、200、400 MPa)处理鲜切莴苣,置于4℃贮藏8 d,测定其在贮藏过程中色泽、褐变指数、失重率、硬度、总酚含量、类黄酮含量、丙二醛(malonaldehyde, MDA)含量、多酚氧化酶(polyphenol oxidase, PPO)活力、过氧化物酶(peroxidase, POD)活力和苯丙氨酸解氨酶(phenylalnine ammonia lyase, PAL)活力等相关指标。结果表明,与对照组相比,HPP处理可有效延缓鲜切莴苣的褐变,其压力越大,抑制的效果越显著。其中400 MPa处理延缓鲜切莴苣褐变的效果最好,能够显著抑制鲜切莴苣的总酚和类黄酮含量的上升,并有效抑制贮藏过程中PPO、POD和PAL的活力及相关基因表达。综上所述,HPP处理可以较好地保持鲜切莴苣贮藏过程中的色泽,有效延长贮藏保鲜期。     

高压静电场处理对鲜切黄甜竹笋冷藏下品质的影响

本实验研究了高压静电场对冷藏鲜切黄甜竹笋品质、木质化和褐变的影响。黄甜竹笋剥壳切段后经高压静电场(600 kV/m）处理120 min，而后于（6 ±1）℃、80%~85%相对湿度环境下贮藏10 d。结果显示:高压静电场处理显著（P<0.05）抑制了黄甜竹笋基部切面的褐变，显著（P<0.05）延缓了黄甜竹笋的呼吸速率、硬度、纤维素、木质素和H₂O₂含量的上升，同时也显著（P<0.05）抑制了苯丙氨酸解氨酶（phenylalanine ammonia lyase, PAL）、过氧化物酶（peroxidase, POD）、肉桂醇脱氢酶（cinnamyl alcohol dehydrogenase, CAD）、多酚氧化酶（polyphenol oxidase, PPO）的活性，显著（P<0.05）提高了超氧化物歧化酶（superoxide dismutase, SOD）和过氧化氢酶（catalase, CAT）的活性。结果表明，高压静电场处理能够抑制采后鲜切黄甜竹笋的木质纤维化和褐变，延缓品质劣变。     

高浓度二氧化碳气调包装通过调节酚代谢抑制鲜切莲藕的酶促褐变

鲜切莲藕褐变的主要原因是酶促褐变,高浓度CO_2气调包装(Modified-atmosphere packaging,MAP)可以有效延缓鲜切果蔬褐变,而苯丙氨酸解氨酶(L-phenylalanine ammonia-lyase,PAL)、多酚氧化酶(Polyphenol oxidase,PPO)和过氧化物酶(Peroxidase,POD)的编码基因是引起果蔬褐变的主要基因。然而,高浓度CO_2 MAP对鲜切莲藕片PAL、PPO、POD酶及其编码基因表达的影响却鲜有报道。本文分析了100%CO_2MAP对鲜切莲藕贮藏过程中褐变度、总酚含量、PAL、PPO和POD酶活性及其编码基因表达的影响。结果表明:100%CO_2 MAP对延缓鲜切莲藕褐变有较好效果,且100%CO_2 MAP贮藏期间鲜切莲藕PAL、PPO和POD酶活性随褐变程度的增加而同步变化。此外,Nn PAL1,Nn PPOA和Nn POD2/3的表达变化与PAL,PPO和POD酶活性的变化及褐变相一致,说明高浓度CO_2 MAP可能通过下调Nn PAL1,Nn PPOA和Nn POD2/3的表达来延缓鲜切莲藕褐变。     

鲜切果蔬酶促褐变发生机理的研究

为了进一步揭示鲜切果蔬酶促褐变发生过程及其机理,采用鲜切茄子和鲜切甘薯为实验材料,研究了与酶促褐变发生密切相关的酶活性变化及伤害胁迫生理。结果表明:两种果蔬经鲜切处理后诱发了酶促褐变的快速发生,鲜切甘薯的酶促褐变反应滞后于鲜切茄子。在贮藏期间两种果蔬的过氧化物酶(POD)活性和丙二醛(MDA)含量逐渐上升,总酚含量与苯丙氨酸解氨酶(PAL)活性变化一致,均先升后降。鲜切甘薯多酚氧化酶(PPO)活性逐渐上升,但鲜切茄子的PPO却呈下降趋势。结果还表明:鲜切果蔬不仅在切割表面发生酶促褐变反应,在远离切割部位也诱发了生理生化反应,这可能是由于切割伤害胁迫产生的刺激信号转导而引致组织的整体协同伤害防御反应的结果。     

鲜切竹笋褐变控制的研究

以鲜切竹笋为原料,蒸馏水为对照,采用3种浸泡液处理,即0.5%柠檬酸处理,45℃热水处理,0.5%柠檬酸和45℃热水联合处理,探讨鲜切竹笋褐变的机理及控制方法.试验结果表明,鲜切竹笋褐变主要是由于过氧化物酶(POD)引起的酶促褐变;0.5%柠檬酸和45℃热水联合处理可有效降低POD和多酚氧化酶(PPO)的活性,抑制鲜切竹笋POD同工酶的合成,从而有效抑制其引起的酶促褐变.     

贮藏期香椿中多酚类物质含量与相关酶活变化的关系

将新鲜香椿于0、5、10℃及20℃系列温度下贮藏,定期取样,测定香椿中的多酚类物质的含量,并对与多酚含量变化密切相关的酶类-多酚氧化酶(PPO)、过氧化物酶(POD)的酶活变化趋势进行考察。结果显示,各贮藏温度下,香椿中的多酚含量随着贮藏时间的延长呈现先上升后下降的趋势,而多酚氧化酶的酶活也呈现先上升后下降趋势,过氧化物酶的酶活则呈现出持续上升的趋势。同时发现贮藏于0℃下的香椿贮藏时间最长,生理变化最为缓慢,且其中多酚含量及多酚氧化酶(PPO)、过氧化物酶(POD)酶活变化最为平缓,可以确定香椿最宜存放于0℃条件下。     

减压贮藏对毛笋采后品质和相关酶活性的影响

研究了减压冷藏(40 kPa)和常压冷藏对毛笋采后生理和品质的影响。结果表明,减压冷藏能够抑制毛笋贮藏期间的组织褐变和霉变的发生,减少组织中丙二醛的积累,降低PAL、POD和PPO等酶的活性,延缓木质素合成和组织硬度的增加。减压贮藏对毛笋具有良好的保鲜效果。     

热激处理对冷藏“解放钟”枇杷果实木质化及相关酶活性的影响

以福建莆田市“解放钟”枇杷为材料,采后50℃热处理30min 后分为冷库(2～5℃)和室温(18～25℃)两种贮藏条件进行贮藏。在贮藏期通过对枇杷果实的木质素含量、硬度、多酚氧化酶(PPO) 、苯丙氨酸解氨酶(PAL)、肉桂醇脱氢酶(CAD)、过氧化物酶(POD)活性变化的分析,研究贮前热处理对冷藏枇杷果实木质化及相关酶活性的影响。结果表明：低温(2～5℃)条件下贮藏,枇杷果实硬度和苯丙氨酸解氨酶活性都有明显升高,且两者呈正相关,相关系数r=0.914。贮前热处理能够延缓冷藏枇杷果实木质素含量及硬度的上升,降低PPO、PAL、CAD、POD 的活性。     

Alleviation of chilling injury and browning of postharvest bamboo shoot by salicylic acid treatment

The effects of salicylic acid (SA) treatment on chilling injury, disease incidence, electrolyte leakage (EL), flesh browning index, malondialdehyde (MDA) and total phenolic content, phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD) activities, and polyamine (PA) content of bamboo shoot, during storage at 1 °C for 50 days, were examined. Chilling injury and disease incidence, EL, MDA content of control shoot increased progressively. Chilling injury promoted PAL, PPO and POD activities, which are associated with shoot total phenolic content and flesh browning index increase. Chilling injury was significantly positively correlated with putrescine (Put) or spermidine (Spd) contents. Suppression of chilling injury by SA treatment was associated with reducing EL, MDA and total phenolic content, retarding activities of PAL, PPO and POD, and promoting PA accumulation. The present findings suggest that SA treatment could be used commercially to control chilling injury in bamboo shoot during cold storage.     

The role of 1‐methylcyclopropene in lignification and expansin gene expression in peeled water bamboo shoot (Zizania caduciflora L.)

BACKGROUND: Water bamboo shoot (WBS) (Zizania caduciflora L.) is a fleshy aquatic vegetable susceptible to lignification. In this study, effects of 1‐methylcyclopropene (1‐MCP) anti‐ethylene treatment on lignification of harvested peeled WBS were investigated. RESULTS: Peeled shoots were treated with 0.5 µL L^?1 1‐MCP for 20 h at 20 °C and then stored at 20 °C for up to 9 days. Sensory quality, lignin content and activities of the lignification‐associated enzymes peroxidase (POD) and phenylalanine ammonia lyase (PAL) were evaluated. Expression of expansin (ZcExp) was also assessed. 1‐MCP application maintained better sensory quality and inhibited the increase in lignin content. Lessened lignification was associated with reduced activities of POD and PAL. Moreover, 1‐MCP‐treated shoots showed lower expression of the ZcExp gene. CONCLUSION: 1‐MCP pretreatment suppressed the synthesis of lignin and thereby delayed lignification in peeled WBS. Copyright © 2011 Society of Chemical Industry     

CHANGES OF CELL WALL COMPONENTS AND PAL ACTIVITY IN FRESH-CUT BAMBOO SHOOTS DURING COLD STORAGE

Changes of cell wall components in relation to softening and lignifying of fresh-cut bamboo shoots (Phyllostachys heterocycla var. pubescens) was investigated. Increased activity of phenylalanine ammonia-lyase (PAL) was related to a rise of lignin content in the basal section but not in the middle and apical sections. PAL activity was also associated with an increase in phenolic content in the middle section, but not in the basal and apical sections. The softening process occurred mainly in the apical section, while lignification took place primarily in the basal section. In the middle section, both softening and lignification also occurred but to a lesser extent.     

Effect of heat treatment on lignification of postharvest bamboo shoots (Phyllostachys praecox f. prevernalis.)

In order to evaluate the effects of heat treatment on the quality of postharvest bamboo shoots, the firmness, disease incidence, respiration and ethylene production, ACC synthase (ACS) and ACC oxidase (ACO) activities, lignin and cellulose contents, and the activities of phenylalanine ammonia-lyase (PAL), cinnamyl alcohol dehydrogenase (CAD) and peroxidase (POD) were examined during storage at 20 °C after heat treatment at 45 °C for 5 h. Heat treatment inhibited disease incidence and respiration, retarded ethylene production, and decreased ACS and ACO activities in bamboo shoots. Furthermore, heat treatment significantly delayed the rise in the activities of PAL, CAD and POD, which were associated with the inhibition of the synthesis of lignin and the delayed tissue lignification. These findings suggest that heat treatment could be a potential tool to delay lignification and decrease disease incidence in bamboo shoots during storage at 20 °C.     

短波紫外线处理对贮藏期鲜切马铃薯的护色作用

为研究短波紫外线(ultraviolet-C,UV-C)对贮藏期鲜切马铃薯的护色作用,在输出功率为15 W条件下对鲜切马铃薯辐照处理6 min。检测0~12 d贮藏期内褐变指数(browning index,BI)、多酚氧化酶(polyphenol oxidase,PPO)活性、过氧化物酶(peroxidase,POD)活性、苯丙氨酸解氨酶(phenylalanine ammonialyase,PAL)活性、总酚含量及丙二醛(malondialdehyde,MDA)含量的变化。结果表明,在贮藏期内,试验组鲜切马铃薯BI值、PPO活性、POD活性、MDA含量均低于对照组。另外,试验组总酚含量在0~3 d显著低于对照组(p<0.05),6 d~9 d内试验组总酚含量显著高于对照组(p<0.05)。试验组鲜切马铃薯的PAL活性在整个贮藏期内显著高于对照组(p<0.05)。总之,在0~12 d贮藏期内,经UV-C处理后,试验组鲜切马铃薯的氧化酶活性均得到抑制,延缓了酶促褐变的发生。