建莲中多酚氧化酶动力学特性的研究

为解决速冻建莲加工与贮藏中出现的褐变问题,本文研究了建莲中多酚氧化酶(PPO)的动力学特性,并对其进行组织定位试验。结果表明:PPO的最适反应条件为:pH6.8,温度40℃,米氏方程为1╱(Vo)=(1.84×1╱(S_0)+1.44)×0.1;建莲尖部和芯部组织中的PPO活性差异不大,但均高于外表部组织中的PPO活性。     

温和热处理对切分莴苣酶促褐变的抑制试验

切分莴苣在加工和贮藏过程中极易发生酶促褐变。本文研究了温和热处理对褐变强度和多酚氧化酶活性的影响,结果表明,45℃90s处理可很好地抑制切分莴苣的酶促褐变,同时可使多酚氧化酶的活性降低40％。温和热处理联合0.1％Vc或50mg/kgH2O2则抑制酶促褐变效果更好。     

氧化白藜芦醇协同抗坏血酸抑制余甘子酶促褐变的机制研究

通过研究氧化白藜芦醇协同抗坏血酸对余甘子酶促褐变的抑制作用,以及对其多酚氧化酶的酶抑制动力学研究,探明氧化白藜芦醇联合抗坏血酸协同抑制褐变酶的作用机理。结果表明,0.02%氧化白藜芦醇、0.15%抗坏血酸、0.02%氧化白藜芦醇+0.15%抗坏血酸均能减缓余甘子的酶促褐变,对3种褐变酶即多酚氧化酶(PPO)、过氧化物酶(POD)、苯丙氨酸解氨酶(PAL)活性均有较好的抑制作用;0.02%氧化白藜芦醇+0.15%抗坏血酸联合处理对余甘子的酶促褐变及对PPO、POD、PAL的抑制活性强于单独使用。酶抑制动力学结果表明,氧化白藜芦醇对PPO的IC50为(3.300±0.010) μmol/L,抑制机理为可逆的混合型抑制,而氧化白藜芦醇+抗坏血酸(1∶7)的IC50为(1.600±0.020) μmol/L,抑制机理为可逆的竞争性抑制,协同使用导致抑制方式也发生改变。氧化白藜芦醇对PPO的抑制常数KI为0.904 μmol/L,对PPO-底物形成的复合物的抑制常数KIS为14.285 μmol/L,而氧化白藜芦醇+抗坏血酸(1∶7)对PPO的抑制常数KI为0.840 μmol/L,联合处理对PPO的抑制性加强。     

莲藕贮期褐变机理与防褐变技术研究

莲藕贮期褐变是影响质量的关键。本文研究了莲藕贮期内多酚氧化酶和褐变度的关系,探讨了温度、氧气等环境条件对多酚氧化酶的活性和莲藕褐变的影响作用,通过褐变抑制效果试验,寻找出了几种较好的处理方法和贮藏环境。实验表明,多酚氧化酶是引起莲藕褐变的主要因素,莲藕贮期内多酚氧化酶的活性与褐变度成正相关,真空包装及低温贮藏能有效地抑制莲藕褐变,具有良好的保鲜作用。     

环糊精及其衍生物对砂梨多酚氧化酶活性的影响研究

<正>本文研究了不同环糊精对砂梨多酚氧化酶活性的影响,发现不同环糊精都具有一定的抑制砂梨多酚氧化酶活性效果,羟丙基-γ-环糊精、甲基-β-环糊精对砂梨多酚氧化酶的抑制效果较为明显;对于同一种环糊精来说,随着其浓度的升高,抑制砂梨多酚氧化酶的活性增强。这为以后开发新型褐变抑制剂奠定了基础。砂梨在加工过程中易发生褐变,使梨的色泽、品质都发生改变。砂梨褐变主要是由其中的多酚氧化酶(Polyphenol     

莲藕采后生理及保鲜技术研究进展

指出莲藕在贮藏过程中发生褐变和衰老的主要原因是组织内部的多酚氧化酶催化氧化酚类物质产生黑色素。概述了近年来莲藕多酚氧化酶的催化反应动力学特性;pH值、温度、金属离子对莲藕多酚氧化酶活性的影响;莲藕采后多酚氧化酶活性与组织褐变、呼吸及衰老之间的关系;莲藕褐变和衰老的抑制及其保鲜技术等方面的研究进展。     

莲藕采后生理及保鲜技术研究进展

指出莲藕在贮藏过程中发生褐变和衰老的主要原因是组织内部的多酚氧化酶催化氧化酚类物质产生黑色素。概述了近年来莲藕多酚氧化酶的催化反应动力学特性；pH值、温度、金属离子对莲藕多酚氧化酶活性的影响；莲藕采后多酚氧化酶活性与组织褐变、呼吸及衰老之间的关系；莲藕褐变和衰老的抑制及其保鲜技术等方面的研究进展。     

复合护色液对鲜切莲藕护色效果研究

采用不同的护色剂组合对鲜切莲藕进行护色处理,并在8℃条件下进行贮藏试验。结果表明:(1)对鲜切莲藕褐变抑制的最佳因子组合为EDTA浓度为0.25%、Vc浓度为0.1%、草酸浓度为0.25%、半胱氨酸浓度为0.7%、处理时间为8min。经过该护色处理的鲜切莲藕,在整个试验期间内,色白,无褐变现象产生;(2)鲜切莲藕在贮藏期间褐变度和多酚氧化酶活性具有很强的相关关系,多酚氧化酶活性上升时,莲藕的褐变度增加速度较快,其活性下降时,褐变度增加有所减缓。     

涩柿贮藏过程中PPO及褐变控制

实验以新鲜的柿子为主要原料,采用测定吸光值的变化,研究了柿果中多酚氧化酶(PPO)活性的最适条件和抑制剂、烫漂温度和时间对柿果中多酚氧化酶(PPO)活性及褐变的影响。结果表明:柿子中的多酚氧化酶的最适温度是19℃,最适pH为6．5,最适底物浓度为12mmol/L。用0．1%亚硫酸钠+0．3%植酸和100℃+120s处理能有效的抑制柿果中PPO的活性,褐变速度明显减慢。     

马铃薯贮藏期间褐变强度与多酚氧化酶活性变化的研究

测定了十个马铃薯品种在六个月窖藏期间褐变强度和多酚氧化酶活性的变化.结果表明:马铃薯的褐变强度和多酚氧化酶活性在品种间的差异达极显著水平,除渭薯8号外,其它品种在贮藏期间的变化也达到极显著水平.在贮藏期间,不同品种的褐变强度和多酚氧化酶活性的变化趋势不同,但同一品种褐变强度与多酚氧化酶活性之间存在中度的正相关,相关系数r为0.736.     

氯化钙处理对速冻蓝莓冻藏期品质的影响

研究不同质量分数氯化钙处理对速冻蓝莓果实于－18 ℃冻藏时品质变化的影响。结果表明：随着冻藏时间延长,速冻蓝莓果实的质量、硬度、可溶性固形物（TSS）、可滴定酸、VC、花色苷和总酚含量均呈下降趋势。浸钙处理可延缓速冻蓝莓果实质量、硬度、TSS、可滴定酸、VC、花色苷和总酚含量的下降,保持果实原有品质。在整个冻藏期多酚氧化酶（PPO）和过氧化物酶（POD）活性不断下降,氯化钙处理组冻藏后期PPO活性明显被抑制,但对POD活性没有显著效果。综合分析各指标,经1.5%氯化钙溶液处理的速冻蓝莓其冻藏期品质最好。     

冻结速率对苹果片多酚氧化酶和过氧化物酶活性影响的研究

低温断裂是果蔬超速冻过程中常见的问题。本文初步研究了速冻过程对苹果片生化特性的影响,发现不同的冻结速率会引起可溶性过氧化物酶(POD)的活性较大幅度变化,而可溶性多酚氧化酶(PPO)活性变化较小。通过对实验结果的初步分析,指出速冻过程与冻藏食品的保存质量有密切关系     

Spraying of 4-hexylresorcinol based formulations to prevent enzymatic browning in Norway lobsters (Nephrops norvegicus) during chilled storage

A comparison was made of the effects on melanosis development in Norway lobsters (Nephrops norvegicus) of treatment by dusting with a commercial sulphite-based product and of spraying with a formulation containing 4-hexylresorcinol (0.1% and 0.05%), in combination with organic acids and chelating agents. The following tests were performed during chilled storage: polyphenol oxidase (PPO) activity, melanosis score, colour parameters, tyrosine and tyramine content, as the main substrate of PPO. Differences among treatments were evaluated by means of statistical analyses (ANOVA, principal components and discriminant analyses). All formulations diminished PPO activity during storage successfully. The melanosis score was higher in sulphite-treated Norway lobsters, and a formulation with 0.05% 4-hexylresorcinol was enough to prevent the appearance of melanosis for 12 days. The tyrosine content decreased during storage, but the tyramine content was insignificant. Formulations with 4-hexylresorcinol improved the appearance of Norway lobsters, in comparison with the commercial sulphite-based product.     

Efficacy of phytic acid as an inhibitor of enzymatic and non-enzymatic browning in apple juice

Browning decreases the commercial value of apple juice, and therefore colour preservation during processing and storage is the main objective of manufacturers. In this study, the efficacy of phytic acid as a browning inhibitor for use on apple juice was investigated. Browning of apple juice treated with phytic acid was monitored during processing and storage. 0.1 mM Phytic acid inhibited the polyphenol oxidase (PPO) from the apple juice by 99.2%. Consequently, the apple juice treated with phytic acid had significantly lower browning formation during processing and after 6 months of storage at room temperature compared with the control (p<0.05). Results indicate that this is a promising way to inhibit browning in apple juice.     

护色处理对冻藏香蕉片多酚氧化酶活性的影响

通过设计单一护色剂、不同浓度L-半胱氨酸、不同热处理时间及多因子护色处理四个实验研究其对冻藏香蕉片多酚氧化酶(PPO)活性的影响,结果表明,5种护色剂均能有效地抑制冻藏香蕉片PPO活性,但L-半胱氨酸对其抑制效果更佳;随着护色液中Cys浓度的增加,残余PPO活力呈下降趋势,表现为CK>0.05%Cys>0.1%Cys>0.2%Cys;热处理能有效地抑制冻藏香蕉片PPO活性,PPO活性随着热处理时间的增加而降低,但热处理却大大降低了冻藏香蕉片的品质;0.1%L-半胱氨酸、0.05%异抗坏血酸、0.1%蔗糖和0.1%氯化钙构成的护色剂组合能有效地抑制PPO活性,并起到良好的保质增脆效果。     

Effect of chitosan coating on maintenance of aril quality,microbial population and PPO activity of pomegranate (Punica granatum L. cv. Tarom) at cold storage temperature

BACKGROUND: Chitosan edible coating was used in an attempt to extend the storage life of pomegranate arils during 12 days at 4 °C. Prior to storage, treated arils were dipped in 0.25, 0.5 and 1% (w/v) chitosan aqueous solutions and 1% (v/v) acetic acid for 1 min, while control arils were dipped in distilled water with 1% (v/v) acetic acid. RESULTS: Chitosan coating inhibited bacterial and fungal growth on the surface of arils. The water content of arils coated with 0.5 and 1% chitosan was maintained during 12 days of storage. Chitosan reduced the increase in total soluble solids (TSS) and titratable acidity (TA) of arils during storage. The lowest TSS and TA were detected in arils coated with 0.5 and 1% chitosan, which maintained the highest TSS/TA ratio after 12 days of storage. In contrast, application of chitosan delayed the decrease in total phenolics, total anthocyanins and antioxidant capacity during storage. The results also showed that chitosan coating suppressed the monophenolase activity of polyphenol oxidase (PPO) with pyrogallol substrate and the diphenolase activity of PPO with dopamine hydrochloride substrate, but the diphenolase activity of PPO with pyrocatechol substrate increased during storage. CONCLUSION: The results suggest that chitosan coating has the potential to extend the storage life of pomegranate arils by reducing the microbial population on their surface. Copyright © 2012 Society of Chemical Industry     

鲜切马铃薯复合褐变抑制剂组合的筛选

利用二次旋转组合设计筛选能取代亚硫酸盐的鲜切马铃薯复合褐变抑制剂组合,分析其对鲜切马铃薯贮藏期间PPO活性和褐变度的影响。结果表明,马铃薯切片最佳复合防褐剂配方组合为0.005%曲酸＋0.045%异抗坏血酸钠＋0.045%半胱氨酸(L-Cys)＋0.01% CaCl2＋0.2992% EDTA-2Na。该褐变抑制剂能够显著抑制鲜切马铃薯贮藏期间PPO活性,整个贮藏期间推迟PPO活性高峰时间6d以上;对鲜切马铃薯组织的褐变有明显延缓作用,处理组感官效果明显优于亚硝酸盐处理组和蒸馏水对照组,可以替代亚硫酸盐作为防褐剂用于鲜切马铃薯的生产和流通环节。     

荔枝与荔枝酒褐变控制

以荔枝及荔枝酒为试料,研究荔枝多酚氧化酶(PPO)的酶学特性及荔枝酒发酵过程中的褐变机理及控制措施。结果表明：荔枝PPO存在同功酶,荔枝PPO最适底物为没食子酸;以没食子酸为底物,荔枝PPO最适反应pH值为8.0,最适反应温度50℃,荔枝PPO的动力学参数为：米氏参数(Km)为26.033mmol/L,最大反应速度(Vmax)为34.816g/(L·min);荔枝PPO对酸碱、对热稳定性较差;荔枝酒发酵过程中褐变的主要原因是其PPO引起的酶促褐变。因此,低温贮藏和高温热处理可有效抑制荔枝及荔枝酒在贮藏和加工中酶促褐变反应。     

过氧化氢处理对采后‘黄冠’梨果皮褐变及果实品质的影响

‘黄冠’梨低温贮藏过程中果皮褐变严重,为解决果皮褐变问题,开发控制果皮褐变的新技术,本研究分别采用3、20 mmol/L的过氧化氢(H2O2)水溶液浸泡处理‘黄冠’梨,探讨H2O2预处理对梨果皮细胞抗氧化防护体系、低温贮藏期间果皮褐变、果实品质的影响。结果表明,与对照组(未经H2O2处理)相比,20 mmol/L的H2O2显著降低了‘黄冠’梨果皮褐变率及褐变指数,抑制了多酚氧化酶(polyphenol oxidase,PPO)的活性和果皮酚类物质尤其是单体绿原酸、儿茶素和熊果苷的消耗,不同程度地提高了过氧化物酶、超氧化物歧化酶、过氧化氢酶、抗坏血酸过氧化物酶活力以及果皮自由基清除能力,降低了丙二醛积累,有效地增强了果皮抗氧化防护能力,并且能够使果实在低温贮藏后的货架期间保持较高的硬度、可滴定酸含量、糖酸比及总可溶性固形物含量,食用感官综合品质在低温贮藏和货架期间均优于对照组。研究表明,采后‘黄冠’梨经H2O2预处理,可以诱导性地增强果皮抗氧化酶活性,抑制PPO酶活性和酚类物质消耗而减少低温贮藏过程中果皮褐变的发生。     

Effect of whey protein concentrate on phenolic profile and browning of fresh-cut lettuce (Lactuca Sativa)

The in vitro kinetics of lettuce PPO with respect to dissolved oxygen using catechin, chlorogenic acid, caffeic acid and gallic acid has been examined. In-vitro lettuce polyphenol oxidase (PPO) activity was determined by measuring the consumption of oxygen during the oxidation reaction. The effect of whey protein concentrate (WPC) was tested on the inhibition of lettuce PPO comparing with ascorbic acid (AA) and cysteine. A competitive model that considered inhibitors was the most appropriate model to explain reaction kinetics. Browning of lettuce was also monitored during storage for 24 h. Addition of WPC prevented loss of lightness in lettuce. Loss of identified phenolic compounds in lettuce was measured during the enzymatic browning process by high-performance liquid chromatography. Degradation of identified phenolic compounds followed first order kinetics during storage. Combination of WPC with cysteine was proposed for the protection of phenolics compounds against PPO-catalysed oxidation.