金针菇中多酚氧化酶活性测定及其护色研究

研究了温度、pH值对金针菇中多酚氧化酶(PPO)活性的影响,设计了不同的护色方案,以确定金针菇的护色条件。结果表明:金针菇中PPO活性的最适温度30℃,最适pH6.4。金针菇的最佳护色条件为:在0.3%柠檬酸和0.07%抗坏血酸的混合溶液中漂烫3 min,经该条件处理的金针菇在整个试验期间内无褐变现象产生。     

山药中多酚氧化酶的活性测定及其护色研究

研究了山药中多酚氧化酶(PPO)的最适pH值、最适温度,设计了不同护色方案,以确立山药的最佳护色条件。采用分光光度法研究pH值、温度对酶活性的影响;比较不同护色液对酶活力的影响;将山药经不同护色条件护色后,低温烘干,粉碎过筛得山药粉,用分光光度法测定其甲醇-水溶液(1∶1)的吸光度。结果表明,以邻苯二酚为底物,山药PPO的最适pH值为5.6,最适温度为35℃,山药的最佳护色条件为:以0.25%的Na2SO3为抗氧化剂,并配以0.25%的柠檬酸和1.5%的NaCl为护色液。     

葛根中多酚氧化酶性质及葛根护色的研究

研究葛根多酚氧化酶(PPO)的性质,以及不同护色方案的护色效果,确定最佳护色方案。结果表明,以邻苯二酚为底物,葛根PPO的最适pH7.0,最适温度40℃,100℃热处理40s可钝化PPO的活性;抗坏血酸、抗坏血酸钠和亚硫酸钠为多酚氧化酶强烈抑制剂;但仅有亚硫酸钠能有效抑制葛根褐变的发生;结合颜色、护色效果、损失以及残留,确定0.2%的亚硫酸钠溶液为护色剂采用喷涂的方式进行护色。     

基于长货架期的菊芋泡菜多酚氧化酶特性及护色效果研究

菊芋在加工过程中容易发生酶褐变,影响菊芋的质量。本实验研究了温度、p H对菊芋中PPO(多酚氧化酶)活性的影响,以及不同泡制盐量、包装材料以及抑制剂对褐变的影响。结果表明,菊芋中多酚氧化酶活性最适温度35~40℃,最适p H为7;当温度≥90℃时,菊芋多酚氧化酶几乎失活。用质量分数为0.1%L-cys、0.15%柠檬酸、0.2%Na SO3、0.1%VC、0.15%EDTA配成的复合护色液作为护色剂,采用7%的盐水泡制以及高阻隔复合透明包装材料EVOH为包装材料,在35℃温度下1个月的贮藏期内菊芋泡菜的酶相对活性显著降低(p0.01),保持了菊芋泡菜的色泽与脆度(p0.05)。     

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。     

杏子多酚氧化酶动力学特性研究

杏子多酚氧化酶是造成杏子果肉褐变的主要因素,研究其动力学特性对杏子深加工中防止果肉褐变有着重要理论意义。采用分光光度计法研究pH、温度、抑制剂和高压二氧化碳处理对杏子多酚氧化酶性质的影响,结果表明:杏子(品种为色买提)的最适底物为邻苯二酚,最适pH5.0,最适温度40℃。多酚氧化酶催化的酶促褐变反应动力学符合米氏方程,该酶促反应的动力学常数Km为0.014mol/L,最大速率为287U/min。控制pH3.0以下,或者采用L-抗坏血酸4mmol/L与柠檬酸8mmol/L复配,或采用高压二氧化碳40MPa处理30min都可以将相对酶活性控制在20%以下;温度90℃处理6min以上或100℃处理4min可以完全抑制酶活性。在实际应用中,可根据产品特性不同选用适宜的处理方法或组合抑制褐变。     

甘薯中多酚氧化酶活性的测定及褐变控制

甘薯加工过程中极易产生酶促褐变,本文采用分光光度法,研究了甘薯组织中不同部位多酚氧化酶（PPO）的活性,以及PPO的最适pH值、厚适温度热稳定性等特性。确定其最适pH值范围为3.0-3.5和6.0-7.0,最适温度为15℃。在此基础上,考察了抗坏血酸、柠檬酸、亚硫酸钠对PPO的褐变抑制效果。     

苹果汁的前褐变及苹果PPO的部分特性研究

苹果汁贮藏过程中色泽加深、色值和透光率不稳定是苹果汁生产中普遍存在的问题,文中尝试采用苹果自身的PPO进行前褐变反应,以减少果汁中的酚类化合物,防止后期褐变。研究表明,果汁经30℃前褐变反应4 0min后,总酚质量含量可下降约30 % ,可溶性固形物质量分数提高了2 8% ,常温下贮藏3个月后,色值和透光率基本保持不变,明显地改善了苹果汁的质量指标。同时,文中还探讨了PPO的最适pH值、最适反应温度及其pH稳定性、热稳定性等性质     

抑制山药中多酚氧化酶活性的研究

采用分光光度法研究了pH值、温度以及护色液对山药中多酚氧化酶(PPO)活性的影响。结果表明,抑制山药PPO活性的pH值应控制在2.4或7.2,温度应控制在5℃左右;质量分数0.03%EDTA、0.4%抗坏血酸、0.5%柠檬酸配比的混合护色液可以有效抑制山药中多酚氧化酶(PPO)的活性。     

冬瓜多酚氧化酶的特性及抑制剂研究

以邻苯二酚为底物,采用'分光光度法在420 nm 处测定冬瓜多酚氧化酶(PPO)的活性,研究了不同温度和 pH 值对其活性的影响,并建立了酶促褐变反应动力学方程,探讨了抗坏血酸、亚硫酸氢钠、柠檬酸和 EDTA-2Na 4 种抑制剂对冬瓜酶促褐变的抑制效果.结果表明,冬瓜多酚氧化酶的最适温度为20℃,最适pH值为6.0;冬瓜多酚氧化酶的米氏方程符合单底物酶促反应动力学,相应的动力学参数为 Kin=0.0118 mol/L,Vm=0.0586 U/min;化学抑制剂抗坏血酸、亚硫酸氢钠、柠檬酸和EDTA-2Na 对多酚氧化酶都有抑制作用,其活性分别为对照的25%、32%、62%和57%.     

Time Course of PPO-Related Browning of Yams

The time course of polyphenol oxidase (PPO) activity and tissue browning was investigated in five Dioscorea species. In three of the yam species, 86% of the browning was associated with the peak of PPO activity. In D dumentorum and D rotundata, only 9 and 40%, respectively, of browning was PPO-related, while most of the tissue browning occurred after PPO activity had declined to the control value. The browning incidence was temperature-dependent such that the optimal temperature for PPO activity (30°C) also coincided with that of maximal browning in all the yam species expect in D dumentorum. Classical inhibitors of PPO prevented the browning in tissues where the enzymic mechanism predominated while failing to reduce browning in D dumentorum and D rotundata where most of tissue browning was not enzyme associated. The results put the incidence of yam discolouration in proper perspective in terms of the timescale of PPO and non-PPO-catalysed discolouration.     

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。     

Effect of basil leaves and wheat bran water extracts on enzymatic browning of shredded storage iceberg lettuce

The impact of functional solutions (water infusions of radish sprouts, wheat bran (WBE), basil leaves (BLE) and lentil protein hydrolysate) on enzymatic browning of shredded iceberg lettuce was studied. BLE and WBE, limiting enzymatic browning in the highest degree, were tested during cold storage. The best inhibitors of PPO activity in lettuce stored for 8 days were 10% WBE (a decrease by 97%). POD activity was substantially decreased by ascorbic acid (by 75%) and 1% BLE (by 83%). POD and PPO inhibition was reflected in a decrease in enzymatic browning, that is 91% and 88% reduction was found in 8-day stored lettuce treated with 1% BLE and 1% WBE, respectively. In the case of POD, mixed inhibition was recorded for BLE and WBE, while these solutions acted as competitive inhibitors of PPO activity. The enzymatic browning of shredded iceberg lettuce during cold storage may be effectively suppressed by natural extracts.     

鲜切苹果抗褐变研究

研究了不同褐变抑制剂对鲜切苹果PPO(多酚氧化酶)活性、褐变度、感官品质的影响。试验结果表明单一的1.5%L-半胱氨酸、1.0%D-异VC钠、1.0?TA-2Na处理均能较好地抑制鲜切苹果褐变。采用0.10%D-异VC钠 0.12?TA-2Na 0.13%L-半胱氨酸,浸泡2min的复合处理,可使鲜切苹果的PPO活性、褐变度、感官品质在14d内保持较优水平。     

Polyphenoloxidase activity and total phenolic content as related to browning of minimally processed ‘Jonagored’ apple

Phenolic content, polyphenoloxidase (PPO) activity and browning have been reported by different authors to vary in different ways, depending on cultivar, picking maturity, storage conditions, etc. Numerous authors have attempted to correlate browning results with the phenolic content and/or enzymatic activity of apples, but data published in the literature are divergent as to which of the two factors, ie the enzyme or the substrate, plays the decisive role in the overall phenomenon of enzymatic browning. The aim of this work was to follow the PPO activity and phenolic content of minimally processed apple (cv ‘Jonagored’) during cold storage and to establish a potential relationship with enzymatic browning. Increasing storage time of minimally processed apple seemed to result in an increase in PPO activity. No changes (P > 0.05) in total phenolic content were observed during storage. Colour degradation of apple cubes, as indicated by changes in colour parameters, was found to be highly correlated with PPO activity. Browning of ‘Jonagored’ apple cubes during storage was found to be moderately correlated with PPO activity. No correlation was found between the browning index and the total phenolic content. © 2001 Society of Chemical Industry     

鲜切甘薯高效化学褐变抑制剂组合的筛选

试验筛选了鲜切甘薯能取代亚硫酸盐的化学褐变抑剂组合,分析了其对甘薯贮藏期间PPO活性和褐变度的影响。研究结果表明0.2%L-Cys+0.30%CA+0.15%EDTA-2Na+0.30NaCl组合抑制褐变效果最好,各因素对鲜切甘薯抑制褐变效果的主次顺序为A>B>C>D。该褐变抑制剂组合能够显著抑制鲜切甘薯贮藏期间PPO活性,对鲜切甘薯组织的褐变有明显延缓作用。     

鲜切苹果品质保持研究

文研究了不同褐变抑制剂对鲜切苹果PPO活性、褐变度、感官品质的影响。试验结果表明:单一的1.5%L-半胱氨酸、1.0%D-异VC钠、1.0%谷胱甘肽处理均能较好地抑制鲜切苹果褐变。采用0.10%D-异VC钠+0.12%谷胱甘肽+0.13%L-半胱氨酸,浸泡2min的复合处理,可使鲜切苹果的PPO活性、褐变度、感官品质在14d内保持较优水平。     

速冻建莲加工与贮藏过程中多酚氧化酶活性抑制的研究

为提高速冻建莲的品质,本文研究了不同的抑制剂组合对建莲多酚氧化酶(PPO)活性的抑制效果,并观察了速冻建莲贮藏期间PP0活性的变化。结果表明:0.025％EDTA-Na_2+0.1％抗坏血酸+0.1％柠檬酸能最大限度地抑制建莲的多酚氧化褐变,以此应用于速冻建莲的生产,能有效抑制冻藏过程中建莲的多酚氧化酶活性,褐变程度明显降低。     

香辛料调味品褐变机理的分析研究

研究了香辛料调味品在贮藏期间褐变度(DB)及有关成分的变化,分析确定了引起褐变的原因及引起酶促褐变的主要底物,并探讨了香辛料调味品中多酚氧化酶(PPO)的部分酶学特性。实验结果表明,香辛料调味品在贮藏过程中PPO活性和褐变度的变化呈显著负相关性(r=-0.9535),即褐变主要是由酚类发生的酶促氧化所致,香辛料调味品PPO的最适反应pH为6.8,PPO与不同底物结合力的大小依次为焦性没食子酸>酪氨酸>儿茶酚>苯酚>愈创木酚;化学抑制剂CA(柠檬酸)、Na2SO3、Vc、Zn(Ac)2、EDTA-2Na、L-cys和植酸对PPO活性均有不同的抑制作用,尤以Na2SO3、L-cys、CA的抑制作用明显。     

Relationship between enzymatic browning and internal disorders in controlled-atmosphere stored pears

The relationship of browning potential and polyphenoloxidase activity (PPO, EC 1.14.18.1) to the internal disorders brown heart (BH) and core breakdown (CB) was studied in pears stored in controlled atmosphere (CA) and ultra low oxygen atmosphere (ULO). Brown discoloration of the core and flesh areas depended on harvest date—the earlier the picking date, the higher the browning. In contrast to browning potential, which declined steadily during storage, PPO activity in flesh increased. No difference was found between the two storage atmospheres (CA and ULO). ULO-stored fruits showed the higher incidence in internal disorders. PPO activity was clearly inhibited in BH-damaged fruits but transiently increased in CB-damaged fruits. These results indicated that enzymatic browning and PPO enzyme are not directly correlated with the BH and CB disorders and not directly involved in their formation. © 1998 Society of Chemical Industry