苹果酒中多酚及其褐变

多酚物质在酒的风味和颜色中起着十分重要的作用,由于其导致酒的褐变和混浊沉淀而被描述成“引起不稳定的因素”。主要对苹果酒中存在的多酚和影响多酚存在的因素进行讨论,同时对其在加工贮藏中引起褐变的机制和对褐变的抑制进行了论述。     

苹果梨和鸭梨酶促褐变机理的研究

以苹果梨和鸭梨为研究对象。在一定的贮藏期内,通过定期测定梨中ｐＨ值,可溶性固形物,褐变度,总酚和多酚氧化酶活性及其与不同底物的结合能力,分析梨的酶褐变机是,苹果梨和鸭梨在贮藏期间,ｐＨ值和可溶性固形物的含量总体呈下降趋势;多酚类物质的含量和多酚氧化酶的活性呈上升趋势,与贮藏期间的褐变度的升高是一致的,多酚氧化酶与底物结合能力的强弱依次为：没食子酸〉儿茶酚〉绿原酸〉咖啡酸;抗坏血酸和还原糖含量对水果     

苹果酒褐变抑制的研究

目的:研究不同处理方法对苹果酒褐变的抑制作用.方法:分别采用不同的热烫处理时间,单因素抗褐变剂柠檬酸、异抗坏血酸钠、焦亚硫酸以及抗褐变剂复合处理对苹果汁420nm处吸光值的影响.观察不同处理对苹果酒褐变的抑制效果.结果:热烫处理5min、柠檬酸30mg/mL、异抗坏血酸钠2mg/mL、焦亚硫酸钠0.2mg/mL以及不同...     

香蕉酶促褐变的研究

本文以邻苯二酚为底物采用分光光度计测定氧化产物的方法对香蕉果肉多酚氧化酶(PPO)的催化特性、最适温度、最适pH值、热稳定性等性质进行了研究。结果表明,香蕉PPO的最适温度为25℃,最适pH为5.0,75℃水浴处理5min酶基本完全失活,100℃水浴处理20s可钝化PPO的活性,并且香蕉PPO具有同功酶。     

盐渍茄子酱菜酶促褐变的酶学特性研究

本文对盐渍茄子酱菜中褐变酶的酶学特性进行了详细研究。结果表明：多酚氧化酶是导致盐渍茄子酱菜褐变的主要原因。多酚氧化酶的最适pH为6．8，当体系pH≤5．0或者pH≥7.4时，能有效降低PPO活性。在30～50℃下PPO具有较高活性，其最适温度为30℃左右。PPO的热稳定性较差，沸水加热lmin时，酶活已丧失87．57％。柠檬酸、抗坏血酸、亚硫酸钠、亚硫酸氢钠、EDTA-2Na等对PPO活性有抑制作用，其中抗坏血酸抑制作用最强。     

枇杷果实酶促褐变控制研究

枇杷果实在贮藏及加工过程中极易产生酶促褐变。本文采用分光光度法,研究了几种因素对枇杷果实多酚氧化酶活性的影响。结果表明:多酚氧化酶的最适 pH 为 6.3,抗坏血酸、L-半胱氨酸、柠檬酸、草酸、柠檬酸-抗坏血酸混合物可明显抑制该酶活性。     

果蔬酶促褐变机理的研究进展

酶促褐变对果蔬在加工保鲜过程中的品质有重大影响,有关酶促褐变机理的相关研究也越来越多.本文整理归纳了国内外围绕褐变机理进行的多酚氧化酶和酚类底物的相关研究,包括对多酚氧化酶种类、催化位点、提取、分离、纯化、活性测定方法的介绍;酚类化合物种类、含量变化及其变化原因的阐述;酚类酶促氧化反应、醌的生成途径、次级代谢过程、氧化...     

库尔勒香梨贮藏期间酶促褐变机理的研究

以贮藏后期的库尔勒香梨为研究对象，在一定的贮藏期内，定期对香梨中多酚氧化酶活性、酚类物质含量、过氧化物酶活性、丙二醛含量作测定。结果表明，香梨在贮藏期间先进行酚类物质合成，后发生降解，多酚氧化酶活性呈先升后降的趋势，丙二醛含量总体上升。     

果蔬酶促褐变机理及其抑制方法研究进展

酶促褐变是果蔬深加工过程中存在的一个普遍且很严重的问题.本文介绍了酶促褐变的基本原理、影响因素,并从物理、化学、生物技术等方面介绍了一些酶促褐变的抑制方法.     

海南黄帝椒酶促褐变控制的研究

本文采用丙酮法提取了海南黄帝椒中的多酚氧化酶（PPO）,并对其酶学特性进行了研究。海南黄帝椒PPO的米氏常数K m为117.38mmol/L,最大反应速率V max为416.67U/min,最适温度为40℃,最适pH为6.0。不同抑制剂对PPO活力的影响表明,较低浓度的柠檬酸、L-抗坏血酸、半胱氨酸盐酸盐对黄帝椒PPO活力具有一定的的抑制作用,而EDTA抑制效果较差;在单因素实验的基础上,通过正交实验设计对黄帝椒酶促褐变的抑制剂配方进行了优化,结果表明当添加L-抗坏血酸0.35%、半胱氨酸盐酸盐0.02%和柠檬酸0.2%时,黄帝椒的褐变度最小。此研究结果为海南黄帝椒产品的深度开发提供了基础。      

Enzymatic Browning of Model Solutions and Apple Phenolic Extracts by Apple Polyphenoloxidase

Model solutions containing chlorogenic acid (CG) and (-)-epicatechin (EP), and phenolics from nine apple cv., were oxidized with apple polyphenoloxidase (PPO). Browning was determined by absorbance at 380–700 nm, and transformed into CIE L*, a* and b*. Multilinear correlations were established between initial and degraded amounts of each phenolic. In model solutions of CG and EP, color values and A₄₀₀ correlated strongly with initial and oxidized CG and EP. Both phenolics contributed to decrease in L* and increase in A₄₀₀. Increase ii CG increased a*, but EP had little effect. The imnact of increased EP on b* was two to three times higher than for CG_: In each phenol class (hydroxycinnamic (HD), flavan-3-ol (FA), flavonol (FO) and dihydrochalcone (DC) derivatives), degraded amounts were increased or decreased by increasing amounts of other classes. Besides major phenolics, HD (mainly CG) and FA (mainly EP and procyanidin B2), FO and DC, appeared to affect color development.     

Polyphenoloxidase Activity, Polyphenols Concentration and Browning Intensity during Soursop (Annona muricata, L.) Maturation

Values for polyphenoloxidase (PPO), total phenols and ascorbic acid, browning intensity and pH in soursops (Annona muricata, L.) decreased during maturation. Optimum pH was 7.5 (fully developed immature, mature unripe and ripe fruits) or 7.0 (fully ripe fruits). High correlation was found between PPO activity and phenolic compounds. The enzymic browning of soursops occurred during maturation. The least browning intensity was in fully ripe fruits.     

苹果酒中模拟体系下非酶氧化与酶促氧化对聚合度影响的研究

以苹果酒中单酚含量较多的4种酚（儿茶素、表儿茶素、绿原酸和咖啡酸）为研究对象。在模拟苹果酒pH体系环境下,对其在非酶氧化和酶促氧化下聚合度的变化进行了研究。结果表明,在非酶氧化过程中,以儿茶素和表儿茶素的聚合反应为主,而在酶促氧化过程中。则是以绿原酸和咖啡酸的聚合反应为主。     

紫甘薯多酚氧化酶性质研究

采用含有30 mmol/L Vc的0.01 mol/L磷酸盐缓冲液从紫甘薯中提取多酚氧化酶(PPO),用分光光度法对紫甘薯中多酚氧化酶的酶学特性进行了系统的研究,其中包括PPO的活力测定、热稳定性、pH稳定性以及pH、温度、抑制剂对PPO活力的影响。实验结果表明,多酚氧化酶催化反应的最佳条件为:温度25℃,pH 7.0,NaHSO3和Vc对酶活力有很强的抑制作用。     

混浊梨汁加工中PPO热失活条件的研究

研究了热处理梨汁（加或不加防褐变剂）,梨浆使其中的PPO完全及部分失活所需要的温度和时间结果为：在90℃处理果汁10s可使其中的PPO完全失活,而对于果浆则需要90℃处理15s以上.加了防褐变剂的果汁经90℃处理10s可使其中的PPO完全失活.此外,经80℃处理30s以上虽不能使其中的PPO完全失活,但添加的防褐变剂及果汁自身的pH可抑制残余的PPO,从而防止酶促褐变的发生.70℃处理梨汁40s不能防止其中的酶促褐变.     

浑浊苹果汁加工中苹果PPO热失活条件的研究

研究了热处理苹果汁(加或不加防褐变剂)、苹果浆使其中的PPO完全及部分失活所需要的温度和时间。结果为:在90℃处理苹果汁15s可使其中的PPO完全失活,而对于苹果浆则需要90℃处理20s以上。加了防褐变剂的苹果汁经90℃处理10s可使其中的PPO完全失活;此外,经80℃处理30s以上虽不能使其中的PPO完全失活,但添加的防褐变剂及果汁自身的pH值可抑制残余的PPO从而防止酶促褐变的发生。70℃处理苹果汁40s不能防止其中的酶促褐变。     

Characterization of Polyphenoloxidase from Stanley Plums

Five plum cultivars were investigated for polyphenoloxidase. Stanley cultivar, which showed highest PPO activity, was selected for characterization of this enzyme. The activity of crude enzyme was 3.5 times greater in the flesh than in the skin of the fruit. The enzyme showed a K_m of 20 raM of catechol and V_max of 5.41 × 10^?1 O.D./ min at pH 6.0. Its pH and temperature optima were 6.0 and 20°C respectively. The enzyme lost activity below pH 4.5, but was stable even at 70°C. Among substrates, 4-methylcatechol was oxidized more rapidy, although catechol, dopamine, pyrogallol and caffeic acid were also good substrates. The enzyme was strongly inhibited by sodium metabisulfite (Na₂S₂O₅), L-cysteine and ascorbic acid.     

Temperature Sensitivity and Pressure Resistance of Mushroom Polyphenoloxidase

Measurements of residual enzyme activity and FTIR-spectroscopy revealed that mushroom polyphenoloxidase is a thermosensitive enzyme readily inactivated by temperatures exceeding 50°C. The enzyme is, however, very pressure stable. At room temperature no enzyme inactivation occurred at pressures up to 6 kbar. FTIR-spectroscopy revealed that a modification in enzyme conformation occurred below 9 kbar. Kinetic studies showed that pressure and temperature did not always act synergistically with respect to enzyme inactivation. FTIR-spectroscopy showed that pressure- or temperature-induced changes were considerably different. Both temperature and pressure-temperature inactivation were only slightly influenced by pH (in the pH-range 5.5–7.5).     

Browning Susceptibility and Changes in Composition During Storage of Carambola Slices

Browning and changes in the composition of sliced and whole carambola (Averrhoa carambola L.) fruit during storage were investigated. Susceptibility to browning after slicing, packaging and storage for 4 wk at 4.4°C varied considerably between four cultivars and five selections. There was no difference in browning susceptibility between fruit harvested at mature green or breaker stages of maturity. Freshly sliced carambola browned only slightly when exposed to air, but packaged slices that had been stored for 2 or more wk at 4.4°C browned rapidly (within 6 hr) when exposed to air. Whole fruit stored at 4.4°C for up to 6 wk, then sliced, showed much less susceptibility to browning. Ascorbic acid decreased and polyphenoloxidase activity increased in carambola slices during storage, but less in whole fruit. Treating slices with 1.0 or 2.5% citric acid + 0.25% ascorbic acid (in water) prior to packaging was very effective in limiting browning.