山药多酚氧化酶的特性和抑制研究

以邻苯二酚为底物,410nm处测定山药多酚氧化酶(PPO)的活性,研究了pH、温度、底物浓度、酶浓度、抑制剂和激活剂对山药多酚氧化酶活性的影响。结果表明,山药PPO最适反应pH为6.5,最适反应温度为40℃;柠檬酸、草酸、L-抗坏血酸、亚硫酸氢钠及半胱氨酸五种抑制剂对山药PPO均有抑制作用,其强弱依次为:L-半胱氨酸>抗坏血酸>草酸>柠檬酸>亚硫酸氢钠;硫酸铜和三氯化铁均有加速酶促褐变作用,强弱为CuSO_4>FeCl_3。     

L-半胱氨酸对香菇贮藏过程中内源性甲醛的转化及子实体品质的影响

目的 研究L-半胱氨酸处理对香菇贮藏过程中内源性甲醛的转化及子实体品质的影响。方法 香菇经L-半胱氨酸浸泡后,于4℃下密封贮藏,并监测其在贮藏期间甲醛含量、硫杂脯氨酸含量、褐变度、多酚氧化酶(Polyphenol Oxidase,PPO)活性、可溶性蛋白质含量、还原糖含量的变化。结果 L-半胱氨酸处理后,香菇子实体的甲醛含量显著低于对照组,并伴随着硫杂脯氨酸的生成,且硫杂脯氨酸的生成量与甲醛的消耗量达到显著正相关;贮藏期间,L-半胱氨酸处理组可显著抑制PPO酶活性的上升、减缓子实体的褐变速度;进一步的研究显示,L-半胱氨酸处理后香菇子实体的还原糖、可溶性蛋白质含量均高于对照组。结论 L-半胱氨酸可与香菇内源性甲醛生成硫杂脯氨酸,抑制子实体褐变和PPO活性,延缓还原糖和可溶性蛋白的降解,具备较好的甲醛清除和保鲜作用。     

番石榴果肉的酶促褐变及其抑制措施

采用分光光度法,对番石榴多酚氧化酶(PPO)的催化特性、最适波长、最适反应时间、最适温度、最适pH等性质进行了研究,同时实验了肉桂酸、抗坏血酸、苯甲酸、L-半胱氨酸四种添加剂对番石榴多酚氧化酶活性的影响,以寻求在果品的保鲜以及果肉初加工过程中抑制PPO活性的各控制手段与果品加工的有机结合方法,为防止褐变提供有效、合理的措施.实验结果表明:以邻苯二酚为反应底物时,番石榴多酚氧化酶催化氧化产物的最适波长为422nm,最佳反应时间为约20min左右,最适反应温度为25℃,最适pH为6.8,90℃水浴处理5min该酶基本已失活.四种添加剂对该酶均表现出不同的抑制效果,单一添加剂对番石榴多酚氧化酶酶促褐变抑制效果的强弱次序为:抗坏血酸>L-半胱氨酸>肉桂酸>苯甲酸,其中抗坏血酸的有效抑制浓度为0.1%,而两种浓度为0.05%的添加剂协同作用又以L-半胱氨酸 抗坏血酸的效果最好.     

双孢菇多酚氧化酶的特性和抑制研究

以邻苯二酚为底物,410nm处测定双孢菇多酚氧化酶(PPO)的活性,研究了pH值、温度、底物浓度、抑制剂和激活剂对PPO活性的影响。结果表明:PPO最适温度35℃,最适pH6.0;柠檬酸、抗坏血酸、L-半胱氨酸、亚硫酸氢钠4种抑制剂对PPO均有抑制作用,其抑制作用强弱依次为抗坏血酸L-半胱氨酸NaHSO3柠檬酸。CuSO4和FeCl3对PPO均有激活作用,三氯化铁的激活作用较明显。     

毛酸浆多酚氧化酶的酶学特性研究

以毛酸浆中多酚氧化酶(PPO)为研究对象,采用分光光度法在420nm处对其酶学特性进行研究。结果表明,毛酸浆PPO的底物邻苯二酚的最适质量分数为0.04%;最适pH为7.0;最适温度为35℃;100℃处理2min,可使酶完全失活;PPO催化的酶促褐变反应动力学符合米氏方程,动力学参数为Km=0.025mol/L,Vmax=125U/min;抗坏血酸、柠檬酸、L-半胱氨酸和亚硫酸钠对PPO酶活性的抑制作用均随浓度的增大而加强,抑制能力由强到弱依次为:抗坏血酸柠檬酸L-半胱氨酸EDTA亚硫酸氢钠。     

“黑美人”马铃薯多酚氧化酶的特性研究

以邻苯二酚为底物,在413nm处测定黑美人马铃薯多酚氧化酶(PPO)的活性,研究了温度、pH、底物浓度对其活性的影响,并建立了酶促褐变反应动力学方程,探讨了L-半胱氨酸、抗坏血酸、柠檬酸、EDTA及亚硫酸氢钠五种抑制剂对酶促褐变的抑制效果。结果表明:黑美人马铃薯多酚氧化酶最适反应pH为6.3;最适反应温度为35℃;酶促褐变反应动力学符合米氏方程描述的单底物酶促反应动力学,以邻苯二酚为底物,Km=0.0011mol/L,Vmax=142.23U/min.g;动力学方程为V=142.23[S]/(0.0011+[S]);五种抑制剂均对PPO酶促褐变具有抑制作用,其强弱依次为亚硫酸氢钠>L-半胱氨酸>抗坏血酸>EDTA>柠檬酸。     

砀山酥梨多酚氧化酶酶学特性及抑制效应的研究

多酚氧化酶是酶促褐变的关键酶,其特性与对其抑制效应研究一直是果蔬酶促褐变生理生化研究的重要内容,本试验以邻苯二酚为底物,采用分光光度法对砀山梨多酚氧化酶的酶学特性及不同抑制剂对多酚氧化酶活性的影响进行了研究。结果表明：砀山梨PPO的最适pH为4.5,最适温度为34℃;短时间高温能显著抑制PPO活性;PPO催化的酶促褐变反应动力学符合米氏方程,该酶促反应的最大速率为178.57U/min,酶反应速度为最大反应速度1/2时的底物浓度为0.125mol/L;柠檬酸、L-半胱氨酸、抗坏血酸,亚硫酸氢钠较柠檬酸能较好地抑制PPO活性,随着浓度的升高,抑制效应逐渐增强,但综合研究表明L-半胱氨酸抑制效应较好。     

抑制剂对杏多酚氧化酶抑制作用

使用冷丙酮分别从黄金杏和晚红杏中提取多酚氧化酶(PPO),以邻苯二酚为底物,利用分光光度计法研究几种抑制剂在不同浓度下对2种杏PPO的抑制作用及酶促反应动力学曲线。结果表明, 2种杏最适波长均为410nm。以邻苯二酚为底物, 2种杏多酚氧化酶的酶促褐变反应均符合米氏方程,晚红杏、黄金杏PPO的动力学参数米氏常数分别为0.042 mol/L和0.114 mol/L。V_(max)分别为100 U/min和167 U/min。抑制剂对2种杏多酚氧化酶的抑制作用存在一定差异。对黄金杏PPO抑制作用:抗坏血酸(40 mmol/L)柠檬酸(10 mmol/L)L-半胱氨酸(10mmol/L)亚硫酸氢钠(10 mmol/L)。对晚红杏PPO抑制作用:亚硫酸氢钠(10 mmol/L)柠檬酸(10 mmol/L)抗坏血酸(40 mmol/L)L-半胱氨酸(10 mmol/L), EDTA-2Na对2种杏PPO抑制作用均较差。     

杏鲍菇多酚氧化酶的酶学特性研究

以杏鲍菇中多酚氧化酶(PPO)为研究对象,采用分光光度法在420nm处对其酶学特性进行研究.结果表明,杏鲍菇PPO的最适底物为邻苯二酚;最适pH为6.0;最适温度为35℃;90℃处理2min,可使酶完全失活;PPO催化的酶促褐变反应动力学符合米氏方程,动力学参数为Km=0.0207mol/L,Vmax=41.32U/min;7种金属离子对PPO酶活性的影响效果各不相同,Al3+、Mn2+对PPO酶活性有一定的抑制作用,Mg2+、Zn2+、Ca2+和Cu2+对PPO酶活性的抑制作用不明显,Fe3+对PPO酶活性有激活作用;抗坏血酸、柠檬酸、L-半胱氨酸和亚硫酸钠对PPO酶活性的抑制作用均随浓度的增大而加强,抑制能力由强到弱依次为:抗坏血酸＞亚硫酸氢钠＞L-半胱氨酸＞柠檬酸.     

芒果多酚氧化酶的特性及抑制研究

以邻苯二酚为底物,采用分光光度法在420nm处测定芒果多酚氧化酶(PPO)的活性,研究了温度、pH值、底物浓度对其活性的影响,并建立了酶促褐变反应动力学方程,探讨了L-半胱氨酸、抗坏血酸、亚硫酸氢钠、柠檬酸和醋酸五种抑制剂对芒果酶促褐变的抑制效果。结果表明,芒果多酚氧化酶的最适温度为50℃,最适pH值为6.86;酶促褐变反应动力学符合米氏方程所描述的单底物酶促反应动力学,以邻苯二酚为底物的最大反应速度Vmax=192(U/min·g),Km=0.0173mol/L,相应的动力学方程为v=192[S]/(0.0173+[S]);五种物质对该酶均表现出不同的抑制作用,抑制效果为:抗坏血酸>L-半胱氨酸>亚硫酸氢钠>柠檬酸>醋酸。     

苹果汁掺假(梨汁)的研究

从相同稀释倍数下的梨汁以不同体积掺入苹果汁后的pH变化,295nm处的吸光度的变化,总糖和还原糖的变化,旋光度的变化以及糖的薄层层析和感官评定等6个方面进行了探讨.结果表明：苹果汁掺入一定量的梨汁后的pH、295nm处的吸光度、总糖和还原糖及旋光度这4个方面的变化幅度较大,可以作为判断苹果汁中是否掺入梨汁的检测依据.     

A rapid spectrophotometric method of determination of thiopropanal s-oxide (lachrymator) in onion (allium cepa l.) and its significance in flavour studies

The method depends upon rapid extraction of the lachrymator (thiopropanal S-oxide) into hexane at 0 °C and observation of the absorbance maximum at 254 nm as compared with that of the synthetic compound as a standard. Thiopropanal S-oxide was synthesised by dehydrochlorination of 1-propanesulphinyl chloride by a published method. Evidence that the observed absorbance was due to the presence of thiopropanal S-oxide was based mainly on agreement of the properties of the synthetic compound with those of hexane extracts of fresh onion juice with respect to λ_max values, reaction with L-cysteine reagent, and thin-layer chromatography. Further confirmation was afforded by the properties of alliinase fission products of synthetic (±)-S-l-propenyl-L-cysteine sulphoxide. A series of applications of the method in determination of onion flavour intensity, including non-destructive sampling, is described.     

银条多酚氧化酶特性及控制的研究

对银条多酚氧化酶(PPO)的酶学特性及控制进行研究。结果表明：银条PPO 的最适反应时间为2.0min,最适pH 值为5.0,最适温度为30℃,银条PPO 的热稳定性较差。抗坏血酸(VC)、L- 半胱氨酸(L-cys)、亚硫酸钠、亚硫酸氢钠等对PPO活性均有极显著地抑制作用;在0.05g/100mL 柠檬酸+0.05g/100mL 抗坏血酸+0.05g/100mLL- 半胱氨酸复合化学抑制剂作用条件下,对银条PPO 的酶活性抑制率可达93.5%。     

Inhibition of Polyphenoloxidase by Sulfite

When polyphenoloxidase (PPO) was exposed to sulfite prior to susbstrate addition, inhibition was irreversible. Trials to regenerate PPO activity, using extensive dialysis, column chromatography, and addition of copper salts were not successful. Increased concentrations of sulfite and pH levels less than 5 enhanced the inhibition of PPO by sulfite. At pH 4, concentrations greater than 0.04 mg/mL completely inhibited 1,000 units of PPO activity almost instantaneously. This suggested that the HSO₃- molecule was the main component in the sulfite system inhibiting PPO. Column chromatography, extensive dialysis, and gel electrophoresis did not demonstrate ³⁵SO₂ bound to purified pear PPO protein. Formation of extra protein bands of sulfite inhibited purified pear PPO fractions on gel electrophoresis was demonstrated. This and other evidence suggested that the major mode of direct irreversible inhibition of PPO was modification of the protein structure, with retention of its molecular unity.     

六堡茶发酵前后多酚氧化酶的分离及酶学性质

为探索六堡茶发酵过程中多酚氧化酶(polyphenol oxidase,PPO)的来源及其酶学活性,采用不同pH值缓冲液、保护剂和液料比对发酵前后六堡茶PPO进行提取,通过(NH4)2SO4沉淀、透析和Sephadex?G-100凝胶过滤层析纯化PPO.结果表明:从六堡茶中分离纯化得到2个PPO同工酶,分子质量分别为5...     

Studies on the purification of banana polyphenoloxidase

Studies on the extractability of polyphenoloxidase (PPO) from the pulp of five banana cultivars revealed a varietal difference in the nature of binding of the PPO in the cell, with the enzyme being entirely in the soluble fraction in one and partly associated with the cell wall in others, necessitating use of a detergent to release it from the latter. Partial purification by acetone precipitation and chromatography using a DEAE-cellulose column yielded two major fractions DE-I and DE-II with purifications of 4- and 16·3-fold and activity recoveries of 38·2 and 43·3% respectively. Further gel filtration of the two fractions on a Sephadex G-100 column improved the purifications to 44- and 50-fold respectively with full activity recovery. Polyacrylamide gel electrophoretic studies showed the two fractions to be composed of isoenzymes differing in pattern. The purified enzyme showed maximum absorption at 275 nm.     

烟草体内外拮抗细菌协同控制根黑腐病及诱导寄主抗性试验

烟草内生细菌T295 和烟草土壤根际细菌R27 均能有效抑制烟草根黑腐病,为探索烟草体内外拮抗细菌协同作用于烟株的防病效果及控病机理,测定了菌株T295 和R27 协同作用对烟草根黑腐病的防效和对菌丝、孢子的抑制作用,以及对烟草体内苯丙氨酸解氨酶(PAL)、过氧化物酶(POD)、过氧化氢酶(CAT)、多酚氧化酶(PPO)和超氧化物歧化酶(SOD)等相关防御酶活性的影响。结果表明:内生细菌T295 和土壤根际细菌R27 协同作用于烟草能明显提高对烟草根黑腐病的控制效果,其无菌发酵液混合处理可以明显提高病原菌菌丝生长的抑制效果,但对孢子萌发抑制作用不明显。经内生细菌T295 处理后的烟草,其体内5 种酶活性高于R27 处理,但混合菌液与T295处理的烟草酶活性变化差异不显著,内生细菌T295 和土壤根际细菌R27 两者诱导抗性未表现出累加效应,表明混合菌液处理的烟株诱导抗性主要与内生细菌T295 能提高烟草中相关防御酶活性有关。      

Inhibition of endive (Cichorium endivia L.) polyphenoloxidase by a Carica papaya latex preparation

When endive polyphenoloxidase (PPO) was incubated with a crude papaya latex extract, it rapidly lost its activity. Inactivation was ascribed to thermostable nonenzymatic factors of low molecular weight. These factors were partially purified by a two step protocol including gel filtration chromatography on Biogel P2 and ion exchange chromatography using DEAE Sephadex A25. The PPO-inactivation rate was first order, when either inactivating agent or proton concentration was evaluated. Inactivation could be partially reversed by CuSO₄, which suggested that the inactivating factor(s) bound to the copper site of the enzyme. On a more rapid time scale than inactivation, papaya latex extract acted also as a weak noncompetitive PPO inhibitor.     

Measurement of Oxidation-Related Changes in Proteins of Freeze-Dried Meats

A new methodology for detection of lipid oxidation in freeze-dried meats, using myoglobin, has been developed. Fresh, cold beef was ground, freeze-dried and stored aerobically at 37°C. Samples, taken at different time intervals, were reconstituted and “meat extract” obtained. Extent of myoglobin insolubilization was determined by absorbance intensity at isobestic point (525 nm). Oxidation of oxymyoglobin to metmyoglobin in meat extract was quantified by measuring α peak intensity of metmyoglobin at 630 nm. Myoglobin polymerization was determined by isolation of myoglobin dimers and monomers from meat extract using gel filtration chromatography. Dimer/monomer ratio was calculated from Soret band absorption intensity at 409 – 415 nm. The three myoglobin-based oxidative indicators correlate well with each other and can be used to detect extent of lipid oxidation in freeze-dried meat products.     

Inhibition of polyphenol oxidase and the browning control of litchi fruit by glutathione and citric acid

Polyphenol oxidase (PPO, EC 1.10.3.2) from litchi peel was partially purified by ammonium sulfate fractionation and gel filtration, and a 16-fold purification of PPO achieved. The use of 10 mmol litre⁻¹ glutathione and 100 mmol litre⁻¹ citric acid was found to give good control of the browning of litchi fruit and 80–85% inhibition of PPO observed. Application of glutathione in combination with citric acid is recommended as a way of slowing the browning of litchi fruit.