二氧化钛修饰葡萄糖氧化酶电极的初步研究

应用TiO2修饰铂电极,制备葡萄糖氧化酶电极,初步探讨其电化学响应特性和实用性。实验表明,该电极具有良好的重现性和选择性。     

蕨菜多酚氧化酶的性质

以冷冻丙酮制备蕨菜多酚氧化酶丙酮粉,用分光光度法研究pH、温度、底物浓度,抑制剂对酶活性的影响,结果表明,以邻苯二酚为底物,该酶的最适pH值为7.4,最适温度为25℃;Km为39.86 mmol/L,Vm为0.686 OD/min,90℃热处理50 s可钝化PPO的活性;抗坏血酸、亚硫酸钠为强烈抑制剂,175 mg/L的亚硫酸钠、225 mg/L的抗坏血酸能有效抑制PPO的活性.     

氧化酶复合乳化剂在馒头中的应用研究

利用正交试验研究了氧化酶复合乳化剂对面团流变学特性和馒头质量的影响。确定了适量的葡萄糖氧化酶、抗坏血酸、硬酯酰乳酸钠一钙,增强了面粉的筋力,改善了馒头的内部组织结构、增大了体积、表面更光亮。     

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。     

Cloning and some properties of Japanese pear (Pyrus pyrifolia) polyphenol oxidase,and changes in browning potential during fruit maturation

A PCR‐amplified genomic DNA fragment encoding Japanese pear (Pyrus pyrifolia) polyphenol oxidase (PPO) was cloned and sequenced. The DNA appears to encode a 66 kDa precursor protein consisting of a 56 kDa mature protein and a 9.5 kDa N‐terminal transit peptide. The amino acid sequence showed high homology with apple PPO. The PPO mainly existed as a soluble fraction in cells and was limitedly proteolysed, while the mature form (56 kDa) was detected in plastids. Immature fruits showing high browning potential had high PPO activity and a high level of phenolics, while mature fruits showing little browning had high PPO activity but a low level of phenolics. Copyright © 2003 Society of Chemical Industry     

Effect of nitric oxide on ethylene production in strawberry fruit during storage

Strawberry is a non-climacteric fruit, with low ethylene production rate after harvest. Its response to nitric oxide (NO), which can be released from sodium nitroprusside (SNP), was studied. We have examined the effect of 1.0, 5.0 and 10.0 μmol l⁻¹ SNP aqueous solution on ethylene production, respiration rate, 1-aminocyclopropane-1-carboxylic acid (ACC) content and the activities of ACC synthase and ACC oxidase in post-harvest strawberry (“Fengxiang”). The most remarkable effect was obtained with 5 μmol l⁻¹ SNP aqueous solution, which significantly inhibited ethylene production, respiration rate, the activity of ACC synthase and reduced the content of ACC, but did not significantly affect the activity of ACC oxidase. SNP at 10 μmol l⁻¹ harmed the fruits; 1 μmol l⁻¹ SNP was too low to significantly extend strawberry storage life. It was suggested that NO could decrease ethylene output, through inhibiting ACC synthase activity reducing ACC content.     

香蕉多酚氧化酶褐变性质的研究

以邻苯二酚为废物通过采用分光光度计测定氧化产物的方法,对香蕉果肉中多酚氧化酶(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 5 min酶基本完全失活,100℃水浴处理20s可钝化PPO的活性,且香蕉PPO存在同功酶。实验中同时考察了柠檬酸、抗坏血酸、NaHSO_3和半胱氨酸对PPO的褐变抑制效果。     

不同酶制剂对信阳地区小麦馒头品质的作用

以信麦1168、信麦126、信麦79、信麦136小麦粉为主要原料,分别添加不同浓度梯度的真菌α-淀粉酶、木聚糖酶、葡萄糖氧化酶制作馒头,测定馒头比容、宽高比和感官品质,并进行相关性的分析.结果表明:真菌α-淀粉酶添加量为25 mg/kg时,信麦79和信麦126的比容分别为2.479 ml/g和2.438 ml/g,达到...     

H2O2对家蝇蛹内部几种酶活性的影响

目的研究外源H2O2对家蝇蛹内与抗性相关的几种酶活性的影响。方法通过H2O2诱导,测定家蝇蛹内过氧化氢酶（CAT）、过氧化物酶（POD）、抗坏血酸过氧化物酶（AsA-POD）以及多酚氧化酶（PPO）的活性变化。结果H2O2处理后蛹内CAT和AsA-POD的活性变化规律与处理前差别不大;POD活性在H2O2处理后12h内出现活性高峰,约为对照组的2.5倍,此后稍高于对照组,最后基本与对照组持平;PPO活性在处理后12h内与对照组相当,此后活性骤然升高,处理后24h达到对照组的2.13倍,然后变化速度减慢,但一直维持在对照组的1.3倍左右,48h后活性开始下降。结论H2O2对CAT和AsA-POD的活性影响较小,对POD和PPO的活性有一定的影响。     

Antioxidative activities of bran extracts from twenty one pigmented rice cultivars

Ethanol–water (70:30, v/v) extracts from the bran of rice seeds from twenty one pigmented and one nonpigmented rice cultivars were evaluated for antioxidative activities using the following tests: inhibition of peroxidation of linoleic acid; inhibition of peroxidation of rabbit lipid erythrocyte membranes; reduction of potassium ferricyanide, and scavenging of superoxide anions and hydroxyl radicals. With some exceptions, extracts from the pigmented rice seeds had higher antioxidative activity than did the nonpigmented variety. The following pigmented cultivars had the highest antioxidative activities in all tests: Jumlalocal-1, Parnkhari 203, DZ78, LK1-3-6-12-1-1, and Elwee. A significant correlation was also noted between reducing power, inhibition of erythrocyte ghost membrane peroxidation, and superoxide anion and hydroxyl radical scavenging. The results suggest that: (a) ferricyanide reducing power might be a useful and simple index for large-scale evaluation of antioxidative potencies of natural products present in rice; (b) pigmented rice varieties with high antioxidative activities provide a source of antioxidants and a genetic resource to develop new health-promoting rice cultivars.