茭白中多酚氧化酶活性的测定及护色效果研究

茭白在加工过程中会发生酶褐变,影响茭白的质量。文中研究了温度、pH值对茭白中PPO(多酚氧化酶)活性的影响,设计了不同的护色方案,以确定茭白的无硫护色条件。结果表明,茭白中多酚氧化酶活性最适温度36℃,最适pH值为5.6。用质量分数为0.1%L-半胱氨酸、0.7%柠檬酸、0.07%抗坏血酸、0.02%CaCl2配成的复合护色液护色20min后,茭白在整个实验期间内,色白,无褐变现象产生。     

Antibacterial Effect of Glucose Oxidase on Growth of Pseudomonas fragi as Related to pH

The effect of glucose oxidase (GOX) catalyzed reaction with glucose on Pseudomonas fragi was analyzed in nutrient broth and fish extract media. Growth of P. fiugi in nutrient broth was clearly suppressed by 1.0, 2.0 and 4.0 mg/mL glucose when combined with 0.5–2.0 U/mL GOX. The same GOX/glucose combinations inhibited P. frasi growth in fish extract media. Viable cell numbers in fish media showed clear growth inhibition with combinations of l.0–2.0 U/mL GOX and 8.0–16.0 mg/mL glucose. Higher GOX and glucose rapidly produced 2.0–2.5 unit decreases in pH, but produced enough gluconic acid to precipitate fish proteins. Use of 0.5 U/mL GOX in fish extract media resulted in slow, sustained activity with potential for inhibition of microbial growth in foods without excessive acidity.     

Identification of (−)-epicatechin as the direct substrate for polyphenol oxidase from longan fruit pericarp

Postharvest browning of longan fruit results in a short life and a reduced commercial value. The experiments were conducted to separate, then purify and finally identify the polyphenol oxidase (PPO) substrates that cause longan fruit to brown. PPO and its substrates were, respectively, extracted from longan fruit pericarp tissues. The substrate for longan PPO was separated and purified using polyamide column chromatography, Sephadex LH-20 column chromatography and silica gel column chromatography, respectively. The substrate was further identified by 0.5% FeCl₃ solution and enzymatic reaction with longan PPO. On the bases of UV, ¹H NMR, ¹³C NMR, and ESI-MS data, the direct substrate for the PPO from pericarp tissues of longan fruit was identified to be (−)-epicatechin. Furthermore, the contents of (−)-epicatechin of pericarp tissues of longan fruit of two major cultivars were determined by high performance liquid chromatography (HPLC). The HPLC analysis exhibited that the contents of (−)-epicatechin of fruit pericarp of ‘Shixia’ and ‘Chuliang’ were 0.26 and 0.56 mg/g on fresh weight (FW) basis at harvest and 0.15 and 0.09 mg/g FW after 3 days of storage. The more rapid decrease in the (−)-epicatechin content of ‘Chuliang’ was due to the oxidization catalyzed by PPO, which was in agreement with the higher browning index.     

Beneficial effect of yam on the amyloid β‐protein,monoamine oxidase B and cognitive deficit in mice with accelerated senescence

This study was designed to evaluate the effect of yam tuber material [Dioscorea alata L. var. purpurea (M.) Pouch.] on the amyloid β‐protein (Aβ) accumulation, monoamine oxidase (MAO) activity, cognitive ability and antioxidative defense system in senescence‐accelerated mice (SAMP8). Three‐month‐old male mice were fed with four different diets for 12 weeks: a casein diet (control group) and a casein diet supplemented with either 100, 200 or 400 g kg^?1 lyophilized yam. The results of the active shuttle avoidance test showed that the mice fed with the yam‐containing diets had significantly better learning and memory ability than the control group. All yam‐containing diet groups had lower Aβ levels and MAO B activities than the control, whereas the MAO A activity did not differ among the four diet groups. At the 400 g kg^?1 level, the yam‐containing diet group showed significantly lower concentration of thiobarbituric acid‐reactive substances (TBARS), higher total thiol level and superoxide dismutase (SOD) activity in the hippocampus than the control, but these values were not altered by the 100 and 200 g kg^?1 yam‐containing diet groups. The addition of 200 or 400 g kg^?1 yam also lowered the triglyceride levels but not the total cholesterol concentration. These results indicate that lyophilized yam could reduce brain Aβ accumulation, MAO B activity and cognitive deficits and promote the antioxidative defense system in SAMP8 mice. The improvements were in a dose‐dependent manner, possibly because the 400 g kg^?1 yam‐containing diet might contain more antioxidative phytochemicals. Copyright © 2006 Society of Chemical Industry     

D-氨基酸氧化酶的研究进展

D-氨基酸氧化酶(DAAO)是一种以黄素腺嘌呤(FAD)为辅基的典型的黄素蛋白酶类.DAAO可氧化D-氨基酸生成相应的酮酸和氨.介绍了D-氨基酸氧化酶的研究现状,包括在自然界的分布、生理功能、生物学特性、催化机理、基因克隆和序列分析以及基因表达.     

超声波对多酚氧化酶酶活力的影响及其机理

以多酚氧化酶(PPO)为对象,研究不同超声波条件对PPO 酶活力的影响及其机理。结果表明：PPO 酶活力随着超声时间增加而降低,随着超声波功率增大先略增大然后逐渐降低;在超声波作用下PPO 的稳定温度和pH值分别为40℃和6.8;经超声波处理后的PPO,其动力学参数米氏常数Km 增大、最大反应速率Vmax 减小;PPO 二级结构中β- 转角相对减少。     

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。     

Inactivation of polyphenol oxidases in cloudy apple juice exposed to supercritical carbon dioxide

The inactivation of polyphenol oxidase (PPO) in cloudy apple juice exposed to supercritical carbon dioxide (SCCO₂) treatment was investigated. Higher pressure, higher temperature, and longer treatment time caused more inactivation of PPO. The maximum reduction of PPO activity reached more than 60% at 30 MPa and 55 °C for 60 min. The experimental data followed first-order reaction kinetics; the kinetic rate constant k and the decimal reduction time D were closely related to the pressure and temperature of SCCO₂ treatment. Higher pressures or higher temperatures resulted in lower D values (higher k), the D value of PPO was minimized to 145 min treated by the combination of 30 MPa and 55 °C. Activation energy of 18.00 kJ /mol, was significantly reduced by SCCO₂ treatment at 30 MPa, as compared to activation energy of 72.0 kJ/mol for identical treatment at atmospheric pressure. Pressure and temperature sensitivity of kinetic parameters were studied. Z_P at 55 °C was 66.7 MPa and Z_T at 30 MPa was 108 °C.     

Inhibition of xanthine oxidase activity by an oxathiolanone derivative of quercetin

An oxathiolanone derivative of rutin could be produced in the stomach after the ingestion of rutin containing foods, and the oxathiolanone derivative could be hydrolysed to an oxathiolanone derivative of quercetin (quercetin-oxathiolanone) in the intestine. Quercetin-oxathiolanone as well as quercetin inhibited xanthine oxidase. Approximately 0.05 μM quercetin-oxathiolanone inhibited the activity by 50%, whereas 50% inhibition by quercetin was observed at approximately 0.4 μM. The results suggested that quercetin-oxathiolanone can be used as an effective inhibitor of xanthine oxidase and that the ingestion of rutin-rich foods may be useful to prevent the increase in the blood concentration of uric acid.     

Consumer acceptability and purchase intent of probiotic yoghurt with added glucose oxidase using sensometrics,artificial neural networks and logistic regression

This research aimed to identify the drivers of acceptance and purchase intent of a probiotic (Bifidobacterium longum BL05) nonflavoured yoghurt supplemented with glucose oxidase, and to model the consumers’ acceptability using sensometrics and artificial neural networks (ANN). Consumers (n = 100) evaluated the degree of liking of yoghurt assays in respect of appearance, aroma, taste, texture and overall linking. Sensometric techniques – multiple linear regression (MLR), partial least squares regression (PLS), principal component regression (PCR) – and ANN were used to model the overall liking. Sensory drivers of global acceptance and purchase intent were also determined using logistic regression (LR). Hierarchical cluster analysis (HCA) identified three consumer segments that presented differences in all sensory attributes evaluated (P < 0.05). The ANN model showed the best performance to predict overall liking, followed by the MLR, PLS and PCR, indicating that taste and texture were the most significant attributes impacting the yoghurts overall liking. In accordance with the logistic models, overall acceptance and purchase intent could be predicted with 81.94 and 85.49% accuracy, respectively. The logistic regression indicated that taste was the attribute that contributed significantly (P < 0.0001) to higher scores for purchase intent and was considered the driver of acceptance.