宣木瓜多酚氧化酶酶学特性与抑制剂研究

研究宣木瓜不同部位的多酚氧化酶(PPO)的活性及其温度、pH值、底物专一性等特性和抑制方法。结果表明：果心中的PPO活性明显高于果皮和果肉,宣木瓜组织的褐变主要是由多酚氧化酶引起;PPO最适底物为邻苯二酚;最适温度20℃,在80℃处理5min即可钝化PPO的活性;最适pH5.5,在酸性条件下稳定性优于碱性;抗坏血酸、L-半胱氨酸、亚硫酸氢钠、柠檬酸和氯化钠均能有效的抑制PPO的活性。     

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。     

雪莲果多酚氧化酶活性及褐变控制的研究

以雪莲果为原料,采用丙酮酸缓冲液提取、硫酸铵提纯法,得到一种活性较高的多酚氧化酶,并对其活性进行了研究。研究发现:环境温度、介质pH值、抑制剂和底物浓度对多酚氧化酶的活性有一定的影响,反映了多酚氧化酶对反应介质的依赖关系,提出在雪莲果加工过程中,可通过钝化酶活性、抑制酶促反应、驱氧处理和复合抑制等途径控制雪莲果酶促褐变。     

苹果浓缩汁加工中热灭酶工艺研究

通过在不同温度和时间下热处理苹果汁,研究了使果汁中多酚氧化酶(PPO)部分或完全失活的条件,并考察了与果汁自然pH值相近的模拟体系对处理后的果汁酶活的抑制情况。表明:75℃、30s虽不能完全灭活PPO,但对其活性破坏较大,处理后的PPO酶活可以较好地被接近果汁自身pH值的低pH(3.8)所抑制,为最佳处理条件。     

板栗多酚氧化酶的酶学特性

分别就pH值与温度对板栗中多酚氧化酶活性的影响进行研究,结果表明板栗多酚氧化酶的最适pH值分别为4.5和6.5,最适温度分别为25℃和45℃;同时研究抗坏血酸与柠檬酸以及复合抑制剂对板栗多酚氧化酶的抑制效果,结果表明抗坏血酸与柠檬酸的最适作用浓度均为0.30%,复合抑制剂的最佳组合与最适作用浓度分别为0.05%柠檬酸+0.05%抗坏血酸+0.06%乙二胺四乙酸+0.20%氯化钠.     

桑叶多酚氧化酶活性的研究

采用分光光度法和扫描电子显微镜法对桑叶多酚氧化酶(PPO)的结构、活性以及不同抑制剂的抑制效果进行研究.结果表明:桑叶多酚氧化酶为纤维状蛋白;它的最适pH值为7.0;最适温度为40℃;在相同抑制剂浓度下,总体抑制效果为:抗坏血酸>亚硫酸氢钠>柠檬酸>氯化镁>氯化钠.     

四棱豆蛋白质提取工艺研究

以四棱豆为原料,采用碱溶酸析法,通过正交试验,以凯氏定氮法测得四棱豆蛋白质含量和提取率,对碱溶pH值、酸析pH值、提取温度、料液比4个因素进行优化研究,以寻求四棱豆蛋白质提取的最佳提取方法.结果表明,四棱豆蛋白质提取的最优工艺条件为碱溶pH值10.0,酸析pH值4.0,提取温度35 ℃,料液比1:15( m:v).     

桑叶多酚氧化酶分离及活性研究

采用分光光度法和扫描电子显微镜对桑叶多酚氧化酶(PPO)的结构、活性以及不同抑制剂的抑制效果进行研究。结果表明:桑叶多酚氧化酶为纤维状蛋白;其最适pH值为7.0,最适温度为40℃;在相同抑制剂浓度下,总体抑制效果为:抗坏血酸>亚硫酸氢钠>柠檬酸>氯化镁>氯化钠。     

交变磁场对鲜切莲藕切片保鲜效果的影响

用不同强度的交变磁场对鲜切莲藕切片进行处理,并对其外观、多酚氧化酶活性、还原糖含量、VC含量和pH值进行对比研究.结果表明:磁场强度为1.2A/m的交变磁场处理的鲜切莲藕切片,其外观最好,多酚氧化酶活性受到抑制,其还原糖含量比对照组的消耗量小,VC含量比对照组的损失量小,pH值比对照组低.     

脂肪氧化酶对啤酒抗氧化性能的影响及其特性研究

分析了目前国内广泛使用的麦芽中的脂肪氧化酶的活性,并研究了脂肪氧化酶对啤酒抗氧化性能的影响.同时对麦芽中的脂肪氧化酶的基本酶学性质进行了调查,跟踪了工业化生产规模的制麦和糖化过程中的脂肪氧化酶的活性.结果表明麦芽含有脂肪氧化酶,在通常的糖化工艺条件下,仍有催化活性,导致麦汁和啤酒TBA增加.麦芽脂肪氧化酶的最适pH为6.5,在20～40℃之间表现出较高的活性,温度高于50℃时,热稳定性迅速下降.大麦经发芽之后脂肪氧化酶大幅度增加,峰值为原大麦的5倍左右,但是经过焙焦之后,酶活又大幅度下降.在糖化过程中,当醪液的温度低于60℃时,醪液中能检测出脂肪氧化酶的活性,是脂肪氧化酶催化氧化脂肪酸的关键阶段.     

Water-Holding Capacity in Hard-to-Cook Beans (Phaseolus vulgaris): Effect of pH and Ionic Strength

The effect of pH and ionic strength (IS) of soaking solution on the water holding capacity (WHC) of hard-to-cook (HTC) and control black beans (Phaseolus vulgaris) was evaluated. Beans were soaked 18 hr in solutions covering the pH range 1–7 at constant IS (1.0 M) or in solutions ranging in IS from 0.01 to 1.3M (prepared with either NaCl or CaCl₂) at pH 7. WHC was significantly reduced in the pH range 3.5 to 5.1 in control beans but the effect was not as pronounced with HTC samples which had a lower WHC at each pH. Solutions prepared with NaCl produced significantly lower WHC values than CaCl₂ solutions in the control but not in the HTC beans. WHC values in control beans tended to increase with higher IS, although this effect was not as apparent for HTC beans.     

Nutritional assessment of protein from beans (Phaseolus vulgaris L) processed at different pH values,in growing rats

The effect of the commonly used processing techniques of soaking (at different pH values) and cooking on the digestive and metabolic utilisation of protein from common beans (Phaseolus vulgaris L) in growing rats was studied. Before the cooking step, beans were soaked in solutions of pH 2.6, 5.3 or 8.4. Analyses of beans soaked at moderately acid pH (5.3) showed a significant increase in essential amino acids, especially cysteine. Food intake and growth indices were also dependent on pH. All indices were better in animals fed with beans soaked in a basic pH solution than when an acid soaking solution was used. In contrast with the findings expected on the basis of the chemical analysis of protein composition of the food, the worst results for food intake and growth were found in rats fed with beans soaked at pH 5.3. There were no significant differences in apparent digestibility coefficient between different groups of animals. The highest metabolic utilisation of protein (balance) was found in animals fed with beans soaked in a basic solution; however, the values were insufficient to account for the faster rate of growth in this group. The better growth rate was probably due to the improved utilisation of carbohydrates in beans soaked in the basic pH (8.4) solution. © 2001 Society of Chemical Industry     

Response of intestinal proteinase activities to the feeding of isolated winged bean (Psophocarpus tetragonolobus) and soya bean (Glycine max) trypsin inhibitors in rats

The antinutritional activities of trypsin inhibitors (TIs) were compared between winged beans (Psophocarpus tetragonolobus) and soya beans (Glycine max). The inhibitors of the two beans were isolated by trypsin‐bound Sepharose 4B, and 50 mg of lyophilised powders were intubated intragastrically into 24 h fasted rats. The activities of trypsin and chymotrypsin were compared after 30, 60 and 180 min in the washings of the upper, middle and lower parts of the small intestine. The elution profiles of TI and non‐TI compounds in the affinity chromatography were similar in the two beans, and the antitryptic activities were concentrated 5.5 and 6.2 times (based on specific activity) for winged beans and soya beans respectively. Regardless of the TI fed to rats, trypsin activity in the upper intestine was suppressed to almost undetectable levels at 30 and 60 min after intubation. The activities in the middle and lower intestines were also substantially lowered when rats were fed winged bean TI, and significant differences were detected at 30 and 60 min after intubation when compared with rats fed soya bean TI. However, at 180 min after feeding, no differences were found in the trypsin activity in any gut segments. Similar inhibitory properties of isolated TIs were observed in chymotrypsin activities in the small intestine. The results suggest that winged bean TI may have greater inhibitory activity on the intestinal proteinase compared with soya bean TI. © 2001 Society of Chemical Industry     

Bioavailability of calcium and magnesium from faba beans (Vicia faba L var major), soaked in different pH solutions and cooked,in growing rats

The nutritive utilisation of calcium and magnesium from faba beans (Vicia faba L var major), soaked in different pH solutions and then cooked, was studied in growing rats. Prior to the cooking process the beans were soaked in acid (pH 2.6 and 5.3) or basic (pH 8.4) solutions. Processing of the bean seeds did not produce appreciable losses of Ca or Mg by solubilisation. Digestive utilisation of calcium was high and did not vary with the different processing conditions assayed. Metabolic utilisation of calcium was significantly improved by soaking and by soaking plus cooking. Both digestive and metabolic utilisation of magnesium were significantly improved by all the different processes assayed. The observed improvement in the nutritive utilisation of Ca and Mg was correlated with a higher weight gain of the animals but not with the content of these minerals in the femur and longissimus dorsi muscle. The higher dietary intake of cellulose, lignin and phytate found in the processed faba bean diets did not have a negative effect on the digestive utilisation of the minerals studied. Overall, soaking in basic solution plus cooking was the most effective treatment. The processing conditions studied were inexpensive and easily applied and have great potential for application at household or industry level for human and animal nutrition. Copyright © 2004 Society of Chemical Industry     

Presence of Nonprotein Trypsin Inhibitor in Soy and Winged Beans

The total trypsin inhibitor was determined in extracts of 11 cultivars of soybeans and 11 strains of winged beans. The proteins in the extracts were precipitated by 16% trichloroacetic acid (w/v), and nonprotein trypsin inhibitor activities were determined in the protein-free supernatants. The nonprotein trypsin inhibitor activities varied between 10.32 ± 1.39 and 24.41 ± 1.04 units/mg defatted soybean samples and in winged beans ranged between 2.65 ± 0.62 and 6.79 ± 0.27 units/mg defatted samples. The nonprotein trypsin inhibitor composed 27–55% of the total trypsin inhibitor activity in the soybeans, and 5–14% of the total activity in winged beans.     

α-Amylase inhibitor levels in seeds generally available in Europe

The α-amylase inhibitor (αAI) levels in 18 seeds, which are generally available throughout Europe, have been determined. Kidney beans, haricot beans, pinto beans and runner beans had high contents of αAI (2–4 g equivalent kg^?1 seed meal). Butter beans, blackeyed peas, chickpeas, field beans and sweet lupinseeds contained 0.1–0.2 g inhibitor equivalent kg^?1 seed meal. No αAI activity was detected in samples of adzuki bean, lentils, mung beans, peas, soya beans, sunflower seeds or winged beans. The αAI activity present in whole kidney beans was relatively heat-resistant. However, it could be completely abolished by aqueous heat treatment of fully imbibed beans at 100°C for 5–10 min.     

Rohament P as a processing aid in Medammis preparation

Two lots of dry faba bean (Viciufubu L.) seeds of different cookabilities were used to prepare Medammis which is considered as a staple food for the majority of the population in Egypt. Seeds were soaked with shaking in a citrate buffer of pH 4.5 containing 0.1 % Rohament P enzyme at 45°C for 12 h. After draining and washing, beans were mixed with distilled water at 1:4 ratio (w/v) and autoclaved at 115°C for 2 h. No obvious differences were observed for the hydration coefficients of beans soaked in presence and/or absence of enzyme. In contrast, cooked beans exhibited appreciable textural differences as assessed objectively for the control and treated samples. Moreover, hard-to-cook beans were softened to the acceptable texture as the five fold of enzyme concentration was applied. Data of quantitative and TLC methods clearly indicated leaching out of sugars as a result of maceration action of middle lamella by means of Rohament P.     

Dehydrated Precooked Pinto Bean Quality as Affected by Cultivar and Coating Biopolymers

The relationship of cultivars and coating treatment to quality of precooked dehydrated pinto beans was investigated. The pinto cultivars, studied were Fiesta, Othello, and Topaz, and 12 types of biopolymers, including modified starches, dextrins, maltodextrins, and alginate, were used as coating agents. Beans were blanched, soaked, steam cooked, coated by dipping in biopolymer solutions at 70°C and dried in a convection oven. Eight biopolymers effectively reduced splitting of beans without detrimental effects on rehydration, firmness, or color. Cultivar had a strong effect on wholeness of bean products and Fiesta was best for dehydration. Residual trypsin inhibitor activity of precooked pinto beans was ～5%.     

Oxidation of polyphenols in unfermented and partly fermented cocoa beans by cocoa polyphenol oxidase and tyrosinase

Unfermented and partly fermented dried cocoa beans have an excessively astringent and bitter flavour owing to their high polyphenol content. Studies on the remaining polyphenol oxidase activity and the oxidation of polyphenols in these beans have been conducted in relation to two factors, ie incubation time (0, 1, 2, 4, 8 and 16 h) and pH of incubation (3.5, 4.5, 5.5 and 6.5). Owing to unsuccessful polyphenol oxidation during incubation of partly fermented beans, incubation–enrichment treatments were carried out by combining incubation time (0, 8, 16, 24 and 32 h) and addition of crude cocoa polyphenol oxidase and purified tyrosinase from mushroom at 88 and 8800 units g^?1 and pH 5.5. Results showed that the remaining polyphenol oxidase activities of unfermented and partly fermented dried beans were 1 and 0.08% with specific activities of 9 and 1% respectively. The polyphenols of unfermented beans were effectively oxidised by incubation at 45 °C and pH 3.5–6.5 without enzyme enrichment; while those of partly fermented beans required enzyme enrichment. Both crude cocoa polyphenol oxidase and tyrosinase could be used for enzyme enrichment, but tyrosinase seemed to be more effective. © 2002 Society of Chemical Industry     

The effect of thermal treatment on β‐glucosidase inactivation in vanilla bean (Vanilla planifolia Andrews)

The conditions for enzyme activity (pH and temperature) and kinetic parameters for the thermal inactivation of β‐glucosidase enzyme in vanilla beans have been investigated. The maximum enzyme activity was detected at pH 6.5 and 38 °C. The values obtained for V_max and K_m were 62.05 units and 2.07 mm, respectively. When hot water treatment (the most practical method of vanilla bean killing) was applied, β‐glucosidase treated at pH 6.0 and 60 °C for 3 min lost 51% of activity, while at 70 °C for 90 s the enzyme lost 60% of activity and at 80 °C for 30 s the enzyme lost 48% of its activity. When vanilla beans were cured in an oven at 60 °C for 36 to 48 h all β‐glucosidase activity was lost.