红枣多酚氧化酶酶促褐变控制研究

确定了红枣多酚氧化酶最适pH为6.0～6.5,最适温度为27℃;其对pH和温度较为敏感,通过调节pH和适当的热处理即可有效抑制其活性。同时在上述最适条件下,研究了以柠檬酸、抗坏血酸、亚硫酸钠作为抑制剂对红枣多酚氧化酶的抑制作用,并在单因素实验的基础上,采用响应面分析法对复合抑制剂的复配进行了优化,获得最佳添加配比为:柠檬酸0.24%,抗坏血酸0.14%,亚硫酸钠0.08%;此条件下红枣多酚氧化酶相对残余酶活为0.51%。     

雪莲果防褐变技术的研究

从雪莲果块茎中提取多酚氧化酶(Polyphenol Oxidase,PPO),采用分光光度法对其最大吸收波长最适反应温度进行研究,还研究了VC、氯化钠、柠檬酸、柠檬汁、橘子汁对雪莲果PPO活性的影响。结果表明:雪莲果多酚氧化酶最大吸收波长为400nm,最佳反应温度为30℃。氯化钠、抗坏血酸、柠檬酸、柠檬汁、橘子汁都有抑制褐变的效果。组合抑制剂抑制褐变效果比单一抑制剂好且最佳组合抑制剂为1.5%氯化钠+0.5%抗坏血酸+1.5%柠檬酸+10%柠檬汁。     

石榴多酚氧化酶的某些特性及其抑制剂的研究

针对石榴贮藏过程中易发生果皮褐变的问题,以分光光度计法研究了石榴果皮中多酚氧化酶(PPO)的某些特性,考察了柠檬酸、抗坏血酸、亚硫酸钠和β-环糊精等抗褐变剂对PPO活性的抑制效果。研究结果表明:石榴皮中多酚氧化酶的最适温度为40℃,最适pH是7．0,几种底物中单宁与PPO的亲和力最大,试验的几种抗褐变剂中柠檬酸对PPO活性有明显的抑制效果,其次是抗坏血酸,而亚硫酸钠、β-环糊精的抑制效果不明显。     

冰温技术结合保鲜剂对南美白对虾品质的影响

研究冰温技术结合4- 己基间苯二酚(4-hexylresorcinol,4-HR)等保鲜剂对延缓虾类黑变和保持品质方面的效果。通过正交试验确定保鲜剂的配方(M),以冻结试验确定冰温贮藏温度,测定贮藏设备的温控范围,通过评定南美白对虾的黑变感官得分,测定多酚氧化酶(PPO)活力、挥发性盐基氮(TVB-N)、pH 值和菌落总数(TBC)等鲜度指标评价保鲜效果差异。结果表明：南美白对虾的冰温带为－ 2.2～0℃,贮藏设备温度波动满足冰温技术要求,M 保鲜剂配方为0.01% 4- 己基间苯二酚+1.5% 柠檬酸+1% 抗坏血酸,冰温能显著减缓TVB-N 值、pH 值和TBC值增加速度,M 配方保鲜剂能有效抑制虾的多酚氧化酶活性和黑变,冰温技术结合M 配方保鲜剂保藏南美白对虾能互补二者优缺点,能显著减低黑变感官得分,PPO 活性、TVB-N、pH 值和TBC 的增长速度。比(4 ± 1)℃冷藏的货架期延长近1 倍。冰温技术结合保鲜剂能有效防止虾类黑变和延长品质货架期。     

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%。     

鸡腿蘑多酚氧化酶特性研究

本文采用分光光度法对鸡腿蘑多酚氧化酶(PPO)的催化特性、最适温度、最适pH值、热稳定性等性质进行研究;同时考察了EDTA-2Na、NaHSO₃、抗坏血酸、柠檬酸四种抑制剂对鸡腿蘑多酚氧化酶活力的影响。结果表明:该酶的最适pH为6.0;最适温度为45℃,80℃水浴处理5min,95℃水浴处理90s该酶全部钝化。四种抑制剂对该酶均表现出不同的抑制效果,抑制效果强弱次序为抗坏血酸>柠檬酸>NaHSO₃>EDTA-2Na。     

葛根中多酚氧化酶性质及葛根护色的研究

研究葛根多酚氧化酶(PPO)的性质,以及不同护色方案的护色效果,确定最佳护色方案。结果表明,以邻苯二酚为底物,葛根PPO的最适pH7.0,最适温度40℃,100℃热处理40s可钝化PPO的活性;抗坏血酸、抗坏血酸钠和亚硫酸钠为多酚氧化酶强烈抑制剂;但仅有亚硫酸钠能有效抑制葛根褐变的发生;结合颜色、护色效果、损失以及残留,确定0.2%的亚硫酸钠溶液为护色剂采用喷涂的方式进行护色。     

Effects of Sulfhydryl Compounds,Carbohydrates, Organic Acids,and Sodium Sulfite on the Formation of Lysinoalanine in Preserved Egg

To identify inhibitors for lysinoalanine formation in preserved egg, sulfhydryl compounds (glutathione, L‐cysteine), carbohydrates (sucrose, D‐glucose, maltose), organic acids (L‐ascorbic acid, citric acid, DL‐malic acid, lactic acid), and sodium sulfite were individually added at different concentrations to a pickling solution to prepare preserved eggs. Lysinoalanine formation as an index of these 10 substances was determined. Results indicate that glutathione, D‐glucose, maltose, L‐ascorbic acid, citric acid, lactic acid, and sodium sulfite all effectively diminished lysinoalanine formation in preserved egg albumen and yolk. When 40 and 80 mmol/L of sodium sulfite, citric acid, L‐ascorbic acid, and D‐glucose were individually added into the pickling solution, the inhibition rates of lysinoalanine in the produced preserved egg albumen and yolk were higher. However, the attempt of minimizing lysinoalanine formation was combined with the premise of ensuring preserved eggs quality. Moreover, the addition of 40 and 80 mmol/L of sodium sulfite, 40 and 80 mmol/L of D‐glucose, 40 mmol/L of citric acid, and 40 mmol/L of L‐ascorbic acid was optimal to produce preserved eggs. The corresponding inhibition rates of lysinoalanine in the albumen were approximately 76.3% to 76.5%, 67.6% to 67.8%, 74.6%, and 74.6%, and the corresponding inhibition rates of lysinoalanine in the yolk were about 68.7% to 69.7%, 50.6% to 51.8%, 70.4%, and 57.8%. It was concluded that sodium sulfite, D‐glucose,L‐ascorbic, and citric acid at suitable concentrations can be used to control the formation of lysinoalanine during preserved egg processing.     

百合鳞茎多酚氧化酶特性的初步研究

用分光光度计法在波长420nm下,以邻苯二酚为底物研究了兰州百合鳞茎中多酚氧化酶(Polyphenoloxidase,PPO)的部分特性。实验发现百合PPO的活性在4～25℃时,随着温度的升高而升高,25℃时PPO活性达到最大值,之后PPO活性随着温度的升高而下降;百合PPO有两个最适pH,分别为4.0和6.0,当pH低于4.0、高于6.0时活性均较低。抗坏血酸、异抗坏血酸钠、半胱氨酸在实验用的五种抑制剂中对PPO的抑制作用最强。     

Prevention of enzymatic browning of apple cylinders using different solutions

Inhibition of enzymatic browning and decay on cut surfaces of Golden Delicious apple using ascorbic acid, cysteine, sodium chloride, calcium chloride, citric acid and sodium ascorbate alone or in combinations was investigated at 4 and 10 °C for a storage period of 0, 7 and 14 days, in an attempt to find the most effective treatment. Apple segments immersed in ascorbic acid and citric acid alone showed visual traces of browning after 7 days storage at 4 °C. After 14 days storage, only ascorbic acid and ascorbic acid plus sodium chloride had moderate browning, while all other treatments were severely affected. However, at 10 °C, only ascorbic acid was effective in reducing the level of browning, although its effect was minimal after 14 days storage. Browning was more severe at 10 °C than 4 °C in all solutions. The browning measurement (a* value) became increasingly positive from 7‐ to 14‐day storage. Microbial decay was absent in all treatments within 7 days at 4 and 10 °C. However, three test solutions showed microbial decay after 14 days storage at 10 °C in addition to the control solution, which showed decay at both 4 and 10 °C storage temperatures.     

双孢蘑菇酶促褐变特性及褐变的控制

为有效控制双孢蘑菇褐变,研究pH值、温度、底物浓度以及抑制剂对双孢蘑菇的多酚氧化酶(polyphenol oxidase,PPO)活性的影响。结果表明：以邻苯二酚为底物,双孢蘑菇PPO最适反应pH6.8,最适反应温度20℃,最适反应底物浓度为0.06mol/L,米氏常数Km为0.1072mol/L。采用计算机图像处理技术对双孢蘑菇褐变程度进行定量检测,得出对双孢蘑菇贮藏保鲜效果较好的褐变抑制剂及其最佳配比为0.30mmol/L半胱氨酸、0.06％抗坏血酸、0.05%乙酸。     

山药中多酚氧化酶的活性测定及其护色研究

研究了山药中多酚氧化酶(PPO)的最适pH值、最适温度,设计了不同护色方案,以确立山药的最佳护色条件。采用分光光度法研究pH值、温度对酶活性的影响;比较不同护色液对酶活力的影响;将山药经不同护色条件护色后,低温烘干,粉碎过筛得山药粉,用分光光度法测定其甲醇-水溶液(1∶1)的吸光度。结果表明,以邻苯二酚为底物,山药PPO的最适pH值为5.6,最适温度为35℃,山药的最佳护色条件为:以0.25%的Na2SO3为抗氧化剂,并配以0.25%的柠檬酸和1.5%的NaCl为护色液。     

速冻建莲加工与贮藏过程中多酚氧化酶活性抑制的研究

为提高速冻建莲的品质,本文研究了不同的抑制剂组合对建莲多酚氧化酶(PPO)活性的抑制效果,并观察了速冻建莲贮藏期间PP0活性的变化。结果表明:0.025％EDTA-Na_2+0.1％抗坏血酸+0.1％柠檬酸能最大限度地抑制建莲的多酚氧化褐变,以此应用于速冻建莲的生产,能有效抑制冻藏过程中建莲的多酚氧化酶活性,褐变程度明显降低。     

紫薯中多酚氧化酶活性的研究及褐变控制

研究紫薯组织中多酚氧化酶(PPO)的活性,最适pH值、最适温度等特性,并在此基础上,研究加热温度、加热时间、抗坏血酸和柠檬酸添加量对PPO褐变的抑制效果。结果表明：紫薯PPO最适pH值范围为5.5～7.5,最适温度为30℃。在较好的分离淀粉的前提下,最佳抑制褐变条件是：加热温度80℃、加热时间10min、抗坏血酸添加量0.9‰、柠檬酸添加量1.2g/L。     

INHIBITION STUDIES ON BURDOCK POLYPHENYL OXIDASE (PPO) ACTIVITY

The inhibitory effect of 4-hexylresorcinol (HR), ascorbic acid (AA), citric acid (CA), and bisulfites on polyphenol oxidase (PPO) of burdock roots was studied. HR was an effective inhibitor at low concentrations used in this study for crude PPO from root slices. A binary mixture of HR and AA at 1.0% concentration for 5 min achieved more than 90% inhibition of crude PPO. AA also showed high antibrowning activity for the purified PPO comparable to that of bisulfites, whereas its activity was much lower than that of HR in the crude extract. The inhibitory effect of the combined use of inhibitors was overall in the decreasing order of HR+AA, HR+CA and AA+CA, irrespective of the crude PPO or the purified PPO from burdock slices.     

荔枝壳中多酚氧化酶活性研究

本文对荔枝壳中多酚氧化酶(PPO)的活性及不同抑制剂的抑制效果进行研究。结果表明:荔枝壳多酚氧化酶的最佳底物浓度为0.04mol/L,最适pH为7.0,最适温度为40℃;柠檬酸、抗坏血酸、硫代硫酸钠对PPO活性表现出较好的抑制效果,三种抑制剂联合作用的最佳条件为0.01mmol/L的柠檬酸+0.04mmol/L的抗坏血酸+0.004mmol/L的硫代硫酸钠,PPO活性的抑制率达85.8%。     

Effect of various inhibitors on enzymatic browning,antioxidant activity and total phenol content of fresh lettuce (Lactuca sativa)

In this study, polyphenol oxidase (PPO) was isolated from fresh lettuce. Its optimum temperature and pH were found to be 40 °C and 7.0, respectively. Lettuce PPO was shown to use catechin, catechol, chlorogenic acid, caffeic acid and gallic acid as substrates. Among the substrates used, the greatest substrate specificity was observed with chlorogenic acid. Lettuce PPO was sensitive to some inhibitors. Ascorbic acid, cysteine, oxalic acid and citric acid were tested as potential inhibitors of lettuce PPO. Cysteine was the most effective inhibitor. Total phenol and total antioxidant activity contents were also determined in the presence of these inhibitors at room and refrigerator temperatures. Ascorbic acid and cysteine increased the total antioxidant activity of lettuce while citric and oxalic acids had no effect on the total antioxidant activity. Lettuce phenolics were protected from oxidation by ascorbic acid and cysteine.     

Inhibitory effect of rice bran extract on polyphenol oxidase of potato and banana

Rice bran was extracted with water and its effects on potato and banana polyphenol oxidase (PPO) were investigated. Rice bran extract (RBE), conc. 0.3 g mL^?1, exhibited PPO inhibition in potato and banana PPO with % inhibition of 69.31% and 47.63%, respectively (P ≤ 0.05). RBE showed a concentration‐dependent inhibition on potato and banana PPO. RBE (conc. 0.3 g mL^?1) inhibited potato PPO higher than ascorbic acid, citric acid, NaCl and EDTA (final conc. 20 mg L^?1); and it also inhibited banana PPO higher than citric acid, NaCl and EDTA (final conc. 20 mg L^?1), respectively. The combination of RBE with citric acid or ascorbic acid appeared to be additive inhibitory effect on banana and potato PPO. Kinetic study of the inhibition on potato and banana PPO by RBE showed that RBE was a mixed‐type inhibitor; however, RBE appeared to be able to act directly on enzyme structure rather than substrate structure.     

仙人掌多酚氧化酶的特性及抑制研究

本文研究了仙人掌中多酚氧化酶(PPO)的特性以及一些抑制剂对其活性的影响。结果表明:仙人掌中PPO的最适温度为50℃,最适pH有两个,分别为pH4.0和pH7.0,因而在仙人掌中的PPO存在同工酶。柠檬酸、抗坏血酸及EDTA对仙人掌PPO均有一定的抑制效果,抑制能力顺序为:柠檬酸>抗坏血酸>EDTA。对各种抑制剂的作用机理进行了探讨。EDTA主要是通过螯合PPO中的辅酶因子Cu2+而起作用,抗坏血酸螯合Cu2+的能力比EDTA弱,但抗坏血酸的还原能力较强,而柠檬酸则是通过降低pH和螯合作用抑制PPO。     

In silico guided pre-treatment of sugarcane juice with natural inhibitors of polyphenol oxidase (PPO) is a new and effective strategy for development of spray-dried formulation

Sugarcane juice is a popular beverage and is also processed to produce sugar. The polyphenol oxidase (PPO) in sugarcane juice causes enzymatic browning and makes the process of sugar production complex and cumbersome. Storage of sugarcane juice is also hampered by the high sugar content and rapid microbial fermentation. The present research assessed the potential of lemon juice (LJ) and ginger extract (GE) as natural inhibitors of PPO. Enzyme kinetics and the mechanism of inhibition of LJ and GE were studied. Primary investigation was carried out using molecular docking approach to assess the inhibitory potential of LJ and GE and to determine the nature of interaction between the enzyme and inhibitors. Extracts were used as inhibitors and studies revealed that both reduced the PPO activity. Subsequently, pure bioactive inhibitors such as ascorbic acid, citric acid, and 6-shogaol present in these natural extracts were used to study the mode of inhibition of PPO. Citric acid decreased PPO activity by lowering pH, while ascorbic acid was found to be a competitive inhibitor of PPO with a K_i of 75.69 µM. The proportion of LJ and GE required in sugarcane juice was optimized on the basis of browning index and sensory acceptance. Further, the sugarcane cane juice after inhibition of PPO under optimized conditions was spray dried and evaluated for reconstitution properties. The product formulated in the present study is a new and effective approach to address quality-compromising issues associated with long-term storage of cane juice.