山药苯丙氨酸解氨酶特性的研究

本文研究了山药苯丙氨酸解氨酶(PAL)的动力学特性。结果表明,PAL最适底物浓度为1mmol/L,底物浓度过高或过低都对酶活力不利。PAL在硼酸-氢氧化钠缓冲液中适宜的pH范围为7.6～9.2,最适pH有2个:pH8.0和pH8.8。PAL不耐酸碱,尤其不耐碱。PAL适宜的温度范围为35～55℃,最适反应温度为45℃,超过70℃则容易钝化。L-酪氨酸和L-半胱氨酸对PAL活性都有抑制作用,抑制程度随抑制剂浓度增加而增强。L-酪氨酸的抑制作用较强,是PAL的竞争型抑制剂。L-胱氨酸对PAL的活性无影响。     

冬枣果实苯丙氨酸解氨酶酶学特性的研究

研究了冬枣果实苯丙氨酸解氨酶(PAL)的酶学特性。L-苯丙氨酸为枣果实PAL的反应底物,结果表明,最适底物浓度为1.0 mmol/L。枣果实PAL属于别构酶,具有2个米氏常数,Km分别为0.115×10-4、8.177×10-4 mol/L。枣果实PAL最适温度为50℃,最适p H为8.8。在浓度为0~4.0 mmol/L范围里,L-半胱氨酸、酪氨酸、色氨酸、组氨酸均对枣果实PAL活性有一定的抑制作用,而抗坏血酸和蔗糖对PAL有激活作用。金属离子对PAL激活作用由强到弱依次为:Cu2+Fe3+Fe2+Na+;金属离子对PAL抑制作用由强到弱依次为:Al3+Mg2+Mn2+Ca2+Zn2+K+。研究结果揭示了冬枣果实PAL酶学特性,为通过调控枣果实PAL酶活性改善果实贮藏特性提供了理论依据。     

1-MCP处理对鲜切山药贮藏品质的影响

以菜山药为试材,用不同浓度的1-MCP处理山药,在10℃贮藏过程中,定期观察山药的感官品质,测定失重率、可滴定酸、可溶性固形物含量、颜色、多酚氧化酶(PPO)活性、苯丙氨酸解氨酶(PAL)活性,考察不同浓度1-MCP处理对鲜切山药保鲜效果的影响。结果表明,1-MCP处理能显著延缓鲜切山药失重率的下降,保持产品的质量。1.0μl/L和1.5μl/L处理组均可抑制鲜切山药可滴定酸和颜色的变化,提高产品的感官评分。1.0μl/L处理组显著地抑制了相对电导率的上升、PPO活性和PAL活性的上升以及可溶性固形物含量的下降。但0.5μl/L处理对延长鲜切山药货架期无明显作用。     

荔枝果肉苯丙氨酸解氨酶特性的研究

研究了荔枝果肉中苯丙氨酸解氨酶(L-phenylalanine ammonia-lyase,PAL)的酶学特性。荔枝PAL动力学曲线并不遵循米氏方程,其最适底物浓度为2 mmol/L。在硼砂-硼酸缓冲液中,荔枝PAL的最适反应p H为8.7。PAL不耐酸碱,尤其不耐酸。荔枝PAL的最适反应温度为45℃,高于75℃则易于钝化,具有较强的耐热性。L-酪氨酸和L-半胱氨酸对荔枝PAL均有明显的抑制作用;金属离子中,Fe2+和Fe3+对荔枝PAL活性具有明显的促进作用,而Ca2+、Cu2+、Co2+、Ag+离子则对其活性有明显的抑制作用。     

芦笋过氧化物酶和苯丙氨酸解氨酶特性及抑制条件的研究

采用分光光度法对芦笋组织中与老化相关的过氧化物酶(POD)和苯丙氨酸解氨酶(PAL)的酶学特性进行了研究。结果表明,芦笋POD和PAL的最适pH分别为4.0和8.8,且在pH值6的柠檬酸缓冲液中酶活力均明显下降;最适温度分别为55℃和60℃,且在20℃以下和60℃以上活性显著降低;1mmol/L Ca~(2+)显著(P<0.05)抑制芦笋POD和PAL酶的活力;POD和PAL最适底物浓度分别为70μL/100mL和0.02mol/L,Km分别为2.694×10~(-4)mol/L和0.1381mmol/L。     

臭氧处理对黄花梨果实褐变的影响

为研究臭氧处理对梨果实褐变的影响,采用5.0、2.5mg/L 臭氧水和蒸馏水浸泡黄花梨整果和鲜切果,5min后晾干,分别贮于20℃和5℃条件下,对贮藏过程中果实和切片的褐变指数、总酚(TP)含量及与酶促褐变相关的多酚氧化酶(PPO)、过氧化物酶(POD)和苯丙氨酸解氨酶(PAL)活性变化进行研究。结果表明：臭氧处理的黄花梨整果与鲜切果各项指标均优于对照组;臭氧处理显著降低贮藏5d 后黄花梨整果果心和整个贮藏期鲜切片的褐变指数,维持梨整果与鲜切果较高的总酚含量,对二者PPO、POD 活性均有一定的抑制作用;可增加梨整果较高的PAL 活性,抑制鲜切梨果PAL 活性。抑制黄花梨整果和鲜切果褐变以2.5mg/L 臭氧水处理为好。     

曲酸对鲜切山药色泽及相关生理变化的影响

以菜山药(Dioscoreae opposite Thumb)为试材,研究曲酸处理鲜切山药在0℃和4℃条件下货架期内的色泽及相关生理变化。结果表明:质量分数为0.1%,0.3%或0.5%曲酸均不同程度地抑制Hunter L*值的下降和Hunter a*、b*值的上升,有效延缓了褐变;抑制了多酚氧化酶(PPO)、过氧化物酶(POD)和苯丙氨酸解氨酶(PAL)的活性。其中,0.3%,0.5%曲酸在保持鲜切山药片色泽及抑制PPO、POD、PAL活性的效果方面优于1%柠檬酸。     

氧化白藜芦醇协同抗坏血酸抑制余甘子酶促褐变的机制研究

通过研究氧化白藜芦醇协同抗坏血酸对余甘子酶促褐变的抑制作用,以及对其多酚氧化酶的酶抑制动力学研究,探明氧化白藜芦醇联合抗坏血酸协同抑制褐变酶的作用机理。结果表明,0.02%氧化白藜芦醇、0.15%抗坏血酸、0.02%氧化白藜芦醇+0.15%抗坏血酸均能减缓余甘子的酶促褐变,对3种褐变酶即多酚氧化酶(PPO)、过氧化物酶(POD)、苯丙氨酸解氨酶(PAL)活性均有较好的抑制作用;0.02%氧化白藜芦醇+0.15%抗坏血酸联合处理对余甘子的酶促褐变及对PPO、POD、PAL的抑制活性强于单独使用。酶抑制动力学结果表明,氧化白藜芦醇对PPO的IC50为(3.300±0.010) μmol/L,抑制机理为可逆的混合型抑制,而氧化白藜芦醇+抗坏血酸(1∶7)的IC50为(1.600±0.020) μmol/L,抑制机理为可逆的竞争性抑制,协同使用导致抑制方式也发生改变。氧化白藜芦醇对PPO的抑制常数KI为0.904 μmol/L,对PPO-底物形成的复合物的抑制常数KIS为14.285 μmol/L,而氧化白藜芦醇+抗坏血酸(1∶7)对PPO的抑制常数KI为0.840 μmol/L,联合处理对PPO的抑制性加强。     

2,4,2',4'-四羟基查尔酮协同抗坏血酸抑制双孢菇酶促褐变的研究

2,4,2’,4’-四羟基查尔酮(2,4,2’,4’-Tetrahydroxychalcone,THDF)与抗坏血酸(维生素C)协同使用对果蔬酶促褐变有很好的效果。文章探索其协同抑制双孢蘑菇的酶促褐变机制。通过研究THDF、THDF+维生素C对双孢蘑菇褐变作用、褐变酶及褐变相关底物的影响，探究两者对双孢蘑菇褐变的抑制作用。结果表明，THDF、THDF+维生素C对导致蘑菇褐变的多酚氧化酶(Polyphenol oxidase,PPO)、苯丙氨酸酶(Phenylalanine ammonia-lyase,PAL)的活性均有抑制作用，后者较前者抑制作用更强；蘑菇褐变度与PPO活性相关性高于PAL。褐变抑制剂THDF、THDF+维生素C对PPO抑制的IC₅₀值分别为0.05、0.04μmol/L。THDF、THDF+维生素C对PPO的抑制方式均为可逆抑制，前者为竞争性抑制，抑制常数K_I为2.183μmol/L；后者为混合型抑制，抑制常数K_I为3.680μmol/L,K_IS值为2.040μmol/L。PPO是...     

赤霉素处理对采后竹笋木质化的影响

本实验研究了不同浓度的赤霉素(GA3)处理对低温贮藏的竹笋的木质化进程及品质的影响.结果表明,GA 3处理能够抑制竹笋木质素和粗纤维含量的上升,降低过氧化氢和超氧阴离子的含量,抑制苯丙氨酸解氨酶(PAL)和多酚氧化酶(PPO)的活性,同时也延缓了丙二醛含量的增加及品质指标的劣变.100mg/L GA3比50mg/L GA3处理的效果好.     

外源亚精胺处理对香菇木质化及相关酶活力的影响

本实验以香菇为原料,分别用10、15 mg/L和20 mg/L亚精胺溶液进行负压渗透处理,4 ℃贮藏16 d,研究了贮藏过程中硬度和木质素、几丁质、纤维素、总酚含量以及苯丙氨酸解氨酶（phenylalanine ammonia lyase,PAL）、过氧化物酶（peroxidase,POD）活力的变化规律。结果表明：所有处理均不能抑制香菇硬度下降,并均促进了纤维素含量升高;15 mg/L的亚精胺处理能够使贮藏末期几丁质含量不发生明显下降;总酚含量在贮藏过程中先增加后降低;15、20 mg/L的亚精胺处理组能够在4～6 d保持较低的PAL活力;而20 mg/L亚精胺处理在贮藏前期（4～6 d）能抑制POD活力,推迟木质化高峰的到来。     

ClO2杀菌复合壳寡糖涂膜对鲜食糯玉米的保鲜效果

分别采用ClO2杀菌处理、壳寡糖（chitosan oligosaccharide,COS）涂膜处理以及ClO2杀菌复合COS涂膜（ClO2-COS）处理鲜食糯玉米,对比不同保鲜处理对鲜食糯玉米贮藏期间的抑菌情况、多酚含量、木质素含量、木质素积累速率、苯丙氨酸解氨酶活力、过氧化物酶活力的影响。结果发现：200 mg/L的ClO2杀菌复合15 mg/mL COS涂膜处理表现出良好的抑菌能力,贮藏35 d时霉菌和酵母菌总数为（2.30±0.12）（lg（CFU/g））,显著低于ClO2杀菌处理组（（3.78±0.16）（lg（CFU/g）））和COS涂膜处理组（（4.18±0.09）（lg（CFU/g）））（P＜0.05）;ClO2-COS处理能够降低木质素积累速率,降低多酚含量并使其基本保持较低水平;ClO2-COS处理可以抑制苯丙氨酸解氨酶活力过快上升,降低苯丙烷代谢水平,还能降低过氧化物酶活力,使其在贮藏期间一直保持较低水平,从而减少木质素积累。     

Effects of Ethephon on Fresh In‐Husk Walnut Preservation and its Possible Relationship with Phenol Metabolism

Fresh walnuts (Juglans regia L.) are in demand due to their high nutrition value and unique flavor of the kernel. In this study the effects of ethephon on decay control and kernel quality of fresh walnuts and its possible relationship with phenolic metabolism were investigated. Fresh in‐husk walnuts treated with 0, 10, 500, and 8000 mg/L ethephon were stored at 0 ± 0.5 °C for 42 d. Decay incidence, total phenolic (TP) compounds, phenylalanine ammonialyase (PAL), polyphenol‐oxidase (PPO), and peroxidase (POD) activities of green husks, and acid values (AV) and peroxide values (PV) of kernels were assessed at 6‐d intervals. The respiration rate of the whole walnut was assessed at 3‐d intervals. Treatment with 500 mg/L ethephon enhanced respiration, reduced the decay index, and inhibited PPO and POD activity and browning of green husks, and also promoted PAL activity and TP content of green husks. This treatment also reduced the PV and AV of kernels. A concentration of 10 mg/L ethephonhad similar, but weaker, effects on walnuts. Treatment with 8000 mg/L ethephon, however, had opposite effects. These data indicate ethephon treatment at a proper concentration can extend storage life and maintain kernel quality of fresh in‐husk walnuts through the manipulation of phenolic metabolism.     

5-氨基乙酰丙酸对苹果幼果多酚含量、苯丙氨酸解氨酶活性及其基因表达的影响

探究5-氨基乙酰丙酸（aminolevulinic acid,ALA）处理对苹果幼果酚类物质、苯丙氨酸解氨酶（phenylalanin ammonia-lyase,PAL）活性及其基因表达量的影响。在苹果疏果期前,利用不同质量浓度ALA处理苹果幼果,采用紫外分光光度法测定ALA处理后12 d内苹果多酚和PAL活性,利用荧光定量法测定苹果幼果PAL基因表达量。结果表明：ALA处理质量浓度在300 mg/L以内,随着质量浓度提高,苹果多酚含量、PAL酶活性及其基因表达量均升高,到400 mg/L时各项指标均表现出下降趋势;相同质量浓度ALA处理苹果幼果后,幼果的上述3 项指标均随时间延长而明显提高,在第9天时达到最高值,12 d后开始下降。为提高苹果疏果多酚含量,实现疏果的最大利用率,生产中需要选择适宜的ALA处理浓度和时间采集幼果。     

诱导子对烟草植株叶片酶活性及香气物质积累的效应

采用盆栽试验,通过叶面喷施诱导子,考察了诱导子对烟草次生代谢关键酶活性及香气物质积累的影响.结果表明,经诱导子处理过的烟草叶片苯丙氨酸解氨酶、多酚氧化酶和过氧化物酶活性均高于对照,且腺毛分泌物、石油醚提取物、类胡萝卜素、多酚类物质含量也高于对照.综合考虑,100 mg/L浓度的茉莉酸甲酯诱导子和200 mg/L浓度的壳聚糖诱导子处理烟叶较有利于烟草香气成分的生成.     

Chlorophyll degradation and lignification of fresh-cut water fennel treated with a complex chemical solution and subsequent packaging

Fresh-cut water fennel was treated with a novel complex chemical solution and subsequently packaged prior to refrigerated storage. Chlorophyll degradation and lignification were investigated. The complex solution consisted of 1.16 g/L calcium lactate, 150 mg/L zinc acetate, and 15.29 mg/L salicylic acid. Chlorophyllase, Mg-dechelatase, and chlorophyll-degrading peroxidase activities of water fennel decreased after immersion in the complex solution, which delayed chlorophyll degradation and increased L* and a* values. Complex solution treatment also reduced phenylalanine ammonia-lyase (PAL) activity and, thus, inhibited accumulation of lignin. After the complex solution treatment, packaging in high-density polypropylene plastic bags further retained chlorophylls and alleviated lignification of water fennel. Treatment with a complex chemical solution and subsequent packaging can maintain the quality, delay senescence, and improve the shelf life of water fennel.     

Sanitizer treatments alleviate lignification of sliced few-flower wildrice (Zizania latifolia Turcz.)

To investigate the effects of sanitation processing on the lignification of few-flower wildrice (FFW), fresh-cut FFW was treated with water (control), 80 mg/L peroxyacetic acid (PAA), 100 mg/L ClO₂ or 50 mg/L H₂O₂, packed in polyethylene film bags and stored at 2 °C for 21 days. Firmness, lignin, cellulose, hemicellulose and lignin forming related enzymes activities were examined. Sanitizer treatments inhibited the increases of firmness, lignin and cellulose than the control. The changes of hemicelluloses did not show a difference between the control and PAA treatment. An increase in the activities of phenylalanine ammonia lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO), and a reduction in catalase (CAT) and superoxide dismutase (SOD) activities, were detected in the sliced FFW in the incompatible interaction. Compared with the control, sanitizers suppressed the activities of PAL, POD and PPO, but enhanced the activities of SOD and CAT during 21 days of storage. These enzymatic activities varied with different sanitizers. These results show that 80 mg/L peroxyacetic acid (PAA), 100 mg/L ClO₂ or 50 mg/L H₂O₂ sanitation processing can maintain tenderness, alleviate the lignification and fibrosis of fresh-cut FFW.     

Effect of ozonated water treatment on microbial control and on browning of iceberg lettuce (Lactuca sativa L.)

We examined the effect of ozonated water treatment on microbial control and quality of cut iceberg lettuce (Lactuca sativa L.). Fresh-cut lettuce was washed in ozonated water (3, 5, and 10 ppm) for 5 min at ambient temperature. The native bacterial population on the lettuce declined in response to a rise in ozone concentration. However, there was no further bacterial reduction (1.4 log CFU/g) above 5 ppm ozone. Although ozonated water treatment increased the phenylalanine ammonia lyase (PAL) activity of the lettuce stored at 10 degrees C compared with the water wash treatment after 1 day of storage, the concentration of ozone did not affect PAL activity. The a* value of the residue of the lettuce methanol extracts, which reflects the extent of browning, increased dramatically in lettuce treated with 10 ppm ozonated water compared with other treatments. Treatment with 3 or 5 ppm ozonated water resulted in more rapid changes in the a* value than after the water treatment. The combined treatment of hot water (50 degrees C, 2.5 min) followed by ozonated water (5 ppm, 2.5 min) had the same bactericidal effect as treatment with ozonated water (5 ppm, 5 min) or sodium hypochlorite (NaOCl, 200 ppm, 5 min), giving a reduction in bacteria numbers of 1.2 to 1.4 log CFU/g. The ascorbic acid content of the lettuce was not affected by these treatments. The combined treatment of hot water followed by ozonated water greatly inhibited PAL activity for up to 3 days of storage at 10 degrees C. Treatment with this combination greatly suppressed increases in the a* value, thus retarding the progress of browning compared with other treatments throughout the 6-day storage. NaOCl treatment also inhibited browning for up to 3 days of storage. Bacterial populations on the lettuce treated with sanitizers were initially reduced but then showed rapid growth compared with that of the water wash treatment, which did not reduce bacterial counts initially.