固体酸SO42-/TiO2催化葡萄糖制备乙酰丙酸甲酯

通过沉淀.浸渍法制备了一系列不同焙烧温度的SO<,4><'2->/TiO<,2>固体酸催化剂,用于在甲醇中催化转化葡萄糖制备乙酰丙酸甲酯,探讨了不同反应条件及催化剂重复使用次数对乙酰丙酸甲酯得率的影响,并利用XRD和NH<,3>-TPD对使用前后的催化剂的结构和酸性进行了表征.实验结果表明:500℃焙烧3h的催化剂,在...     

茉莉酸甲酯诱导采后番茄果实抗病的作用

为寻找安全无毒的采后保鲜防病途径,探讨茉莉酸甲酯(MeJA)在采后番茄果实诱导抗病性中的作用和机制。以绿熟期“丽春”番茄为材料,接种灰霉菌,并观察该菌对诱导抗病性的作用,研究MeJA对采后抗病的反应及其诱导作用,并对不同处理中番茄果实抵抗病原菌侵染能力、茉莉酸类物质含量、植物抗菌物质含量的诱导差异进行检测。结果表明：外源MeJA处理能够有效抑制番茄果实采后病害的发生,提高果实对琏格孢霉(Alternaria solani)、灰葡萄孢霉(Botrytis cinerea)、扩展青霉(Penicillium expansum)、匍枝根霉(Rhizopus stolonifer)病原菌侵染的广谱抗性,并通过诱导包括病程相关蛋白、酚类、番茄红素在内的抗菌物质积累,达到诱导抗病效果。     

Effect of methyl jasmonate on quality and antioxidant activity of postharvest loquat fruit

BACKGOUND: Loquat fruit is rich in natural antioxidants and has shown a remarkably high antioxidant activity. To search for an effective method for maintaining or even improving antioxidant activity during postharvest storage, we investigated the effect of 10 µmol L^?1 methyl jasmonate (MeJA) treatment on levels of major individual sugars and organic acids, total phenolics, total carotenoids, total flavonoids and antioxidant activity in loquat fruit during storage at 1 °C for 35 days. RESULTS: The MeJA‐treated fruit exhibited significantly lower levels of respiration rate, ethylene production, phenylalanine ammonia‐lyase and polyphenol oxidase activities, and higher levels of sugars, organic acids, total phenolics and total flavonoids than control fruit. Meanwhile, the treatment also maintained significantly higher antioxidant activity as measured by the scavenging capacity against 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH), superoxide and hydroxyl radicals, and by the reducing power test compared to the control. There was a significant positive linear relationship between total phenolic content and DPPH radical scavenging activity. CONCLUSION: MeJA treatment can improve the quality and functional properties of harvested loquat fruit by maintaining a higher level of antioxidants and enhancing antioxidant activity. Copyright © 2009 Society of Chemical Industry     

Control of anthracnose rot and quality deterioration in loquat fruit with methyl jasmonate

BACKGROUND: Loquat (Eriobotrya japonica Lindl.) fruit has a short shelf‐life, mainly due to fungal decay. Current control of postharvest disease of the fruit is mainly dependent on fungicides. However, because of the increasing consumer concern over food safety, there is an urgent need to search for effective alternatives to control disease. The objective of this work was to determine the efficacy of methyl jasmonate (MeJA) in controlling anthracnose rot caused by Colletotrichum acutatum and maintaining quality of loquat fruit. RESULTS: Loquat fruit were treated with 10 µmol L^?1 MeJA and wound inoculated with C. acutatum spore suspension of 1.0 × 10⁵ spores mL^?1 24 h after treatment, and then stored at 20 °C for 6 days. The percentage of infected wounds showing decay symptom was reduced from 54.4% to 16.7% and the lesion diameter was reduced from 7.26 mm to 4.00 mm by MeJA treatment on the 4th day after inoculation. MeJA treatment induced higher activities of two defense‐related enzymes—chitinase and β‐1,3‐glucanase—during 6 days storage. Meanwhile, the treatment inhibited increases in fruit firmness and internal browning index, and maintained higher extractable juice rate and total soluble solids and titratable acidity contents, thereby delaying the development of flesh leatheriness. CONCLUSION: MeJA treatment effectively inhibited anthracnose rot and maintained quality in loquat fruit. Inhibition of the disease was mainly because of resistance induced in loquat fruit by MeJA. A postharvest application of MeJA could be an alternative to chemical fungicides for control of postharvest disease in loquat fruit. Copyright © 2008 Society of Chemical Industry     

Alcohol dehydrogenases that catalyse methyl formate synthesis participate in formaldehyde detoxification in the methylotrophic yeast Candida boidinii

Methyl formate synthesis during growth on methanol by methylotrophic yeasts has been considered to play a role in formaldehyde detoxification. An enzyme that catalyses methyl formate synthesis was purified from methylotrophic yeasts, and was suggested to belong to a family of alcohol dehydrogenases (ADHs). In this study we report the gene cloning and gene disruption analysis of three ADH-encoding genes in the methylotrophic yeast Candida boidinii (CbADH1, CbADH2 and CbADH3) in order to clarify the physiological role of methyl formate synthesis. From the primary structures of these three genes, CbAdh1 was shown to be cytosolic and CbAdh2 and CbAdh3 were mitochondrial enzymes. Gene products of CbADH1, CbADH2 and CbADH3 expressed in Escherichia coli showed both ADH- and methyl formate-synthesizing activities. The results of gene-disruption analyses suggested that methyl formate synthesis was mainly catalysed by a cytosolic ADH (CbAdh1), and this enzyme contributed to formaldehyde detoxification through glutathione-independent formaldehyde oxidation during growth on methanol by methylotrophic yeasts.     

茉莉酸处理对采后葡萄果实贮藏期间落粒的影响

以"巨峰"葡萄果实为试材,研究了茉莉酸甲酯(methyl jasmonate,MeJA)处理对采后葡萄果实在1℃贮藏期间落粒的影响。结果显示:10μmol/L MeJA处理可显著降低葡萄果实贮藏期间落粒率和腐烂率,并延缓果穗离区组织中脱落酸(ABA)含量和乙烯释放量的上升、赤霉素(GA3)含量的下降以及ABA/GA3比值的增长,并显著抑制离区果胶甲酯酶(Pectinesterase,PME)活性的下降和多聚半乳糖醛酸酶(Golygalacturonase,PG)活性的上升。同时,经MeJA处理的果穗离区细胞壁中胶层中乙醇不溶物(AIR)和Na2CO3溶性果胶含量也明显高于对照水平,而水溶性和环己二胺四乙酸(CDTA)溶性果胶含量却低于对照水平。实验表明,MeJA处理可通过调控葡萄果穗离区组织中内源激素水平来平衡细胞壁水解酶PME和PG的活性,从而抑制离区细胞壁中胶层的水解,维持细胞壁结构的完整,最终降低采后葡萄果实的落粒率,起到改善果实贮藏品质的效果。     

Effects of ripening on microstructure and texture of “Ameixa d’Elvas” candied plums

The plums used to produce a traditional candied product, “Ameixa d’Elvas”, were obtained from two orchards, Vila Viçosa (VV) and Cano (CA). These orchards were selected because the fruits were behaving differently: (1) The day of harvesting for candying, established by the total soluble solids and titratable acidity, was one week earlier in VV; (2) VV yielded candied plums with good texture properties whereas CA gave poor processed fruits. In order to understand the origin of these differences, fruits from both orchards were harvested on the day established as the harvesting day for VV (day 1) and for CA (day 8). Comparable texture properties were obtained in firmness, rigidity and deformation work between the VV fresh plums harvested on day 1 and the CA plums harvested on day 8 but these were lower in CA when the flesh was analysed separately, in accordance with the activities of pectin methyl esterase (PME), polygalacturonase (PG) and cellulase (Cel). The increase of the intercellular area of parenchyma cells and the decrease in cell area caused by boiling, which resulted in a pronounced loss of textural properties, were partially recovered after the immersion of the fruits in sucrose syrup. The CA plums harvested on day 8 had a more pronounced degradation with boiling and lower recovery of cell shape, size and textural characteristics than had those of VV harvested on day 1. Upon candying, similar properties were observed for the fruits harvested on the same day: good candied products were observed for VV and CA fruits harvested on day 1 and poor candied products were observed for VV and CA fruits harvested on day 8. This work shows that the characteristics of the flesh of the fresh fruits are key parameters in defining the textural properties of the candied plum. The establishment of the harvesting moment for candying should take into account the changes that occur in the flesh of the plums during ripening.     

二叔丁基氮氧自由基对AN_MA和MMA的高效阻聚作用

用混浊法和沸腾法分别研究了二叔丁基氮氧自由基(DTBNO)对丙烯腈(AN)及丙烯酸甲酯(MA)、甲基丙烯酸甲酯(MMA)自由基聚合的阻聚作用。结果表明,DTBNO对AN有较强的阻聚作用;DTBNO与对苯二酚(HQ)、苯醌(BQ)、二乙基羟胺(DEHA)等分别组成二元混合物时,其阻聚效果非常明显。当DTBNO-DEHA和DtBNO-HQ的浓度(ppm,下同)比分别为500:1000和1000:500时,对AN的阻聚效果最好;在二元混合阻聚剂中加入适量吩噻嗪(PT),其阻聚效果更佳,如DTBNO-DEHA-PT(500:500:500)在100℃时可使MMA完全终止聚合反应。     

磷钨酸催化合成二苯甲烷二氨基甲酸甲酯

以磷钨酸为催化剂,考察了苯氨基甲酸甲酯(MPC)与甲醛缩合制备二苯甲烷二氨基甲酸甲酯(MDC)的工艺条件。结果表明,磷钨酸对二苯甲烷二氨基甲酸甲酯的合成具有较好的催化效果;在二乙二醇二乙醚为溶剂,n(MPC)∶n(HCHO)=5∶1,催化剂用量m(磷钨酸)∶m(MPC+HCHO)=(0.08～0.10)∶1,于110℃反应4.5h的条件下,MDC的收率为64.9%,选择性达到80.9%。     

氮化硼填充甲基乙烯基硅橡胶导热复合材料的性能

用0.3,6.0,20.0μm 3种粒径的氮化硼(BN)(质量比为1:1:3)混合填充甲基乙烯基硅橡胶(MVQ),研究了BN用量对MVQ导热系数、热失重、热膨胀系数、硫化特性的影响.结果表明,随着BN用量的增加,MVQ的导热系数和热分解温度升高,热失重量和热膨胀系数明显降低,但对MVQ的硫化反应影响不大;当BN填充量为150份时,MVQ的综合性能较佳.