Anaerobic metabolism during short and long term storage of kiwifruit

Kiwifruit were stored in 0.25% O₂ (ULO), 1% O₂ (LO) and 2% O₂ + 5% CO₂ (CA) and the controls were kept in air. The fruit were held at 0 °C for 34 and 94 d of storage and, after these times, were transferred to 20 °C in air for 14 d of shelf life. During the short term storage (34 d), a significant increase in anaerobic metabolites, above all ethanol, was observed in ULO, LO, and CA fruit (166, 131, 120 μL/L). After the shift to shelf life, a large and unexpected increase in PDC (pyruvate decarboxylase), ADH (alcohol dehydrogenase in the direction of ethanol oxidation), LDH (lactate dehydrogenase), and GPT (glutamate-pyruvate transaminase) was observed, resulting in ethanol depletion (ULO) or no further increase, and an increase in acetaldehyde which, in turn, could have hastened fruit ripening. Even the control fruit showed an increase in ethanol during storage and an increase in enzyme activity during shelf life, especially in ADH, but to a lesser extent without an increase in acetaldehyde. During the long term storage, anaerobic metabolites (ethanol and acetaldehyde) still increased and GPT activity rose significantly in the ULO and CA samples. A burst of enzyme activity was also observed during the second shelf life in the CA and LO samples, but not in the control, while in ULO fruit the activity rose continuously. GPT activity showed the highest peaks in CA and ULO fruit. An ethylene burst was observed in ULO and CA fruit during the second shelf life (about 25 μL/kg-h) but not during the first shelf life. The potential role of these enzymes in kiwifruit stress response during storage and shelf life is discussed.     

保加利亚乳杆菌发酵特性的研究

酸奶具有抑制肠道内腐败菌的生长繁殖、克服乳糖不耐症、降低胆固醇含量,甚至抗癌等功能。发酵菌种是生产优质酸奶的关键,保加利亚乳杆菌(现更名为德氏乳杆菌保加利亚亚种,Lactobacillus delbrueckiisubsp.bulgaricus)是酸奶发酵中最常见的发酵菌种之一。为进一步了解保加利亚乳杆菌的发酵特性,本文对保加利亚乳杆菌的产酸、产黏、产香(主要是乙醛)特性进行了测定。结果表明,该菌种产酸和产黏能力在发酵期强,后发酵期间能力较弱;产香能力则在后发酵期间逐渐增强。     

超高效液相色谱(UPLC)同时测定水性胶黏剂中甲醛、乙醛、丙烯醛

建立了超高效液相色谱(UPLC)法同时测定水性胶黏剂中甲醛、乙醛和丙烯醛的分析方法.水性胶黏剂采用去离子水进行振荡萃取,在酸性条件下,经2,4-二硝基苯肼(DNPH)衍生化后,采用ACOUITY UPLC(R)BEH C18 2.1 mm×100 mm(1.7 μm)柱为分离柱,以乙腈-水为流动相,采用优化后的条件二极管阵列检测器进行检测,分析时间为8.0 min.结果表明,甲醛、乙醛、丙烯醛的回收率分别为:100.66％、96.57％、99.56％,相对标准偏差为2.1％～3.4％;该方法分析时间短、流动相消耗量少、结果准确可靠,适合于水性胶黏剂中甲醛、乙醛和丙烯醛的快速测定.     

乙醛、丙醛和反式石竹烯在黄瓜发育和贮藏过程中的变化

采用固相微萃取(SPME)气相色谱(GC)法,对黄瓜在20 ℃下贮藏和果实发育过程中乙醛、丙醛和反式石竹烯的含量变化进行了分析。结果表明,反式石竹烯在果实贮藏3 d后全部消失,而在发育过程中其含量并不随发育天数的变化而变化。乙醛和丙醛则随着果实发育和贮藏天数的增加而逐渐减少,丙醛的变化趋势更为明显。