遮光及复光处理对紫叶狼尾草叶色及生理变化的影响

为探寻光照对紫叶狼尾草（Pennisetum setaceum ‘Rubrum’）的叶色及生理变化的影响,以自然光为对照,用透光率为10%的遮阳网对其进行遮光处理,直至新叶成熟完全变绿后,撤去遮阳网用自然光进行复光处理,而后测量各阶段的叶色参数和相关生理指标的动态变化。结果显示,遮光后紫叶狼尾草新叶为绿色,叶色参数L、b值显著增加,a值显著减少;生理指标叶绿素a、叶绿素b含量显著增加,花色素苷、类黄酮、可溶性糖含量和苯丙氨酸解氨酶（phenylalnine ammonialyase,PAL）、查尔酮异构酶（chalcone isomerase,CHI）活性显著减少,PPO多酚氧化酶（polyphenol oxidase,PPO）、过氧化物酶（peroxidase,POD）活性无明显变化。复光处理后,叶色逐渐转紫,叶色参数变化与遮光相反;生理指标变化与遮光后减少或增加的指标呈相反趋势,PPO、POD活性变化不明显。     

油菜素内酯对香蕉不定芽增殖的影响

以香蕉不定芽为材料,MS+6-BA 4.0 mg·L-1+NAA 0.2 mg·L-1为基本培养基,采用单因素试验设计方法,研究油菜素内酯对香蕉不定芽增殖及酶活性变化的影响。结果表明,随着香蕉不定芽的形成,不加油菜素内酯,SOD活性逐渐下降,然后急剧上升;POD活性先上升,然后不断下降。油菜素内酯处理下SOD活性总体呈下降-上升-下降的变化规律,POD活性呈下降-上升-下降的规律。培养基中加入0.3 mg·L-1油菜素内酯的香蕉不定芽中的可溶性糖(3.73 mg·g-1)、脯氨酸含量(67.10μg·g-1)和株高(5.00 cm)都显著高于其他处理。     

水稻OsUAP2基因生物信息学分析及原核表达活性鉴定

UAGPase广泛存在于生物体,是糖代谢过程中一类重要酶。我们前期发现水稻Os UAP1具有单向催化UDPG分解代谢活性,Os UAP2与Os UAP1序列相似性极高。本研究对Os UAP2进行生物信息学分析,构建并表达重组蛋白,并鉴定其酶蛋白活性。结果表明,OsUAP2基因位于4号染色体,编码区序列长1482 bp,编码493个氨基酸;Os UAP2具有UDPGP保守结构域,无跨膜区域,N-端不含信号肽;二级结构分析显示,该蛋白含α-螺旋和无规则卷曲较多;同源性分析表明,Os UAP2与玉米UAGPase的亲缘关系最近。在16℃下经0.1 mmol/L IPTG诱导8 h,原核菌株BL21表达出分子量约55 kD可溶性重组蛋白。体外酶活性测定表明,Os UAP2能同时催化UDPG降解和合成,表现出双向可逆催化的特点。本研究结果为进一步深入研究OsUAP2基因的生物学功能提供了科学依据。     

Combined effects of sodium chlorite dip treatment and chitosan coatings on the quality of fresh-cut d’Anjou pears

This study evaluated the effects of sodium chlorite (SC) alone and its sequential treatment with edible coatings on browning inhibition and quality maintenance of fresh-cut d’Anjou pears. Edible coatings were prepared from chitosan (CH) and its water-soluble derivative carboxymethyl chitosan (CMCH), separately. Pear wedges were immersed in SC solution, followed by coating with CH or CMCH solutions. The samples were packed in unsealed bags and stored at 4 °C for subsequent color, firmness, and weight loss measurement. The effects of the SC and coating treatments on polyphenol oxidase (PPO) inhibition and microbial inactivation were also evaluated. Results indicated that SC exhibited significant (P < 0.05) inhibition of browning and PPO activity. The SC treatment was also strongly effective in inactivating Escherichia coli O157:H7 on pear slices. Coating SC-treated pear slices with CH adversely affected the quality of pear slices by accelerating the discoloration of cut surfaces and increasing the PPO activity. On the contrary, coating SC-treated samples with CMCH significantly prevented the browning reaction and inhibited PPO activity. In addition, SC and CH/CMCH coatings maintained tissue firmness and did not affect weight loss. Our study may provide a scientific basis for the use of SC + CMCH treatment as an alternative preservation treatment for fresh-cut fruits and vegetables.     

Effect of antioxidants in controlling enzymatic browning of minimally processed persimmon ‘Rojo Brillante’

‘Rojo Brillante’ is an important variety of persimmon that after removal of the astringency with high levels of CO₂, maintains firmness and sweetness, making possible its commercialization as a fresh-cut commodity. However, the commercial success of the product is limited mainly by enzymatic browning. This work presents the effect of a wide range of antioxidants on enzymatic browning of ‘Rojo Brillante’ persimmon combining in vitro (extracts and precipitates) and in vivo (cut tissue) studies. Preliminary screening of the antioxidants, determined by absorbance and color measurements of persimmon extracts and pellets, showed that 4-hexylresorcinol (Hexyl), citric acid (CA) and calcium chloride (CaCl₂) were effective at controlling browning at 10 mM; whereas, ascorbic acid (AA) required a higher concentration (25 mM). Peracetic acid, cyclodextrin, cysteine, and hexametaphosphate were not effective at controlling browning, even at a concentration of 50 mM. In in vivo studies, AA (1.12%) and CA (0.21%) were the most effective treatments to control enzymatic browning of fresh-cut material, reaching the limit of marketability in 5–7 days, whereas, Hexyl and CaCl₂ did not reach 1 day of storage. The results showed that optimum concentrations in cut tissue did not always correlate with the in vitro studies, indicating that antioxidants have an effect not only in browning reactions, but also in metabolic activity and cell wall changes during wound-induced reactions. The results provide relevant information for further development of minimally processed ‘Rojo Brillante’ persimmon during storage at 5 °C.     

氧等离子体改性酶解木质素/杨木纤维复合材料热压工艺研究

采用响应面法优化了氧等离子体改性酶解木质素/杨木纤维复合材料的热压工艺参数。结果表明,纤维含水率和热压温度对复合材料的物理力学性能有显著影响。优化后的热压工艺参数范围为:热压温度205～210℃,纤维含水率17%～20%,热压时间63～68 s/mm。     

A multispectral vision system to evaluate enzymatic browning in fresh-cut apple slices

Increased regulation of chemical fumigants has forced the almond industry to seek alternatives for postharvest control of insect pests in raw almonds. This paper reports developments of non-chemical treatment for postharvest disinfestation of almonds using radio frequency (RF) energy. A pilot-scale 27 MHz RF unit was used to evaluate effects of a RF treatment protocol on quality attributes in treated in-shell and shelled almond samples. The RF treatment protocol used 0.75 kW RF power, a forced hot air at 63 °C, back and forth movements on the conveyor at 0.56 m/min, and single mixing, which all improved the final heating uniformity. RF treatments sharply reduced the heating time from 86 and 137 min for hot air heating to only 6.4 and 8.8 min for the center of 1.5 kg in-shell and 2.4 kg shelled almond samples to reach 63 °C, respectively. Almond quality was not affected by the RF treatments because peroxide values, fatty acid and kernel color of treated almonds were better than or similar to untreated controls after 20 d at 35 °C, simulating 2 years of storage at 4 °C. RF treatments did not significantly affect the kernel moisture content of both types of almonds but reduced the moisture content in the shell. RF treatments may hold great potential to replace chemical fumigation for disinfesting almonds.     

酶解油菜蜂花粉抑制超氧阴离子自由基的研究

【研究目的】探讨油菜蜂花粉中水溶性有效组分的抗氧化能力及其在黄嘌呤氧化酶体系中抑制O2-.的机理。【方法】采用酶解技术和膜分离技术提取分离油菜蜂花粉中水溶性抗氧化有效组分,用黄嘌呤氧化酶体系测定酶解物的不同相对分子质量级分淬灭超氧阴离子自由基(O2-.)的能力。【结果】实验结果表明,经酶解和超滤后得到的相对分子质量大于1000的组分抑制O2-.的效果非常显著【结论】酶解和膜分离技术是提高花粉抗氧化功效成分含量的有效途径。     

棉花纤维中木质素的相对分子量

分子量是聚合物的重要特性之一,木质素的分子量及其分布是研究苯丙烷类结构的反应、物理化学特性和评价其改性产物质量的内容之一。本研究以陆地棉TM-1成熟纤维为材料,分别利用酶解-温和酸解木质素法和二氧六环法提取棉纤维中木质素,结合凝胶渗透色谱法(gel permeation chromatography,GPC)调查和评价2种方法获得的棉纤维中木质素的相对分子量。结果表明,经二氧六环处理提取的棉花纤维中的木质素(dioxane lignin,DL)的重均分子量为2924g mol~(–1)、数均分子量2403 g mol~(–1),略高于由酶解-温和酸解处理提取的木质素(enzymatic hydrolysis-mild acidolysis lignin,EMAL)的重均分子量(2169 g mol~(–1))和数均分子量(1970 g mol~(–1)),EMAL的多分散系数稍低,说明木质素的均一性比DL高。表明EMAL法提取的木质素更适用于分析棉纤维中木质素的相对分子量。利用EMAL法分析棉纤维中木质素相对分子量表明,不同棉花品种的木质素重均分子量分布范围为938~2169 g mol~(–1),数均分子量分布范围为857~1970 g mol~(–1),多分散性系数在1.09~1.74间,均小于2。重均分子量与纤维马克隆值呈显著负相关,数均分子量与纤维长度呈显著负相关,与纤维马克隆值呈极显著负相关。     

花生乳状液体系中蛋白质的酶解动力学研究

采用碱性蛋白酶Alcalase 2.4L水解花生乳状液体系中蛋白质,研究了蛋白酶在乳状液体系中的水解特性。结果表明：蛋白质水解度随着初始酶浓度的增加而提高,在酶浓度一定的情况下水解度随着初始底物浓度的提高而降低。蛋白质水解度与乳状液的破乳率存在显著正相关(r=0.983)。在花生乳状液体系中Alcalase 2.4L的水解动力学参数Km=0.0698mol/L,Vmax=3.71×10-4mol/(min·L)。由实验数据推导出蛋白质酶解初级阶段的动力学方程,确定蛋白质水解和乳状液破乳的临界初始底物质量浓度为8.73g/L（加酶量为0.05%）。在酶和底物初始浓度以及反应时间确定的前提下,通过动力学方程可预测破乳过程中蛋白质的水解度及破乳率。