Desorption isotherms,net isosteric heat and the effect of temperature and water activity on the antioxidant activity of two varieties of onion (Allium cepa L)

The standard static gravimetric method was used to determine moisture desorption isotherms (MDIs) of two onion varieties (Goudami and Galmi Violet) at 30 °C, 45 °C and 60 °C in the water activity ranging from 0.055 to 0.83. The combined effects of temperature and water activity on the antioxidant activities of the onion varieties were also studied. GAB, Oswin, Smith and BET equations were tested to fit the experimental data. The net isosteric heat of sorption was calculated. Equilibrium moisture content (EMC), total phenolic content (TPC) and antiradical activity were also measured. The isotherm and the EMC vary significantly with the onion variety and drying temperature, irrespective of water activity (a_w). Desorption isotherms were best described by the GAB model. The maximum net isosteric heats for Galmi Violet (32.58 kJ mol^?1) were greater than those of Goudami (23.50 kJ mol^?1) at each EMC. The TPC and antiradical activity of the Galmi Violet were significantly (P ≤ 0.05) higher than that of the Goudami at all investigated temperatures and water activities.     

Long-term storage of onion and the factors that affect its quality: A critical review

Storage of onions is a multifaceted issue, which involves many preharvest and postharvest factors. One of the major factors that affect onion storage is the selection of the proper cultivar, since there are significant differences in storability between the cultivars and not all of them are suitable for storage. Proper preharvest and postharvest conditions are essential for storability of onion bulbs, whereas they also affect marketability (weight losses, texture and color depth of bulbs) and quality (chemical composition, nutritional value, antioxidant activity). Irrigation and fertilization are essential preharvest factors that substantially affect storability, whereas curing methods and storage conditions (temperature, relative humidity, controlled atmospheres) and processing treatments are postharvest factors. This review article examines the effect of long-term storage on the main quality features of onions, such as the incidence of sprouting and root growth, water losses, and changes in chemical composition (mineral composition, sugar content, nutritional value) and antioxidant activity (phenolic and flavonoid contents, DPPH [2,2-diphenyl-1-picrylhydrazyl] scavenging activity).     

Effect of storage temperature and size of stalks on quality of minimally processed leeks

Minimally processed leek stalks were produced by trimming of freshly harvested leeks (Allium porrum L.) to sizes of 0–22, 0–11 and 11–22 cm. Trimmed stalks were then stored at 0, 10 and 20 °C in air for 8 days to determine the effects of temperature and stalk size on quality during storage, including inner leaf growth, fresh weight loss and discoloration. Both inner leaf growth and fresh weight loss were increased linearly with storage duration. Growth of cut leek inner leaves was significantly reduced to 4 mm at the end of 0 °C storage in all three types of cut stalks. Inner leaf growth was maximized during storage at 10 and 20 °C in 0–11 cm stalks, medium in 0–22 cm stalks and minimal in 11–22 cm stalks. Fresh weight loss of 0–11 cm size was significantly higher than that of 0–22 cm size at both 0 and 10 °C, whereas there was no difference between 0–11 and 11–22 cm sizes. At 10 and 20 °C the 0–11 cm size lost more weight than the 11–22 and 0–22 cm ones. Differences in color attributes were observed in most cases between stalk sizes, due to different coloration of intact leeks. Discoloration was observed particularly at the stalk base at 20 °C. Low temperatures effectively control discoloration, and reduce considerably inner leaf growth of minimally processed leeks, but do not control it. Copyright © 2005 Society of Chemical Industry     

Effects of Onion (Allium cepa L.) and Garlic (Allium sativum L.) Essential Oils on the Aspergillus versicolor Growth and Sterigmatocystin Production

Abstract: In the present study the effects of individual and combined essential oils (EOs) extracted from onion (Allium
cepa L.) bulb and garlic (Allium sativum L.) clove on the growth of Aspergillus versicolor and sterigmatocystin (STC) production were investigated. The EOs obtained by hydrodistillation were analyzed by GC/MS. Twenty one compounds were identified in onion EO. The major components were: dimethyl‐trisulfide (16.64%), methyl‐propyl‐trisulfide (14.21%), dietil‐1,2,4‐tritiolan (3R,5S‐, 3S,5S‐ and 3R,5R‐ isomers) (13.71%), methyl‐(1‐propenyl)‐disulfide (13.14%), and methyl‐(1‐propenyl)‐trisulfide (13.02%). The major components of garlic EO were diallyl‐trisulfide (33.55%), and diallyl‐disulfide (28.05%). The mycelial growth and the STC production were recorded after 7, 14, and 21 d of the A. versicolor growth in Yeast extract sucrose (YES) broth containing different EOs concentrations. Compared to the garlic EO, the onion EO showed a stronger inhibitory effect on the A. versicolor mycelial growth and STC production. After a 21‐d incubation of fungi 0.05 and 0.11 μg/mL of onion EO and 0.11 μg/mL of garlic EO completely inhibited the A. versicolor mycelial growth and mycotoxins biosynthesis. The combination of EOs of onion (75%) and garlic (25%) had a synergistic effect on growth inhibition of A. versicolor and STC production. Practical Application: A substitution of synthetic preservatives with natural antimicrobial compounds in food safety to control fungal contamination and mycotoxin production.     

不同包装条件下冷却肉品质变化及腐败菌相研究

为寻找冷却猪肉合理的包装方式,延长货架期,将猪后腿肉分别进行托盘包装、真空包装、高氧气调包装（20%CO₂+80%O₂）和低氧气调包装（65%CO₂+35%O₂）处理,并以无包装组为对照,测定样品在4℃贮藏过程中挥发性盐基氮（TVB-N）值、色差值a*、丙二醛（MDA）值、微生物菌落（菌落总数、假单胞菌菌落数和热杀索丝菌菌落数）和感官评分。结果表明:无包装和托盘包装冷却猪肉货架期不超过4 d,高氧气调包装（20%CO₂+80%O₂）货架期为6 d,真空包装和低氧气调包装（65%CO₂+35%O₂）货架期长达9 d。真空和气调包装均有利于延长冷藏猪肉货架期,但真空包装使肉呈暗红色。气调包装中O₂和CO₂的含量影响肉的品质,高氧气调包装有利于好氧菌假单胞菌和热杀索丝菌的生长繁殖,同时促进脂质氧化,但可以很好维持肉色,低氧气调包装（65%CO₂+35%O₂）可以抑制细菌的生长和脂肪氧化。综合各项评判结果,得到最佳包装方式为低氧包装（65%CO₂+35%O₂）。      

Effect of cinnamaldehyde on melanosis and spoilage of Pacific white shrimp (Litopenaeus vannamei) during storage

BACKGROUND: Shrimp is a very perishable product and postmortem changes occur rapidly. Sulfiting agents were once and are still widely used as a preservative in the shrimp industry. However, the application of sulfite in shrimp may pose a risk to human health. Thus development of a natural preservative as a sulfite alternative to extend the shelf life of Pacific white shrimp is urgently needed. RESULTS: The effects of cinnamaldehyde essential oil (1 and 5 g kg^?1) on the shelf life of Pacific white shrimp stored at 4 °C were investigated. As the concentration of cinnamaldehyde increased, residual polyphenoloxidase (PPO) enzyme activity decreased. Kinetic analysis showed that cinnamaldehyde was a noncompetitive inhibitor for the oxidation of L ‐DOPA (L ‐3,4‐dihydroxyphenylalanine) by PPO of Pacific white shrimp. Based on this study, shrimp treated with 5 g kg^?1 cinnamaldehyde possessed the lowest aerobic plate count, total volatile basic nitrogen, and pH values in all treatments after 10 days of storage. According to the results of L*, cinnamaldehyde showed inhibitory activity toward the formation of melanosis. CONCLUSION: Treatment with cinnamaldehyde could improve the sensory properties and extend the shelf life of Pacific white shrimp to 8 days. Therefore, cinnamaldehyde could be used as a promising natural preservative for inhibiting melanosis and preventing the growth of microbes during the chilled storage of Pacific white shrimp. Copyright © 2012 Society of Chemical Industry     

洋葱中抗氧化物质的提取工艺研究

对洋葱中抗氧化活性物质提取工艺及其成分分析进行研究.通过单因素和正交实验,得到洋葱中抗氧化物质提取工艺条件为:乙醇浓度80％,微波温度60℃,微波功率500 W,料液比1:25(g/mL)、提取时间80 s,此条件下得到的提取物对DPPH自由基的清除率最大,达84.51％.提取物活性成分分析表明:提取物中总黄酮含量4.12 mg/g,总多酚含量为6.12 mg/g,多糖含量370.77mg/g.     

The effect of packaging treatment on the storage quality of minimally processed bunched onions

Storage quality of minimally processed (MP) bunched onions, as affected by plastic film packaging, was investigated to determine the optimum packing method for this vegetable product. Five different packaging treatments, including two passive modified atmosphere packaging (MAP), two active MAP and a moderate vacuum packaging (MVP), were used for MP bunched onions. Quality attributes of the samples were evaluated periodically in terms of weight loss, colour, decay ratio, microbial counts and sensory properties during storage at 10 °C for 28 days. Various sealed‐packaging treatments did not significantly influence changes in colour of white stem and green leaf tissues, flesh weight loss and microbiological populations including mesophiles, psychrotrophs and lactic acid bacteria. However, sensory attributes and disease incidence were affected by packaging type. MVP with a gas‐permeable plastic film retained better quality bunched onions, with reduced microbial decay and visual sensory aspects, as compared with the other packages.     

三种洋葱籽脂肪酸成分的对比研究

采用索氏提取法提取洋葱籽油脂肪酸,提取出的脂肪酸经甲酯化处理后用GC/MS法分析和鉴定其组成。三种洋葱籽油中共分离鉴定出23种脂肪酸,主要成分均为亚油酸、油酸和十六烷酸等,其中不饱和脂肪酸占总量的81.35%(白皮)、82.8%(红皮)和78.94%(黄皮)。结果表明,洋葱籽中不饱和脂肪酸含量丰富,且亚油酸含量很高,将其开发成为药食两用功能性调味品,当具有良好应用前景。     

Effect of heat treatment on internal atmosphere and leaf extension of minimally processed leek stalks

Leeks trimmed at 20 cm from their base were immersed in a 55 °C hot water bath. During the heat treatment (HT), the internal gases released from each stalk were collected, and their volume as well as CO₂ and O₂ concentrations were determined. After HT, cooling and storage at 10 °C for 8 days, the weight, maximum leaf extension and internal atmosphere (volume and gas composition) were measured. It was found that HT inhibited leaf extension during storage at 10 °C for 8 days and induced significant modification of the stalk internal atmosphere, both immediately after HT and after storage. Therefore, in heat‐treated leek stalks, the growth zone of the innermost leaves was subjected to an environment of elevated CO₂ concentration, which was accompanied by the inhibition of leaf extension growth.     

鲜湿米粉贮藏过程中品质变化的考察

桂林米粉属于鲜湿米粉,由于其水分含量高、易受微生物污染而不易保存,因此分析其腐败菌及筛选抑菌剂对延长其货架期、保持其口感与营养价值十分重要。为了研究桂林米粉贮藏过程中微生物生长情况,本文从室温贮藏1~3 d的桂林米粉中分离纯化得到13株腐败菌,再通过反证试验得到6株主要腐败菌MF1、MF2、MF3、MF4、MF6和MF12,通过常规鉴定结合分子鉴定确定桂林米粉的主要腐败菌为苏云金芽孢杆菌（Bacillus thuringiensis）、蜡样芽孢杆菌（Bacillus cereus）、贝莱斯芽孢杆菌（Bacillus velezensis）、柠檬酸杆菌属（Citrobacter sp.）和乙酰微小杆菌（Exiguobacterium acetylicum）。通过平板培养从五种食品添加剂中筛选有效抑菌剂及最适抑菌浓度,结果表明,不同浓度的抗坏血酸和柠檬酸对6种腐败细菌均有良好的抑菌效果,最适抑菌浓度分别为90和120 mg/mL。这说明抗坏血酸和柠檬酸可作为桂林米粉的防腐剂,在桂林米粉贮藏保鲜上有一定的应用前景。

     

草莓保存过程中的质构与理化性质变化研究

主要探讨草莓在存放过程中各种质量指标的变化。定时测定了草莓在常温存放过程中穿刺强度、剪切功、还原糖含量、酸度、Vc、色泽、失重等因素的变化,分析了各个指标之间的相关性及与成熟度或者新鲜度的关系。结果显示,草莓在常温存放过程中,水分损失和Vc的损失呈线性变化,总糖和总酸变化不显著,还原糖在存放前期轻微上升,后期几乎不变化,穿刺力与剪切功都呈现对数下降态势,色泽变化前期呈现指数上升趋势,48h后就色泽几乎完全改变。     

微波处理对香菇杀菌及贮藏品质的影响

为了研究微波处理对香菇后期贮藏过程中微生物生长及品质变化的影响,本文以市售原木香菇为对象,测定微波处理后于两个常用贮藏温度下保存的香菇样品的一系列指标,包括微生物、颜色、质构、多酚氧化酶活性、总酚、抗氧化性等。结果表明:合适的微波处理条件(1000W,1min)结合低温冷藏(4℃)可实现对香菇中微生物生长繁殖的抑制,同时维持良好的感官与营养特性。      

不同处理方式对厚皮甜瓜贮藏品质的影响

以‘千玉1号’厚皮甜瓜为试材,采用噻苯咪唑（TBZ）熏蒸、焦亚硫酸钠（Na2S2O5）、1-甲基环丙烯（1-MCP）结合气调贮藏等处理方法,研究了不同处理方式下厚皮甜瓜贮藏期间果实品质的变化。结果表明,厚皮甜瓜经TBZ熏蒸后置于贮藏环境中,放入Na2S2O5和1-MCP,在气体成分5%O2+7%CO2+88%N2、温度（1.0±0.5）℃、相对湿度85%⁹0%条件下贮藏,能延缓果实可溶性固形物含量和可滴定酸含量下降,减少水分散失,抑制相对电导率上升,有效地保存总糖含量和原果胶含量,降低果实腐烂损失,使果实硬度保持在较高水平。经该处理后贮藏50 d,甜瓜商品果率91%,果实外观新鲜,感官品质良好,保鲜效果理想。      

Effect of microbial transglutaminase on spaghetti quality

ABSTRACT:  To examine the potential application of microbial transglutaminase (MTG) on semolina dough properties and quality of raw and cooked spaghetti, the effects of various MTG addition levels on the solubility of proteins, SDS-PAGE pattern of semolina dough proteins, and textural and structural properties of raw and cooked spaghetti were investigated using semolina from a high-protein good variety (MACS 1967) and a low-protein poor variety (PDW 274) durum wheat. To increase the concentration of lysyl residues and possibly enhance the extent of cross-linking of protein matrix by MTG, a commercial soy protein isolate (SPI) was added at a level of 3% (w/w) in combination with MTG, and its effect on semolina dough properties and spaghetti quality was investigated. The addition of MTG significantly decreased the solubility of semolina dough proteins. SDS-PAGE results showed that with increasing levels of MTG, a progressive decrease in the intensity of the bands corresponding to molecular weight of around 66 kDa was observed. Protein cross-linking reaction catalyzed by MTG resulted in changes in dough properties, dry spaghetti quality, cooking quality characteristics, and microstructure of cooked spaghetti. However, the quality improvements were more evident in spaghetti from the poor variety PDW 274 than from the good variety MACS 1967. The results also showed the ability of MTG in the formation of heterologous polymers between SPI and durum wheat proteins to improve the quality of spaghetti samples.     

CO发色对罗非鱼片贮藏过程质量影响

以罗非鱼片为研究对象,通过理化、质构及微生物指标分析CO发色处理对鱼片贮藏质量的影响。结果表明,CO发色处理可将鱼片初始pH由6.75降低至6.62左右。冷藏过程中,发色处理后的样品TVB-N值5d内基本保持稳定,较未发色样品延长约2d;未发色和活体发色样品冷藏5d后硬度、粘性、咀嚼性出现明显下降,但传统发色样品在1d以后上述指标就明显下降;活体发色处理使鱼片初始细菌数量降低,并延缓冷藏过程中的变化。冻藏过程中三种处理方式对鱼片各项质量指标影响不显著。      

不同处理对棉粕储存期间品质的影响

该研究考察了不同方法处理的棉粕,在自然条件下储存15个月的新鲜度和品质变化规律。结果表明,未处理组棉粕的挥发性盐基氮(T–VBN)和硫代巴比妥酸值(TBA)随储存时间的延长而逐渐升高,酸价(AV)先上升后下降。不同处理可显著抑制长时间储存棉粕的T–VBN、AV和TBA的增加,其抑制效果为1 h脱水>0.5 h脱水>9 mm颗粒>3 mm颗粒。