基于电子鼻技术对不同类型洋葱提取液的识别

洋葱提取液作为新型的生物果蔬保鲜剂,因天然、安全等特点受到消费者信赖。然而不同类型洋葱提取液对果蔬的保鲜效果并不相同,因此对不同类型洋葱提取液的快速识别是有实践意义的。本试验以云南、甘肃、安徽、四川、山东、江苏的紫皮洋葱,甘肃、吉林、云南的黄皮洋葱和新疆的白皮洋葱为试验对象,测定植物学性状后提取洋葱的提取液,运用电子鼻检测分析提取液的挥发性物质,采用费舍尔判别(Fisher判别)和反向传播神经网络(back propagation neural network, BPNN)建立预测模型。结果表明：电子鼻的10个传感器对不同类型的洋葱提取液的响应值有显著性差异(P < 0.05),Fisher判别模型和BPNN模型均可有效的识别不同类型的洋葱提取液,其中BPNN识别的正确率比Fisher判别高。因此,电子鼻技术结合BPNN更适合不同类型洋葱提取液的识别。     

洋葱皮提取物对营养性肥胖大鼠的减肥作用

研究洋葱皮提取物对营养性肥胖大鼠的减肥作用。采用营养性肥胖模型法,选取茶多酚为阳性对照,分别以茶多酚0.57%、洋葱皮提取物1.33%比例添加于营养饲料中,饲喂营养性肥胖模型大鼠,研究洋葱皮提取物对营养性肥胖模型大鼠的体重、Lee’s指数、摄食量、食物利用率的影响;对洋葱皮提取物的减肥功能进行评价。结果表明,洋葱皮提取物具有控制体重增长的作用;并能有效抑制脂肪细胞膨大,减少体内脂肪堆积。     

Inhibition of lysophospholipase D activity by fish egg extracts

Lysophospholipase D (lysoPLD) is known to convert lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA). In this study, we examined the inhibitory effect of fish egg extracts, containing lipids, on bovine lysoPLD activity. Fish eggs extracts were tested for the inhibition of lysoPLD activity, and the inhibitory action was expressed as 50% inhibitory concentration (IC₅₀). Among fish egg extracts of 20 fish species, the most potent inhibition was expressed by Hairtail egg extract (IC₅₀, 0.07 ± 0.01 mg egg weight/mL), followed by extract of Spanish mackerel egg extract (0.11 ± 0.02 mg egg weight/mL) and extract of Pacific saury egg (0.48 ± 0.03 mg egg weight/mL). In ESI/MS analysis, major lysoPLD-inhibitory lipid components in egg extracts were identified to be species of LPC, LPA and fatty acid. From these results, it is suggested that the strong inhibition of lysoPLD activity by fish egg extracts might be ascribed to the presence of lysophospholipids. In a separate study, enzymatic oxidation using lipoxygenase or non-enzymatic oxidations such as HOCl oxidation or Cu²⁺-catalyzed oxidation enhanced the inhibitory activity to some extent, suggesting that the oxidation of polyunsaturated lysophospholipids might contribute to the increase of lysoPLD-inhibitory action. Taken together, it is suggested that fish eggs may contain potent lipid inhibitors of lysoPLD, and that the inhibitory action of lipid inhibitors was enhanced by oxidative process.     

Relationship between thiosulfinates and pink discoloration in onion extracts,as influenced by pH

The influence of immediate and delayed pH control, and added S-methyl-L-cysteine sulfoxide (MCSO) on the progress of pink discoloration in relation to the fate of thiosulfinates in extracts of yellow onion (Allium cepa) bulbs was evaluated over an incubation period of about 3 weeks at 21–24°C. Greatest discoloration occurred in extracts prepared with immediate pH control at 6.1, and least discoloration occurred at pH 3.2, over the pH range of 3.2–6.1. Initial thiosulfinate levels, in descending order of abundance, occurred at pH 6.1 > 5.0 > 4.2 > 3.2 for extracts subject to immediate pH control. However, over 21 days incubation, the lowest residual levels (ranging 20–60% of maximum levels) were observed for extracts adjusted to pH 3.2 and 6.1. Extracts subject to delayed (10 min after tissue disruption) pH control (initial extract pH of 5.2–5.4) displayed the greatest extent of discoloration, in descending order, at pH 4.0 > 5.0, 6.0 > 3.0. In these samples, initial thiosulfinate levels were similar and the greatest residual thiosulfinate levels over the 21-day incubation period were observed at pH 3.0 and 4.0 (about 50% of maximum levels), with the lowest residual levels observed for extracts adjusted to pH 6.0 (about 20% of maximum levels). Tissue extracts supplemented with 9- to 18-fold excess MCSO were subject to modest increases in both extent of discoloration and thiosulfinate levels.     

Anti-influenza A virus effects of fructan from Welsh onion (Allium fistulosum L.)

A fructan that acts as an anti-influenza A virus substance was isolated from hot water extract of the green leafy part of a Welsh onion (Allium fistulosum L.). The structure of the fructan was characterised and elucidated by chemical and spectroscopic analyses. The fructan was composed of terminal (21.0%) and 2,1-linked β-d-Fruf residues (65.3%) with 1,6-linked β-d-Glcp residues (13.7%). The molecular weight of the polysaccharide and polydispersity was estimated to be 1.5 × 10³ and 1.18, respectively. Although the fructan did not show anti-influenza A virus activity in vitro, it demonstrated an inhibitory effect on virus replication in vivo when it was orally administered to mice. In addition, the polysaccharide enhanced the production of neutralising antibodies against influenza A virus. Therefore, the antiviral mechanism of the polysaccharide seemed to be dependent on the host immune system, i.e., enhancement of the host immune function was achieved by the administration of the polysaccharide. From our observations, the fructan from Welsh onions is suggested to be one of the active principles which exert an anti-influenza virus effect.     

Inhibition of Propionibacterium acnes lipase by extracts of Indian medicinal plants

Lipases play an important role in pathogenesis of acne by hydrolysing sebum triglycerides and releasing irritating free fatty acids in the pilosebaceous follicles. Lipase is a strong chemotactic and proinflammatory antigen. Therefore, lipase has generated a high interest as a pharmacological target for antiacne drugs. The aim of this study was to identify inhibitory effects of plant extracts on the lipase activity of Propionibacterium acnes. Colorimetric microassay was used to determine lipase activity. Extracts from Terminalia chebula and Embelia ribes showed lower IC(50) value (1 μg mL(-1) ) for lipase inhibition as compared to Vitex negundo and Picrorhiza kurroa (19 and 47 μg mL(-1) , respectively). The active component responsible for lipase inhibition was isolated. This study reports for the first time the novel antilipase activity of chebulagic acid (IC(50) : 60 μmol L(-1) ) with minimum inhibitory concentration value of 12.5 μg mL(-1) against P. acnes. The inhibitory potential of plant extracts was further confirmed by plate assay. The organism was grown in the presence of subinhibitory concentrations of extracts from P. kurroa, V. negundo, T. chebula, E. ribes and antibiotics such as clindamycin and tetracycline. Extract from T. chebula showed significant inhibition of lipase activity and number of P. acnes.     

Inhibition of tumor growth with possible immunity by Egyptian garlic extracts

Garlic bulbs (Allium sativum) were extracted with distilled water or ethanol. The extracts were then incubated with Ehrlich ascites carcinoma cells at 37 degrees C for 1 h. These pretreated cells were injected into swiss albino mice which survived over 12 weeks. To the contrary, tumor cells which were pretreated with garlic extracts, produced ascites tumor in all mice that died 2 or 4 weeks after intraperitoneal injection. When mice were treated twice at intervals of 7 days with freshly prepared tumor cells exposed to watery or ethanolic extracts of fresh garlic, they acquired resistance against a challenge with Ehrlich ascites tumor cells. Administration of garlic extracts to mice for at least 2 weeks before tumor transplantation, caused a slight delay of 10-20 days in tumor growth and animal death. Generally, the ethanolic extract of garlic gave more pronounced effect as tumor inhibitor as well as immunity induction than watery extract. No change in serum electrophoretic pattern was detected in mice, whether the tumor cells injected were incubated or not with garlic extract. In animals treated with unincubated tumor cells, albumin and globulin percentages as well as albumin: globulin ratios (A/G) were decreased as compared to normal mice. A/G ratio was also decreased in immunized mice, pretreated with garlic extract, due to the increase of gamma globulin and unchanging of albumin.     

Changes in antioxidant properties and their relationship to paclobutrazol‐ induced flooding tolerance in Welsh onion

BACKGROUND: Flooding is an important factor affecting Welsh onion production, because under such stress the production and quenching of reactive oxygen species (ROS) in plants will fail to be kept in a balanced state. The purpose of this study was to examine the effect of paclobutrazol (PBZ) on the growth and development of Welsh onion plants (Allium fistulosum L.), particularly to evaluate changes in antioxidant properties. RESULTS: Welsh onion plants were treated with 0 and 2 ppm per plant of PBZ, subsequently subjected to non‐flooding and flooding‐stress conditions for 0, 1, 5, 9 and 13 days, followed by a 4‐day drainage period. Flooding stress was judged by any decrease in biomass production and chlorophyll content. The results indicated that PBZ applied to plants was able to protect Welsh onion from flooding stress. The increased levels of antioxidant activity in different systems, including α,α‐diphenyl‐β‐picrylhydrazyl (DPPH)‐radical scavenging activity, superoxide anion radical scavenging, metal chelating activities and reducing power observed on flooding, afforded the Welsh onion improved flooding tolerance. Under non‐flooding conditions, the antioxidative activity of Welsh onion was regulated and elevated by PBZ pretreatment. CONCLUSION: It seems that the PBZ‐induced flooding tolerance of Welsh onion is mediated through increased activities of various antioxidative systems. Thus, pre‐applying 2 ppm per plant of PBZ 24 h prior to flooding could mitigate flooding stress. Copyright © 2008 Society of Chemical Industry     

Use of UV photography to identify aflatoxin-producing strains ofAspergillus flavus andA. parasiticus

UV photography in glucose, yeast extract (GY) agar medium was tested as a simple and rapid method for the distinction of afiatoxin-positive from aflatoxin-negative strains ofAspergillus flavus andA. parasiticus. In the UV photographs aflatoxin-producing moulds were identified as grey or black colonies, whereas aflatoxin-non-producing moulds appeared as white colonies. Of the afiatoxin-positive strains detected by the UV photographic method, 10% was confirmed by extraction of the GY agar medium and mould mycelium in chloroform, extracts which were analysed subsequently using thinlayer chromatography. Confirmation of aflatoxigenic strains was achieved by biosynthesis on liquid medium yeast extract sucrose (YES) broth.     

Comparison of antioxidant activities of onion and garlic extracts by inhibition of lipid peroxidation and radical scavenging activity

The antioxidant activities of the methanol extracts of selected varieties and parts of garlic and onion were determined by two methods: inhibition of lipid peroxidation induced by tert-butyl hydroperoxide in isolated rat hepatocytes and scavenging activity against diphenylpicrylhydrazyl radical. The total phenolics and the main flavonoids of the hydrolysed onion and garlic samples were also analysed. The antioxidant activities obtained by the two methods were compared. Both methods gave similar antioxidant activities for pure compounds and Allium extracts. However, the radical scavenging method had many benefits compared to the lipid peroxidation method, being easier, cheaper, more specific and reproducible. The radical scavenging activities also correlated positively with the total phenolics of the extracts. Onions had clearly higher radical scavenging activities than garlic, red onion being more active than yellow onion. The skin extracts of onion possessed the highest activities.     

Antioxidative properties of onion peel extracts against lipid oxidation in raw ground pork

Onion peels extracted with various concentrations of ethanol were examined for their extraction yield, total phenolic content, DPPH scavenging activity, and reducing power. Onion peel extracted with 50% ethanol exhibited higher extraction yields, total phenolic content, and DPPH scavenging activity than extracts from distilled water, 70 or 95% ethanol. Thus, the antioxidative efficiency to inhibit lipid oxidation of ascorbic acid (0.05%) and 50% ethanol extract of onion peel (0.05, 0.1, and 0.2%) in raw ground pork was investigated during chilled storage (16 days). The pH of the samples decreased considerably during storage (p<0.05). Addition of ethanol onion peel extract significantly improved the thiobarbituric acid reactive substances and peroxide values in raw ground pork meat (p<0.05). Therefore, onion peel extract by 50% ethanol is a very effective inhibitor of lipid oxidation and has potential as a natural antioxidant in raw ground pork.     

Effect of freezing upon alliinase activity in onion extracts and pure enzyme preparations

Alliinase is the enzyme ultimately responsible for the development of the flavour compounds in onions and other alliums. Freezing of onions has been shown to result in a lack of flavour and pungency due to the destruction of alliinase activity. It was therefore thought that the enzyme is susceptible to freezing. However, the results of this paper show that purified alliinase can be stored at –80°C without any loss of activity. The enzyme also remains active after quick freezing of fresh tissue in liquid nitrogen. Inactivation of the enzyme occurs only after slow freezing or thawing procedures. Resu'ts show that cell proteases are not likely to be involved.     

Effects of different polarity of onion skin extracts on antioxidative properties and non-volatile profiles

Onion skins are agricultural by-products that contain high levels of antioxidants, including quercetin and protocatechuic acid. The solubility of extracts can affect their antioxidant capacity in food oil matrices. The antioxidative properties of onion skin extracts with different polarity were compared and the chemical profiles of the extracts were identified by GC-MS. Highly lipophilic, moderately hydrophilic and highly hydrophilic onion skin extracts (HLE, MHE and HHE, respectively) were prepared and their antioxidant properties were tested using in vitro assays and bulk oil or oil-in-water (O/W) emulsions. The most abundant phenolic compounds in the onion skin extracts were quercetin and protocatechuic acid. The lipophilicity levels of HLE, MHE and HHE were 0.674, 0.394 and −1.225, respectively. HLE showed higher antioxidant capacity in bulk oil and O/W emulsion matrices compared to MHE and HHE. The antioxidant capacity of HLE was higher in the O/W emulsion than in the bulk oil system. Therefore, highly lipophilic onion skin extracts can be used as effective natural antioxidants in oil matrices, especially O/W emulsions.     

Antimicrobial and antioxidant activity of crude onion (Allium cepa,L.) extracts

Antioxidant and antimicrobial activity of the ethyl acetate and water subfractions of methanolic extracts of three Spanish onion varieties were assayed. Flavonoids were mainly present in ethyl acetate subfraction being 34.92 ± 0.75, 7.95 ± 0.16, 0.38 ± 0.01 μmol of rutin eq. g^?1 D.W. and its antioxidant capacity was 74.86 ± 1.77, 24.59 ± 0.67, 4.55 ± 0.44 μmol Trolox g^?1 D.W. of Grano de Oro, Fuentes de Ebro and Calçot de Valls varieties, respectively. The antimicrobial activity of flavonol standards and onion extracts was evaluated against some food spoiler microorganisms. Quercetin and kaempferol were inhibitory against gram positive bacteria such as Bacillus cereus, Staphylococcus aureus, Microcroccus luteus and Listeria monocytogenes. Gram negative bacteria Escherichia coli and Pseudomonas aeruginosa were less sensible to the antimicrobial effect of both flavonol standards and Candida albicans was totally resistant. Among the onion extracts tested only ethyl acetate subfraction showed antimicrobial inhibition.     

甘草醇提物抑制霉菌及其抗氧化活性研究

利用超声醇提甘草活性成分,并利用活性成分进行抑制霉菌和抗氧化研究,甘草醇提物对油脂能有效地延长其氧化的反应发生期。甘草醇提物在油脂中的浓度达到0.15%时,其抗氧化效能便超过了维生素C,且随着添加量的增大,其抗氧化效果显著增强。抑菌研究发现高浓度的甘草醇提物有很好的抑菌活性,而且抑菌活性随浓度的升高而增大,低浓度的甘草醇提物无抑菌作用。     

Detection of aflatoxin-producing molds in Korean fermented foods and grains by multiplex PCR

An assay based on multiplex PCR was applied for the detection of potential aflatoxin-producing molds in Korean fermented foods and grains. Three genes, avfA, omtA, and ver-1, coding for key enzymes in aflatoxin biosynthesis, were used as aflatoxin-detecting target genes in multiplex PCR. DNA extracted from Aspergillus flavus, Aspergillus parasiticus, Aspergillus oryzae, Aspergillus niger, Aspergillus terreus, Penicillium expansum, and Fusarium verticillioides was used as PCR template to test specificity of the multiplex PCR assay. Positive results were achieved only with DNA that was extracted from the aflatoxigenic molds A. flavus and A. parasiticus in all three primer pairs. This result was supported by aflatoxin detection with direct competitive enzyme-linked immunosorbent assay (DC-ELISA). The PCR assay required just a few hours, enabling rapid and simultaneous detection of many samples at a low cost. A total of 22 Meju samples, 24 Doenjang samples, and 10 barley samples commercially obtained in Korea were analyzed. The DC-ELISA assay for aflatoxin detection gave negative results for all samples, whereas the PCR-based method gave positive results for 1 of 22 Meju samples and 2 of 10 barley samples. After incubation of the positive samples with malt extract agar, DC-ELISA also gave positive results for aflatoxin detection. All Doenjang samples were negative by multiplex PCR and DC-ELISA assay, suggesting that aflatoxin contamination and the presence of aflatoxin-producing molds in Doenjang are probably low.