Prevalence,enumeration, and characterization of Salmonella isolated from aquatic food products from retail markets in China

This study aimed to estimate the extent and level of Salmonella contamination of aquatic food products in China, and to determine serotype, virulotype, and the antimicrobial resistance profiles of recovered Salmonella isolates. Out of 554 samples collected from July 2011 to May 2014, 86 (15.5%) tested positive for Salmonella. The highest contamination rate occurred in oysters (23.1%, 6/26), followed by freshwater fish (18.6%, 43/231), shrimp (13.0%, 13/100), and saltwater fish (12.2%, 24/197). The contamination levels generally corresponded to a most probable number (MPN)/g of 0.3–10, although one sample exceeded 110 MPN/g. Among the 103 isolates, S. Typhimurium, S. Wandsworth, S. Thompson, and S. Derby were the most prevalent serovars. Sixty-eight isolates (66.0%) were resistant to at least one antimicrobial, and 35 (34.0%) were resistant to more than three. High rates of resistance were observed for tetracycline (35.9%), ampicillin (28.2%), nalidixic acid (26.2%), trimethoprim-sulfamethoxazole (25.2%), chloramphenicol (20.4%) and streptomycin (18.4%). Of note, S. Thompson isolates exhibited resistance to multiple extended-spectrum cephalosporins, ciprofloxacin, and other antimicrobials. PCR analysis of 15 virulence genes showed that ssaQ, mgtC, siiD, sopB, and bcfC were present in all 103 isolates, whereas the remaining loci were variably distributed. S. Typhimurium, S. Enteritidis, and S. Weltevreden isolates exhibited a wider range of pathogenicity determinants compared with the other strains. Our study provides a comprehensive surveillance on prevalence of Salmonella in aquatic food products from China and indicates its potential risk to public health. These data are valuable for epidemiological studies, risk management, and public health strategies.     

A QM/MM study of the catalytic mechanism of aspartate ammonia lyase

Aspartate ammonia lyase (Asp) is one of three types of ammonia lyases specific for aspartate or its derivatives as substrates, which catalyzes the reversible reaction of l-aspartate to yield fumarate and ammonia. In this paper, the catalytic mechanism of Asp has been studied by using combined quantum-mechanical/molecular-mechanical (QM/MM) approach. The calculation results indicate that the overall reaction only contains two elementary steps. The first step is the abstraction of C_β proton of l-aspartate by Ser318, which is calculated to be rate limiting. The second step is the cleavage of C_αN bond of l-aspartate to form fumarate and ammonia. Ser318 functions as the catalytic base, whereas His188 is a dispensable residue, but its protonation state can influence the active site structure and the existing form of leaving amino group, thereby influences the activity of the enzyme, which can well explain the pH dependence of enzymatic activity. Mutation of His188 to Ala only changes the active site structure and slightly elongates the distance of C_β proton of substrate with Ser318, causing the enzyme to remain significant but reduced activity.     

槲皮素对高脂日粮小鼠学习记忆能力的影响研究

探讨槲皮素对高脂日粮小鼠学习记忆的影响及可能机制。4周龄C57B/L雌性小鼠45只,随机分为三组:对照组（基础日粮）,高脂组（约20%脂肪）,槲皮素组（高脂日粮+0.01%槲皮素）。第26周进行Morris水迷宫实验,实验结束后取小鼠大脑皮层和海马组织测定氧化应激指标,荧光定量PCR检测海马组织中脑源性神经营养因子（BDNF）、核转录因子Nrf2及血红素单加氧酶（HO-1）的基因表达。结果显示,高脂组小鼠学习记忆能力显著下降,脑组织出现明显的氧化应激,Nrf2、HO-1和BDNF基因表达显著下调;槲皮素干预后,大脑氧化应激程度减轻,Nrf2、HO-1和BDNF基因表达上调,学习记忆能力得到显著改善。槲皮素改善高脂日粮小鼠学习记忆,可能与上调Nrf2/HO-1通路及BDNF的基因表达有关。      

Novel mechanisms for the decomposition of 1-(amino acid)-1-deoxy-D-fructoses (Amadori compounds): A mass spectrometric approach

A study of the mechanisms involved in unimolecular mass spectral fragmentations of 1-(amino acid)-1-deoxy-D-fructoses (Amadori rearrangement products, or ARPs) has led to proposals for a number of new mechanistic routes to Maillard reaction products. One of the proposed mechanisms involves decomposition by initial dehydration or dehydroxylation directly from the cyclic hemiketal forms of the ARPs rather than from the open chain carbonyl forms. Another proposed mechanism involves formation of the pyrylium ion which could be the key intermediate in the formation of polymeric material. A number of other important Maillard reaction heterocycles could also be formed via the reactive pyrylium ion. The effect of variation of the ARP amino acid on 1,2- and 2,3-type enolization products was demonstrated. Intramolecular nucleophilic reactions observed in the mass spectral fragmentations also gave clues to the mechanisms of formation of compounds such as β-carbolenes from the tryptophan ARP.     

Effect of ‘wheat Qu’ addition on the formation of ethyl carbamate in Chinese rice wine with enzymatic extrusion liquefaction pretreatment

Ethyl carbamate (EC), which has been confirmed as probably carcinogenic to humans, can be formed during the alcoholic fermentation of Chinese rice wine. In this study, EC and two possible precursors (urea and arginine) were analysed in wines fermented from rice processed by enzymatic extrusion liquefaction pretreatment, with different wheat Qu content gradients from 6 to 18% (dry basis, d.b.). The EC concentration decreased 22.5% with the addition of wheat Qu reduced to 6% for the enzymatic extrusion‐processed rice wine (EE). Moreover, although the arginine was generated 6.33–8.39 times higher in the enzymatic extruded rice, instead of the traditional treated rice at the same wheat Qu level, the corresponding level of urea formed from arginine was not high in the EE. In addition, rice treated by extrusion combined with enzymatic hydrolysis was found to be more utilizable and fermentable, and the lost quality of the final traditional rice wine with the low wheat Qu level (6–14%) could be improved using enzymatically extruded rice as the fermenting material. Therefore, it may be feasible to inhibit EC accumulation in Chinese rice wine by wheat Qu control, combined with enzymatic extrusion pretreatment for rice. Copyright © 2015 The Institute of Brewing & Distilling     

不同种源绿色型香椿特征风味的分析

目的:研究不同种源表型为绿色的香椿香气成分的差异。方法:选用顶空固相微萃取法（HS-SPME）结合气相色谱-嗅闻-质谱（GC-O-MS）联用仪对太和青油椿、永济香椿、十堰香椿、岚皋香椿四个不同种源绿香椿的挥发性成分进行提取和鉴定,并对特征香气成分进行分析。结果:在温度为50℃时,用65 μm PDSM/DVB的萃取头对样品萃取40 min,可以使萃取效率达到最大。采用GC-MS对挥发性成分进行分析,在四种绿香椿中共鉴定出46种挥发性成分,其中永济香椿检测到的挥发性成分最多,共40种,萜烯类化合物有23种,占比最大;而十堰香椿检测到的挥发性成分最少,共26种,萜烯类只有10种。经过嗅闻仪分析,发现绿香椿中有18种特征香气成分,萜烯类和含硫类化合物是绿香椿的主要挥发性成分,其中2-巯基-3,4-二甲基-2,3-二氢噻吩的香气强度最高。结论:这四个不同种源香椿在萜烯类化合物的种类和含量上差异明显,其中青油椿与永济香椿中的萜烯类化合物种类和含量都比较高,因此其风味也优于十堰香椿和岚皋香椿。     

人参、甘草、五味子复合醋提物对老年小鼠急性炎性肝损伤保护作用的研究

目的:本研究旨在通过脂多糖(Lipopolysaccharide,LPS)诱导肝损伤小鼠考察复合醋提物(MVE)对老年小鼠炎性肝损伤的保护效果.方法:将小鼠随机分为正常对照组、MVE组、LPS组、LPS+MVE组.通过苏木精-伊红染色评估肝组织病理情况和免疫组织化学染色判断髓过氧化物酶的表达变化.同时,检测肝组织中白介...     

Properties of amidated pectins. I. Preparation and characterization of amidated pectins and amidated pectic acids

The preparation of high molecular weight pectic acids with varying degrees of amidation (15–61%) is described. The samples are characterized by analytical parameters, viscosity and behaviour on gel permeation and ion-exchange chromatography columns. Results show that the monomer composition is not changed and that aggregation may occur in aqueous solution of highly amidated pectic acids.     

水-离子液体混合溶液对玉米淀粉溶解的影响

研究新型离子液体(ionic liquid,IL)-1-烯丙基-3-乙烯基咪唑醋酸盐对普通玉米淀粉溶解性能的影响.采用偏光显微镜(polarized light microscopy,PLM)、X-射线衍射仪(X-ray diffraction,XRD)、差示扫描量热仪(differential scanning ca...