五倍子单宁对常见食品腐败菌和致病菌抑制作用研究

研究了五倍子单宁对6种常见食品腐败菌和致病菌的抑菌作用。采用琼脂二倍稀释法和牛津杯法测定了五倍子单宁的最小抑菌浓度及抑菌活性;用扫描电镜观察了高敏杆菌大肠杆菌的形态变化。结果表明,五倍子单宁对各测试菌均有抑制作用,对大肠杆菌效果最好,最小抑菌浓度为0.25mg/mL,并且使菌体出现明显的凹陷。      

Overexpression of Aspergillus aculeatus cellobiohydrolase I in Aspergillus oryzae

To express the cbhI gene, encoding Aspergillus aculeatus cellobiohydrolase I (CBHI), in Aspergillus oryzae, a plasmid was constructed. The strain that displayed the strongest CBHI activity among the transformants produced about 941 mg/l in liquid culture. It was confirmed by a PCR method that the plasmid was integrated at the niaD locus.     

马尾松针黄酮类物质对食品腐败菌的抑制活性

以丙酮、乙醇和水为溶剂提取马尾松针黄酮类化合物,测定了提取物对食品腐败菌的抑菌效果和毒力,并采用颜色反应、薄层层析、红外光谱及比色法对马尾松针丙酮提取物黄酮类物质进行定性定量分析。结果显示,丙酮提取物的抑菌效果最强,抑菌圈直径>18mm,对7种供试菌的EC50分别为:金黄色葡萄球菌18.5236mg/mL、枯草芽孢杆菌43.8153mg/mL、蜡样芽孢杆菌36.5882mg/mL、大肠杆菌33.0075mg/mL、变形杆菌28.2322mg/mL、铜绿假单胞菌14.4666mg/mL、乙型副伤寒沙门氏菌22.1227mg/mL。热处理和紫外光照射对丙酮提取物的抑菌活性无明显影响。颜色反应、薄层层析及红外光谱结果显示丙酮提取物中以黄酮类化合物为主,总黄酮含量为4.218mg/mL。      

两株米曲霉菌种的发酵性能研究

将2株米曲霉扩大培养后用于生产试验,并将其发酵酱油的性能进行对比。结果表明,米曲霉1号酱油的氨基酸态氮、pH值、A530 nm、总氮低于米曲霉2号菌,总酸高于米曲霉2号;米曲霉2号酱油的游离氨基酸总含量为6.05 g/100 mL,是米曲霉1号（4.18 g/100 mL）的1.45倍;米曲霉1号酱油中醇类物质、酸类物质和醚类物质相对含量分别达61.53%、14.16%和1.26%,高于米曲霉2号的57.3%、13.07%和0.46%,而酯类物质（3.73%）、酮类物质（1.83%）和醛类物质（16.33%）低于米曲霉2号的3.96%、1.95%和21.31%;米曲霉1号酱油香气浓郁偏醇香味,米曲霉2号酱油香气浓郁偏酯香;米曲霉2号酱油的加热沉淀达到204 mm2,远高于米曲霉1号酱油的25 mm2。加热后过滤可去除米曲霉2号酱油中的沉淀。     

Molecular monitoring of spoilage yeasts during the production of candied fruit nougats to determine food contamination sources

In the present work, we have analysed the yeast microbiota present in a manufacturing plant of candied fruits and nougats. Four yeasts species (Zygosaccharomyces bailii, Zygosaccharomyces rouxii, Sporobolomyces roseus, and Debaryomyces hansenii) and a filamentous fungi (Nectria mauriiticola) were identified according to restriction analysis of 5.8S-ITS rDNA. These identifications were subsequently confirmed by sequencing the D1/D2 domain of the 26S rRNA gene. Z. rouxii and Z. bailii were isolated at high frequency along the whole manufacturing process. Since food alteration by Z. bailii and Z. rouxii is the cause of important economic losses for the food industry, there is a need for differentiating yeasts at the strain level as an essential part of quality control programs in this industry. For this purpose, we have tested the performance of three molecular techniques (RFLP mtDNA, RAPD-PCR, and microsatellite with (GAC)5 and (GTG)5 primers) to differentiate strains belonging to these two Zygosaccharomyces species. Those techniques with the best discriminatory power were applied to differentiate Zygosaccharomyces species isolates. The results of this analysis indicate that one strain of Z. bailii and two strains of Z. rouxii were involved in the spoilage of candied fruits. Moreover, the Z. bailii strain was also present in the spoiled nougat, hence being responsible of this alteration.     

Physiology of food spoilage organisms.

A thorough understanding of the physiological responses of microorganisms to stresses imposed during food preservation is essential if novel combination systems based on mild food processing procedures are to be developed effectively. The influences of intrinsic characteristics as well as external factors such as water activity, temperature, preservatives, composition of the gaseous atmosphere, etc. on the stress response of microorganisms are discussed. The interaction of spoilage organisms with each other as well as with food pathogens and the ultimate consequences for food safety and quality are also explored in this review.     

Characterization of Staphylococcus aureus strains associated with food poisoning outbreaks in France

Enterotoxins produced by Staphylococcus aureus are responsible for staphylococcal food-poisoning outbreaks (SFPO). In France, SFPO are the second cause of food-borne diseases after Salmonella. However, very little is known about the strains involved. The objective of this study was to characterize the staphylococcal strains related to these SFPO through phenotypic and genotypic analyses. A total of 178 coagulase-positive staphylococcal isolates recovered from 31 SFPO (1981-2002) were screened through biotyping. Thirty-three strains representative of the different biotypes in each SFPO were further examined for SmaI macrorestriction-type, phage-type, resistance to various antimicrobial drugs, presence of staphylococcal enterotoxin (se) genes sea to sei, and production of enterotoxins SEA to SED. All these 33 strains were identified as S. aureus species: 27 were of human biotypes and six ovine or non-host-specific biotypes. Most (74.1%) strains reacted with group III phages. Eleven strains were resistant to at least two classes of antibiotics and among them, two were resistant to methicillin. Twenty-nine strains carried one or several of the eight se genes tested; the gene sea was most common (n=23), and often linked to sed (n=12) or seh (n=5). The novel se genes seg-i were in all cases associated with se genes sea to sed except for one strain which carried only seg and sei. Pulsed-Field Gel Electrophoresis (PFGE) of SmaI macrorestriction digests of the 33 strains discriminated 32 PFGE patterns grouped into nine biotype-specific clusters. All five strains carrying sea and seh were grouped together into the same sub-cluster. Three of the four se-gene-negative strains were in one PFGE cluster: all four should be tested for se genes not included in this study and, if negative, be further investigated for the presence of unidentified SEs.     

两种生产用米曲霉的形状及蛋白酶性质研究

研究对比了两株米曲霉的形态特征以及成曲的蛋白酶酶学性质。结果显示,两株米曲霉的形态差异明显:米曲霉1号菌落较大、发芽和产孢子较快,种曲及成曲颜色偏黄,菌丝较短,孢子较多;而米曲霉2号菌落较小,孢子发芽时间及产孢子时间比1号晚,成曲孢子较1号少,但菌丝长且粗壮,种曲颜色偏绿,成曲颜色偏白,米曲霉2号的产酶能力强。蛋白酶性质的研究结果显示,两株米曲霉成曲的蛋白酶性质有差异,1号和2号的最适反应温度分别为45℃和50℃,最适反应pH分别为6.0和9.0。此外,两株米曲霉的成曲蛋白酶的耐盐性相当,随着盐浓度的增大,酶活力均逐渐降低,在20%氯化钠条件下,酶活力均降至无盐条件下的20%~30%。     

Gamma irradiation of Aspergillus flavus strains associated with Indonesian nutmeg (Myristica fragrans)

Food Science and Biotechnology - The aims of this work were to investigate the effects of gamma irradiation on population, viability and aflatoxin B1 production of Aspergillus flavus strains...     

Overexpression and purification of Aspergillus aculeatus beta-mannosidase and analysis of the integrated gene in Aspergillus oryzae

An expression plasmid for the manB gene encoding Aspergillus aculeatus beta-d-mannosidase (MANB) was constructed by using an expression vector carrying an improved promoter. After transformation of A. oryzae by the plasmid, several transformants formed colonies emitting fluorescence on a plate containing 4-methylumbelliferyl beta-d-mannopyranoside (MU-Man) under UV-irradiation. The transformant that displayed the strongest fluorescence, named A. oryzae BMN1, produced about 270 mg MANB/l in liquid culture. Recombinant MANB overproduced in BMN1 was purified by two steps of column chromatography to a single protein band on SDS-polyacrylamide gel electrophoresis and had a molecular weight of 130,000. Analyses by Southern blotting and genomic PCR demonstrated that a single copy of the plasmid was integrated into the chromosome by recombination at the niaD locus.     

Ochratoxin formation in Aspergillus ochraceus with particular reference to spoilage of coffee

Production of ochratoxin on media by eight isolates of Aspergillus ochraceus from coffee or its processing environment in India, Indonesia, Kenya, and Brazil, and seven Brazilian isolates from other commodities, has been compared with yields in shaken fermentation on shredded wheat and coffee (Coffea arabica). Shredded wheat most consistently allowed expression of biosynthesis of ochratoxins A and B in yields up to 3.5% of the dry product. Culture on artificial media was an unreliable predictor of ochratoxin yield on both shredded wheat and coffee. Coffee was a relatively poor substrate for ochratoxin production particularly when sterilised. Notably, two Asian coffee isolates produced 400 mg kg(-1) ochratoxin A on unsterilised ground green coffee, showing this to be a preferred substrate for further experimentation. The study focused on isolates of A. ochraceus, which from evidence of culture on media would not be expected to be suitable fungi for future studies to establish both the fact of spoilage of coffee by A. ochraceus and the dynamics of ochratoxin formation by isolates of this species.     

棘孢曲霉利用蚕沙发酵产果胶酶的条件优化研究

果胶酶是能够分解果胶物质的多种酶类的统称。本研究以前期选育所得高产果胶酶菌株棘孢曲霉(Aspergillus aculeatus)DW75作为实验菌株,通过蚕沙固体发酵,对产果胶酶的发酵条件进行了优化。通过单因素试验和正交试验得出了该菌株的最佳产酶条件为:发酵培养基初始p H值5.0,最佳氮源硫酸铵添加量0.1%,培养基料水比(W/V)1.8∶2,发酵温度25℃,发酵时间144h。在此优化发酵条件下菌株的产酶能力可达到19.146U/m L,是优化前酶活10.166U/m L的1.88倍。     

Detection of pathogenic and spoilage micro-organisms in food with the polymerase chain reaction

Traditional biochemical and immunochemical methods for the detection of micro-organisms in food have been supplemented by a number of DNA-based methods during the last decade. Besides the development of direct hybridization techniques, emphasis has been laid onin vitroamplification methods.In vitromethods such as the self-sustained sequence replication (3SR) or the nucleic acid sequence based amplification (NASBA), the Q-beta replicase amplification and the ligase chain reaction (LCR) have had, until now, only limited practical relevance for food monitoring and control. The most developedin vitroamplification method is the polymerase chain reaction (PCR) that allows rapid and selective identification of micro-organisms. Because PCR is increasingly raising interest as a detection method in food hygiene and control, an overview of PCR-systems for the detection of bacteria and viruses in food is provided with this paper. Although the PCR method has advantages (particular specificity, sensitivity) it also has limitations, one of which is its inability to allow differentiation between viable and non-viable micro-organisms. Furthermore, the inhibition of PCR by food-derived inhibitors can result in false negative results. Possible reasons for PCR inhibition and ways to differentiate between viable and dead micro-organisms are discussed in this review.     

Analysis of the inhibition of food spoilage yeasts by vanillin

The antimicrobial potential of vanillin, the major component of vanilla flavour, was examined against the growth of three yeasts associated with food spoilage, Saccharomyces cerevisiae, Zygosaccharomyces bailii and Zygosaccharomyces rouxii. Minimum inhibitory concentration (MIC) values of 21, 20 and 13 mM vanillin were determined for the three yeast strains, respectively. The observed inhibition was found to be biostatic. During fermentation, the bioconversion of sub-MIC levels of vanillin in the culture medium was demonstrated. The major bioconversion product was identified as vanillyl alcohol, however low levels of vanillic acid were also detected. Neither the vanillyl alcohol nor the vanillic acid was found to be antagonistic to yeast cell growth. The results indicate the importance of the aldehyde moiety in the vanillin structure regarding its antimicrobial activity and that the bioconversion of vanillin could be advantageous for the yeasts, but only at levels below MIC. These bioconversion activities, presumably catalysed by non-specific dehydrogenases, were shown to be expressed constitutively. It was observed that increased vanillin concentrations inhibited its own bioconversion suggesting that the activity required intact cells with metabolic capacity.     

六氢β-酸抗菌实验研究

以李斯特氏菌为指示菌,研究六氢β-酸的抗菌作用并考察温度、酸碱度、金属离子、非离子表面活性剂等因素对其抗菌性能的影响.结果表明,六氢β-酸对李斯特氏菌有显著的抑制作用,最低抑菌浓度为0.5×10-6g/mL;六氢β-酸具有良好的酸碱稳定性;非离子表面活性剂吐温-80随着浓度的增加抑菌效果而略降低,聚乙二醇-400对抗菌作用没有太大影响;金属离子Na 、K 、Ca2 、Zn2 对抑菌效果有一定的促进作用.     

Insights into the role of quorum sensing in food spoilage

Food spoilage is a consequence of the degrading enzymatic activity of some food-associated bacteria. Several proteolytic, lipolytic, chitinolytic, and pectinolytic activities associated with the deterioration of goods are regulated by quorum sensing, suggesting a potential role of such cell-to-cell communication in food spoilage. Here we review quorum sensing signaling molecules and methods of their detection and quantification, and we provide insights into the role of quorum sensing in food spoilage and address potential quorum sensing inhibitors that might be used as biopreservatives.     

芥末精油包合物对棘孢曲霉的抑菌机理

为探明芥末精油包合物对红毛丹病原菌棘孢曲霉（Aspergillus aculeatus）的抑菌活性及机理,通过扫描电子显微镜、透射电子显微镜结合转录组技术进行观察与分析。结果表明,芥末精油包合物能够显著抑制棘孢曲霉的生长,其半最大效应浓度为1.00 g/L;扫描电子显微镜结果显示菌丝、分生孢子和孢子顶囊的形态发生显著变化且孢子顶囊数量大幅度减少;透射电子显微镜结果显示菌丝细胞不再充盈、细胞壁变薄、细胞膜边界模糊、细胞内部发生了严重的溶解;转录组测序结果显示1 057 个差异表达基因中分别有528 个基因上调和529 个基因下调。采用实时荧光定量聚合酶链式反应对8 个差异基因进行验证,得到与转录组测序结果一致的基因表达量变化趋势。抑菌机制可能涉及以下几方面,包括细胞结构损伤、影响DNA和RNA合成和代谢、抑制酶活性、影响跨膜运输能力、抑制有丝分裂、下调能量代谢水平等。     

Potential of aflatoxin B1 production by Aspergillus flavus strains on commercially important food grains

In this study, we investigated the potential of aflatoxin B₁ (AFB1) production by five Aspergillus flavus strains previously isolated from sorghum grains on cereals (barley, maize, rice, wheat and sorghum), oilseeds (peanuts and sesame) and pulses (greengram and horsegram). Five strains of A. flavus were inoculated on all food grains and incubated at 25 °C for 7 days; AFB1 was extracted and estimated by enzyme‐linked immunosorbent assay. All A. flavus strains produced AFB1 on all food grains ranging from 245.4 to 15 645.2 μg kg^?1. Of the five strains tested, strain Af 003 produced the highest amount of AFB1 on all commodities ranging from 2245.2 to 15 645.2 μg kg^?1. Comparatively, the AFB1 accumulation was high on rice grains ranging from 3125.2 to 15 645.2 μg kg^?1, followed by peanuts ranging from 2206.2 to 12 466.5 μg kg^?1. Less AFB1 accumulation was observed in greengram and sesame seeds ranging from 645.8 to 2245.2 and 245.4 to 2890.6 μg kg^?1, respectively. Our results showed that all food grains tested are susceptible to A. flavus growth and subsequent AFB1 production.