金黄色葡萄球菌污染牛奶后的代谢产物研究

为解决食品安全中存在的隐患,作者构建了气相色谱-质谱（GC-MS）结合顶空固相微萃取（HS/SPME）技术用于探究金黄色葡萄球菌的挥发性代谢产物,并结合代谢组学和基因组学分析牛奶中金黄色葡萄球菌的差异性代谢产物及其代谢途径。结果表明,金黄色葡萄球菌的差异性代谢物包括N-甲硫基甲酰胺、1-丁醇、乙酸、乙苯、均三甲苯、辛酸、苯甲酸、正癸酸、十二烷酸、乙醇、苯酚和丙二醇。之后对其进行基因组学分析得到金黄色葡萄球菌主要是以基础的生命代谢为主,明确了代谢网络中参与代谢的物质（乙醇、乙酸、1-丁醇）的代谢途径和相关基因。本研究为金黄色葡萄球菌的生物标志物研究提供了理论基础。     

乳源凝固酶阴性金黄色葡萄球菌挥发性代谢特征分析

为探究乳源金黄色葡萄球菌的挥发性代谢特征,从牛乳中分离得到5株凝固酶阴性金黄色葡萄球菌(31B、0250H、777H、S12-1和S2-2),采用顶空固相微萃取/气相色谱-质谱联用技术,分别对接种这5株菌的胰蛋白胨大豆肉汤(tryptic soy broth,TSB)和牛乳的挥发性代谢产物进行动态测定。结果表明,TSB中5株菌总计检出33个挥发性代谢产物,1-丁醇、乙酸、3-甲基-丁酸和2-丁酮是5株菌共同检出的典型挥发性代谢产物。牛乳中5株菌总计检出28个挥发性代谢产物,2-呋喃甲醇、辛酸和3-甲基-丁酸是5株菌共同检出的典型挥发性代谢产物。无论是在TSB还是牛乳中,3-甲基-丁酸始终是凝固酶阴性金黄色葡萄球菌稳定的挥发性代谢产物。不同菌株产生3-甲基-丁酸的强度不相同,同一菌株在TSB和牛乳两种不同基质中3-甲基-丁酸的产生强度也不相同。     

古井桃花曲中一株酵母菌的鉴定及其发酵代谢产物分析

为探寻古井桃花曲中微生物与古井贡酒风味物质之间的相关性,以古井桃花曲中分离出的一株酵母菌为研究对象,通过形态特征观察并利用Biolog微生物鉴定系统进行鉴定,采用顶空气相色谱与质谱联用(HS-SPME-GC-MS)技术和气相色谱分析技术对其发酵代谢产物进行分析。结果表明,该菌株为异常毕赤酵母(Pichia anomala),其主要挥发性产物为乙酸乙酯、苯乙醇、乙醇、4-乙烯基-2-甲氧基苯酚、己酸乙酯、3-甲基丁醇、乙酸异戊酯、乙酸等多种香味物质,28℃培养72h,产乙酸乙酯量为3.586g/L。     

平遥与月盛斋酱牛肉挥发性成分分析

采用同时蒸馏萃取法结合气质联用技术对平遥和月盛斋酱牛肉的挥发性成分进行分析鉴定,结果分别鉴定出64、63种挥发性成分,其中,共有的成分为柠檬烯、乙酸乙酯、2,3-戊二酮、3-羟基-2-丁酮、苯甲醛、苯乙醛、十四醛、十五醛、十六醛、乙醇、2-甲基二氢-3(2H)-呋喃酮、糠醛、5-甲基糠醛、茴香脑、十六酸等物质;平遥酱牛肉特有的成分有(E)-2-辛烯醛、3,4-二甲基苯甲醛、异丙醇、2-丁醇、2-甲基吡嗪、2,6-二甲基吡嗪、乙酸、癸酸等物质;月盛斋酱牛肉特有的挥发性物质有松油烯、反式石竹烯、2-庚酮、薄荷烯酮、(E)-肉桂醛、桉叶油醇、芳樟醇、4-萜烯醇、2-乙酰基呋喃等成分。     

温度对固相微萃取法分析南果梨果酒香气的影响

应用顶空固相微萃取法(HS-SPME)和气质联用(GC-MS)快速测定南果梨果酒中的香气成分。设立不同的温度条件,研究温度对固相微萃法分析南果梨果酒香气成分的影响。结果表明,在不同温度下,酯类和醇类化合物是鉴定出的主要香气成分;乙醇、乙酸乙酯、2- 甲基-1- 丙醇、异戊醇、2- 甲基-1- 丁醇、丁酸乙酯、乙酸异戊酯、3- 甲硫基丙酸乙酯、苯乙醇、癸酸乙酯是不同温度下共有的成分,温度在40℃鉴定出的香气成分种类最多。     

基于SPME-GC-MS法比较新疆哈萨克族不同居住区奶酪风味差异

采用顶空固相微萃取-气相色谱-质谱联用技术,对采集自新疆哈萨克族不同居住地区20?种奶酪样品中挥发性风味组分进行研究。结果表明：20?种奶酪样品中共检测出52?种主要挥发性化合物,其中主要特征风味包括酸类（乙酸、丁酸、庚酸、辛酸）、醇类（乙醇、苯乙醇、3-甲基丁醇）、酯类（乙酸乙酯、己酸乙酯、辛酸乙酯、丁二酸二甲酯）、酮类（2-壬酮、2-庚酮、乙偶姻）、醛类（正己醛、庚醛、壬醛）等。主成分分析显示不同地区奶酪的挥发性风味组分差别较大,和地区相吻合,其中伊犁地区和哈密地区奶酪风味物质差异显著,得到明显区分。阿勒泰和塔城地区奶酪风味成分相似度较高,归为一类。伊犁地区样品主要风味物质乙酸、乙酸乙酯、3-甲基-1-丁醇乙酸酯、己酸乙酯、2-甲基丁酸乙酯、3-羟基-2-丁酮、2-丁醇、2-羟基丙酸乙酯和2-甲基丙醇含量较高,区别于其他地区样品。哈密地区样品中,巴里坤（H1）风味物质良好,明显区别于同地区其他样品,其中醛类（己醛、2-庚醛、壬醛、苯甲醛）、酯类物质（丙酸乙酯、乙酸丁酯、丙酸丁酯、2-丙烯酸丁酯、丁酸丁酯）和2-壬酮含量较高。     

乙酸2-甲基-1-丁酯与2-甲基-1-丁醇共沸体系萃取精馏分离的模拟

在杂醇油的后继处理中,涉及到乙酸2-甲基-1-丁酯与2-甲基-1-丁醇的共沸问题.通过实验验证了乙酸2-甲基-1-丁酯与2-甲基-1-丁醇的共沸温度.讨论了通过选用不同的萃取剂二甲基亚砜(DMSO)和N,N-二甲基甲酰胺(DMF),研究不同的操作条件(进料温度、进料板位置、萃取剂进料量、原料配比、回流比)共沸体系乙酸2-甲基-1-丁酯与2-甲基-1-丁醇的分离情况,得到了最终的优化分离条件.     

三种食源性致病菌挥发性代谢产物谱快速检测研究

主要采用固相微萃取-气质联用(SPME-GC-MS)技术,检测了副溶血弧菌、大肠杆菌和金黄色葡萄球菌三种食源性致病菌的挥发性代谢产物谱(MVOCs),研究其变化规律和代谢特征性产物。结果表明,65μm PDMS/DVB纤维头萃取30min效果最好,三种致病菌MVOCs谱随培养时间延长而变化,其中,两株副溶血弧菌出峰数在30h达到最大值,可检出数分别为28和31个,特征性成分为2-氯-4-(4-甲氧基苯基)-6-(4-硝基苯基)嘧啶、二叔丁基过氧化氢、3-甲基-1-丁醇等;大肠杆菌和金黄色葡萄球菌在12h和8h出峰数最多,可检出数为42和47个,特征性成分分别为环十二烷、2-甲基-1-丁醇和吲嗪、3-甲基丁酸和4-甲氧基苄腈等。实验结果为寻找三种食源性致病菌挥发性标志物和快速检测提供研究基础。     

清香型大曲酿酒酵母株系分类及其可挥发代谢产物分析

为解析牛栏山清香型大曲酿酒酵母（Saccharomyces cerevisiae）的遗传多样性和株系分类,研究了清香型大曲酿酒酵母的菌株分型,并对不同株系酿酒酵母进行了代谢产物分析。利用传统分离方法及聚合酶链反应（PCR）鉴定技术从牛栏山清香型大曲中分离酿酒酵母,对酿酒酵母IGS1区VR1/VR2片段进行单链构象多态性（SSCP）基因多态性分析和菌株分型,确定酿酒酵母种下的不同株系,并利用固态发酵实验分析不同株系酿酒酵母的可挥发代谢产物。结果表明,牛栏山清香大曲酿酒酵母可分为5个株系,其中一个数量较为优势,在模拟发酵中,5种酿酒酵母发酵产物主要为酸、醇、酯3大类共28种风味物质,其风味种类差异较小,但在乙酸、3-甲基丁醇、2-甲基丙醇、苯乙醇和壬酸乙酯生成量之间存在较大差异。     

酵母酒精发酵中杂醇油形成影响因素的研究

<正> 杂醇油和乙醇一样,也是酵母酒精发酵的正常代谢产物,它主要由高级醇中正丙醇,异丁醇(2-甲基-1-丙醇)、异戊醇及活性戊醇(2-甲基-1-丁醇)组成。其中以异戊醇(3-甲基-1-丁醇)为主,一般占总量的50％以上。 高级醇是饮料酒类风味的重要组成物之一,是酒中呈香,呈味物质。少量的高级醇赋予白酒特殊的风味,但含量过高则影响产品的质量,并对人体有害。因此在蒸馏酒中将它列为质量指标,予以控制。国家卫生标准规定,各类白酒(以60°酒汁)中杂醇油含量不得超过0.15g/100ml。     

沙门氏菌污染豆腐干和牛肉干后代谢物的研究

鼠伤寒沙门氏菌可引发沙门氏菌病,且耐药性强,严重危害人畜健康。利用气相色谱-质谱法（Gas Chromatography - Mass Spectrometer,GC-MS）显示沙门氏菌接种于NB培养基、豆腐干和牛肉干培养基后的代谢物,采用主成分分析和正交偏最小二乘判别鉴别特征性和差异性代谢产物,结合沙门氏菌的基因注释分析特征性和差异性代谢产物可能的代谢路径。结果表明：沙门氏菌污染两种食品后有显著的生长,特征性和差异性代谢产物包括烷烃,酚类及小分子酸、醇等;沙门氏菌的基因注释表明存在大量的碳水化合物代谢基因,参与了1-丁醇的生成,因此1-丁醇是沙门氏菌污染豆腐干和牛肉干的典型代谢物。     

Effects of Tropical Citrus Essential Oils on Growth, Aflatoxin Production, and Ultrastructure Alterations of Aspergillus flavus and Aspergillus parasiticus

Ethyl acetate extracts and hydrodistillated essential oils from five cultivars of tropical citrus epicarps were evaluated for their inhibitory activities against Aspergillus fumigatus, Aspergillus niger, Aspergillus flavus, Aspergillus parasiticus, and Penicillium sp. using disk diffusion and broth microdilution assays. Essential oils prepared from kaffir lime (Citrus hystrix DC) and acid lime (Citrus aurantifolia Swingle) epicarps exhibited stronger antifungal activity to all fungi than their ethyl acetate extracts with minimum inhibitory concentration and minimum fungicidal concentration values of 0.56 and 1.13 mg/ml (dry matter), respectively, against aflatoxin-producing A. flavus and A. parasiticus. The dominant components of the essential oil from kaffir lime were limonene, citronellol, linalool, o-cymene, and camphene, whereas limonene and p-cymene were major components of acid lime essential oil. Pure limonene, citronellal, and citronellol were five to six times less fungicidal than the natural essential oils, indicating the synergistic activity of many active compounds present in the oils. Kaffir and acid lime essential oils significantly reduced aflatoxin production of A. flavus and A. parasiticus, particularly lime essential oil, which completely inhibited growth and aflatoxin production of A. flavus at the concentration of 2.25 mg/ml. Target cell damage caused by acid lime essential oil was investigated under transmission electron microscopy. Destructive alterations of plasma and nucleus membrane, loss of cytoplasm, vacuole fusion, and detachment of fibrillar layer were clearly exhibited in essential-oil-treated cells.     

Production of cyclopiazonic acid by aflatoxigenic and non-aflatoxigenic strains of Aspergillus flavus

96 strains of Aspergillus flavus isolated from samples of stored grain and smoke-dried meat products were examined for ability to produce cyclopiazonic acid and aflatoxins, grown on mycological broth medium and malt extract agar. Five strains produced cyclopiazonic acid in the range of 0.5 — 30 mg/kg and 9 produced aflatoxin B1 (0.1 — 14.8 mg/kg) but none of them produced both cyclopiazonic acid and aflatoxins.     

Identification of novel metabolites from Aspergillus flavus by high resolution and multiple stage mass spectrometry

The filamentous fungus Aspergillus flavus is one of the most important species in the Aspergillus genus and is distributed worldwide as a prevalent aflatoxin-producing food and feed contaminant. A. flavus contains more than 55 gene clusters that are predicted to encode proteins involved in secondary metabolite production. One of these, cluster 27, contains a polyketide synthase (pks27) gene that encodes a protein that is highly homologous to the aflatoxin cluster PKS. Comparative metabolomics, using ultra-high performance liquid chromatography (UHPLC) coupled to high resolution Orbitrap mass spectrometry (MS) was used to detect metabolites differentially expressed in the A. flavus wild-type and ?pks27 mutant strains. Metabolite profiling was aided by a statistical differential analysis of MS data using SIEVE software. This differential analysis combined with accurate mass data from the Orbitrap and ion trap multiple stage MS allowed four metabolites to be identified that were produced only by the wild-type culture. These included asparasone A (358 Da), an anthraquinone pigment, and related anthraquinones with masses of 316, 340 and 374 Da. These latter three compounds had similar fragmentation patterns to that of asparasone A. The 316 Da anthraquinone is particularly interesting because it is most likely formed by incorporation of seven malonyl-CoA units rather than the eight units required for the formation of asparasone A. The 340 and 374 Da metabolites are the dehydration and an oxy-derivative of asparasone A, respectively. Asparasone A was also identified in extracts from several other Aspergillus species.     

Biochemistry of non-starter lactic acid bacteria isolate Lactobacillus casei GCRL163: Production of metabolites by stationary-phase cultures

Physiological and metabolic traits of Lactobacillus casei strain GCRL163 were studied in a buffered semi-defined medium supplemented with different concentrations of lactose. The extent of growth (maximum OD₆₀₀ reached) was limited by concentrations of ≤1% lactose in this medium. Survival of the strain during extended incubation periods (up to 30 days) in cultures without lactose was found to be better than in cultures supplemented with lactose. Important metabolites detected in lactose-starved (0% lactose) cultures were acetate, as a major end product, as well as ethanol, diacetyl, 3-methyl-1-butanol, benzyl alcohol, 1-butanol, isopropanol, 3-(methylthio)-propanoic acid and other compounds. Viability of recovered cells declined but metabolic products continued accumulating, when the pH was kept constant at pH 5.2. It was proposed that cells entered a non-culturable state but remained metabolically active. Results indicated the potential of this strain, as a possible non-starter lactic acid bacteria adjunct, to survive and utilize alternative available substrates as energy source in cheese curd.     

Effect of Select Parameters of the Sourdough Rye Fermentation on the Activity of Some Mixed Starter Cultures

The effect of select parameters (i.e., rye flour ash content, temperature, and dough yield) of the sourdough fermentation on the fermentation activity of different starter cultures (lactic acid bacteria Lactococcus lactis ssp. Lactis, Weissella confusa, Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus helveticus, and yeast Kluyveromyces marxianus subsp. Marxianus) was determined. The major metabolic end products of fermentation (D, L-lactic acid, acetic acid, ethanol and glycerol) and the evolution of total phenolic content and folic acid during bread making were measured. Lactobacillus helveticus and Kluyveromyces marxianus allowed obtaining sourdoughs with the highest lactic acid/acetic acid ratios. The mixed starter culture with Lactococcus lactis and Saccharomyces cerevisiae generated the most important quantities of D/L lactic acid. The maximum values of ethanol concentration were obtained in case of the sourdoughs from whole rye flour fermented at lower temperature (30°C) with mixed starter cultures containing Sacchomyces cerevisiae. The fermentation process and type of starter culture are also tools to increase the bioactive compounds, enabling the increase of the phenolic content of the sourdough.     

Monitoring Chemical Changes in Cheddar Cheese During Aging by High Performance Liquid Chromatography and Gas Chromatography Techniques

The concentrations of several chemical metabolites in Cheddar cheese were monitored by various chromatographic techniques during the aging process to learn which metabolites were the best predictors of the glycolytic, lipolytic, and proteolytic age of the cheese. Pyruvic, lactic, acetic, and propionic acids were measured by ion-exchange high performance liquid chromatography; acetone, 2-butanone, ethanol, 2-pentanone, 2-butanol, and n-propanol were monitored by headspace gas chromatography; free fatty acids were quantitated (without derivatization) by gas chromatography; and free amino acids were determined as their o-phthaldehye derivatives by high performance liquid chromatography.The best predictors of the glycolytic age were propionic acid and acetic acid; the best predictors of lipolysis were the free fatty acids C₁₀, C₁₂, C₁₄, and C₁₆; and the best predictors of proteolysis were the free amino acids leucine, methionine, and glutamic acid. The volatile metabolites determined by headspace gas chromatography were not good indicators of aging; however, they did provide useful information related to flavor problems.Cheddar cheese aged at elevated temperatures produced propionic acid, acetic acid, and free amino acids at significantly faster rates than the other chemicals that were monitored.     

Flavour of sourdough wheat bread crumb

This study investigates the effect of adding sourdough to wheat bread dough on the production of flavour compounds in wheat bread crumb. The sourdoughs were fermented with starter cultures of lactic acid bacteria alone and in combination with sourdough yeasts. The volatile compounds in the bread crumb were isolated by a dynamic headspace technique and extraction analysis, analysed by gas chromatography (GC), and identified on the basis of GC retention times for reference compounds and mass spectrometry (MS). The chemical analyses were combined with sensory evaluation. The volume of the loaves increased significantly when the doughs had 5–20% sourdough added compared with the control bread (bread without sourdough). In the sourdough bread, the content of acetic acid, 2-methylpropanoic acid, and 3-methylbutanoic acid was generally higher, and loaves made with the addition of sourdoughs fermented withLactobacillus plantarum, L. delbrueckii, orL. sanfrancisco had a higher content of 2- or 3-methyl-1-butanol than control bread. Interactions were seen between the starter cultures and the sourdough yeasts, and the production of the following compounds was increased depending on the starter culture used and on the sourdough yeast: ethanol, 2-methylpropanol, 2/3-methyl-1-butanol, 2-phenylethanol, benzyl alcohol, acetic acid, 2-methylpropanoic acid, and 3-methylpropanoic acid. Bread made with an addition of 5% to 15% sourdough fermented withL. sanfrancisco had a pleasant, mild and sour odour and taste.L. plantarum bread had a strong, sour and unpleasant odour and a metallic sour taste with a sour aftertaste, but when the sourdough was also supplemented with the sourdough yeastSaccharomyces cerevisiae, the bread attained a more aromatic wheat bread flavour, which may be caused, in part, by a higher content of 2/3-methyl-1-butanol, 2-methylpropanoic acid, 3-methylbutanoic acid and 2-phenylethanol.