羊肉屠宰加工场主要污染菌的分布及其对熟制羊肉的致腐能力

对江苏省苏州市具有代表性的某羊屠宰场的屠宰环境及熟制品加工车间进行微生物检测,重点对熟制品加工过程进行检测,包括煮制车间的接触面、各加工车间的空气以及清洗前后的生肉与煮制后的熟肉,以确定熟制品加工过程中污染菌群的分布。结果表明,熟制品加工过程中各加工车间空气细菌数均低于10 CFU/皿,表明空气质量合格。而煮制车间的接触面污染较严重致使交叉污染造成熟制羊肉的菌落总数达到3.23(lg(CFU/cm~2))。结合形态观察和16S rDNA菌种鉴定,所污染的菌主要为芽孢杆菌、腐生葡萄球菌、变形杆菌、金黄杆菌和微杆菌等。随后选取3个污染菌芽孢杆菌(Bacillus sp.M1、Bacillus sp.M9)和腐生葡萄球菌(Staphylococcus saprophyticus M7),通过对熟制羊肉的感官评分、pH值、菌落总数、挥发性盐基氮值和腐败代谢产物产量因子的测定评定它们对熟制羊肉的致腐能力。结果显示,Bacillus sp.M1的致腐能力最强且明显高于S.saprophyticus M7和Bacillus sp.M9,为有效预防和控制熟制羊肉的微生物污染提供依据。     

冷鲜猪肉内外细菌菌群分离鉴定及变化规律研究

采用选择性培养基,分别对冷鲜猪肉内外的菌相组成进行分析鉴定,并研究其在储藏过程中的变化规律。实验鉴定出热杀索丝菌、假单胞菌、乳酸菌、肠杆菌科各2株以及葡萄球菌属1株;热杀索丝菌为托盘包装冷鲜猪肉的主要优势菌;整个培养过程中肠杆菌科和假单胞菌生长趋势明显;肉块内部的微生物生长速度高于肉块表面。     

高光谱图像对灰葡萄孢霉、匍枝根霉、炭疽菌的生长拟合及区分

利用高光谱成像系统获取真菌在马铃薯葡萄糖琼脂板上培养期间的高光谱图像,采用400～1 000 nm全波段光谱响应值,并计算全波段的平均值、波峰716 nm处的光谱值和全波段内光谱值第1主成分的得分值,利用这3 种参数计算方法构建真菌生长模拟模型。结果表明,3 种方法建立的模型测试集的决定系数（R2）为0.722 3～0.991 4,均方误差和均方根误差分别为2.03×10－4～5.34×10－3、0.011～0.756。建立的生长模型与传统菌落计数法建立的生长模型之间的相关系数为0.887～0.957。另外,主成分分析和偏最小二乘法判别分析可以区分3 种不同菌种。其中,偏最小二乘法判别分析模型对培养36 h的3 种真菌及对照组的区分准确率为97.5%。高光谱图像技术能够用来对真菌生长进行模拟和真菌的种类区分。     

食品中酵母菌的分离鉴定及其致腐能力

参照食品安全GB 4789.15-2010《食品安全国家标准 食品微生物学检验 霉菌和酵母计数》中酵母菌的检测方法,从水果、蜂蜜中分离筛选酵母菌并根据其26S rDNA D1/D2区序列进行鉴定。从蜂蜜、草莓、香蕉、橙子、油桃、芒果中共分离得到3 株固囊酵母（Citeromyces matritensis）、3 株异常威客汉姆酵母（Wickerhamomyces anomalus）、12 株季也蒙毕赤酵母（Meyerozyma guilliermondii）、1 株长孢洛德酵母（Lodderomyces elongisporus）、2 株葡萄有孢汉逊酵母（Hanseniaspora uvarum）和1 株海洋酵母菌（Metschnikowiareukaufii）。将每种酵母菌接种于苹果、油桃和香蕉中与空白对照进行对比,以食品腐烂的速率来判断酵母菌的腐败能力,确定了W. anomalus和 C. matritensis是上述3 种水果中主要的腐败酵母菌,除此之外,M. reukaufii对油桃有较强的腐败作用,M. guilliermondii对香蕉的腐败效果明显。食品工业中加强对上述这些腐败酵母菌的检测与控制,可以更好地防止腐败酵母对于食品工业造成的危害。     

冷藏海鲈鱼优势腐败菌的筛选和鉴定

分离鉴定4 ℃冷藏条件下海鲈鱼的优势腐败菌,通过选择性培养基筛选获得单一菌株,对各菌株进行致腐能力的测定,确定冷藏海鲈鱼的优势腐败菌。对冷藏海鲈鱼的优势腐败菌进行菌落形态观察及部分生理生化实验、16S rDNA分子鉴定。结果表明,有4 株冷藏海鲈鱼优势腐败菌,其中1 株为草莓假单胞菌（Pseudomonas fragi）,1 株为腐败希瓦氏菌（Shewanella putrefaciens）,其余2 株为假单胞菌（Pseudomonas sp.）。在4 ℃冷藏条件下,草莓假单胞菌的致腐能力最强,其次是腐败希瓦氏菌和假单胞菌。     

Detection of culturable and viable but non‐culturable cells of beer spoilage lactic acid bacteria by combined use of propidium monoazide and horA‐specific polymerase chain reaction

Current methods of detecting beer spoilage lactic acid bacteria (LAB) are time‐consuming and do not differentiate between viable and non‐viable bacteria. In this study, a combination of the conventional polymerase chain reaction (PCR) and propidium monoazide (PMA) pretreatment has been described to circumvent the disadvantages. The horA‐specific PMA‐PCR described here identifies beer spoilage LAB based not on their identity, but on the presence of a gene that is shown to be highly correlated with the ability of LAB to grow in beer. The results suggest that the use of 20 µg/mL or less of PMA did not inhibit the PCR amplification of DNA derived from viable, but putatively non‐culturable (VPNC) Lactobacillus acetotolerans. The minimum amount of PMA to completely inhibit the PCR amplification of DNA derived from dead L. acetotolerans cells was 1.5 µg/mL. The detection limit of established PMA‐PCR assays was found to be 100 VPNC cells/reaction for the horA gene. Furthermore, the horA‐specific PMA‐PCR assays were subjected to 18 reference strains, representing 100% specificity with no false positive amplification observed. In conclusion, the use of horA‐specific PMA‐PCR allows for a substantial reduction in the time required for the detection of potential beer spoilage LAB and efficiently discriminates between live and dead cells. Copyright © 2016 The Institute of Brewing & Distilling     

水果腐败关键病原微生物检测研究进展

果蔬病害腐败会导致严重的经济耗损,不仅会影响经济效益,也会损失水果中果胶、蛋白质等营养成分,人食用含有致病微生物的腐败水果后也会引发一系列疾病。造成水果腐败的关键致病微生物主要为霉菌及酵母菌,霉菌主要有葡萄孢属(Botrytis)、青霉属(Penicillium)和链格孢属(Alternaria),酵母菌主要包括掷孢酵母属(Sporobolomyces)、梅奇酵母属(Metschnikowia)。其中,霉菌占有主要地位,造成食品腐败变质的霉菌以青霉属为主。目前,检测水果腐败的关键致病微生物的方法主要包括分子生物学方法、生化检测技术、依靠代谢组学的检测方法以及免疫学技术等。研究拓展关于水果腐败的关键致病微生物的检测方法,对于预防控制水果病害及提高水果产出质量都有十分重要的意义。本文主要介绍引起水果腐败的关键致病微生物的形态及其适宜生长条件,同时着重论述检测腐败水果中关键致病微生物的方法。     

125th Anniversary Review: Bacteria in brewing: The good,the bad and the ugly

Beer is a beverage that is produced in a multistage process, where some stages of that process are intentionally influenced by microorganisms, while at other stages of the production process microorganisms are actively discouraged. Most of the intentional microbial activity is facilitated by yeast; however bacteria also play an influential role in beer production. This paper will describe the beneficial role of bacteria in the beer production process (the Good), but will also pay due attention to the negative influences bacteria might have on the quality of beer as a commodity (the Bad), and the properties of beer that have given it the status of an inherently safe food for human consumption with regards to disease‐causing bacteria (the Ugly). Copyright © 2013 The Institute of Brewing & Distilling     

Microbiological spoilage of vacuum and modified atmosphere packaged Vietnamese Pangasius hypophthalmus fillets

This study investigated the identity, growth and metabolite production of micro-organisms causing spoilage of Pangasius hypophthalmus fillets packaged in air, vacuum and modified atmospheres (MAP) (MAP 1: 50%CO(2)-50%N(2) and MAP 2: 50%CO(2)-50%O(2)) during storage at 4 °C. Based on the time it took for psychrotrophic total colony counts to exceed 7 log cfu g(-1), the shelf life of the fillets packaged in air, vacuum, MAP 1 and MAP 2 was estimated to be 7, 10, 12 and 14 days respectively. The longest lag phases were observed in the samples packaged in MAP 2 (50%CO(2)-50%O(2)). In the fillets packaged in air and under vacuum, the dominant flora identified by partial 16S rDNA sequencing at the end of the shelf life generally consisted of Gram-negative bacteria mostly belonging to the genera Serratia and Pseudomonas. In contrast, lactic acid bacteria (Carnobacterium maltaromaticum and Carnobacterium divergens) and Brochothrix thermosphacta were identified as the dominant spoilage flora in the samples packaged under the two MAPs investigated. By means of solid-phase microextraction gas chromatography mass spectrometry (SPME GC-MS) analysis, volatile organic compounds in the headspace of the samples at the end of the shelf life were identified for each packaging condition. Based on these results, a selective ion flow tube mass spectrometry (SIFT-MS) method was developed to quantify the production of volatile metabolites during storage of the fillets. The results of these analyses indicated that several compounds contributed to the bacterial spoilage of Pangasius fillets e.g., ethanol, 2,3-butanediol, diacetyl, acetoin, ethyl acetate, acetic acid and sulfur compounds. It also emerged that the production of these compounds was dependent on the packaging condition applied.     

Occurrence of non-lactic acid bacteria populations involved in protein hydrolysis of cold-stored high moisture Mozzarella cheese

The aim of this study was to analyse non-lactic acid bacteria populations (NLABPs) and evaluate their role in proteolysis of cold-stored high moisture (HM) Mozzarella cheese. NLABPs reached values close to 8 log cfu mL⁻¹ after seven days of cold storage. Sequencing of 16 rDNA and rpoB genes and molecular biotyping allowed to identify 66 bacterial strains belonging to 25 species from 15 genera, mainly represented by Pseudomonas, Acinetobacter, and Rahnella. Fifteen strains showed proteolytic activity values higher than 1000.00 μg Gly mL⁻¹ after 24 h of growth in skimmed milk. Moreover, as shown by Urea-PAGE, 11 proteolytic strains caused partial or total disappearance of at least one of the caseins. Their proteolytic behaviour was assessed even when they grew inside the governing liquid together with HM Mozzarella cheese at 4 °C for 12 days. This is the first report that throws light on the complexity of NLABPs in HM Mozzarella cheese, demonstrating that some strains caused the partial hydrolysis of α, β, and γ caseins on its outer surface where a concomitant wrinkling and successive exfoliation became visible without significant changes in texture characteristics.