Ercolini Danilo, Russo Federica, Nasi Antonella, Ferranti Pasquale, Villani Francesco
Department of Food Science, School of Biotechnological Sciences, University of Naples Federico II, Via Università 100, 80055 Portici, Italy.
Appl Environ Microbiol. 2009 Apr;75(7):1990-2001. doi: 10.1128/AEM.02762-08. Epub 2009 Feb 5.
Mesophilic and psychrotrophic populations from refrigerated meat were identified in this study, and the spoilage potential of microbial isolates in packaged beef was evaluated by analyzing the release of volatile organic compounds (VOC) by gas chromatography-mass spectrometry (GC/MS). Fifty mesophilic and twenty-nine psychrotrophic isolates were analyzed by random amplified polymorphic DNA-PCR, and representative strains were identified by 16S rRNA gene sequencing. Carnobacterium maltaromaticum and C. divergens were the species most frequently found in both mesophilic and psychrotrophic populations. Acinetobacter baumannii, Buttiauxella spp. and Serratia spp. were identified among the mesophilic isolates, while Pseudomonas spp. were commonly identified among the psychrotrophs. The isolates were further characterized for their growth at different temperatures and their proteolytic activity in vitro on meat proteins extracts at 7 degrees C. Selected proteolytic strains of Serratia proteamaculans, Pseudomonas fragi, and C. maltaromaticum were used to examine their spoilage potential in situ. Single strains of these species and mixtures of these strains were used to contaminate beef chops that were packed and stored at 7 degrees C. At time intervals up to 1 month, viable counts were determined, and VOC were identified by GC/MS. Generally, the VOC concentrations went to increase during the storage of the contaminated meats, and the profiles of the analyzed meat changed dramatically depending on the contaminating microbial species. About 100 volatiles were identified in the different contaminated samples. Among the detected volatiles, some specific molecules were identified only when the meat was contaminated by a specific microbial species. Compounds such as 2-ethyl-1-hexanol, 2-buten-1-ol, 2-hexyl-1-octanol, 2-nonanone, and 2-ethylhexanal were detectable only for C. maltaromaticum, which also produced the highest number of aldehydes, lactones, and sulfur compounds. The highest number of alcohols and ketons were detected in the headspace of meat samples contaminated by P. fragi, whereas the highest concentrations of some alcohols, such as 1-octen-3-ol, and some esters, such as isoamyl acetate, were produced by S. proteamaculans. In conclusion, different microbial species can contribute to meat spoilage with release of different volatile compounds that concur to the overall quality decrease of spoiling meat.
本研究鉴定了冷藏肉中的嗜温菌和嗜冷菌菌群，并通过气相色谱 - 质谱联用（GC/MS）分析挥发性有机化合物（VOC）的释放情况，评估了包装牛肉中微生物分离株的腐败潜力。通过随机扩增多态性DNA - PCR分析了50株嗜温菌和29株嗜冷菌分离株，并通过16S rRNA基因测序鉴定了代表性菌株。麦芽香肉杆菌和分歧肉杆菌是在嗜温菌和嗜冷菌菌群中最常发现的物种。嗜温菌分离株中鉴定出了鲍曼不动杆菌、布蒂亚菌属和沙雷氏菌属，而嗜冷菌中常见的是假单胞菌属。进一步对分离株在不同温度下的生长情况及其在7℃下对肉蛋白提取物的体外蛋白水解活性进行了表征。选用蛋白酶产黄菌、脆弱假单胞菌和麦芽香肉杆菌的蛋白水解菌株来原位检测它们的腐败潜力。使用这些菌株的单菌株及其混合物污染包装后在7℃下储存的牛排。在长达1个月的时间间隔内，测定活菌数，并通过GC/MS鉴定VOC。一般来说，在受污染肉类的储存过程中，VOC浓度会升高，并且根据污染的微生物种类不同，分析的肉类的挥发性成分会发生显著变化。在不同的受污染样品中鉴定出了约100种挥发物。在检测到的挥发物中，一些特定分子仅在肉被特定微生物种类污染时才被鉴定出来。诸如2 - 乙基 - 1 - 己醇、2 - 丁烯 - 1 - 醇、2 - 己基 - 1 - 辛醇、2 - 壬酮和2 - 乙基己醛等化合物仅在麦芽香肉杆菌污染时可检测到，该菌还产生了最多数量的醛、内酯和含硫化合物。在脆弱假单胞菌污染的肉样顶空中检测到的醇类和酮类数量最多，而蛋白酶产黄菌产生了一些醇类（如1 - 辛烯 - 3 - 醇）和一些酯类（如乙酸异戊酯）的最高浓度。总之，不同的微生物种类通过释放不同的挥发性化合物导致肉类腐败，这些化合物共同导致了腐败肉类整体质量的下降。
