Mugampoza Diriisa, Gkatzionis Konstantinos, Swift Benjamin M C, Rees Catherine E D, Dodd Christine E R
School of Biosciences, University of Nottingham, Nottingham, United Kingdom.
Department of Food Technology, Kyambogo University, Kampala, Uganda.
Front Microbiol. 2020 May 12;11:904. doi: 10.3389/fmicb.2020.00904. eCollection 2020.
This study has characterized the dominant non-starter species isolated from different sites in a Stilton cheese to establish its diversity, stress-tolerance, anti-microbial activity and potential contribution to quality of cheese. Fifty-nine isolates were cultured from the outer crust, blue veins and white core of the cheese and were speciated phenotypically and by 16S rDNA sequence analysis. was the dominant species detected with only two isolates identified as . Strains were typed by pulse-field gel electrophoresis (PFGE) using the enzyme I to examine their genomic diversity. Cluster analysis of PFGE patterns produced five major clusters which associated isolates with their sites of isolation within the cheese. One isolate from each cheese site was selected and evaluated for salt, acid, relative humidity, and heat tolerance to determine whether stress conditions within the isolation site selected their phenotype. values were 6, 13, and 17 s for strains from the crust, veins and core, respectively, suggesting strains on the crust may not have been able to survive pasteurization and therefore had been added post-pasteurization. All strains recovered from heat injury within 24-48 h at 4°C. pH values of 3, 3.5, and 4 suppressed growth but strains showed a varying ability to grow at pH 4.5 and 5; isolates from the core (which has the lowest pH) were the most acid-tolerant. All strains grew at 3.5 and 5% salt but were suppressed at 10%; those from the crust (which has a lower water activity) were the most halo-tolerant, growing at 8% salt whereas strains from the core were sensitive to this salt concentration. All 57 isolates were examined for antimicrobial activity and variable activity against and other genera was demonstrated; plantaricin EF genes were present in 65% of strains. It was concluded that there are varied phenotypes and genotypes of in a Stilton cheese according to site of isolation. Occurrence of different genotypes could contribute to variation in the cheese quality from batch to batch and provides criteria for selecting isolates as potential adjunct cultures.
本研究对从斯蒂尔顿奶酪不同部位分离出的主要非发酵剂菌种进行了特性分析，以确定其多样性、耐胁迫能力、抗菌活性以及对奶酪品质的潜在贡献。从奶酪的外皮、蓝纹和白芯中培养出59株分离株，并通过表型和16S rDNA序列分析进行了菌种鉴定。检测到的优势菌种为，仅两株分离株鉴定为。使用酶I通过脉冲场凝胶电泳（PFGE）对菌株进行分型，以检查其基因组多样性。PFGE图谱的聚类分析产生了五个主要聚类，将分离株与其在奶酪中的分离部位相关联。从每个奶酪部位选择一株分离株，评估其对盐、酸、相对湿度和耐热性，以确定分离部位的胁迫条件是否选择了它们的表型。来自外皮、蓝纹和白芯的菌株的D值分别为6、13和17秒，这表明外皮上的菌株可能无法在巴氏杀菌中存活，因此是在巴氏杀菌后添加的。所有从热损伤中恢复的菌株在4°C下24 - 48小时内恢复。pH值为3、3.5和4时抑制生长，但菌株在pH 4.5和5时显示出不同的生长能力；来自芯部（pH最低）的分离株最耐酸。所有菌株在3.5%和5%的盐浓度下生长，但在10%时受到抑制；来自外皮（水分活度较低）的菌株最耐盐，在8%的盐浓度下生长，而来自芯部的菌株对该盐浓度敏感。对所有57株分离株进行了抗菌活性检测，结果表明其对和其他属具有不同的活性；65%的菌株中存在植物乳杆菌素EF基因。得出的结论是，根据分离部位的不同，斯蒂尔顿奶酪中的存在多种表型和基因型。不同基因型的出现可能导致批次间奶酪品质的差异，并为选择作为潜在辅助培养物的分离株提供标准。
