Department of Agricultural Sciences, University of Naples Federico II, Italy.
Department of Public Health, University of Naples Federico II, Via Pansini, 5, 80131 Naples, Italy.
Int J Food Microbiol. 2022 Dec 16;383:109956. doi: 10.1016/j.ijfoodmicro.2022.109956. Epub 2022 Oct 1.
In the last several years, the popularity of homebrewed beers has skyrocketed. However, this type of product is extremely vulnerable to microbial deterioration. Twelve homemade beers, some characterized by defects or stuck fermentation, were analysed by using a polyphasic approach encompassing culturomics and culture-independent techniques to better understand mechanisms that drive microbiota evolution throughout production and to highlight determinants responsible for crowning with success. Two sour beers, one apple-flavoured ale, two Italian grape ales, and seven standard ales were sampled. Microbiological characterization was obtained by plating on nine different media coupled with High-throughput sequencing analysis of fungal and bacterial communities by targeting ITS1-2 and the V3-V4 regions of the 16S rRNA, respectively. Total microflora on PCA largely varied among samples, ranging from <10 CFU/mL up to around 10 CFU/mL often reflecting yeast counts on WL and LM. LAB population's levels on MRS and SDBm did not overlap, with the counts on the latter being even 5 Log CFU/mL greater. Acetic Acid bacteria were retrieved in Sour beers, as well as in one IGA, even though acetic acid was not detectable by HPLC in this last sample. Brettanomyces spp. were only found in sour beers, as expected, whereas Enterobacteriaceae were never counted. A total of 63 yeasts were randomly isolated from countable plates. Saccharomyces cerevisiae and Wickerhamomyces anomalus were the most frequently isolated species. In many cases, Interdelta analysis biotyping of S. cerevisiae isolates consistently allowed the detection of the starter strain. By HST S. cerevisiae dominated the mycobiota in four samples, even if in one of them residual maltose and ethanol contents suggested a stuck fermentation. W. anomalus was found to be the dominant species in two beers. Fifty-five LAB cultures were isolated and identified. Pediococcus damnosus was the only species retrieved in sour beers and two Ales, while Levilactobacillus brevis was found in two Ale samples. HTS did not confirm this result in one Ale sample since the genus Panotea spp. accounted for over 90 % of the microbiota. Enterobacteriaceae which were never counted dominated the microbiome of two Ale beers. Biogenic amines content largely varied with three Ale samples greatly contaminated. Based on chemical and microbiological outcomes only one beer ASAle out of 12 could be considered acceptable. Furthermore, the widespread presence of LAB by culturomics and Enterobacteriaceae by HTS raises concerns about the final products' safety.
在过去的几年中，家庭酿造啤酒的受欢迎程度急剧上升。然而，这种产品极易受到微生物恶化的影响。我们使用包含培养组学和非培养技术的多相方法分析了 12 种自制啤酒，其中一些具有缺陷或发酵停滞的特征，以更好地了解驱动微生物群落进化的机制，突出成功酿造的决定因素。我们采样了两种酸啤酒、一种苹果味麦芽酒、两种意大利葡萄麦芽酒和七种标准麦芽酒。通过在九种不同培养基上进行平板培养，并分别针对 ITS1-2 和 16S rRNA 的 V3-V4 区进行高通量测序分析，获得了微生物学特征。PCA 上的总微生物菌群在样品之间差异很大，范围从<10 CFU/mL 到约 10 CFU/mL，通常反映 WL 和 LM 上的酵母计数。MRS 和 SDBm 上的 LAB 种群水平没有重叠，后者的计数甚至高出 5 个对数 CFU/mL。在酸啤酒中以及在一种 IGA 中都可以回收醋酸菌，尽管在最后一个样品中用 HPLC 检测不到醋酸。正如预期的那样，只有在酸啤酒中才发现了 Brettanomyces spp.，而肠杆菌科从未被计数。从可计数的平板上随机分离出 63 株酵母。酿酒酵母和异常威克汉姆酵母是最常分离到的物种。在许多情况下，对酿酒酵母分离株的 Interdelta 分析生物分型一致允许检测到起始菌株。通过 HST，酿酒酵母在四个样品中主导了真菌群，即使在其中一个样品中，残留的麦芽糖和乙醇含量表明发酵停滞。W. anomalus 被发现是两种啤酒中的优势种。分离和鉴定了 55 株 LAB 培养物。在酸啤酒和两种麦芽酒中仅发现了肠球菌属，而在两种麦芽酒样品中发现了短乳杆菌。在一个麦芽酒样品中，HTS 并没有证实这一结果，因为泛菌属 spp.占微生物组的 90%以上。从未计数的肠杆菌科在两种麦芽酒的微生物组中占主导地位。生物胺含量差异很大，三个麦芽酒样品受到严重污染。根据化学和微生物学结果，只有 12 种啤酒中的一种 ASAle 可以被认为是可接受的。此外，通过培养组学检测到的广泛存在的 LAB 和通过 HTS 检测到的肠杆菌科引起了对最终产品安全性的关注。
