Liao Chao, Wang Luxin
Department of Food Science and Technology, University of California, Davis, Davis, CA, United States.
Front Microbiol. 2022 Apr 11;13:850720. doi: 10.3389/fmicb.2022.850720. eCollection 2022.
In the United States, due to the limited information about the microbial quality and safety of fresh produce after the labeled open dates, unnecessary discarding of fresh produce in good conditions and food loss have been caused. The aim of this study was to address this knowledge gap and evaluate the microbial quality of commercial chopped Romaine lettuce (RL) on the "Use By" dates (UBD) and 5 days after the "Use By" dates (UBD5). The microbial quality was evaluated using culture-dependent and culture-independent methods. Three brands of RL samples, from early and late harvest seasons, were purchased from local grocery stores and stored at 4°C until 5 days after their UBD. On the UBD and UBD5, bagged lettuce was opened, homogenized, diluted, and plated onto plate count agar and anaerobic agar to obtain total aerobic plate counts (APC) and total anaerobic plate counts (AnPC). For the culture-independent method, DNA was extracted from each sample homogenate and used for 16S rRNA gene sequencing. The culture-dependent results showed that there was no significant change in APC or AnPC between UBD and UBD5 samples. The APC and AnPC ranged from 5.71 ± 0.74 to 7.89 ± 0.10 Log CFU/g and 1.75 ± 0.08 to 7.32 ± 0.61 Log CFU/g, respectively. No significant difference in alpha diversity, based on observed features and Shannon index values, was detected between UBD and UBD5 samples using 16S rRNA sequencing. Similarly, no difference was observed in beta diversity based on the Jaccard distance matrixes and the weighted Unifrac distance matrixes. Taxonomic analysis revealed 128 genera in all RL samples. The top five genera were (with relative abundance ranging from 16.47 to 92.72%), (0-52.35%), (0-42.42%), (0.17-21.33%), and (0-24.30%). The differential abundance analysis based on the ANCOM test showed that no bacteria were detected to have significantly differential abundance in RL between UBD and UBD5. In summary, both the culture-dependent and culture-independent results showed that there was no significant difference in the microbial quality of RL before and shortly after the UBD.
在美国，由于关于新鲜农产品在标明的开封日期后微生物质量和安全性的信息有限，导致了处于良好状态的新鲜农产品被不必要地丢弃以及食物损失。本研究的目的是填补这一知识空白，并评估市售切碎的长叶生菜（RL）在“使用截止日期”（UBD）及“使用截止日期”后5天（UBD5）的微生物质量。使用依赖培养和不依赖培养的方法评估微生物质量。从当地杂货店购买了三个品牌的RL样本，分别来自早季和晚季收获，储存在4°C下直至其UBD后5天。在UBD和UBD5时打开袋装生菜，匀浆、稀释，然后接种到平板计数琼脂和厌氧琼脂上，以获得总需氧平板计数（APC）和总厌氧平板计数（AnPC）。对于不依赖培养的方法，从每个样本匀浆中提取DNA并用于16S rRNA基因测序。依赖培养的结果表明，UBD和UBD5样本之间的APC或AnPC没有显著变化。APC和AnPC分别在5.71±0.74至7.89±0.10 Log CFU/g和1.75±0.08至7.32±0.61 Log CFU/g范围内。使用16S rRNA测序，在UBD和UBD5样本之间，基于观察到的特征和香农指数值，未检测到α多样性的显著差异。同样，基于杰卡德距离矩阵和加权非加权组平均距离矩阵，在β多样性方面也未观察到差异。分类学分析在所有RL样本中揭示了128个属。排名前五的属是（相对丰度范围为16.47至）、（0至52.35%）、（0至42.42%）、（0.17至21.33%）和（0至24.30%）。基于ANCOM检验的差异丰度分析表明，在UBD和UBD5之间的RL中未检测到有显著差异丰度的细菌。总之，依赖培养和不依赖培养的结果均表明，RL在UBD之前和之后不久的微生物质量没有显著差异。 （注：原文中部分属名未完整给出，故翻译时也保留不完整状态）
