College of Biomass Science and Engineering, Sichuan University, Chengdu 610065, China; Key Laboratory of Leather Chemistry and Engineering, Ministry of Education, Sichuan University, Chengdu 610065, China.
Zigong Yanweiyuan Food Co. Ltd, Zigong 643010, China.
Int J Food Microbiol. 2023 Mar 2;388:110087. doi: 10.1016/j.ijfoodmicro.2023.110087. Epub 2023 Jan 13.
Pellicle formation is an obvious indicator of spoilage and is followed by a loss of flavor in a variety of fermented vegetables. In this study, the pellicle-forming microorganisms were isolated using culture-dependent approaches, then a comparative analysis between the pellicle-forming (PF) radish paocai and normal fermented paocai in the diversity and function of microbial community was conducted by metagenome sequencing. Based on a pairwise t-test and OPLS-DA analysis, diallyl sulfide, (z)-1-allyl-2-(prop-1-en-1-yl) disulfane, and terpineol were considered to be the main components responsible for the unpleasant flavor of PF paocai. Yarrowia spp., Enterobacter spp., and Pichia spp. were the main pellicle-forming microorganisms. All 17 isolated Enterobacter strains showed pectinase-producing and cellulase-producing abilities, and 3 isolated Pichia strains showed gas-producing capacity. According to LEfSe analysis based on metagenomes, unclassified_g__Citrobacter and Yarrowia lipolytica were the uppermost biomarkers that distinguished the PF paocai from normal paocai. Unclassified_g__Lactobacillus and Lactobacillus plantarum were found to be actively engaged in starch and sucrose metabolism, cysteine and methionine metabolism, galactose metabolism, fructose and mannose metabolism, lysine biosynthesis, fatty acid biosynthesis, and arginine biosynthesis, all of which contributed to the flavor formation of paocai. Combining the results of metagenome sequencing with the data obtained based on the culture-dependent method, we could deduce that the growth of Yarrowia lipolytica first promoted the increase of pH and the formation of pellicle, which provided a suitable niche for the growth of some harmful bacteria such as Enterobacter, Citrobacter, and Serratia. These hazardous bacteria then worked in concert to induce the odorous stench and texture softening of paocai, as well as more pellicle formation.
菌膜形成是变质的明显指标，随后各种发酵蔬菜的风味都会丧失。在这项研究中，采用培养依赖的方法分离菌膜形成微生物，然后通过宏基因组测序对菌膜形成（PF）萝卜泡菜和正常发酵的萝卜泡菜的微生物群落多样性和功能进行比较分析。基于成对 t 检验和 OPLS-DA 分析，二烯丙基二硫、（Z）-1-丙烯基-2-（丙烯-1-基）二硫烷和萜品醇被认为是导致 PF 萝卜泡菜不愉快风味的主要成分。拟酵母属、肠杆菌属和毕赤酵母属是主要的菌膜形成微生物。17 株分离的肠杆菌属菌株均表现出果胶酶和纤维素酶产生能力，3 株分离的毕赤酵母属菌株均表现出产气能力。根据基于宏基因组的 LEfSe 分析，未分类_g__柠檬酸杆菌和拟酵母属脂解酵母是区分 PF 萝卜泡菜和正常萝卜泡菜的最高生物标志物。未分类_g__乳杆菌和植物乳杆菌被发现积极参与淀粉和蔗糖代谢、半胱氨酸和蛋氨酸代谢、半乳糖代谢、果糖和甘露糖代谢、赖氨酸生物合成、脂肪酸生物合成和精氨酸生物合成，所有这些都有助于萝卜泡菜的风味形成。将宏基因组测序的结果与基于培养依赖的方法获得的数据相结合，我们可以推断，拟酵母属脂解酵母的生长首先促进了 pH 值的升高和菌膜的形成，为肠杆菌属、柠檬酸杆菌属和沙雷氏菌属等一些有害细菌的生长提供了合适的小生境。这些有害细菌随后协同作用，导致萝卜泡菜产生恶臭气味和质地变软，并形成更多的菌膜。
