Abstract
This study revealed for the first time the dynamic changes of bacterial community and physic-chemical properties in the process of tomatoes fermentation. In the early phase of fermentation, Proteobacteria and Firmicutes account for 86.04% and 9.97%, respectively. Then, Firmicutes replaced Proteobacteria to be the dominant phylum from day 10. Among then, Lactobacillus decreased from 20 to 30 days and then rapidly increased. The total sugar showed a gradual decreased while the nitrite content increased in the early phases. The total acid content increased from initial 0.6% to 2.03% on day 30, mainly including citric acid, malic acid and lactic acid. In the later stages, the number of microorganisms and bacterial community tended to be stable, along with the content of organic acids and nitrite. During fermentation, the physic-chemical parameters inevitably change, mainly due to microbial metabolism, affecting in turns the development of the micro-ecosystem. These results contribute to our knowledge about bacterial participation in the process of fermentation and will help improve the quality of fermented food and vegetables.
Highlights
Vegetables and fruit are basic sources of water-soluble vitamins, vitamin A, phytosterols, dietary fibre, minerals and phytochemicals in a human diet (Di Cagno et al, 2013)
Total acid content gradually reduced after day 30. These results are in agreement with observed variation in the microbial community structure, as after day 30 Lactobacillus, which possesses a strong acid-producing ability and acid resistance became a prominent component of the community (Wang et al, 2013): on the one hand, the low pH may affect the growth, reproduction and metabolism of some microorganisms to prevent contamination of miscellaneous bacteria and food spoilage; on the other hand, the lactic acid fermentation by Lactobacillus changes polybasic acids into monobasic acids in the later stages of fermentation, which will inhibit the increase of total acids
This study revealed for the first time the dynamic succession of the bacterial community during natural fermentation of tomatoes by high-throughput sequencing
Summary
Vegetables and fruit are basic sources of water-soluble vitamins, vitamin A, phytosterols, dietary fibre, minerals and phytochemicals in a human diet (Di Cagno et al, 2013). Fermented food is a functional product made from one or more kinds of fresh vegetables, fruits or mushrooms, fermented by many kinds of beneficial bacteria (Di Cagno et al, 2013; Dimidi et al, 2019; Raghuvanshi et al, 2019); it plays an important role in the human diet and is widely consumed all over the world. Fermented products have unique and appealing flavours and are rich in a large number of vitamins, amino acids, minerals (Di Cagno et al, 2013; Hur et al, 2014), and enzymes, secondary metabolites and other nutrients (Anal, 2019), which can supplement nutrition in the absence of fresh vegetables. The natural fermentation of fruit and vegetables involves Lactobacillus, Leuconostoc and Weissella, which can promote the formation of flavourful substances (Tamang et al, 2016; Hao & Sun, 2020)
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