Abstract
The consumption of fermented vegetables is widespread throughout the world and represents an important component of the human diet with considerable contribution to the food supply for a world population in continuous growth. Many of the fermented vegetables share a general process which requires salting and acidification steps. Among the microorganisms responsible for fermentation, lactic acid bacteria are the most relevant with important organoleptic, quality and safety benefits. This review deals with the microbial ecology of fermented vegetables focusing on the biodiversity of lactic acid bacteria, the most important molecular techniques used for their identification and genotyping, their importance for the formation of biofilms as well as their use as starter cultures for obtaining high-quality and safe vegetable products.
Highlights
In addition to lactic acid bacteria (LAB) and yeasts, which are typically found in vegetable fermentations, gram-negative bacteria of the genera Enterobacter, Citrobacter and Escherichia are generally present at the beginning of fermentation
The diversity of LAB species present in the different fermented vegetables that can be found on the market is wide, and responds to the different compositions presented by raw material, the environment and the physicochemical conditions prevailing during the fermentation process (Hurtado et al, 2012)
In the particular case of fermented vegetables, metagenomics has become an ideal tool for the study of the bacterial biodiversity of table olives (Cocolin et al, 2013; De Angelis et al, 2015; Medina et al, 2016b; 2018; De Castro et al, 2018), cucumbers (Medina et al, 2016a), kimchi (Hong et al, 2015, Kyung et al, 2015) and other fermented vegetables (Reina et al, 2015)
Summary
The microorganisms present during vegetable fermentation are very diverse and may considerably affect the quality and safety of the final product. Excessive growth of fermentative yeasts (Saccharomyces cerevisiae and Wicherhanomyces anomalus) could trigger an active production of CO2, which damage the fruits with the formation of gas pockets or produce wiring in table olives (Vaughn et al, 1972; Garrido-Fernández et al, 1997) Certain yeasts, such as Pichia manshurica and Issatchenkia occidentalis, are associated with alterations in fermented vegetables due to their capacity to consume lactic acid and increase the pH of the product (Franco et al, 2012). In addition to LAB and yeasts, which are typically found in vegetable fermentations, gram-negative bacteria of the genera Enterobacter, Citrobacter and Escherichia are generally present at the beginning of fermentation These microbial communities are inhibited because of lactic acid production by LAB, with a concomitant decrease in pH (GarridoFernández et al, 1997). Clostridium bifermentans and Enterobacter cloacae which can metabolize the lactic acid and generate butyric and propionic acids, respectively (Breidt et al, 2013a; Franco and Pérez-Díaz, 2013), and are responsible for the aroma of cheese and manure characteristic in spoilt fermented pickles
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