Fermented Food and Microbiota ^†

Abstract

Fermented foods are defined as foods or beverages resulting from controlled microbial growth and conversion of major and minor food and enzymatic components. Once ingested, microorganisms or compounds produced during the fermentation process can affect the gut microbiome in the short and long term. Moreover, in recent years, the health benefits of fermented foods have been intensively studied and most studies have shown a correlation between the consumption of these foods and the composition of the gut microbiota, which were recently identified as a surprising organ. Although studies conducted on the effect of fermented foods on the gut microbiota take up a large space in the literature, the number of studies that consider the mechanisms of action of these foods seems very rare compared to other experiments that test the effect of these foods on intestinal dysbiosis and the improvement of host health. The aim of this work is to synthesize data on the mechanisms of action of some fermented foods and their effect on the modulation of the intestinal microbiota. Further studies should be conducted in vitro and in vivo in order to fully understand the mechanisms of action of fermented foods on this complex ecosystem.

1. Introduction

The role of the gut microbiota in human and animal health has increased in popularity in recent years, due to the increase in research on how the gut affects various body systems [1]. Moreover, thanks to improved genomic strategies, the analysis of this complex population has allowed the characterization of non-culturable microbial taxa. The application of these omic strategies suggests that the microbiota can be modified by many factors [2]. On the other hand, fermented foods are proving to be real treasures for our health. Recent research has highlighted the close link between our gut microbiota and our general well-being. Different authors have reported changes in gut microbiota populations following the ingestion of fermented foods fermented tea and sausages etc. [3,4].

These foods contain relatively stable microbial ecosystems composed mainly of lactic acid bacteria and primary metabolites of these bacteria, such as lactic acid [3]. However, not all fermented foods can be classified as probiotics but some of them can be considered as potential biotics depending on whether their fermented substrate is always present (stable) and acts as a prebiotic in addition to the presence of lactic acid-producing bacteria (LAB), alive at the time of their consumption [5]. Although many studies have recommended the consumption of fermented foods for their positive effects on health, the mechanism of action of these foods remains uncertain [6]. The aim of this work is to mainly highlight the mechanisms of action of certain fermented foods and their influence on the intestinal microbiota.

2. Materials and Methods

A search for articles was carried out using both Google Scholar and NCBI PubMed databases. Ten articles were used to compare their results, particularly in the search for the mechanisms of action of fermented foods used on the modulation of the intestinal microbiota. The words used in the searches were “fermented foods”, “mechanisms of action”, “gut microbiota”, and “effect”.

3. Results and Discussion

Table 1. Summary of results.

Reference	Fermented Food	Study Model/Design	Product Dose	Duration	Active Strain/Active Compound	Beneficial Effect on Gut Microbiota
Veiga et al. (2014) [7]	Fermented milk product	Volunteers	(250 g) × 2/day	4 weeks	Bifidobacterium animalis, Streptococcus thermophilus, Lactobacillus delbrueckii, Lactococcus lactis	$\downarrow$ Bilophila wadsworthia $\uparrow$ 2 benefic Clostridiales
Nielsen et al., 2018 [8]	Sauerkraut	Randomised, double-blind controlled trial	75 g/day unpasteurised sauerkraut	6 weeks	Lactic acid bacteria	No significant effects
Nougalli Roselino et al., 2020 [9]	Fermented sausages	Dynamic colonic model	/	2 weeks	Lactiplantibacillus plantarum LC38	$\downarrow$ Lactobacillus spp. + Bacteroides spp. + Enterobacteriaceae
Yamamoto et al., 2018 [10]	Fermented tea	Volunteers	2.14 g/day	4 weeks	Aspergillus luchuensis, Lactobacillus spp.,	$\uparrow$ Clostridium cluster XIVa $\downarrow$ Cluster IX
Firmesse et al., 2007 [11]	Camembert Cheese	Volunteers	40 g × 2/day	4 weeks	S.thermophilus, Lactobacillus spp., L. lactis, Leuconostoc, Hafnia alvei, and Geotrichum	$\uparrow$ Enterococcus faecalis
Yilmaz et al., 2019 [12]	Kefir	Inflammatory bowel disease patients	400 mL/day	4 weeks	N.D	$\uparrow$ Lactobacillus
Ullrich et al., 2021 [13]	Fermented vegetables + Sauerkraut	randomized crossover trial	150 g/day	2 weeks	N.D	$\uparrow$ alpha diversity + Lactobacillus
Jaquet et al. [14]	Coffe	Volunteers	3 cups/day	3 weeks	N.D	$\uparrow$ Bifidobacterium
Queipo-Ortuño et al., 2022 [16]	Red wine	Crossover intervention	272 mL/day	20 days	Polyphenol	$\uparrow$ Enterococcus, Prevotella, Bacteroides, and Bifidobacterium
Mitsui et al., 2006 [17]	Natto (Soy Product)	Controlled trial	50 g/day	2 weeks	Bacillus subtilis	$\uparrow$ ratio of stool Bifidobacteria: total bacteria

$\uparrow$: Increase; $\downarrow$: decrease; N.D: no determined.

represents the analysis of data carried out from some selected papers and relating to the fermented food effect on gut microbiota. Table 1 summarizes a mosaic of results, where the authors studied the beneficial effect of the fermented foods tested on the composition of the intestinal microbiota with the direct role of some strains of probiotics identified in these fermented foods such as Lactobacillus spp., and Bifidobacterium [7,8,9,10,11]. Some authors have shown that some substrates of plant and animal origin are subject to the activities of microorganisms that develop over a period of several days and weeks and are largely predigested by bacteria and yeasts, which contributes to a better absorption of their nutrients that would not be digested efficiently in their unfermented form in the intestine with a synthesis of enzymes essential to the digestive process. This could explain how the consumption of fermented foods is beneficial for the intestinal microbiota [5,6]. On the other hand, another study provided preliminary evidence on alcoholic and non-alcoholic red wine, which can positively modify the composition of the gut microbiota and whose modulation is Thus, the metabolites resulting from the action of bacteria and yeasts of a food during the fermentation process such as polyphenols, vitamins and short-chain fatty acids; provide gut microbes with a source of nutrients and enzymes essential for the metabolism of beneficial taxa [5,6]. In addition, the work of [12,13,14] did not shed light on the strains or biomolecules active in the foods listed in Table 1, they only tested their effects on the composition of the gut microbiota. On the other hand, it is necessary to take into account the risk of consuming fermented foods, especially if they are contaminated by pathogenic agents (Escherichia coli, Clostridium botulinum, viruses…), which could cause an imbalance in the composition of the intestinal microbiota, leading to poisoning or other more serious consequences on health [15]. Thus, it is important to note that despite the good reputation of fermented foods, the number of studies working on the mechanisms of action of these foods in the modulation of the gut microbiota remains rare.

4. Conclusions

The gut microbiota has received significant attention in recent years, with increasing evidence of its impact on health. Fermented foods offer the potential to positively impact the gut microbiota. However, few studies to date have specifically investigated which bioactive compounds are produced by the microorganisms present in these foods and strains. For this, experimental studies in vivo and in vitro, metagenomic and metabolomic analyses are needed to better understand this complex ecosystem.