Enrichment of Food With Tannin Extracts Promotes Healthy Changes in the Human Gut Microbiota

Abstract

Food and food bioactive components are major drivers of modulation of the human gut microbiota. Tannin extracts consist of a mix of bioactive compounds, which are already exploited in the food industry for their chemical and sensorial properties. The aim of our study was to explore the viability of associations between tannin wood extracts of different origin and food as gut microbiota modulators. 16S rRNA amplicon next-generation sequencing (NGS) was used to test the effects on the gut microbiota of tannin extracts from quebracho, chestnut, and tara associated with commercial food products with different composition in macronutrients. The different tannin-enriched and non-enriched foods were submitted to in vitro digestion and fermentation by the gut microbiota of healthy subjects. The profile of the short chain fatty acids (SCFAs) produced by the microbiota was also investigated. The presence of tannin extracts in food promoted an increase of the relative abundance of the genus Akkermansia, recognized as a marker of a healthy gut, and of various members of the Lachnospiraceae and Ruminococcaceae families, involved in SCFA production. The enrichment of foods with tannin extracts had a booster effect on the production of SCFAs, without altering the profile given by the foods alone. These preliminary results suggest a positive modulation of the gut microbiota with potential benefits for human health through the enrichment of foods with tannin extracts.

Keywords: chestnut; gut microbiota; in vitro digestion-fermentation; quebracho; short chain fatty acids; tannins; tara.

Figure 1

Representation of the study design.

Figure 2

Microbiota diversity measured as (A) phylogenetic diversity and (B) Shannon index in fermentations of food matrices with and without tannin extracts. Diversity increases for quebracho wood extract (QUE) and tara pods extract (TE) when all food matrices are considered together (p = 0.016, adjusted p = 0.023, and p = 0.008, adjusted p = 0.023, respectively). w/o T, without tannins; QUE, quebracho tannins extract; CHE, chestnut tannins extract; TE, tara tannins extract.

Figure 3

Barplot of gut microbial community structure at genus level. w/o T, without tannins; QUE, quebracho tannins extract; CHE, chestnut tannins extract; TE, tara tannins extract. Relative abundance obtained by total-sum scaling (TSS) from genus-level abundance table. “Others” include genera with relative abundance lower than 1% for all conditions.

Figure 4

Principal coordinate analysis (PCoA) plot of total variation based on weighted UniFrac distances among microbial communities in all profiled samples, evaluated at genus level. The food sources were grouped in three food types: cereal-based foods (breakfast cereals, breakfast cereals with sugar, and bread), meat (meat and meat with 30% fat), and dairy products (milk, low fat yogurt, and full-fat Greek yogurt). w/o T, without tannins, QUE, quebracho tannins extract; CHE, chestnut tannins extract; TE, tara tannins extract.

Figure 5

Changes in microbiota composition with tannin addition in all foods. (A) Decrease of Bacteroides (QUE: p = 0.0078, adjusted p = 0.048; CHE: p = 0.0078, adjusted p = 0.11; TE: p = 0.023, adjusted p = 0.14) and (B) increase of Akkermansia (QUE: p = 0.0078, adjusted p = 0.048; CHE: p = 0.0078, adjusted p = 0.11; TE: p = 0.0078, adjusted p = 0.079) with every tannin tested. Initials indicate the different food matrices (C, breakfast cereals; CS, breakfast cereals with sugar; B, bread; M, meat; MF, meat with 30% fat; L, milk; Y, low fat yogurt; and YG, full-fat Greek yogurt). (C) Fold-changes in the relative abundance of bacterial families with each tannin. All changes significant at nominal level by Wilcoxon signed-rank tests are shown (p < 0.05). ^*Indicates statistically significant differences (p < 0.05) after correction for multiple testing.

Figure 6

Genera responsible for the main differences in gut microbiota composition due to the addition of tannin extracts to (A) dairy products and (B) cereal-based products, detected by Linear Discriminant Analysis (LDA) Effect Size (LEfSe). Differences are represented as LDA score (>3) by color gradient. All represented biomarkers are significant at p < 0.05. NA taxon refers to unclassified ASVs at f. (family) or g. (genus) level.

Figure 7

Short chain fatty acids (SCFAs) released after in vitro fermentation of the food matrices with and without tannins. (A) Principal component analysis (PCA) based on Euclidean distance. (B) Sum of the concentration of SCFAs (in mmol/ml) per each sample, represented by color gradient as shown next to the heatmap. w/o T, without tannins; QUE, quebracho tannins extract; CHE, chestnut tannins extract; TE, tara tannins extract. ^*Indicates statistically significant differences by ANOVA and Bonferroni post-hoc test: ^*p < 0.05, ^**p < 0.01, ^***p < 0.001.