**4. Effect of microorganisms on fruit phenolic compounds**

After the consumption of fruits, the colon is the main site of microbial fermentation, where high molecular weight phenolic compounds are transformed into low molecular weight phe‐ nolic compounds such as phenolic acids or lactone structures by intestinal microbiota. The human healthy adult gut microbiota already identified can be classified into three dominant phyla: *Bacteroidetes, Firmicutes* and *Actinobacteria*. This highly complex and diverse bacterial ecosystem is mainly composed by a dominant group(> 109 Colony Forming Units (CFU)/g) of anaerobic bacteria, including genera *Bacteroides, Eubacterium*, *Bifidobacterium, Peptostreptococcus,* 


**Table 3.** Major metabolites resulting by phenolic compounds (flavonoids and non‐flavonoids) biodegradation and bacteria implicated in their transformation (adapted from Marín et al. [88]).

*Ruminococcus, Clostridium and Propionibacterium*, and sub‐dominant groups (< 109CFU/g), of bacteria of the Enterobacteriaceae family, especially E. *coli*, and the genera *Streptococcus, Enterococcus, Lactobacillus, Fusobacterium, Desulfovibrio* and *Methanobrevibacter* [89]. Thus, the microbial metabolism (**Table 3**) of most of the phenolic classes such as flavonoids, isoflavo‐ noids, lignans, phenolic acids, and tannins may produce metabolites with biological activity, presenting increased antioxidant activity, with evidence on health benefits for consumers. As most dietary polyphenolic compounds occur in glycosylated form in plants [87], for acquiring bioactivity in human body after being absorbed at enterocytes, these compounds must suffer various intestinal transformations, including the activities of digestive and microbial enzymes [88]. After cleavage of sugar responsible for glycosylation, the final absorbed compounds enter the vein circulation toward liver (**Figure 4**). Other enzymatic transformations occur from the liver to other organs, including digestive tract or via blood being excreted by urine [88].

the astringency metabolic pathway, and their spatio‐temporal expression patterns as well as tannin biosynthesis‐related transcription factor genes must be considered in future work to

After the consumption of fruits, the colon is the main site of microbial fermentation, where high molecular weight phenolic compounds are transformed into low molecular weight phe‐ nolic compounds such as phenolic acids or lactone structures by intestinal microbiota. The human healthy adult gut microbiota already identified can be classified into three dominant phyla: *Bacteroidetes, Firmicutes* and *Actinobacteria*. This highly complex and diverse bacterial ecosystem is mainly composed by a dominant group(> 109 Colony Forming Units (CFU)/g) of anaerobic bacteria, including genera *Bacteroides, Eubacterium*, *Bifidobacterium, Peptostreptococcus,* 

**Precursors Major metabolites Bacteria Ref.**

*Clostridium orbiscidens, Eubacterium oxidoreducens*

*Clostridium coccoides, Bifidobacterium* spp.

*casei, acidophilus LA‐5) Bifidobacterium lactis* 

*BB‐12*

*Escherichia coli, Bifidobacterium lactis, Lactobacillus gasseri*

[90–92]

[91–93]

[94–97]

[98, 99]

[100–102]

[90]

2‐(3‐Hydroxyphenyl) acetic acid

3‐(3‐Hydroxyphenyl)propionic acid

2‐(3,4‐Dihydroxyphenyl)acetic acid 2‐(3‐Hydroxyphenyl)acetic acid

5‐(3',4'‐Dihydroxyphenyl)‐γ‐valerolactone

3‐(3,4‐Dihydroxyphenyl)propionic acid

5‐(3',5'‐Dihydroxyphenyl)‐γ‐valerolactone

Malvidin 3,4‐Dimethoxybenzoic acid *Lactobacillus (plantarum,* 

3‐Hydroxyphenyl propionic acid

3‐(4‐Hydroxyphenyl) propionic acid

**Table 3.** Major metabolites resulting by phenolic compounds (flavonoids and non‐flavonoids) biodegradation and

finally make it possible to control fruit astringent substances quantitatively (…)"[86].

**4. Effect of microorganisms on fruit phenolic compounds**

270 Phenolic Compounds - Natural Sources, Importance and Applications

Myricetin 2‐(3,5‐Dihydroxyphenyl) acetic acid

Kaempferol 2‐(4‐Hydroxyphenyl)propionic acid

Catechin 3‐(3‐Hydroxyphenyl)propionic acid

Epicatechin 5‐(3,4‐Dihydroxyphenyl) valeric acid

valerolactone

Benzoic acid

Vanillin

Epigallocatechin 5‐(3',4'‐Dihydroxypheny[l)‐γ‐

Cyanidin 3,4‐Dihydroxybenzoic acid Peonidin 3‐Methoxy4‐hydroxybenzoic acid

Pelargonidin 4‐Hydroxybenzoic acid

bacteria implicated in their transformation (adapted from Marín et al. [88]).

Quercetin 3‐(3,4‐Dihydroxyphenyl) propionic acid

**Flavonoids**

**Flavan‐3‐ols**

**Anthocyanins**

**Hydroxycinnamates**

Caffeic, ferulic, and *p*‐coumaric acids linked to a quinic acid to form, respectively, caffoylquinic feruloylquinic, and *p*‐ coumaroylquinic acids

**Non‐flavonoids**

**Figure 4.** Absorption and metabolism routes for dietary polyphenols and their derivatives in humans. Adapted from Marín et al. [88].
