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Metabolic diseases can change the gut microbiota composition and function, and pathogenic bacteria contribute to the development of metabolic disorders. Polyphenols may act in the gut microbiota to favor the increase of beneficial bacteria and hamper the increase of pathogenic bacteria. In addition, the microbiota may act on polyphenols to increase their bioavailability. This two-way interactions between polyphenols and the gut microbiota could affect human metabolism and reduce cardiometabolic risk. Despite the possible benefits of polyphenols for human health through modulating the microbiome, studies are scarce, and present several limitations. This review provides an overview of the polyphenol-microbiota interactions and its effects on metabolic disorders.

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The grumixama (Eugenia brasiliensis Lam.), also known as Brazilian cherry, is a fruit native to Brazil. This study identified the flavonoids in the flesh and seeds and ellagitannin in the flesh of purple and yellow varieties. The physicochemical characteristics and antioxidant capacity of these fruits were also evaluated. Anthocyanins and flavonols were found in high levels in the flesh of purple (32-180 mg 100 g(-1) FW) and yellow grumixama (13-41 mg 100 g(-1) FW), respectively. The major flavonoids identified were cyanidin 3-glucoside and quercetin aglycone. Furthermore, ellagitannins were found in high levels in the flesh of purple (82-243 mg ellagic acid equiv 100 g(-1) FW) and yellow grumixama (92 mg ellagic acid equiv 100 g(-1) FW) and seeds (2220-2905 mg ellagic acid equiv 100 g(-1) FW). The ellagitannin profiles of both varieties were first characterized in which pedunculagin isomers, strictinin isomers, and ellagic acid galloyl hexoside were the major ellagitannins identified. In summary, both varieties of the grumixama fruit as well as the seeds could be good sources of bioactive compounds, mainly ellagitannins.

Banana fruits are important foods, but there have been very few studies evaluating the phenolics associated with their cell walls. In the present study, (+) catechin, gallocatechin, and (-) epicatechin, as well as condensed tannins, were detected in the soluble extract of the fruit pulp; neither soluble anthocyanidins nor anthocyanins were present. In the soluble cell wall fraction, two hydroxycinnamic acid derivatives were predominant, whereas in the insoluble cell wall fraction, the anthocyanidin delphinidin, which is reported in banana cell walls for the first time, was predominant. Cell wall fractions showed remarkable antioxidant capacity, especially after acid and enzymatic hydrolysis, which was correlated with the total phenolic content released after the hydrolysis of the water-insoluble polymer, but not for the posthydrolysis water-soluble polymer. The acid hydrolysis released various monosaccharides, whereas enzymatic hydrolysis released one peak of oligosaccharides. These results indicate that banana cell walls could be a suitable source of natural antioxidants and that they could be bioaccessible in the human gut.

Quorum sensing (QS) regulates bacterial gene expression and studies suggest quercetin, a flavonol found in onion, as a QS inhibitor. There are no studies showing the anti-QS activity of plants containing quercetin in its native glycosylated forms. This study aimed to evaluate the antimicrobial and anti-QS potential of organic extracts of onion varieties and its representative phenolic compounds quercetin aglycone and quercetin 3-β-D-glucoside in the QS model bacteria Chromobacterium violaceum ATCC 12472, Pseudomonas aeruginosa PAO1, and Serratia marcescens MG1. Three phenolic extracts were obtained: red onion extract in methanol acidified with 2.5% acetic acid (RO-1), white onion extract in methanol (WO-1) and white onion extract in methanol ammonium (WO-2). Quercetin 4-O-glucoside and quercetin 3,4-O-diglucoside were identified as the predominant compounds in both onion varieties using HPLC-DAD and LC-ESI-MS/MS. However, quercetin aglycone, cyanidin 3-O-glucoside and quercetin glycoside were identified only in RO-1. The three extracts showed minimum inhibitory concentration (MIC) values equal to or above 125 µg/ml of dried extract. Violacein production was significantly reduced by RO-1 and quercetin aglycone, but not by quercetin 3-β-D-glucoside. Motility in P. aeruginosa PAO1 was inhibited by RO-1, while WO-2 inhibited S. marcescens MG1 motility only in high concentration. Quercetin aglycone and quercetin 3-β-D-glucoside were effective at inhibiting motility in P. aeruginosa PAO1 and S. marcescens MG1. Surprisingly, biofilm formation was not affected by any extracts or the quercetins tested at sub-MIC concentrations. In silico studies suggested a better interaction and placement of quercetin aglycone in the structures of the CviR protein of C. violaceum ATCC 12472 than the glycosylated compound which corroborates the better inhibitory effect of the former over violacein production. On the other hand, the two quercetins were well placed in the AHLs binding pockets of the LasR protein of P. aeruginosa PAO1. Overall onion extracts and quercetin presented antimicrobial activity, and interference on QS regulated production of violacein and swarming motility.

Orange juice is considered an excellent dietary source of several bioactive compounds with beneficial properties for human health. Citrus sinensis Osbeck cv. 'Cara Cara' is a bud mutation originated from 'Washington' navel orange, also known as 'Bahia' navel orange. The ascorbic acid, flavonoid, and carotenoid contents in pasteurized and nonpasteurized Bahia and Cara Cara juices using two LC-MS/MS platforms were investigated. Higher ascorbic acid content was observed in Bahia compared to Cara Cara in both pasteurized and nonpasteurized juices. Total flavanones content as well as hesperidin levels were higher in Cara Cara with respect to Bahia pasteurized juice. Cara Cara was also characterized by a significantly higher and diversified carotenoid content compared to Bahia juice with a mixture of (Z)-isomers of lycopene, all-E-β-carotene, phytoene, and phytofluene isomers accounting for the highest carotenoid proportion. The exceptionally high carotenoid content of Cara Cara may be particularly interesting for nutritional or functional studies of uncommon carotenes in a citrus food matrix.