Abstract
Onions are the main dietary source of flavonols that have been associated with important health-promoting properties. Onion treated by high-pressure processing (HPP-treated onion) was subjected to a dynamic gastrointestinal digestion and colon fermentation simulator (DGID-CF) to study the effect on the gut microbiota metabolism in the three colon regions (ascending—AC, transverse—TC, and descending—DC) by means of chronic feeding with 27 g/day for 14 days. HPP-treated onion presented a high content of the flavonols quercetin-3,4’-diglucoside and quercetin-4’-glucoside, and a large percentage of them reached the AC without change. TC and DC progressively increased the total phenolic metabolites 2.5 times respective to day 2, mainly 3-hydroxyphenylacetic, 4-hydroxyphenylacetic, 3-(4-hydroxyphenyl)-propionic, and 3,4-dihydroxyphenylpropionic acids. In addition, the chronic feeding increased the beneficial colon bacteria Bifidobacterium spp. and Lactobacillus spp. and the production of total SCFAs (acetic, propionic, and butyric acids) 9 times (AC), 2.2 times (TC), and 4.4 times (DC) respective to day 1. A multivariate analysis (principal component analysis, PCA) showed a clear separation between the three colon regions based on their phenolic composition (precursors and metabolites). These results showed that HPP-treated onion modulated the human gut microbiota’s metabolism and the DGID-CF is a good system to study these changes.
Highlights
Onions (Allium cepa L.) are the second main crop grown worldwide after tomatoes with a current production estimated at 96.77 million tons [1] and are considered a primary ingredient of major worldwide diets [2]
There are no published studies about the effect of a natural food source of flavonols, such as an onion product treated by high-pressure processing (HPPtreated onion) and subsequently lyophilized, on human gut microbiota metabolism by the simulation of chronic feeding with 27 g/day for 14 days using a dynamic in vitro gastrointestinal digestion and colon fermentation (DGID-CF) simulator
This simulator was composed of different reactors that mimic the conditions of the stomach, small intestine, and the three colon regions, ascending (AC), transverse (TC), and descending colon (DC)
Summary
Onions (Allium cepa L.) are the second main crop grown worldwide after tomatoes with a current production estimated at 96.77 million tons [1] and are considered a primary ingredient of major worldwide diets [2]. Onions are an essential source of nutrients and bioactive compounds (such as phenolic and organosulfur compounds) and dietary fibers (mainly oligosaccharides) [3]. Onion consumption has long been associated with health-promoting properties including antimicrobial, antibiotic, antioxidant, analgesic, antiplatelet, antithrombotic, anti-inflammatory, antidiabetic, anticarcinogenic, hypolipidemic, antihypertensive, hepatoprotective, and immunoprotective effects [2,3]. The health-protecting effects of onion consumption have been extensively related with their phenolic composition, mainly flavonols, a subgroup of flavonoids [4,5]. Onion is one of the main dietary sources of the flavonol quercetin (Q) along with apples. Quercetin has shown cardioprotective effects related to its anti-inflammatory activity, inhibition of LDL oxidation, reduction of adhesion molecules, platelet antiaggregating, and vasodilator effects [8,9]
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