BIOACCESSIBILITY AND BIOAVAILABILITY OF THE HYDROALCOHOLIC EXTRACT OBTAINED FROM ONION (ALLIUM CEPA L.) TUNICS

A large body of evidence suggests that high dietary consumption of polyphenol-rich fruit and vegetables protects against the development of chronic inflammatory diseases [1]. After consumption of plant-derived foods and beverages, dietary polyphenols are partially modified during gastrointestinal digestion and then absorbed in the small intestine and metabolized by the body, or reach the colon, where are subjected to catabolism by the gut microbiota followed by absorption of the resulting products. After absorption, polyphenols are submitted to metabolic detoxication processes, including glucuronidation, methylation and sulfation, and then are excreted through urine and bile. Quercetin, a flavonol present in many fruits and vegetables, especially onion (Allium cepa L.), is commonly found as glycosides, since the aglycone is highly reactive and relatively insoluble in aqueous media [2]. The pathways of quercetin absorption in the gastrointestinal tract of humans and other mammals are quite well understood. The present study aimed to provide more information regarding the in vitro bioaccessibility and bioavailability of an onion tunic hydroalcoholic extract rich in quercetin and its derivatives. In particular, to evaluate the bioaccessibility, the extract was submitted to a simulated in vitro gastro-, gastro-duodenal- and duodenal-digestion. After HPLCPDA- MS analysis, a significant increase in all quercetin derivatives was found in the extract after the in vitro digestion. The bioavailability of quercetin and its derivatives was determined using the Parallel Artificial Membrane Permeation Assay (PAMPA) model system for the evaluation of passive transcellular permeability. Through the use of PAMPA model system, the passive transport of quercetins was demonstrated. The measured rate of quercetins absorption was limited, and in line with literature data.