Bioaccessibility and unravelling of polyphenols, sulforaphane, and indoles biotransformation after in vitro gastrointestinal digestion of a novel lactofermented broccoli beverage

Abstract

This study assesses the transformation and stability of polyphenols, sulforaphane, and indoles in a fermented beverage made from broccoli leaves during in vitro gastrointestinal digestion (GID). This process was simulated using a dialysis membrane to assess intestinal absorption. The total phenolic compounds (TPC) and antioxidant TEAC assays showed an increase in phytochemical content due to the GID process. The higher TPC and antioxidant activity observed after digestion was likely due to the enzymatic transformation of polyphenols in mildly alkaline conditions. Individual phytochemical analysis revealed that hydroxycinnamic acids, particularly 3CQa, remained stable initially but then decreased significantly during intestinal digestion. Acylated flavonoids exhibited a decrease during intestinal digestion, while deacylated flavonoids initially decreased before stabilising. This indicated the occurrence of enzymatic hydrolysis of more structurally complex flavonoids to glycosylated flavonoids such as kaempferol-3,7-diglucoside, and kaempferol-3-sophoroside-7-glucoside. Consequently, deacylated flavonoids were highlighted for their high bioaccessibility rate after in vitro GID. Glucosinolate-hydrolysis products, including sulforaphane and indoles, exhibited a general decrease during digestion, with sulforaphane showing 51% bioaccessibility. The study highlights the dialysed in vitro GID process, which affects the release and transformation of bioactive compounds, potentially increasing their bioaccessibility and the subsequent health benefits of the lactofermented beverage made from broccoli leaves.