Change in Flavonoid Composition and Antioxidative Activity during Fermentation of Onion (Allium cepa L.) by Leuconostoc mesenteroides with Different Salt Concentrations

Abstract

The aim of this study is to investigate the change in flavonoid composition and antioxidative activity during fermentation of onion (Allium cepa L.) by Leuconostoc mesenteroides with different NaCl concentrations. In order to qualify and quantify the flavonoids during fermentation of onion, 7 flavonoids, [quercetin 3,7-O-β-d-diglucopyranoside (Q3,7G), quercetin 3,4'-O-β-d-diglucopyranoside (Q3,4'G), quercetin 3-O-β-d-glucopyranoside (Q3G), quercetin 4'-O-β-d-glucopyranoside (Q4'G), isorhamnetin 3-O-β-d-glucopyranoside (IR3G), quercetin (Q), and isorhamnetin (IR)], were isolated and identified from onion. During fermentation, the contents of flavonoid glucosides (Q3,7G, Q3,4'G, Q3G, Q4'G, and IR3G) gradually decreased, whereas the contents of flavonoid aglycones (Q, IR) gradually increased. Decline rates of the flavonoid glucosides increased with the addition of L. mesenteroides. Furthermore, the activity of β-glucosidase, which is produced by L. mesenteroides, is dose-dependently inhibited with different NaCl concentrations during fermentation. The presence of L. mesenteroides enhanced the antioxidative activity of onion as demonstrated using the 1,1-diphenyl-2-picrylhydrazyl, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), and reducing power assays. The enhancement of antioxidative activity was considered because the content of flavonoid aglycones increased during fermentation. However, the addition of NaCl may decrease the antioxidative activity; we surmise that this phenomenon occurs because of the inhibition of β-glucosidase by NaCl. Therefore, we conclude that the addition of NaCl may be useful for the regulation of antioxidative activity via the control of β-glucosidase action, during the fermentation of flavonoid glucoside-rich foods.

Effects of different processing methods on the antioxidant and immune stimulating abilities of garlic

“…During fermentation however, proteolytic enzymes from microorganisms hydrolyze complexes of polyphenol into free and soluble phenols which are more active and readily absorbed (Ademiluyi & Oboh, ; Shrestha, Dahal, & Ndungutse, ). Other studies have also reported that LAB release β‐glucosidase which hydrolyze flavonoid‐bound compounds to make flavonoids readily available (Lee, Cho, Kim, & Moon, ; Lee, Joo, & Kwon, ; Yang et al., ). Our results therefore demonstrate that the ability of such bioactive molecules to be released during fermentation is strain dependent.…”

“…The antioxidant effect was evaluated using two widely used methods; DPPH assay and ABTS assay. The DPPH radical has a characteristic absorption at 517 nm in ethanol, which disappears with the acceptance of an electron from antioxidant molecules (Lee, Cho, Kim, & Moon, ; Lee, Joo, & Kwon, ). All the fermented samples showed better DPPH radical scavenging activity than the unfermented samples.…”

“…Nonetheless, the garlic‐derived bioactive compounds contained in these fermented products remain unknown. Also, very few reports are available on the effects of heat drying and subsequent solid‐state fermentation on the biological activities of garlic (Lee, Cho, Kim, & Moon, ; Lee, Joo, & Kwon, ).…”

“…However, the effects of this process on bioactivity of the final product remain unknown. Other studies have shown that fermenting garlic with lactic acid bacteria (LAB) significantly improves its pharmacological effects (Lee, Cho, Kim, & Moon, 2016;Lee, Joo, & Kwon, 2016;Lee, Lee, Yu, Lee, & Cho, 2017). By submerged fermentation, garlic has been fermented with Pediococcus (Ham et al, 2010) and Monascus species (Sumioka, Hayama, Shimokawa, Shiraishi, & Tokunaga, 2006) in an effort to improve its antimicrobial and hypolipidemic activities.…”

“…Nonetheless, the garlic-derived bioactive compounds contained in these fermented products remain unknown. Also, very few reports are available on the effects of heat drying and subsequent solidstate fermentation on the biological activities of garlic (Lee, Cho, Kim, & Moon, 2016;Lee, Joo, & Kwon, 2016). Therefore, in this study, we investigated the effects of freeze drying, heat drying, and solid-state fermentation on the antioxidant and immune stimulating effects of garlic.…”