Investigation on the profile of flavonoids in onions and their reduction effects on bioaccessibility of heavy metal using in vitro digestionmodel

Abstract

The bioaccessibility of flavonoids and heavy metals(As, Cd, and Pb), the total phenolic acids, and antioxidant activity in all parts of yellow and red onions were evaluated using HPLC, ICP-OES, Folin-Ciocalteu assay, and DPPH method, respectively, in in vitro digestion model. Then, ability of flavonoids to chelate heavy metals was investigated by UV/Vis spectrometry. The skin of yellow and red onion contained 2.5 and 7 times larger amounts of total flavonoids than the flesh in the undigested samples. Myricetin was most bioaccessible among flavonoids in both onions. The amount of total phenol compounds in yellow onion was about twice larger than that in red onion, but those in both onions were not significantly different after digestion. Yellow onion showed high antioxidant activity compared to red onion, even after digestion. A strong correlation was found between antioxidant activity and total phenolic content (R2=0.927). Our result revealed that antioxidant activity of red and yellow onions after digestion could be well predicted by measuring total phenolic content. As the amounts of flavonoids of skin and flesh of yellow and red onions increased, the concentrations of heavy metals in soluble digestive fluids reduced. Bioaccessibility of heavy metals was reduced by all parts of yellow and red onions, especially, skin of yellow onion. Myricetin had strong interaction with heavy metal, whereas kaempferol was ineffective in preventing heavy metals.;본 연구에서는 양파의 가식, 비가식 부위에 있는 플라보노이드와 중금속(As, Cd, Pb), 총 페놀의 양(total phenolic contents) 및 항산화성을 in vitro digestion 을 이용하여 HPLC, ICP-OES, Folin-Ciocalteu assay, DPPH 법으로 측정하였다. 노란 양파와 적 양파의 껍질에 있는 총 플라보노이드의 양은 가식부위에 있는 총 플라보노이드의 양보다 2.5 배, 7 배 높았으며, 플라보노이드 중 myricetin는 bioaccissible이 가장 높았다. 노란 양파의 총 페놀의 양이 적 양파보다 두배 높았으나, 유의적인 차이를 보이지 않았다. 항산화성과 총 페놀의 양의 상관관계는 R2=0.927로 항산화성과 플라보노이드의 상관관계보다 높았다. In vitro digestion을 이용하여 노란 양파와 적 양파의 가식, 비가식 부위의 플라보노이드의 양이 증가할 수록 중금속의 bioaccessibility는 감소하였다. 플라보노이드 중, OH 기가 많은 myricetin이 OH기가 적은 kaempferol보다 중금속의 bioaccessibility를 크게 감소시킨다.