The Study of the Antioxidant Activity and Phenolic Compounds of Different <i>Allium</i> Species

Allium species, widely known as food flavoring, vegetables, and folk medicine, have been extensively studied for their therapeutic and pharmacological effects. While the health benefits of onions have been well-documented, there is limited research on Mongolian onions. Previous studies have shown that their beneficial effects are associated with their total phenolic contents, especially quercetin derivatives. This study aims to determine the in vitro antioxidant activity of various Allium species cultivated in Mongolia and Taiwan region. Different onion species, including Allium tagar. L, Allium fistulosum. L and Allium cepa. L were collected in Mongolia, and yellow and red onions (Allium cepa L) were collected in Taiwan region. The total phenolic content (TPC) was measured by the Folin-Ciocalteu assay. Furthermore, the quercetin derivatives of TPC were measured by HPLC. The antioxidant activity of water and methanol extracts was determined via DPPH and FRAP assays. The results showed that the highest TPC was in the methanol extracts of Allium tagar. L (4.23 ± 0.03 mg GAE/g dry weight), Allium fistulosum. L (3.96 ± 0.08 mg GAE/g dry weight) in Mongolia, and the TPC following the addition of red and yellow onion in Taiwan region. Therefore, quercetin-4-O-glucoside is the dominant methanol extract of Allium tagar. L (1.37 ± 0.15 mg/g dry weight) had the highest content compared to other extracts—the methanol extracts of Allium tagar. L and red onion (Allium cepa L) showed the highest free radical scavenging activity in both the DPPH and FRAP assays (79.2% ± 4.37% DPPH inhibition, 63.7 ± 1.07 mg Trolox/g FW, and 86.7% ± 7.27% DPPH inhibition, 28.6% ± 1.0 mg Trolox/g FW). Our study found that onion species are good sources of phenolic compounds, including quercetin-4-O-glucoside, and methanol extracts of onions had higher content than water extract. Moreover, it positively affects antioxidant in vitro systems, DPPH radical scavenging ability, and FRAP antioxidant capacity.