Quantification of flavonoids, total phenols and antioxidant properties of onion skin: a comparative study of fifteen Indian cultivars

Onion waste disposal issue could be solved by using onion skin as food ingredient. Therefore, the aim of present study is the estimation of flavonoid concentration, total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activities of onion skin of fifteen Indian cultivars. Flavonoid quantification was achieved by high performance liquid chromatography, which showed highest concentration of quercetin, quercetin 3-β-D-glucoside, luteolin and kaempferol in cv. ‘NHRDF Red’ (11,885.025 mg/kg), ‘Hissar-2’ (1432.875 mg/kg), ‘Pusa Riddhi’ (1669.925 mg/kg) and ‘Bhima Shakti’ (709.975 mg/kg), respectively in dry weight. Highest TPC and TFC were found in cv. ‘NHRDF Red’ while lowest were measured in cv. ‘Bhima Shubhra’. DPPH assay (%), ABTS assay (%) and FRAP assay (µmol gallic acid/g) were showed maximum antioxidant capacity for cv. ‘NHRDF Red’ whereas least obtained for cv. ‘Bhima Shubhra’. Skin of cv. ‘Hissar-2’ and ‘NHRDF Red’ are the best source of flavonoids and natural antioxidants.