Flavonoid quantification in onion by spectrophotometric and high performance liquid chromatography analysis

Abstract

Direct spectrophotometric determination of quercetin content in onions (Allium cepa L.) was investigated as a possible alternative to high-performance liquid chromatography (HPLC) analysis. Quercetin content in five onion varieties was monitored at 362 nm and quantified using simple spectrophotometric and HPLC methods. HPLC revealed that 3,4′-Qdg and 4′-Qmg comprised up to 93% of total flavonol content detected in the studied varieties. These major quercetin conjugates combined (3,4′-Qdg + 4′-Qmg) and total flavonol conjugates quantified by HPLC correlated closely with spectrophotometer values. Correlation coefficients were 0.96 (P < 0.0001) for 3,4′-Qdg + 4′-Qmg and 0.97 (P < 0.0001) for total flavonol conjugates in onion. Simple spectrophotometric procedure proved to be a valid, efficient, and cost-effective method for the quantification of total quercetin in onion. Chemical names used: quercetin-3,4′-O-diglucoside (3,4′-Qdg); quercetin-4′-O-glucoside (4′-Qmg).