Occurrence of Flavonols in Tomatoes and Tomato-Based Products

Abstract

The flavonol contents of 20 varieties of tomato fruit were investigated in relation to variety, size, season, and country of origin. Ten commonly consumed tomato-based food products were also assessed. Free and conjugated flavonols were identified and quantified using reversed-phase HPLC. Ninety-eight percent of flavonols detected in tomatoes were found to occur in the skin. Tomatoes contained, primarily as conjugates, quercetin and kaempferol. The main quercetin conjugate was identified as rutin (quercetin 3-rhamnosylglucoside) by LC-MS. The total flavonol content of the different varieties of tomato that were analyzed varied from 1.3 to 22.2 μg/g of fresh weight (fw). Smaller cherry tomato fruits originating from warm sunny climates, such as Spain and Israel, were found to contain the highest concentration of flavonols. Among the tomato-based products investigated, tomato juice and tomato purée were rich in flavonols, containing 14−16 μg/mL and 70 μg/g fw, respectively. In contrast to fresh tomatoes, most tomato-based products contained significant amounts of free flavonols. Keywords: Flavonols; rutin; quercetin; kaempferol; fresh tomatoes; canned tomatoes; tomato juice; tomato purée; tomato soup; HPLC