Modulation of flavanone and furocoumarin levels in grapefruits (Citrus paradisi Macfad.) by production and storage conditions.

Grapefruits grown under organic or conventional systems were analyzed for 6,7-dihydroxybergamottin (DHB) and flavanones using HPLC, and DPPH activity and ORAC using a micro-plate reader. Grapefruits harvested in November 2008 (E-1) and February 2010 (E-2) were stored at room temperature (RT) and 9 °C for four weeks. Higher levels of DHB were observed in conventional grapefruits during the second (4.7 ± 0.2 μg/g), third (1.5 ± 0.2 μg/g) and fourth (2.5 ± 0.2 μg/g) week of storage at room temperature in E2. Among flavonoids analyzed, narirutin (666.7 ± 33.9 μg/g), neohesperidin (17.5 ± 1.3 μg/g), didymin (75.5 ± 5.6 μg/g) and poncirin (130.8 ± 10.4 μg/g) levels were significantly higher (P⩽0.05) in organic grapefruits over conventional grapefruits at harvest and storage in E-1. Although DPPH levels were moderately correlated with grapefruit flavanone content, variability in the individual flavanone activity was pronounced, resulting in non-significant differences in antioxidant activity between organic and conventional grapefruits.