Effect of boiling and roasting on the polyacetylene and polyphenol content of fennel (Foeniculum vulgare) bulb

Fennel (Foeniculum vulgare cv dulce.) is a hardy, perennial, umbelliferous (Apiaceae) plant as a source of the secondary metabolites group's polyacetylenes and polyphenols. The present study investigated the effect of boiling (100 degrees C for 30 min) and roasting (160 degrees C for 15 mm) on the levels of these phytochemicals. Boiling resulted in a significant decrease in the levels of polyacetylenes (falcarinol, falcarindiol, falcarindiol-3-acetate) and polyphenols (caffeic acid, gallic acid, apigenin-7-o-glucoside, ferulic acid, syringic acid, isovitexin, phloridzin). The loss of polyphenols from the boiled bulbs may be in part due to leaching of these components in the water. Roasting resulted in a significant decrease in falcarindiol, falcarindiol-3-acetate, and falcarinol by 81%, 78%, and 66% when compared to raw unprocessed fennel bulbs. In general, levels of all polyphenols decreased in roasted samples. The exceptions were ferulic acid which showed an increase and gallic acid which did not show any decrease. In line with results for polyphenol levels, antioxidant activity decreased following thermal processing, and the presence of hydroxymethylfurfural was confirmed in roasted samples of fennel. (C) 2011 Elsevier Ltd. All rights reserved.