ARS | Publication request: Effect of UV-B light and genotype on antioxidant enhancement of carrot slices

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: February 9, 2012
Publication Date: N/A

Technical Abstract: Fresh-cut processing (such as slicing) has been shown to enhance the nutrient content of carrots by stimulating the synthesis of secondary metabolites, including phenolic compounds. Ultraviolet-B (UV-B) light exposure in conjunction with wounding further promoted the formation of soluble phenolic compounds and significantly increased the antioxidant content of sliced orange carrots. In this study, 21 carrot varieties (six orange and purple, and three red, yellow and white) were used to investigate the influence of genotype on carrot responsiveness to UV-B treatment. Freshly harvested whole carrots were sliced to 3 mm thickness and exposed on both the top and bottom surfaces to a total energy dose of 144.8 mJ/cm2 in 14 s with a bimodal peak irradiance UV-B light of 21.2 mW/cm2. After incubation (15 °C, 72 h) to allow enzyme activation, responsiveness was assessed in terms of total soluble phenolic contents (TSP), antioxidant capacity (AC), chlorogenic acid (CA), phenylalanine ammonia-lyase (PAL) activity and total anthocyanin content. UV-B treatment only slightly increased the surface temperature of the samples. TSP and AC values determined for non-UV B treated purple carrots were initially 10-fold higher than the rest of the carrot varieties, which exhibited a similar range of TSP and AC values. With the exception of purple colored carrots, all the remaining samples responded to UV treatment with increases in TSP and AC levels. CA was the main phenolic compound that increased as a result of UV-B treatment. PAL activity also increased after UV-B treatment. The content of anthocyanins, only found in purple carrots, was reduced after 72 h of incubation. Analysis of the twenty-one colored carrot varieties revealed that response and the level of responsiveness to UV-B light exposure were dependent upon the color of the carrots, suggesting that genotype and phenotype play a role in determining responsiveness.