Effect of food preparation on the isocoumarin, 6-methoxymellein, content of UV-treated carrots

Abstract Pre-storage treatment of carrots with ultraviolet radiation (UV-C) induces the accumulation of the phytoalexin 6-methoxymellein (an isocoumarin) and increases their resistance against fungal pathogens. For this reason, UV-C could be envisaged as an alternative to fungicides for the control of post-harvest diseases of carrots. This research was carried out to determine the acceptability of UV-treated carrot after food preparation in terms of 6-methoxymellein (6-MM) content, a suspect in the bitterness of carrots, and sensory quality. The peeling operation alone removed most of the phytoalexin from the tissue, and the peeled roots had 6-MM levels similar to those of untreated carrots. The level of 6-MM in carrot tissue was also considerably reduced by boiling in water. However, 6-MM did not degrade during boiling, but was simply leached out into the boiling water. As expected, microwave heating did not alter 6-MM levels. Sensory evaluation showed that there was no difference in taste between UV-treated and control carrots after peeling. It was concluded that the presence of 6-methoxymellein in UV-treated carrots would not pose a problem because the major accumulation of 6-MM in the root was localized in the peel and could be easily removed by the peeling operation.