The enhancement of fresh produce antioxidant capacity by wounding stress and phytohormones
Abstract
The use of postharvest abiotic stresses, wounding and plant hormones, can
enhance the nutraceutical content of fresh produce. Wounding increased the phenolic
content (TP) of carrots, lettuce, jicama, red onions, white onions and celery with a
corresponding increase in antioxidant capacity (AOX). Similarly, phenylalanine
ammonia lyase (PAL) activity increased with the corresponding increase in total
phenolics. The diversity of antioxidant phenolic compounds present in each fresh
produce provided specific antioxidant capacities which could be related to important
biological activities. The combination of wounding and ethylene (ET) showed a higher
increase in TP and AOX for these same tissues. The reason of the synergistic effect is
not clear. However, we propose that both stresses may be sharing in part a common
signaling molecule that amplifies the response. Studies with carrot tissue identified the
individual phenolics responsible for the AOX of wounded and hormone wounded
stressed carrots. ET treated carrot tissue showed accumulation of mainly chlorogenic
acid (CHA) and dicaffeoylquinic acid (diCQA), but also a slight increase in the synthesis
of the bitter compound isocoumarin. On the other hand, the use of methyl jasmonate
(MJ) did not increase the levels of isocoumarins but did increase CHA and diCQA.
Studies were performed to understand the mechanism by which wounding and hormone
stress stimulated the phenylpropanoid metabolism. The blockers phenidone (PHE),
diphenyleneiodonium (DPI), and 1-methylcyclopropene (1MCP) provided information
relevant to signaling molecules including reactive oxygen species (ROS), MJ and ET,
and their effect on the synthesis of TP. Results with DPI blocker suggest that ROS are greatly responsible for the accumulation of phenolics in wounded- and wounded-hormone
stressed carrot tissue.
Citation
Heredia, Jose Basilio (2006). The enhancement of fresh produce antioxidant capacity by wounding stress and phytohormones. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /186959.