Chitosan is an elicitor that induces resistance in fruits against postharvest diseases, but there is little knowledge about the wound healing ability of
chitosan on apple fruits. Our study aimed at revealing the effect of
chitosan on the phenylpropanoid pathway by determining some
enzyme activities, products metabolites,
polyphenol oxidase activity, color (L*, b*, a*),
weight loss, and disease index during healing. Apple (cv. Fuji) fruits wounded artificially were treated with 2.5%
chitosan and healed at 21-25°C, relative humidity = 81-85% for 7 days, and non-wounded fruits (coated and non-coated) were used as control. The result shows that
chitosan treatment significantly decreased
weight loss of wounded fruits and disease index of Penicillium expansum inoculated fruits. The activities of
phenylalanine ammonia-lyase (PAL),
cinnamic acid 4-hydroxylase (C4H), 4-coumaryl
coenzyme A ligase (4CL),
cinnamoyl-CoA reductase (CCR), and
cinnamyl alcohol dehydrogenase (CAD) were elicited throughout the healing period by
chitosan, which increased the biosynthesis of
cinnamic acid,
caffeic acid,
ferulic acid,
sinapic acid,
p-coumaric acid,
p-coumaryl alcohol,
coniferyl alcohol, and
sinapyl alcohol. Also, total
phenol,
flavonoid, and
lignin contents were significantly increased at the fruits
wounds. In addition,
chitosan's ability to enhance
polyphenol oxidase activity stimulated enzymatic browning of
wounds. Although wounding increased phenylpropanoid
enzymes activities before healing,
chitosan caused higher
enzyme activities for a significant healing effect compared with the control. These findings imply that
chitosan accelerates apple wound healing by activating the phenylpropanoid pathway and stimulating enzymatic browning of
wounds.