*4.5. Preharvest Application of Chitosan Might Improve the Antioxidant Activity of 'Garmrok' Kiwifruit by Positively Affecting Phenolic Metabolism*

Phenolic compounds, the major secondary metabolites in plants, are responsible for the flavor and color of fruits with antioxidant potential [22,26,36,42]. The (+)-catechin, chlorogenic acid, rutin, (−)-epicatechin, quercetin, and tannin are the major phenolics identified in kiwifruit [26] and are responsible for the antioxidant capacity of fruit while being involved in the antioxidant metabolism [22,26]. Over the 90 days of storage period at 0 ◦C, preharvest application of chitosan increased the total phenolic content in 'Garmrok' kiwifruit, as similarly shown in other fruits treated with preharvest chitosan [22,34,36,42,45,47,48]. The low level of total phenolic content observed in the untreated kiwifruit might be due to the rapid breakdown of cell structure compared with the chitosan-treated kiwifruits. The fact that kiwifruit treated with preharvest chitosan that retained higher total content of phenolic compounds may be associated with the reduced activity of polyphenol oxidase (PPO) that oxidizes the phenolic compounds. The increased content of total phenolic compounds could possibly have obtained the antioxidant capacity of kiwifruit during the cold stor-

age [36,42], which not only elicited immune responses but also improved the quality of 'Garmrok' kiwifruit during cold storage that delayed the ripening.
