Antioxidant metabolism in stem and calyx end tissues in relation to flesh browning development during storage of 1-methylcyclopropene treated ‘Empire’ apples

Authors: LEE, JINWOOK - Chung-Ang University; CHENG, LAILIANG - Cornell University; Rudell, David; NOCK, JACQUELINE - Cornell University; WATKINS, CHRISTOPHER - Cornell University

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2018
Publication Date: 3/1/2019
Citation: Lee, J., Cheng, L., Rudell Jr, D.R., Nock, J.F., Watkins, C.B. 2019. Antioxidant metabolism in stem and calyx end tissues in relation to flesh browning development during storage of 1-methylcyclopropene treated ‘Empire’ apples. Postharvest Biology and Technology. 149:66-73. https://doi.org/10.1016/j.postharvbio.2018.11.015.
DOI: https://doi.org/10.1016/j.postharvbio.2018.11.015

Interpretive Summary: Internal browning disorders of apples continue to result in significant annual economic losses and food wastage. A variety of conditions can lead to or contribute to internal browning depending upon the type of apple. Symptoms and conditions that cause the different types of internal browning indicate that internal browning is a collection of different disorders. Firm flesh browning is one of these disorders that afflicts some economically important cultivars including Empire. In this case, a common ripening inhibitor, 1-methylcyclopropene can make the fruit more susceptible to this disorder putting Empire producers at a disadvantage as this crop protectant improves quality retention over long term storage. Here, we characterized any relationships with oxidative stress and its potential mediation by fruit-produced antioxidants. We found that mechanisms associated with oxidative stress and antioxidants had little relationship with disorder development as exacerbated by 1-methylcyclopropene.

Technical Abstract: Firm flesh browning, a physiological storage disorder, develops in ‘Empire’ apples during long term controlled atmosphere (CA) storage, and its incidence can be enhanced by 1-methylcyclopropene (1-MCP), an inhibitor of ethylene perception. The disorder develops earlier in stem-end tissue than in calyx-end tissue. The antioxidant scavenging systems in the tissue zones of fruit stored under CA conditions (2 kPa O2/2 kPa CO2) at 3 oC for up to 40 weeks were investigated. Flesh tissue browning as indicated by lightness (L*) and hue angle (ho) was greater in 1-MCP treated than in untreated fruit, and in stem-end tissue than in calyx-end tissue. 1-MCP treatment decreased superoxide production as indicated by nitroblue tetrazolium reducing activity but increased H2O2 concentrations, while treatment effects on malondialdehyde concentrations were inconsistent. Ascorbic acid (AsA) and glutathione (GSH) concentrations declined during storage, regardless of 1-MCP treatment, but were lower in stem-end tissue than in calyx-end tissue. While ascorbate peroxidase activity was not affected by 1-MCP treatment, its activity in untreated fruit was lower in stem-end tissues than in calyx-end ones. The activities of superoxide dismutase (SOD) and copper/zinc-superoxide dismutase (Cu/Zn-SOD) increased during storage. The activities of catalase and peroxidase went descending by 1-MCP treatment but effects on activities of other enzymes were inconsistent. Overall, higher browning may be associated with lower AsA and GSH concentrations in stem-end tissues, but the enhanced browning resulting from 1-MCP treatment does not appear to be directly related to antioxidant metabolism.