Abstract
The effects of harvest time, 1-methylcyclopropene (1-MCP) and air storage time on the susceptibility of flesh browning in ‘Empire’ apples were studied during a seven-day shelf life period after air storage at 0.5 °C for seven months. Early- or late-harvested ‘Empire’ apples without 1-MCP increased production of ethylene, respiration rates and internal ethylene concentration during the shelf life. Respiration rates increased in the late-harvested fruit for the shelf life period with/without 1-MCP treatment. The 1-MCP-treated fruit was approximately 10 N firmer than fruit not treated with 1-MCP at an early harvest for the entire shelf life duration. Peroxidase activity and percent change in electrical conductivity in the flesh were elevated in late-harvested fruit for the shelf life duration, whereas polyphenol oxidase activities were found to be stimulated by 1-MCP treatment, regardless of harvest time. Late-harvested fruit treated with 1-MCP exhibited increased susceptibility to flesh browning during shelf life, mostly due to reduction of the antioxidant defense mechanism of the fruits to stress in extending storage life, increasing polyphenol oxidase (PPO) activity and electrolyte leakage rate.
Highlights
Internal flesh browning of ‘Empire’ apples (Malus sylvestris (L.) Mill Var. domestica Borkh.) is a physiological disorder known to occur intermittently during long-term storage that considerably reduces the postharvest quality of the fruit and renders it unacceptable in the market [1,2,3,4,5]
Peroxidase activity and percent change in electrical conductivity in the flesh were elevated in late-harvested fruit for the shelf life duration, whereas polyphenol oxidase activities were found to be stimulated by 1-MCP treatment, regardless of harvest time
Late-harvested fruit treated with 1-MCP exhibited increased susceptibility to flesh browning during shelf life, mostly due to reduction of the antioxidant defense mechanism of the fruits to stress in extending storage life, increasing polyphenol oxidase (PPO) activity and electrolyte leakage rate
Summary
Internal flesh browning of ‘Empire’ apples (Malus sylvestris (L.) Mill Var. domestica Borkh.) is a physiological disorder known to occur intermittently during long-term storage that considerably reduces the postharvest quality of the fruit and renders it unacceptable in the market [1,2,3,4,5]. Biochemical browning in apples mostly results from the oxidation of phenolic compounds to o-quinones by polyphenol oxidase (PPO) leading to brown discoloration and synergistically reacting with peroxidase (POX) activity [5,6,7,8]. The oxidation of phenolic compounds in apple flesh is dependent upon numerous factors including a fruit’s nutritional status, flesh structure, the geographic location of orchards, irrigation systems, seasonal variability, tree age, harvest time, 1-MCP (1-methylcyclopropene) treatment, CO2 and O2 levels, storage temperature and duration and adoption or non-adoption of CA (controlled atmosphere) storage with low temperatures [9,10]. PPO (peroxidase) or POX (polyphenol oxidase) antioxidants in controlled atmosphere-stored ‘Empire’ apples increased with 1-MCP treatment likely due to extended duration of fruit sensitivity to stress and lower energy
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