1-MCP Differentially Affects Postharvest Physiological Attributes and Incidence of Internal Browning in Cold Stored ‘Gala' Apples

The risk of internal browning (senescent browning or stem-end browning) developing in ‘Gala’ apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] fruit during cold storage increases with increased fruit size.  The objective of this study was to further investigate relationships between fruit size and development of internal browning and other physiological characteristics of ‘Gala’ apples held in cold storage.  Fruit segregated at harvest based on size (small: less than 200 g; medium: 200–240 g; large: 241–280 g; extra large: greater than 280 g) were untreated or treated with 1 µL·L^-1 1-MCP and then stored at 0.5 °C in air for 3 or 6 months.  Internal browning was only detected in apples stored 6 months, regardless of 1-MCP treatment.  In both control and 1-MCP treated fruit, browning incidence increased with fruit size while browning severity was less associated with size.  Severity of internal browning in 1-MCP treated fruit greater than 240 g was lower compared with control fruit of similar size.  However, browning symptoms were mostly senescent browning in the cortex tissues of control fruit but browning was primarily in the stem-end localized tissues of 1-MCP treated fruit.  Internal ethylene concentration (IEC) decreased with increased fruit size in control fruit but IEC was not associated with size in 1-MCP treated fruit.  Cortex tissue lightness (L*) increased with fruit size irrespective of tissue localization (stem-end, equatorial, calyx-end) at harvest but during storage, L* decreased with increased fruit size in control fruit.  In 1-MCP treated fruit, L* at 3 months was similar to that at harvest but at 6 months, L* was not associated with fruit size, regardless of tissue localization. Fruit fresh weight loss during storage increased with fruit size and storage duration more so in controls compared with 1-MCP treated fruit.  Furthermore, fruit circumference increased with fruit size only for control fruit stored for 6 months. These physiological changes appear to contribute to the susceptibility of large fruit to internal (or senescence) browning more so than small fruit.  Reduced browning incidence and severity in 1-MCP treated fruit may indicate browning is related to fruit senescence while stem-end browning results from a lack of ethylene action during cold storage.