Starch Metabolism In Apple Fruit And Its Relationship With Maturation And Ripening

Abstract

Harvest timing of apples, an important factor determining fruit quality after storage, is often based on maturity assessments that include the starch pattern iodine (SPI) test. The SPI test provides a visual indicator of starch degradation in the equatorial region of the fruit. SPI and starch concentrations in apple cultivars, and the effects of factors such as aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene (1-MCP), have been investigated. SPI values increased as starch concentrations declined in 'Gala, 'Honeycrisp', 'McIntosh', and 'Empire' apples during maturation. The two factors have a curvilinear relationship for all cultivars. Declines in percentage of amylose were found to be linear and cultivar dependent. Computer-based image analysis of SPI-based staining revealed a wide range of values, and a linear correlation was found between SPI value and percentage stained area. Starch concentrations in stem-end tissues were lower than in equatorial and calyx-end tissues of 'Empire' and 'Gala' apples. AVG and 1-MCP applied preharvest to inhibit ethylene production and perception, respectively, had cultivar as well as application timing-dependent effects on maturation. Effects of these treatments on starch degradation were limited in both 'McIntosh' and 'Empire' fruit. Weak correlations were found for 'Empire' apples between harvest indices and differences in absorbance (IAD) readings, which reflect chlorophyll concentrations in the skin. However, preharvest treatment of fruit with AVG and 1-MCP altered the relationships between IAD and other harvest indices, especially the internal ethylene concentration (IEC). 'Empire' apples are susceptible to firm flesh browning when stored at temperatures close to 0 °C, or after treatment with postharvest 1-MCP. This storage disorder causes major losses for the apple industry every year and no storage regime has been found so far to alleviate the problem. A full economic analysis indicated that there is an economic tradeoff between harvest date, occurrence of flesh browning, and likely net profits. Overall maturity assessment at harvest could be used as an indicator for storage disorders and/or storage length if factors such as differences in fruit maturation between cultivars and within the fruit are better understood.