Relationship of IAD index to internal quality attributes of apples treated with 1-methylcyclopropene and stored in air or controlled atmospheres

Abstract

The research was conducted to evaluate the relationship between IAD index (index of absorption difference between 670 and 720nm) values and internal quality attributes of apples treated with 1-methylcyclopropene (1-MCP) and stored in air and controlled atmospheres (CA). Apples of ‘8S6923’ (Aurora Golden Gala™), ‘Fuji’ and ‘Royal Gala’ were tested. The results with Aurora Golden Gala™ show that IAD index values were maintained at higher levels if the fruit were stored in CA and that 1-MCP had no significant effect on retaining at-harvest values. The IAD values correlated with chlorophyll a content in the peel (R2=0.95, P<0.0001), but not with chlorophyll b content, internal ethylene levels, firmness or titratable acidity. ‘Royal Gala’ apples showed a similar response to Aurora Golden Gala™ apples, showing no correlation between IAD index values and internal quality attributes of those apples when treated with 1-MCP and/or CA. In contrast, ‘Fuji’ apples showed a relationship between IAD index value changes and internal ethylene concentrations (R2=0.67, P<0.05) and titratable acidity changes (R2=0.89, P<0.01), but not firmness. These results suggest that when 1-MCP and/or CA are applied to apples after harvest, that IAD index values do not consistently correlate to any internal quality attributes other than peel chlorophyll a content.