Treatments that suppress ethylene production or ethylene action modify ADH and AAT gene expression and aroma-related enzyme activities in 'Delbarde Estivale' apple: consequences for the aroma profiles of fruit

The effects of aminoethoxyvinylglycine (AVG; ReTain®) and 1-methylcyclopropene (1-MCP; SmartFreshTM) on the biosynthesis of aroma volatiles and overall quality in ‘Delbarde Estivale’, an early apple variety, are reported for the first time. Apple fruit were treated with AVG 3 weeks before commercial harvest, following standard procedures. 1-MCP was applied directly after harvest. Treated and untreated fruit were kept at room temperature and analysed periodically thereafter.The results indicated that both ethylene-suppressing treatments improved fruit firmness, total acidity, and preserved skin colour during shelf-life. However, both treatments had a negative impact on the biosynthesis of aroma volatiles, a major quality attribute for the sensory quality of apples.The production of straightchain esters was particularly affected. The activities of lipoxygenase (LOX), alcohol dehydrogenase (ADH), and pyruvate decarboxylase (PDC) were reduced by both treatments, in some instances to values well below 50% of those in untreated controls; whereas the activity of alcohol o-acyltransferase (AAT) was higher in 1-MCP-treated fruit. Measuring the levels of expression of the genes encoding ADH and AAT confirmed these results and the importance of an adequate supply of substrates for the biosynthesis of volatile esters in apple fruit