Aroma Production in Climacteric Fruit: A Comparison of Tomato, Apple, and Banana

Abstract

Volatile aroma compounds produced by apple, banana, and tomato are produced throughout development, however, those associated with ripening and edible quality are dependent upon ethylene action. In apple and banana, characteristic aroma is, in large part, dependent upon the formation of volatile esters. In tomato, many of the characteristic aromas are dependent upon tissue disruption and result from aldehydes and alcohols following lipid degradation. For apple and banana, the enzyme alcohol acyl-CoA transferase (AAT, EC 2.3.1.84) is the enzyme responsible for the final reaction in the pathway for ester formation and catalyzes the union of an alcohol and the CoA derivative of fatty acids. In both tissues, AAT gene expression was detected prior to the onset of ester production. In apple, AAT expression was found to be closely tied with the onset of autocatalytic ethylene synthesis. In banana, ethylene synthesis peaked and began to decline well before ester synthesis began. However, the expression of AAT increased as ester production increased for both tissues. Tomato fruit, like apple and banana, produced characteristic aromas following the onset of the ethylene climacteric, suggesting changes in the activity of various components of the lipoxygenase pathway. In all three tissue types, there are continuous, significant shifts in the aroma profile as fruit ripen age, suggesting shifts in specific metabolic pathways associated with precursor synthesis or degradation.