The Bounty of the Bite: Kinetics of Volatile Synthesis Following Cellular Disruption of Apple Fruit Tissue

During mastication and food preparation, cellular disruption of apple and other fresh fruit causes the mixing of cellular contents and induction of numerous chemical and enzymatic reactions not normally present in the intact tissue. Reactions associated with the lipoxygenase pathway result in the synthesis of significant quantities of volatile aldehydes, with the potential to contribute to alcohol, acid, and ester synthesis. These volatiles are known to impact aroma, herbivory, pathogen development, and insect predation. We wanted to determine if the kinetics of these reactions in apple changed with fruit ripening stage and if the changes in these parameters could impact the sensory quality of fresh fruit during consumption. Using a model system consisting of volatile collection chambers adhered to the surface of ‘Jonagold' apple fruit, we found transient 'waves' of volatiles were produced. The initial wave was almost exclusively aldehyde products of the lipoxygenase pathway, which were then converted to alcohols, which, in turn, were incorporated into esters. The rate constants of these sequential reactions were estimated using mathematically-derived equations, providing a tool for comparing enzymatic capacities during ripening. The data indicate that lipoxygenase-derived aldehydes contribute to aroma of apple fruit during mastication, but alcohols and esters from these aldehydes do not. It is suggested that the impact of the lipoxygenase pathway on aroma is largely negative for apple during the eating experience