Enhancing apple aroma: The impact of exogenous precursors and application conditions on uptake and ester formation in ‘Fuji Kiku’ apples

This study investigated the effects of an exogenous precursor on the biosynthesis of volatile organic compounds (VOCs) in ’Fuji Kiku’ apples. The apples were exposed to ethanol, 1-butanol, 2-methyl-1-butanol and hexanal at concentrations of 50 and 500 μg/L. The uptake of the precursors was concentration-dependent, with ethanol and hexanal showing the highest uptake rates. Application of ethanol and hexanal at a concentration of 50 μg/L increased the production of a broader ester spectrum (13/21 for ethanol and 12/21 for hexanal), while a higher concentration of 500 μg/L resulted in a narrower ester spectrum (0/21 for ethanol and 8/21 for hexanal), with hexanal also showing inhibitory effects on the synthesis of certain esters. The application of hexanal under different conditions showed that the concentration of the precursor, time and temperature play an important role in ester production. Experiments with deuterated precursors confirmed that the increased ester production is not only due to the direct incorporation of the added precursors into the final products but also includes indirect influences on metabolic pathways in apple tissue. These results show the potential of using natural precursors to adjust the aroma profile of apples and offer a promising approach to produce high-quality, natural fruit aromas.