As part of the dissertation, we investigated the influence of volatile aromatic precursors on the regulation of biosynthetic pathways of volatile compounds in apples. Using gas chromatography coupled with mass spectrometry (GC-MS), we analysed the effects of storing selected apple varieties ('Granny Smith', 'Gala', 'Fuji Kiku', 'Braeburn') in controlled atmospheres enriched with hexanal, ethanol, 1-butanol, and 2-methyl-1-butanol. We found that the formation of volatile compounds from precursors depends on concentration, time, and temperature. The addition of hexanal selectively stimulated the synthesis of hexyl acetate in all varieties, while ethanol had the most significant effect on the formation of 2-methylbutyl acetate and ethyl 2-methylbutanoate in the 'Gala' variety. High concentrations of precursors more selectively increased ester production, whereas lower concentrations stimulated the production of a wider range of volatile compounds in 'Fuji Kiku'. Analysis of odor activity values (OAV) showed that the addition of precursors contributed to increased aroma, while the precursors themselves did not affect the aroma profile of 'Gala' apples. The combination of ethanol and 1-butanol did not increase ester biosynthesis compared to the individual application of the alcohols. Increased contents of esters and alcohols such as hexyl acetate, 2-pentanol, and 2-pentanone were also found in the apple juice of 'Braeburn' and 'Granny Smith' after storage in an atmosphere containing ethanol or hexanal. Higher amounts of esters, including 2-methylbutyl acetate, butyl and hexyl acetate, in juice from 'Fuji Kiku' flesh after storage in an atmosphere with added hexanal confirmed that the precursor penetrates into the interior of the fruit, where it is converted into compounds important for apple aroma. The use of deuterium-labelled precursors also confirmed that precursors influence metabolic pathways not only as substrates but also as regulators of the biosynthesis of volatile aromatic compounds.
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