Changes in the composition of volatiles by post‐harvest application of alcohols to red delicious apples

Abstract

The effect of exogenous short-chain n-alcohols on the concentrations of main aroma components in mature intact Red Delicious apples and aged apple tissue discs has been studied. Storage of intact apples in an atmosphere containing ethanol vapours for 24 h resulted in a more than threefold increase in the sum of ethyl ester concentrations. The simplified model of tissue discs was applied to examine the influence of various ethanol concentrations on rate and time course of ester formation. On supplying a range of n-alkan-1-01s and 2-keto valeric acid in equimolar amounts to the discs, maximum conversion into esters was found with butanol and pentanol. The possibility of an in vivo aroma enrichment before processing of fruits is discussed,

Biochemistry of apple aroma: A review

“…In other studies, the addition of 1-to 6-carbon linear alcohols to pulp disks and skin from recently harvested Red Delicious apples achieved the maximum production of esters with 1-butanol converting to butyl and butanoate esters and 1-pentanol converting almost exclusively to pentyl esters, while methanol and ethanol had very low esterifi cation rate (192). All alcohols formed acetate esters, and ethanol, propanol and butanol also formed their corresponding aldehydes (192).…”

“…It has been demonstrated that precursors added to whole apples diff use towards the internal tissues of the fruit (46). However, the exogenous application of substrates in apple has been used more to elucidate the metabolic pathways (16,17,192) than to increase the production of volatile compounds (193).…”

“…However, because high-molecular--mass substrates evaporate poorly and diff use only weakly through cellular membranes (37,46,83), the results obtained with 7-and 8-carbon alcohols have not been suc cessful. Ester production is proportional to the concentration of the added alcohol, and the concentration of acyl-CoA is not a limiting factor (43,192), although the diff erence in the aroma composition among varieties can be due to differences in the preference for acyl-CoA molecules (47). The fruit can effi ciently catabolize alcohols with 8 or few-er carbons exogenously added aft er 8 months under ultra-low oxygen, suggesting that ADH remains active (184).…”

“…With the addition of an alcohol, mostly acetate esters are produced (43). However, at the same time, a decrease in the formation of other esters, especially those with 4 or more carbon atoms, can be observed in a kind of antagonism between substrates (46,47,192). Given that the addition of a single alcohol at high concentration can inhibit the production of esters from other alcohols (194), these compounds have been added in equimolar solutions.…”

“…However, Dixon (194) reports that ethanol forms ethyl acetate when added individually but not when added in a mixture. Ethanol and methanol added separately to Red Delicious apples form the corresponding ethyl and methyl esters (192). In Golden Delicious apples stored for 5 months under ultra-low oxygen and exposed to 3-to 6-carbon linear alcohols, isobutanol and isopentanol added separately increased the biosynthesis of acetate esters (mostly) and butanoate (to a lesser degree) (179).…”