Synthesis of aroma compounds by apples supplied with alcohols and methyl esters of fatty acids

Abstract

Ester synthesis by apples supplied with alcohols (C2-CS) and methyl esters of short chain fatty acids (C4-C8) was studied using gas chromatographic analysis of the products. The substrates were supplied as vapours to whole fruits stored in 2% O2 at 3°C. The alcohols were converted to the corresponding acetate ester; butanol, pentanol and hexanol were converted most rapidly. The methyl esters of short chain fatty acids (C,) were converted to esters with an alkyl group (Cn-2, Cn-4) confirming the presence in whole fruits of an active 0-oxidation pathway for fatty acids. Ester synthesis was stimulated when apples were supplied with methyl octanoate at different periods during long term storage in 2% 02. Treatment of the fruit immediately postharvest did not enhance ethylene synthesis.

Biochemistry of apple aroma: A review

“…This occurs in both fatt y acid and amino acid catabolism (15,43,44). In ripe apples, alcohols constitute 6 to 16 % of the total volatiles (8), whereas esters represent, depending on the apple variety, from 80 % in Golden Delicious and Golden Reinders (14,45) to 98 % in Starking Delicious (36).…”

“…The volatile compounds released by the fruit are carried by a continuous air current and recovered with a trap for subsequent analysis using gas chromatography. The incubation period lasts 24 hours or more and the evaluation period lasts several days (9,16,17,43,46,179). The use of cortical or epidermal tissue disks, usually 9 to 12 mm in diameter and 1 to 3 mm thick, has the advantage of allowing easier access of the precursors, reducing the incubation time to less than 24 hours.…”

“…The addition of fatt y acids causes the formation of aldehydes, alcohols and their corresponding esters, in addition to the formation of new shorter fatt y acids by the β-oxidation pathway, which stimulates a wide range of volatile compounds (43,47). The optimal fatt y acid concentration to be added decreases with the length of the chain.…”

“…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).…”

“…However, aft er 7 months under ultra-low oxygen, intact Golden Delicious apples exposed to a mixture of alcohols synthesized only 20 % of volatiles compared to apples stored under regular atmosphere (179). 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).…”