Metabolism of propionic acid by golden delicious apples

Biochemistry of apple aroma: A review

“…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). Esters can have linear or branched chains, and their concentration depends on the availability of precursors (37,46,47) and on the selectivity and activity of the enzymes involved (48)(49)(50)(51). Butyl acetate, hexyl acetate, 2-methylbutyl acetate and ethyl 2-methyl--butanoate are the most important esters due to their high content and impact on apple aroma of several varieties (6,52).…”

“…Substrate availability is an important factor in the recovery of aroma in apples stored for long periods (15,36,124). 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).…”

“…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.…”

“…However, no change in the total concentration of volatiles occurred. On the other hand, butanoic acid was converted to butanoate esters (46). In this variety, which was stored for 7 months under low oxygen concentration conditions, butanoic acid increased the biosynthesis of ethyl esters and butyl butyrate (184).…”

“…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).…”