Relationship of Ethylene Biosynthesis to Volatile Production, Related Enzymes, and Precursor Availability in Apple Peel and Flesh Tissues

Abstract

Regulation of ethylene biosynthesis or action has a major effect on volatiles production in apples. To understand the biochemical processes involved, we used Greensleeves apples from a transgenic line with a high suppression of ethylene biosynthesis. The study was focused at the level of the aroma volatile-related enzymes, including alcohol acyltransferase (AAT), alcohol dehydrogenase (ADH), and lipoxygenase (LOX) and at the level of amino acids and fatty acids as aroma volatile precursors in peel and flesh tissues. In general, volatile production, enzyme activity levels, and precursor availability were higher in the peel than the flesh and were differentially affected by ethylene regulation. AAT enzyme activity showed a clear pattern concomitant with ethylene regulation. Contrarily, ADH and LOX seem to be independent of ethylene modulation. Isoleucine, an important precursor of aroma compounds including 2-methylbutanoate esters, showed a major increase in the peel during ripening and responded significantly to ethylene regulation. Other important aroma volatiles precursors, like linoleic and linolenic acid, showed an accumulation during ripening associated with increases in aldehydes. The significance of these changes in relation to aroma volatile production is discussed.

Biochemistry of apple aroma: A review

“…The most important amino acids for the biosynthesis of volatile compounds in apples are GD (14) GS (14) MG (53) G R ( 45) FJ ( (76,77). The concentration of most amino acids decreases with the maturation of apples (78)(79)(80)(81) due to the synthesis and metabolism of proteins (78). During storage, an initial reduction in the content of amino acids occurs, without signifi cant change aft erwards (78).…”

“…Fig. 2 shows the formation of volatile aroma compounds from linoleic and linolenic acids through the LOX pathway, and Table 3 shows some studies that have been performed on enzymes from the LOX pathway in diff erent developmental stages of apples (13,15,34,40,44,45,54,72,73,75,79,85,96,106,(118)(119)(120)(121)(122)(123)(124)(125)(126)(127)(128)(129)(130)(131)(132)(133)(134)(135)(136).…”

Analyses of Expressed Sequence Tags from Apple

“…Branched-chain esters are characteristic of many cultivars of apple, including Royal Gala (Young et al, 1996(Young et al, , 2004. These are produced from Ile (Rowan et al, 1996), which increases in quantity in apple fruit skin during ripening (Defilippi et al, 2005a). Ile is synthesized from the amino acid Thr via five enzymatic steps.…”

Sensory and metabolic profiles of “Fuji” apples (Malus domestica Borkh.) grown without synthetic agrochemicals: the role of ethylene production

“…These observations agree with the well-known phenomena that apple ripening and aroma synthesis are promoted by ethylene. 21,22) Stronger correlations with flavor components than with QDA further indicated that flavor profiles were directly regulated by ethylene, and sensory descriptions varied accordingly. The present data demonstrate the utility of metabolite profiling for sensory descriptions of agricultural products.…”