Biosynthesis of Straight-Chain Ester Volatiles in Red Delicious and Granny Smith Apples Using Deuterium-Labeled Precursors

Abstract

Biosynthesis of straight-chain ester volatiles by Granny Smith and Red Delicious apples was investigated using deuterium-labeled fatty acids, C-6 aldehydes, and alcohols. Perdeuterated saturated and monounsaturated fatty acids were metabolized to hexyl-d(11), hexanoate-d(11), heptanoate-d(13), and octanoate-d(15) esters, whereas perdeuterated linoleic acid produced only hexyl-d(11) and hexanoate-d(11) esters. Exposure of fruit to vapors of deuterated 3Z-hexenal, 2E-hexenal, and hexanal identified the following biosynthetic processes: (1) isomerization between 3E, 3Z, and 2E-hexenals; (2) reduction to 3E, 3Z, and 2E-hexenyl esters; (3) reduction to hexanol and hexyl esters; (4) oxidation to hexanoic acid and formation of hexanoate esters; (5) beta-oxidation of hexanoic acid leading to butyl and butanoate esters; and (6) alpha-oxidation of hexanoic acid leading to pentyl and pentanoate esters. Unsaturated straight-chain ester volatiles appear to arise only by the lipoxygenase pathway and may be useful indicators of lipoxygenase activity in fruit.

The draft genome of tropical fruit durian (Durio zibethinus)

“…Ripening-related gene sets included genes regulated by the MADS-BOX transcription factor family 29,30 , SEPALLATA transcription factor family, and ethylene-related genes such as ACS (aminocyclopropane-1-carboxylic acid synthase), a key ethylene-production enzyme involved in ripening 31 . Other upregulated processes related to taste and odor included triterpenoid metabolism, which has been associated with the intensely bitter taste of Ganoderma lucidum (Lingzhi) 32 , and lipid-related genes involved in the production of C 6 volatile compounds (hexanal and hexanol), which have been associated with the green odor profiles of apples, tomatoes, and bananas, as well as undesirable rancid odors when present at high levels 33,34 . Conversely, processes enriched in non-fruit organs included photosynthetic pathways and the regulation of nitrogen metabolism, likely required by roots and leaves to manufacture amino acids.…”

Analyses of Expressed Sequence Tags from Apple

“…The major group of compounds produced from ripe fruit of apple cultivars, such as Royal Gala, is esters (Young et al, 1996(Young et al, , 2004, including straight-chain esters derived from fatty acids (Rowan et al, 1999) and branched-chain esters derived from branchedchain amino acids (Rowan et al, 1996). Of the straightchain esters, C-6 constituents are thought to be derived via the lipoxygenase pathway from linoleic acid (Fig.…”

Identification of Genes with Potential Roles in Apple Fruit Development and Biochemistry through Large-Scale Statistical Analysis of Expressed Sequence Tags

“…Ester formation in apple is largely confined to the fruit tissue and, more specifically, the skin (Knee and Hatfield, 1981). It has been demonstrated that the LOX and b-oxidation pathways permit the catabolism of fatty acids during fruit ripening to supply precursors for ester formation (Rowan et al, 1999). Consequently, the expectation is that gene expression for some of the enzymes involved in these pathways will increase during ripening and/or be localized within fruit skin tissues.…”