De Novo Fatty Acid Biosynthesis Contributes to Ester Formation in Some, but not All, Fruits

In edible fruit, pathways for the synthesis of esters and other important aroma compounds are still being elucidated.  Recent evidence points to the formation of ester precursors de novo, rather than strictly via catabolic processes degrading previously formed molecules.  To evaluate whether fatty acid biosynthesis via the ubiquitous 2-carbon elongation system could supply 4 to 10-carbon chain fatty acids for ester formation, we tracked the incorporation of isotopically-labeled acetate into esters formed from straight-chain fatty acids.  We fed ¹³C-acetate (20 mM) in a buffered (pH 6) solution to tissue discs of several fruit species and evaluated the level of incorporation in esters containing acetate, butanoate, hexanoate, octanoate, and decanoate moieties.  We found rapid and extensive incorporation in to physalis (Physalis peruviana) and mountain papaya (Vasconcellea pubescens), modest and slow incorporation into diploid strawberry (Fragaria vesca), minimal incorporation into cultivated strawberry (Fragaria virginiana) and no incorporation into apple (Malus domestica).  The data suggest that de novo fatty acid synthesis via the 2-carbon elongation pathway does contribute to the formation of precursors of esters in a number of plant species.  However, the data also suggest the routes of ester precursor biosynthesis vary for different plant species such that more than one pathway can contribute to the formation of a single ester species.