Biosynthese des produits volatils de la pomme: Formation des alcools et des esters a partir des acides gras

The biosynthesis of apple volatiles (alcohols and esters) was studied using disks of aged tissues. After adding each substrate, the volatiles formed were analysed and estimated by GLC and their qualitative and quantitative composition compared with those of the control. Alcohols were formed from aliphatic acids having either the same number of carbon atoms, or from higher homologues through β-oxidation. Fatty acids with an even carbon number gave rise to butanol and hexanol, while odd carbon fatty acids generated propanol and pentanol. Esters were synthesized from the corresponding acid and alcohol and the yield was very high. Volatile profiles differed from one variety to another, yellow-skinned varieties producing chiefly acetic acid esters and the red-skinned mainly butyric acid esters. Provided the right substrates were given, all the esters were synthesized by the different tissues assayed, and the nature of the volatiles produced by each variety depends on the substrates present in the fruit. However, in Golden Delicious apples, which have a low content of butyric esters, erogenous butyrate was rapidly and completely transformed into acetate.