Synthesis of Aroma Compound By Controlled AT-Mosphere (CA) Stored Apples Supplied With Aroma Precursors :Alcohols,Acids And Esters

Abstract

The biosynthesis of volatiles by 'Golden Delicious' apple fruits are highly diminshed after a long term controlled atmosphere (CA) or ultra low oxygen (ULO) storage. To study the mechanisms of volatile production at both harvest time and after long term storage and to explain the reasons for the inability of fruits to produce adequate amounts of volatiles, aroma precursors were supplied to the fruits at different times during storage. Fruits were supplied with the following aroma precursors: Alcohols (ethanol, propanol, butanol, pentanol, hexanol, isobutanol and isopentanol), acids (acetic-, propionic-, butyric-, pentanoic- and hexanoic acid) and esters (methyl heptanoate and methyl linolenate). Each aroma precursor was applied separately both at harvest time (October) and in March, after the apples were stored in ultra low oxygen conditions (1% O2: 3% CO2) for 5 months. Alcohols, except ethanol, induced in both application times a strong increase in the biosynthesis of its volatiles. Butanol enhanced the production of butyl acetate, ethyl butyrate, butanol and pentyl butyrate. Hexanol enhanced the synthesis of butyl butyrate, hexyl acetate, hexyl propionate, hexanol and hexyl hexanoate. The biosynthesis of butyl butirate or propyl acetate by fruits stored for 5 months in ULO-storage after the treatments with hexanol or pentanol is evidence for an active beta-oxiodation process. The influence of acids was negligible at harvest time but they, except acetic and hexanioc acids, induced at the second date the biosynthesis of their esters.

It is proposed that the long chain unsaturated fatty acids (linol- and linolenic acids) are the ultimate precursors for aroma (Bartley et al., 1985). The content of both fatty acids were found to be highly and positively correlated with volatile production. They decreased strongly after 6 months in ULO-storage in about the same manner as aroma production.