Biosynthesis of volatile aroma compounds in pear fruit stored under long-term controlled-atmosphere conditions

Abstract

The production of butyl and hexyl acetates and the contents of ethanol and acetaldehyde in relation to the activity of some related enzymes (lipoxygenase, pyruvate decarboxylase, alcohol dehydrogenase and alcohol o -acyltransferase) was studied in ‘Doyenne du Comice’ pears during ripening at 20 8C, following long-term cold storage under different conditions: air, or CA in 2 kPa O2 with various CO2 partial pressures (0.7, 2 or 5 kPa). A decrease in volatile production was found for fruit stored under low O2 upon return to ambient conditions. Results suggest that inhibition of volatile biosynthesis by CA storage is caused mainly by limited precursor/substrate supply to the related enzymes rather than by enzyme degradation or inactivation. Ethanol production by the fruit did not correlate well with ADH activity. The possibilities of a feedback inhibition of enzyme activity by excess product and of oxidation into acetaldehyde upon return to air are discussed. Hypoxic conditions caused a decrease in LOX activity after 5 months storage, possibly leading to shortage of lipid precursors for ester biosynthesis. # 2002 Elsevier Science B.V. All rights reserved.