MODE OF OXYGEN AND CARBON-DIOXIDE ACTION ON STRAWBERRY ESTER BIOSYNTHESIS

'Chandler' strawberries (Fragaria ananassa Duck.) were kept in air, 0. 25% O2, 21% O2 + 50% CO2, or 0.25 O2 + 50% CO2 (balance N2) at 5C for 1 to 7 days to study the effects of controlled atmospheres (CAs) on vo latiles and fermentation enzymes. Concentrations of acetaldehyde, etha nol, ethyl acetate, and ethyl butyrate were greatly increased, while c oncentrations of isopropyl acetate, propyl acetate, and butyl acetate were reduced by the three CA treatments compared to those of air-contr ol fruit. The CA treatments enhanced activities of pyruvate decarboxyl ase (PDC) and alcohol dehydrogenase (ADH) but slightly decreased activ ity of alcohol acetyltransferase (AAT). The results indicate that the enhanced PDC and ADH activities by CA treatments cause ethanol accumul ation, which in turn drives the biosynthesis of ethyl esters. The incr eased ethanol concentration also competes with other alcohols for carb oxyl groups for esterification reactions. The reduced AAT activity and limited availability of carboxyl groups due to ethanol competition de crease production of other acetate esters.