Factors Influencing Ethylene-induced Isocoumarin Formation and Increased Respiration in Carrots

Abstract

Ethylene-induced formation of isocoumarin was characterized in relation to ethylene-enhanced respiration in whole or cut carrots ( Daucus carota L.). Ethylene concentrations (0.1 to 5 ppm) and temperatures (1 to 15C) that increased respiration also favored a more rapid formation of isocoumarin (8-hydroxy-3-methyl-6-methoxy-3,4-dihydro-isocoumarin). Exposing mature carrots to 0.5 ppm C 2 H 4 for 14 days at 1 or 5C resulted in isocoumarin contents of 20 and 40 mg/100 g peel, respectively. These levels were easily detected as a bitter flavor in the intact carrot roots. Immature carrots formed higher levels of isocoumarin than mature carrots; 180 mg/100 g peel were detected in young carrots stored 14 days at 5C in air containing 0.5 ppm C 2 H 4 . Freshly harvested carrots exposed to 5 ppm C 2 H 4 accumulated 4-fold higher isocoumarin levels than those formed by carrots stored 30 days at 5C before exposure to C 2 H 4 . An atmosphere of 100% O 2 potentiated the effect of C 2 H 4 on isocoumarin formation, resulting in a 5-fold increase over that found in carrots treated with C 2 H 4 in air. A storage atmosphere of 0.5 ppm C 2 H 4 in 1% O 2 resulted in isocoumarin levels about one-half those attained in 0.5 ppm C 2 H 4 in air. Sliced, cut, or dropped carrots exposed to C 2 H 4 showed greater isocoumarin accumulation rates than intact uninjured carrots. Peeled baby carrots, however, had little capacity to form isocoumarin. In general, the more rapid the respiratory rise in response to C 2 H 4 , the more rapidly isocoumarin accumulated. The greater the respiratory response to ethylene, the higher the level of isocoumarin formed.