ETHYLENE EFFECT ON ACC CONTENT AND ACC OXIDASE DURING RIPENING OF ‘MARADOL’ PAPAYA

Abstract

‘Maradol’ papaya (Carica papaya L.) fruits were subjected to atmospheres containing certified mixtures of synthetic air and ethylene (0, 100, 300 and 500 µL L^-1) in fiberglass containers for different periods (8, 16 and 24 h). After exposure, fruits were transferred to ambient conditions (25 °C) for ripening. The analyses performed on each treatment were: firmness, soluble solids content, reducing sugars content, titratable acidity, peel and flesh color (Hue), ethylene production rate (EPR), 1-aminocyclopropane-1-carboxylic acid (ACC) content and ethylene-forming enzyme (ACC oxidadese) activity. Results showed that the first noticeable change in fruits was the yellow and red color turning in peel and flesh respectively, both typical of a fully ripe and ready-to-eat-papaya fruit. Fruits exposed to 500 µL L^-1 of ethylene for 16 and 24 h showed a climacteric peak one day after treatment, while fruits exposed for only 8 h displayed their climacteric peak 2 d after ethylene exposure. Papayas treated for 16 and 24 h developed very low Hue values in a shorter time then the control, and their ACC content increased to 2.7 nmol g^-1 h^-1. ACC oxidase activity also increased to 3 nL g^-1 h^-1, and EPR reached 24 nL g^-1 h^-1. This set of conditions allowed fruits to reach firmness values of 5.2 kgf cm^-2 and 12 % of soluble solids after 6 d at 25 °C. Reducing sugars content and percent age of titratable acidity were not different (P > 0.05) between treatments. Similar values were found in control fruits after 8 d at normal ripening conditions. Results suggest that it is possible to shorten ripening of ‘Maradol’ papaya fruit from 8 to 3 d after application of exogenous ethylene.