Oxidative/Fermentative Behavior in the Flesh of Hass Avocado Fruits Under Natural and Controlled Atmosphere Conditions

Fermentation should be avoided when fruits and vegetables are handled through modified/controlled atmosphere (MA/CA) systems in postharvest. In several fruits, fermentation has been detected after remaining in environments with nonlimited O-2 and this can be a cause of confusion when assessing whether an MA/CA technique was correctly applied. In this work, gradients of physiological variables were evaluated in tissue of Hass avocado fruits of different maturity stages in postharvest to explain the effect of changing O-2 concentration in the external environment on the internal oxidative/fermentative metabolic behavior. Storage during 16 days was conducted where fruits were maintained in conditions of natural air (NA; 20.95% O-2, 79% relative humidity) at 20 A degrees C, and their oxidative/fermentative behavior was compared with that of other fruits exposed to CA through a humidified mixture with 5.3% O-2 at the same temperature for 24 h. Differences in O-2 concentration, pH, acidity, and accumulation of acetaldehyde and ethanol were identified after evaluating four tissue sections taken from different depths of the equatorial region of fruits. Internal O-2 concentration diminished with tissue depth, remaining above tolerance in all sections of fruits of the NA treatment, but not in fruits exposed to CA where there were sections with O-2 concentration lower than the limit. It was verified that fermentative activity can develop in both anaerobic and aerobic conditions in response to low O-2 concentration and pH, the latter being able to evaluate the effect of external O-2 concentration on fruit fermentative behavior.