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The aim of this work was to determine the anaerobic compensation point (ACP) in ‘Hass’ avocado fruits as a function of temperature and the advance in ripening. Controlled atmosphere treatments with oxygen in a range from 0 to 4%, with two temperature levels, 5.5 and 20°C, applied to fruits of three firmness levels which included the pre-climacteric, the mid-zone of the climacteric rise and the post-climacteric phase. Mean ACP values of 1.44% and 1.81% were found for 5.5°C and 20°C, respectively. These values increased with ripening. The production of fermentative metabolites was not exclusive of O2 concentrations below to ACP, and temperature affected the accumulation of these compounds, with values of 10.7 mol/100mL at 5.5°C and 101.3 mol/100mL at 20°C. The production of those metabolites significantly increased with ripening and the values were, in the post-climacteric stage, 20 and 39 times greater than in the pre-climacteric one, at 5.5°C and 20°C, respectively. Results obtained here could be used to define adequate storage conditions for ‘Hass’ avocado fruits in modified atmosphere systems.

The gas skin permeance and the internal atmosphere composition of 'Hass' avocado (Persea americana Mill.) fruits were evaluated during the ripening period by using surface chambers. Plant material was harvested at physiological maturity at Uruapan, Michoacan, Mexico, in November of 2001. Storage was conducted under natural atmosphere at 20 C and 81% RH; the physiological stages were expressed in terms of ethylene internal partial pressures and pulp firmness. The climacteric onset occurred at 18.2 N and the peak was reached at 5.0 N. The internal partial pressure decreased consistently for O 2 while for CO 2 increased. This result suggested that the resistance to gas exchange imposed by skin caused that O 2 taken up was not enough to supply fruit requirements and also that CO 2 was produced faster than the rate at which it was given off to ambient. It was found that skin permeance to O 2 and CO 2 could vary during ripening period and that avocado skin was more permeable to O 2 than to CO 2 with a 1.7 : 1 ratio. Surface chambers were useful to determine internal concentrations and gas skin permeance, but care must be taken to select the best sampling procedure to allow getting accurate values of these parameters.