SHORT-TERM EXPOSURES TO REDUCED O2 AND ELEVATED CO2 ATMOSPHERES DIFFERENTLY AFFECT THE RESPIRATORY CHARACTERISTICS OF GRAPEFRUIT AND MANDARIN

Abstract

Respiratory responses of citrus fruit to controlled atmospheres (CA) are of great importance, since CA treatments can be used in postharvest handling only as long as they do not cause any detrimental effects on fruit quality. In this study, we evaluated the physiological responses of 'Star Ruby' grapefruit (Citrus paradisi Macf., 'Star Ruby') and 'Murcott' mandarin (Citrus reticulata Blanco, 'Murcott') to different concentrations of O 2 (5, 10, 15, and 21%) or CO 2 (0, 5, 10, and 20%) at 20°C for a short-term period (1 week). Exposure to reduced O 2 atmospheres greatly reduced respiration rates and internal CO 2 levels, but 5% O 2 dramatically increased juice ethanol, and to a lesser extent, acetaldehyde (AA) levels. Exposure to 5% and 10% O 2 reduced ethylene evolution rates in grapefruit but increased their levels in mandarin. Exposure to 10% and 20% CO 2 markedly increased respiration rates and internal CO 2 levels, but reduced ethylene production. Exposure to 20% CO 2 substantially increased juice ethanol and AA levels as compared with air controls, but to a less extent as compared with exposure to 5% O 2 atmosphere. Mandarin exhibited stronger and more rapid responses to reduced O 2 than grapefruit, as revealed by the accumulation of juice ethanol and AA, two important indicators of anaerobic respiration. Mandarin also showed earlier and higher increases in respiration rates and internal CO 2 levels than grapefruit following exposure to elevated CO 2 . Results indicate that reduced O 2 and elevated CO 2 atmospheres affect citrus fruit' respiratory characteristics differently. The possible mechanisms involved are briefly discussed.