EFFECT OF CARBON-DIOXIDE ON THE INTERNAL LOWER OXYGEN LIMITS OF APPLEFRUIT

The effect of elevated CO2 between 0 and 8 kPa on steady-state lower O -2 limits based on internal atmospheres (LOLi) was estimated for postc limacteric 'Cox's Orange Pippin' and 'Braeburn' apples at 0 and 20 deg rees C. Two types of LOLi were estimated: the anaerobic compensation p oint (ACP(i)), and the internal fermentation threshold based either on the respiratory quotient (FTRQi) or ethanol (EtOH) accumulation (FTEt OHi). ACP(i), for both cultivars and temperatures, remained constant a t 0.5 kPa O-2 for 'Cox's Orange Pippin' and 0.8-1.0 O-2 for 'Braeburn' apples for levels of CO2 external to the fruit between 0 and 8 kPa. H owever, for FTRQi and FTEtOHi no consistent trend with level of CO2 wa s evident at 20 degrees C for either cultivar. In contrast, at 0 degre es C FTRQi and FTEtOHi were 0.2-0.8 kPa O-2 higher at 8 kPa CO2 than a t 0 kPa CO2 (with the exception of FTRQi for 'Cox's Orange Pippin'). A small decrease in O-2 uptake (estimated from the difference in extern al and internal O-2 atmospheres) was observed between 2 and 8 kPa CO2 at 20 degrees C. Elevated CO2 slightly lowered the respiratory quotien t (RQ(i), estimated from the ratio of differences between external and internal atmosphere partial pressures of CO2 and O-2) of 'Cox's Orang e Pippin' in 8 kPa CO2 and 'Braeburn' in 2 to 8 kPa CO2 at 20 degrees C, and more markedly in 8 kPa CO2 at 0 degrees C. The RQ(i) of 'Cox's Orange Pippin' and 'Braeburn' apples was slightly and markedly higher respectively at 0 degrees C compared to 20 degrees C, The lower RQ(i) of 'Braeburn' at 20 degrees C compared to 'Cox's Orange Pippin' apples indicated 'Braeburn had a higher permeance to CO2 relative to O-2 com pared to 'Cox's Orange Pippin'. This study indicates the tolerance of 'Cox's Orange Pippin' and 'Braeburn' apples to low O-2 levels may be a ffected by levels of CO2. (C) 1997 Elsevier Science B.V.