Temperature effects on the internal lower oxygen limits of apple fruit

Abstract

Abstract Exposure of packaged fresh produce in modified atmospheres (MA) to elevated temperatures can cause the partial pressure of oxygen inside the produce (PO2i) to fall below internal lower O2 limits (LOLis), resulting in fermentation and loss of quality. In this study, two types of LOLi were estimated from steady-state external chamber atmospheres: the anaerobic compensation point (ACPi), and the fermentation threshold based on the respiratory quotient (FTRQi) and on ethanol (EtOH) accumulation (FTEtOHi). Mean estimates of LOLis of apple cultivars ‘Cox's Orange Pippin’ and ‘Braeburn’ ranged between 0.5 and 1.0 kPa internal partial pressure of O2 (pO2i for ACPi; 0.8 and 1.7 kPa pO2i for FTRQi, and 0.5 and 2.0 kPa pO2i for FTEtOHi, for fruit temperatures between 0 ° and 28 °C. Values for ACPi estimated at 32 °C were higher than those between 0 ° and 28 °C. In general, estimates of dissolved O2 concentration at ACPi and FTRQi tended to decrease with increasing temperature for ‘Braeburn’ apples, changed little for ‘Cox's Orange Pippin’ apples, but increased again for ACPi at 32 °C. On average, estimates of LOLis were higher for ‘Braeburn’ than ‘Cox's Orange Pippin’ apples. The effect of temperature on diffusion coefficients and solubility were considered unlikely to contribute significantly to variation in LOLis except for solubility at higher temperatures, but differences in tissue porosity may have influenced differences in LOLis between cultivars. Results of the current study indicate temperature effects on LOLis would not be significant except for MA packages destined for markets with ambient temperatures in excess of 28 °C. On the other hand it seems that to assume that ACPi is independent of temperature may be too simplistic, particularly if fruit are exposed to a very wide range of temperatures. LOLis were relatively constant compared with lower O2 limits based on package atmospheres, and can be used to estimate optimum MA package atmospheres that account for fruit within a population with the highest respiration rates and lowest permeance to O2.