TEMPERATURE EFFECTS ON THE INTERNAL LOWER OXYGEN LIMITS OF APPLE FRUIT

Exposure of packaged fresh produce in modified atmospheres (MA) to ele vated temperatures can cause the partial pressure of oxygen inside the produce (p(O2)(i)) to fall below internal lower O-2 limits (LOL(i)s), resulting in fermentation and loss of quality. In this study, two typ es of LOLi were estimated from steady-slate external chamber atmospher es: the anaerobic compensation point (ACP(i)), and the fermentation th reshold based on the respiratory quotient (FTRQi) and on ethanol (EtOH ) accumulation (FTEtOHi). Mean estimates of LOL(i)s of apple cultivars 'Cox's Orange Pippin' and 'Braeburn' ranged between 0.5 and 1.0 kPa i nternal partial pressure of O-2 (p(O2)(i)) for ACP(i); 0.8 and 1.7 kPa p(O2)(i) for FTRQi, and 0.5 and 2.0 kPa p(O2)(i) for FTEtOHi, for fru it temperatures between 0 degrees and 28 degrees C. Values for ACP(i) estimated at 32 degrees C were higher than those between 0 degrees and 28 degrees C. In general, estimates of dissolved O-2 concentration at ACP(i) and FTRQi tended to decrease with increasing temperature for ' Braeburn' apples, changed little for 'Cox's Orange Pippin' apples, but increased again for ACP(i) at 32 degrees C. On average, estimates of LOL(i)s were higher for 'Braeburn' than 'Cox's Orange Pippin' apples. The effect of temperature on diffusion coefficients and solubility wer e considered unlikely to contribute significantly to variation in LOL( i)s except for solubility at higher temperatures, but differences in t issue porosity may have influenced differences in LOL(i)s between cult ivars. Results of the current study indicate temperature effects on LO L(i)s would not be significant except for MA packages destined for mar kets with ambient temperatures in excess of 28 degrees C. On the other hand it seems that to assume that ACP(i) is independent of temperatur e may be too simplistic, particularly if fruit are exposed to a very w ide range of temperatures. LOL(i)s were relatively constant compared w ith lower O-2 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 t o O-2. (C) 1997 Elsevier Science B.V.