Effect of gamma irradiation and modified atmospheres on physiology and quality of minimally processed apples

Demand for minimally processed fresh produce has increased dramatically over the last two decades, but production of minimally processed apples has been limited due to lack of methods to enhance quality and safety. The use of irradiation and high CO₂ atmosphere has therefore, been studied.; Apple slices from four cultivars and with different maturities were irradiated at doses ranged from 0 to 11 kGy using a CO60 source. Effects of calcium and modified atmospheres (MA) containing high CO₂ levels (up to 30 kPa) on the response of slices to irradiation were also investigated. Physiology and quality of slices were assessed by measuring respiration, ethylene production, texture, pectin content, and color of the slices.; Doses above 1.2 kGy increased respiration of ‘Idared’, ‘Law Rome’ and ‘Empire’ slices curvilinearly with maximum respiration occurring at 3–6 kGy. However, the response of ‘Delicious’ slices was linear between 0 and 11 kGy. The stimulatory effect decreased with post-irradiation storage. Respiration rate of pre-climacteric ‘Delicious’ apples slices was stimulated more than the post-climacteric slices, but the reverse occurred for ‘Empire’. The respiratory quotient increased with dose. Irradiation reduced ethylene production of apple slices.; Fruit firmness decreased as irradiation dose increased beyond 0.34 kGy. The high dose rate initially prevented softening, but not by day 3. O ₂ level M the irradiation atmosphere did not affect firmness. The softening was associated with increased water-soluble pectin and decreased oxalate-soluble pectin. Calcium prevented irradiation-induced softening of 3–4 mm thick slices, but was not effective with wedges due to its limited penetration.; High pCO₂ and low pO₂ resulted in reduced respiration and ethylene production. Inhibition of respiration was explained best by an enzyme kinetics model that combined competitive and uncompetitive types of inhibition. Browning of slices during storage was only slightly reduced by CO₂. Firmness decreased during storage, but was not affected by atmosphere. CO₂ levels (>7.5 kPa) reduced accumulation of fermentation products.; These results indicate that use of irradiation is limited for apple slices because of increased softening. Storage atmospheres with high CO₂ (15–30 kPa) and low O₂ (0.5 kPa or lower) have beneficial effects on physiology and quality of minimally processed apples.