PHYSIOLOGY AND PREDICTION OF FRUIT TOLERANCE TO LOW-OXYGEN ATMOSPHERES

Fruits of 'Granny Smith' and 'Yellow Newtown' apples (Malus domestica Borkh), '20th Century' pear (Pyrus serotina L.), and 'Angeleno' plum (Prunus domestica L.) were kept in air and in 0.25% or 0.02% O2 at 0, 5, or 10C for 3, 7, 14, 25, or 35 days to study the effects of low-O2 atmospheres on their postharvest physiology and quality attributes. Soluble solids content (SSC), pH, and external appearance were not significantly influenced, but resistance to CO2 diffusion was increased by the low-O2 treatments. Exposures to the low-O2 atmospheres inhibited ripening, including reduction in ethylene production rate, retardation of skin color changes and flesh softening, and maintenance of titratable acidity. The most important detrimental effect of the low-O2 treatments was development of an alcoholic off-flavor that had a logarithmic relation with ethanol content of the fruits. The ethanol content causing slight off-flavor (E(o)) increased with SSC of the commodity at the ripe stage, and it could be estimated using the following formula: (Log E(o))/SSC = 0.228. Using SSC of ripe fruits and average ethanol accumulation rate per day (V(E)) from each low-O2 treatment, the tolerance limit (T1) of fruits to low-O2 atmospheres could be predicted as follows: T1 = E(o)/V(E) = (10(0.228)SSC)/V(E).