Temperature induces differential softening responses in apple cultivars

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Loss of firmness in ‘Royal Gala’ (RG), ‘Cox's Orange Pippin’ (COP), ‘Granny Smith’ (GS) and ‘Pacific Rose™’ (PR) apples (Malus domestica Borkh.) was quantified in fruit held continuously at temperatures from 0 to 35 °C. Softening was triphasic, consisting of an initial slow softening phase, followed by a rapid phase, and a final slow softening phase. Loss of firmness at each temperature was described by an asymmetric, sigmoidal equation. Rate of firmness change (k) at different temperatures was described by a modified Arrhenius equation for RG and COP, where k increased with temperature from 0 through ∼22 °C, and decreased through 35 °C. This equation did not describe k at different temperatures for GS and PR, as k was similar from 0 to 12 °C, and could not be calculated for fruit at 20–35 °C as rapid phase softening was not initiated. Transition between the initial slow softening phase and the rapid softening phase was related to a rapid increase in internal ethylene concentration (IEC) for all cultivars. GS and PR had slow softening at 20–35 °C, and had delayed and slow increases in IEC. Equations used in this study could be used to estimate firmness loss at different parts of the commercial post-harvest handling chain, especially where fruit are at non-optimal storage temperatures.