Temperature induces differential softening responses in apple cultivars

Loss of firmness in 'Royal Gala' (RG). 'Cox's Orange Pippin' (COP), 'Granny Smith' (GS) and 'Pacific Rose (TM)' (PR) apples (Malus domestica Borkh.) was quantified in fruit held continuously at temperatures from 0 to 35 degreesC. 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 similar to 22 degreesC, and decreased through 35 degreesC. This equation did not describe k at different temperatures for GS and PR, as k was similar from 0 to 12 degreesC, and could not be calculated for fruit at 20-35 degreesC 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 degreesC. 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. (C) 2001 Elsevier Science B.V. All rights reserved.