The influence of crop-load, delayed cooling and storage atmosphere on post-storage quality of ‘Honeycrisp’™ apples

The influence of crop-load, delayed cooling and storage environment on fruit quality and disorder, and on the incidence of rot was investigated on 7 year-old ‘Honeycrisp’ apple (Malus domestica Borkh.) trees on ‘Malling 26’ rootstocks at three different sites during 2003 and 2004. Fruit from non-thinned (control) trees, or trees thinned to three, six or nine fruit cm–² trunk cross-sectional area (TCSA) were harvested and: (1) immediately cooled over 24 h to 3°C [commercial (Comm)] then stored at 3°C in refrigerated air (RA) or in a controlled atmosphere (CA; 2.5 kPa O₂, 1.0 – 1.5 kPa CO₂); or (2) held at 20°C for 6 d, followed by 1 d at 3°C [= 7 d pre-storage warming treatment = delayed cooling (DC)] then stored at 3°C under RA or in CA storage. After 3 and 6 months of storage, fruit mass (g), firmness (N), colour (% red), soluble solids content (SSC; %), titratable acidity (TA; mg malic acid equivalents 100 ml–¹ juice), “greasiness” (0–3 scale), the extent of disorders such as soft scald (%) and low temperature breakdown (LTB; %), as well as the incidence of rot (%) were assessed. In general, as crop-load increased fruit mass, firmness, colour, SSC and TA decreased regardless of the effects of DC and storage treatment. Crop-load did not influence fruit “greasiness” and had an inconsistent and less-pronounced effect on soft scald, LTB and rot. The 7 d pre-storage warming treatment reduced the incidence of soft scald and LTB, irrespective of crop-load, but had little influence on other fruit quality measurements. Although the storage environment did not consistently alter quality, CA-stored ‘Honeycrisp’ apples tended to be more acidic, less “greasy” and develop less soft scald. Overall, the data indicate that the highest fruit quality was attained by thinning ‘Honeycrisp’ trees as close to three fruit cm–² TCSA as possible, by subjecting newly-harvested fruit to a 7 d pre-storage warming period of 20°C, followed by CA storage at 2.5 kPa O₂, 1 – 1.5 kPa CO₂ at 3°C.