Classification of ‘Granny Smith’ apples with different levels of superficial scald severity based on targeted metabolites and discriminant analysis


  • Asanda Mditshwa Stellenbosch University
  • Olaniyi A Fawole Stellenbosch University
  • Filicity Vries Agricultural Research Council – Infruitec/Nietvoorbij
  • Kobus van der Merwe Agricultural Research Council – Infruitec/Nietvoorbij
  • Elke Crouch Stellenbosch University
  • Umezuruike Linus Opara Stellenbosch University



Apples, scald severity, Alpha-farnescence, ethylene, quality, reactive oxygen species


To study the metabolic changes in ‘Granny Smith’ apples with different severities of superficial scald, fruit were stored in normal refrigerated air (0°C, 95% RH) for 12 weeks followed by 7 d shelf-life under room conditions (20°C, 65% RH). Fruit were graded to five groups based on scald severity and analysed for ethylene, α-farnesene and 6-methyl-5-hepten-2-one (MHO) levels. Reactive oxygen species (ROS) were measured by confocal laser-scanning microscopy on apple peel treated with fluorescent probe 2’,7’-dichlorodihydrofluorescein diacetate. Ethylene production rate, α-farnesene and MHO contents and ROS intensity increased with increasing scald severity but declined in severely scalded fruit. Malondialdehyde (MDA) concentration in fruit peel, a measure of membrane damage, increased linearly (R=0.891) with increase in scald severity. Discriminant analysis was used to classify fruit by scald severity on the basis of metabolites accumulated. The stepwise model indicated that three attributes (ROS, ethylene production and MDA) contributed significantly (R2≥0.5) to the separation of the five scald severity indexes, with ROS having the highest contribution (partial R² =0.961; p<0.0001), followed by ethylene (R2=0.718; p<0.0001) and MDA (R2=0.578; p<0.0001). 

Author Biographies

Asanda Mditshwa, Stellenbosch University

PhD Student, Department of Horticultural Sciences, Stellenbosch University

Olaniyi A Fawole, Stellenbosch University

Postdoctoral Research Fellow

Umezuruike Linus Opara, Stellenbosch University

Distinguished Professor & DST/NRF South African Research Chair in Postharvest Technology, Faculty of AgriSciences, Stellenbosch 7600, South Africa