Drying characteristics and thermal degradation kinetics of hardness, anthocyanin content and colour in purple- and red-fleshed potato (Solanum tuberosum L.) during hot air drying

Purple-fleshed potatoes (PFP) and red-fleshed potatoes (RFP) were dried using hot air. The hardness, anthocyanin content and colour in PFP and RFP during drying were evaluated at 60, 70 and 80 degrees C. The hardness was characterised by a softening stage in the early drying period, followed by a hardening stage. The times to reach at the transition were 420, 300 and 240min at 60, 70 and 80 degrees C, respectively, for PFP, and 480, 360 and 240min for RFP. However, the moisture content of both PFP and RFP at the transition time was identical at 0.3 (d.b.). The two stages of hardness changes were well described by combining two modified first-order kinetics models. The activation energy (E-a) for the degradation of anthocyanin in PFP and RFP was 25.12 and 28.43kJmol(-1), respectively. The E-a values demonstrated that the thermal sensitivity of PFP was higher than that of RFP.