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

Summary 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 °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 240 min at 60, 70 and 80 °C, respectively, for PFP, and 480, 360 and 240 min 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 (Ea) for the degradation of anthocyanin in PFP and RFP was 25.12 and 28.43 kJ mol−1, respectively. The Ea values demonstrated that the thermal sensitivity of PFP was higher than that of RFP. Hot air drying induced the thermal degradation of hardness, anthocyanin content and colour of purple‐fleshed potatoes (PFP) and red‐fleshed potatoes (RFP). The quality changes of PFP and RFP can be controlled by drying temperature and predicted by first‐order reaction kinetics.