Drying characteristics, functional properties and in vitro digestion of purple potato slices dried by different methods

The drying characteristics, physico-chemical and functional properties, as well as starch digestibility, of purple potato slices dried using different methods (such as, vacuum freeze-drying, VFD; hot-air drying, HAD; air-impingement jet drying, AIJD; and far-infrared assisted heat-pump drying, FIHPD) were investigated. Drying rate was the highest (3.0 g 100 g−1 min−1) using AIJD, followed by FIHPD and HAD, and the rate of VFD was the lowest one (0.3 g 100 g−1 min−1). Drying data were fitted to 12 thin-layer drying models, with the Midilli model giving the best predictions. Moreover, AIJD showed higher diffusivity (5.5×10−10 m2 s−1) and energy efficiency (55 J g−1) than any other drying method used in this study. With reference to the samples dried by VFD, the starch granules of the samples obtained by HAD, FIHPD, and AIJD exhibited different extent of disruption, which significantly increased their water absorption capacity, swelling power, and in vitro digestibility, but decreased the peak viscosity. The sample resulting from AIJD had the greatest water absorption capacity (7.9 g g−1) and solubility (21.6%), but the smallest syneresis rate (48%). Good correlation coefficients (R2>0.98) implied that the pseudo-first order kinetic model adequately described the rate and extent of starch digestion of dried potato flours. Samples from AIJD and FIHPD showed the highest digestibility percentages, reaching to 72.4 and 72.5%. Based on the drying rate, specific energy consumption, functional properties and digestibility, AIJD appeared to be quite effective and suitable to be transferred on the industry scale.