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Thermal transition and thermo-physical properties of potato (Solanum tuberosum L.) var. Russet brown

Krishna Kumar, Pavitra, Bhunia, Kanishka, Tang, Juming, Rasco, Barbara A., Takhar, Pawan S., Sablani, Shyam S.
Journal of food measurement & characterization 2018 v.12 no.3 pp. 1572-1580
Solanum tuberosum, differential scanning calorimetry, foods, freezing, freezing point, frozen storage, melting, models, potatoes, specific heat, storage conditions, temperature, thermal conductivity, thermal diffusivity, water content
Potatoes are an important food in many regions of the world and are commonly used in a variety of food products. Thermal transition and thermo-physical properties of potatoes are important in order to design efficient food processes and select appropriate storage conditions. In this study, we determined the thermal transitions and thermophysical properties of raw and blanched/par-fried potato for a temperature range of − 32 to 21.1 °C. Using differential scanning calorimetry, we found an initial freezing point (Tf) at − 1.8 ± 0.1 °C, an onset of melting (Tₘ′) at − 9.9 ± 0.2 °C and an unfreezable water content (X′w) for maximally freeze-concentrated raw potato at 0.21 kg water/kg potato. Corresponding values for blanched/par-fried potatoes were − 0.9 ± 0.1 °C, − 11.0 ± 0.2 °C and 0.18 kg water/kg potato. Results show that an increase in solids content decreased Tf of both raw and blanched potatoes. We modelled the relationship between them using the Chen model. The apparent specific heat (Cₐₚₚ) increased around Tf to 31.7 ± 1.13 kJ/kg K for raw potato and 26.7 ± 0.62 kJ/kg K for blanched/par-fried potato. For frozen raw potato at − 32 °C, thermal diffusivity (α) was 0.89 ± 0.01 × 10 ⁻⁶ m²/s and thermal conductivity (k), 1.82 ± 0.14 W/m K, respectively. These values were higher for frozen raw potato than for the unfrozen raw potato (0.15 ± 0.01 × 10 ⁻⁶ m²/s and 0.56 ± 0.08 W/m K, respectively at 21.1 °C). The apparent density (ρ) of frozen raw potato (992 ± 4.00 kg/m³ at − 32 °C) was less than that for unfrozen raw potato (1053 ± 4.00 kg/m³ at 21.1 °C), and a similar trend was obtained for blanched/par-fried potato (993 ± 2.00 kg/m³ at − 32 °C and 1188 ± 7.00 kg/m³ at 21.1 °C, respectively). This study established a correlation between thermo-physical properties and temperature. Findings may be used to inform the design and optimization of freezing processes and frozen storage for potato products.