Thermal properties of whole and tissue parts of pomegranate (Punica granatum) fruit

Abstract

The thermal properties of two pomegranate fruit cultivars (Wonderful and Acco) and their epicarp, mesocarp and arils were experimentally determined. A transient heating probe system was first calibrated and used for accurate measurement of the specific heat capacity, thermal conductivity, and thermal diffusivity over a temperature range of 7–45 °C. The thermophysical properties did not vary significantly between the two cultivars. The density of the whole ‘Wonderful’ and ‘Acco’ fruit was 986.99 ± 23.82 and 1041.23 ± 18.93 kg m⁻³, respectively. The epicarp of both cultivars had significantly lower density compared to the mesocarp and arils. The values of thermal conductivity and diffusivity of the two pomegranate cultivars increased significantly with increase in tissue temperature. In both cultivars, the aril part was observed to have the highest values of thermal conductivity and specific heat capacity. For ‘Acco’ at 7 °C, values were 0.419 ± 0.047 W m⁻¹ K⁻¹ and 2775.244 ± 298.120 J kg⁻¹ K⁻¹, respectively, compared to the mesocarp (0.352 ± 0.040 W m⁻¹ K⁻¹ and 2560.803 ± 231.028 J kg⁻¹ K⁻¹) and epicarp (0.389 ± 0.030 W m⁻¹ K⁻¹ and 2681.888 ± 135.460 J kg⁻¹ K⁻¹). For both ‘Wonderful’ and ‘Acco’, the in-plane thermal property values (measured along layers of peel slices) were the same as the cross-plane property values (measured through layers of slices).