Thermal conductivity measurement of biological materials: a case study in moderate ambient temperatures

Abstract

This study analyzed the influence of temperature on the thermal conductivity and thermal capacity of kefir grains during heating and cooling in the temperature range between 3 and 30°C. The correlations between the thermal conductivity vs temperature of kefir grains during heating differed from those observed during cooling. During heating, the thermal conductivity of kefir grains decreased from 0.46 to 0.40 W m À1 K À1 according to the Arrhenius law. During cooling, the thermal conductivity remained stable at 0.36 ± 0.03 W m À1 K À1 . The observed differences in the behavior of thermal conductivity of heated and cooled kefir grains could be related to the stimulating impact of heat on microbial activity inside the grains. The maximum thermal capacity of 3776 J kg À1 K À1 was noted at 9.3°C and the minimum thermal capacity of 2987 J kg À1 K À1 ,at 30.0°C. In-depth knowledge of the thermal properties of kefir grains can contribute to improving their efficiency and optimizing the kefir production process.