Thermal and Mechanical Properties of Black Pepper at Different Temperatures

Abstract

AbstractBlack pepper is mainly preferred in the powder form that invariably requires the properties of the pepper for the design of the process and grinder. The thermal properties were investigated for a temperature range of −45 to 5°C, while, the breaking characteristics of the black pepper were examined at ambient (36°C) and subzero (−25°C) temperature conditions at a moisture content of 3.90% dry basis. The glass transition temperature (Tg) varied between −28.61 and −20.03°C with the peak value of −21.27°C indicating the phase transformation of black pepper from amorphous to crystalline (vice versa). Accordingly, the temperature showed a significant effect on the thermal and mechanical properties. The thermal conductivity (W/m.K) and thermal diffusivity (m2/s) decreased from 0.775 to 0.18 and 12.25 × 10−7 to 1.77 × 10−7 with the increase in the temperature. However, specific heat showed an increasing (1169 to 1907 J/kg.K) trend with the rise in temperature. Average failure force (90.62 N) and deformation modulus (54.10 N/mm) were found to be higher under the subzero temperature condition as compared with that of ambient condition (76.08 N and 30.13 N/mm). While failure deformation (0.89 mm), failure strain (17.67%), and failure energy 25.35 N.mm) showed lower values as compared with that of ambient condition (1.56 mm, 31.13% and 31.48 N.mm). These results will serve as a useful guide for the commercial production of high quality of the powder; indicating that a maximum grinding temperature of −21.27°C (below Tg) should be used for the cryogenic grinding of black pepper.Practical ApplicationsThe findings of this study facilitate the spice industry and the researchers to select relevant thermal and mechanical properties of black pepper for design and simulation of process and equipment for thermal processing, storage, cryogenic grinding, freezing, freeze drying and transportation to ensure the higher quality of end product and lower expenditure. Considering the example of the design of a cryogenic grinder the appropriate grinding temperature should be chosen based on the thermal and mechanical properties of grinding material, for example, black pepper and the grinder metal like stainless steel under such conditions. Further, for selection of the position of liquid nitrogen nozzle in the precooler and the grinder, the temperature profile of the process should be known, that also requires the basic thermal and mechanical properties of grinding material under such low temperature condition.