Combined mechanical (DMA) and dielectric (DETA) thermal analysis of carrot at temperatures 30-90 °C

The outer part of carrot was tested using dynamic mechanical analysis (DMA), in air with 90% humidity between 30 and 90 °C. Temperature plots of storage (SM i.e. elastic) and loss (LM i.e. inelastic) moduli were obtained. The SM and LM values were the basis for the calculation of the loss tangent (LT), the parameter expressing the ratio of inelastic to elastic parenchyma toughness. The DMA was followed by Dielectric thermal analysis (DETA). The tissue toughness decreased with increasing temperature; the kinetic analysis of the data led to two characteristic temperatures (approximately 50 °C and 70 °C) where the physical parameters changed their temperature dependence. The characteristic temperatures can serve as a basis of division of the whole temperature range into four parts (A-D). The DMA results supported phase transitions at temperatures below 70 °C, whereas DETA strongly support changes observed at and above 70 °C. These changes were interpreted as a consequence of changes and destructions of the cell membrane - plasmalemma. A similar analysis on other tissues gave similar but little different results supporting the idea of possible application of the method to study product differences.