Effect of high pressure pretreatment on the drying characteristics of the beetroot (Beta vulgaris) cubes

Effect of high pressure (100–300 MPa for 5–15 min) pretreatments on the drying characteristics and microstructure of beetroot (Beta vulgaris) were studied. The drying experiments were performed using the dehumidified air dryer at varying temperatures (50–70 °C) and air velocities (1–2 m/s). The drying data was modelled based on seven selected mathematical models to assess the effect of the pretreatment on the drying rate. It was observed that HPP pretreatment enhanced the drying rate and hence resulted in about 20% decrease in the drying time for 300 MPa treated sample to 4% for the 100 MPa treated sample. The Modified Page and Two-term exponential models effectively explain the drying data for the beetroot cubes. Colour change was minimal for HPP pretreated samples than the thermally processed samples. Further, rehydration studies showed a decreasing trend of rehydration ability from 0.251 to 0.169 from 100 MPa to 300 MPa treatments. SEM images of the microstructure revealed a greater pore opening of the pressure treated samples as compared to the control sample resulting in a lesser drying time. From the optimization of the drying data based on maximum drying rate constant, minimum drying time and maximum rehydration ability, 200 MPa pressure treated sample for a dwell time of 5 min followed by drying at 70 °C temperature, and air velocity 2 m/s was the best condition to yield best quality dried beetroot product having better rehydration ability.