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Evaluation of high pressure pretreatment for enhancing the drying rate of selected fruits and vegetables

Yücel, Umut
Drying is a process of moisture removal due to simultaneous heat and mass transfer. High hydrostatic pressure (HHP) processing subjects liquid and solid foods, with or without packaging, to pressures between 100 and 800 MPa. The application of HHP affects cell wall structures, leaving the cells more permeable, facilitating the diffusion and providing higher drying rates. In this study, two variety of apples, i.e. Amasya and red delicious, green beans and carrots were pretreated with HHP at different pressure-time-temperature combinations (100 300 MPa for 5 45 min at 20 and 35°C) prior to drying. Hot air drying experiments were carried at different temperatures (27, 45, 65, and 85°C) and air velocity of 0.4 and 0.8 m/s. To obtain the drying data, samples were subjected to hot air drying under constant external conditions. The applicability of 14 kinetic models selected from the literature for the drying of fruits and vegetables was determined by appropriate statistical analyses procedures. Improving the drying conditions by increasing the drying temperature generally masked the effect of HHP pretreatment on drying rate. Only for green beans, HHP treatments at 20°C decreased the drying rate. Generally pressures of HHP pretreatment higher than 100 MPa caused cell permeabilization resulted in higher drying rates for apples and carrots. Among the 14 models, modified Page model for apples, and modified Page and two term exponential models for green beans and carrots were found to best explain the drying behaviors.