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The study aimed for the analysis of the impact of pulsed electric field (PEF) pre-treatment on convection (CD) and microwave (MW-CD) assisted air drying. Drying kinetics acceleration and retention of bioactive compounds of PEF pre-treated carrots and apples has been demonstrated. Moreover, the direct and indirect environmental energy impacts of CD and MW-CD technologies with consideration of bioactive compounds preservation has been evaluated. PEF assisted CD and MW-CD demonstrated lower energy use, especially for indirect energy consumption, in the case of carotenoids preservation in dried carrots.
In this study the effect of PEF pre-treatment on the microstructure of freeze-dried strawberry dices was investigated. The PEF treatment has been performed at an electric field intensity of 1.07 kV/cm and a specific energy input of 1 kJ/kg. The samples were freeze-dried at a temperature of 45 °C and a pressure of 1 mbar. The microstructure of dried material was evaluated by different physical and optical methods, such as SEM, μ-CT and thermogravimetry. Moreover, mechanical and acoustic properties as well as the colour of processed material have been analyzed. PEF pre-treated strawberry dices showed a more uniform shape, a better retention of volume and a visual better quality compared to untreated ones. Moreover, PEF pre-treatment led to a more homogeneous distribution and a greater thickness of pores. In accordance, analysis of textural properties evidenced that PEF treated freeze-dried strawberry dices were crispier than untreated ones. Measurement of L*a*b*-values showed that PEF treated material was characterized by a more preserved colour after freeze-drying than untreated ones.