Multi‐frequency ultrasound and sequential infrared drying on drying kinetics, thermodynamic properties, and quality assessment of sweet potatoes. (14th June 2019) - Rashid, Muhammad T.
Abstract: Different ultrasound frequencies as pretreatments with different infrared drying temperatures were tested for drying of sweet potatoes to study the drying kinetics, mathematical modeling, energy activation, and thermodynamic properties of dried sweet potatoes. The treated samples showed a significant reduction in drying time by 110 to 60 min as compared to the control ones. Hii model, Page model, and Silva models found satisfactorily described the drying kinetics among 13 different tested mathematical models. The effective diffusion varied from 1.01 × 10 −06 to 9.21 × 10 −06, while the lowest activation energy recorded as 24.69 kJ/mol in samples pretreated with 40 kHz. The enthalpy and Gibbs free energy decreased with the increase in drying temperature while entropy decreased and obtained as negative during drying. In addition, the moderate ultrasound frequency of 40 kHz positively and significantly ( p < 0.05) influenced the surface color, enzyme inactivation, enzymatic browning, and microstructure of dried sweet potatoes. Practical applications: This study investigated the impact of sequential ultrasound (US) frequencies and infrared (IR) temperatures. The study provides significant evidence that the US in combination with IR not only reduces drying time but also improve the quality of the dry product on moderate US frequency. Higher US frequency (60 kHz) at higher temperature did not significantly improve the drying time but also showed big pores in SEM analysis. Abstract :