Justyna Szadzińska

Ultrasonic-Assisted Osmotic Dehydration of Carrot Followed by Convective Drying with Continuous and Intermittent Heating

The aim of the studies was to analyze the effect of ultrasound action on osmotic pretreatment and then on drying kinetics in continuous and intermittent drying conditions, and on the final product quality. This article presents the results of intermittent-convective drying of carrot preceded by ultrasonic assisted osmotic dehydration in fructose aqueous solutions. The theoretical drying kinetics developed from the numerical solution of mathematical model is validated using the experimental data. It has been shown that combination of ultrasonic assisted osmosis with intermittent-convective drying accelerates the drying process and improves the quality of dried biomaterial. A good adherence of the numerically determined kinetic curves confirms the usefulness of the presented model and its possible application to construction of controlled and optimized drying processes.

Kinetics and Quality Aspects of Beetroots Dried in Non-Stationary Conditions

This paper presents the results of experimental studies on convective drying of beetroot (Beta vulgaris L.) in non-stationary conditions. The effect of stepwise changing air temperature and pretreatment methods such as osmotic dehydration and blanching on the material quality were investigated. The main aim of the studies was to find a drying mode by which the product quality degradation is minimized. Therefore, except for drying kinetics, the total color change, water activity, retention of betanin, and ability to rehydration were examined. It was proved that drying of beetroots in intermittent conditions contributes to shorter drying time, higher retention of betanin, better color preservation, and less water activity.

Microwave- and ultrasound-assisted convective drying of raspberries: Drying kinetics and microstructural changes

ABSTRACT The drying kinetics, microstructural alteration, and rehydration properties of raspberry samples were studied experimentally in this work. Five different drying programs with the application of microwaves (MW) and ultrasound (US) were used, including convective drying (CV) as a reference test. The drying experiments were performed using a hybrid chamber dryer equipped with airborne ultrasound and microwave generators. The modified Page model was successfully used to describe the drying kinetics of raspberry fruits. Next, microstructural properties (porosity and total pore volume) of the dried samples were determined from the postprocessing of the images which were acquired using a lab-scale X-ray microtomograph. The results show a significantly shorter drying time by 54–64% for CVUS, 69% for CVMW, and 79% for CVMWUS; and a lower energy consumption resulting in energy saving of 14–23% for CVUS, 54% for CVMW, and 59% for CVMWUS as compared to CV. It is also shown that the average drying rate of raspberry samples increases by maximum fourfold with the application of both ultrasound and microwave radiations in CV. In addition, a higher porosity, total pore volume, and a better rehydration property were found for the raspberry samples dried with US than with MW assistance.

Ultrasound- and microwave-assisted convective drying of carrots – Process kinetics and product’s quality analysis

The aim of these studies was to investigate the influence of airborne ultrasound-assisted convective drying and microwave-assisted convective drying, as well as their combination, on process kinetics, total color change, water activity, content of carotenoids, polyphenols and antioxidant activity of carrots (Daucus carota L.). The global model of drying kinetics based on coupled ordinary differential equations was used to describe the moisture and material temperature profiles during drying. Application of ultrasound and microwave in convective drying reduced drying time in the range of 9-81%, but the shortest drying time was observed for simultaneous action of convection, ultrasound and microwave. The results of qualitative analysis showed a product improvement due to ultrasound as compared to convective drying and microwave-convective drying. The proposed mathematical model of drying kinetics successfully simulated real drying processes. The proposed mathematical model of drying kinetics successfully simulated real hybrid drying processes.

Hybrid and Non-stationary Drying—Process Effectiveness and Products Quality

During last decades a lot of new drying techniques have been developed. Some of them are focused on breaking the limits of convective drying usually by applying intermittent conditions or utilization of few drying techniques in one process (hybrid drying). The purpose of the chapter is to discuss these new opportunities. Hence the convective non-stationary drying and various hybrid drying techniques (convective–microwave, convective–microwave–infrared, convective–microwave–ultrasonic and microwave-vacuum drying) are discussed. Many examples are provided in this chapter to illustrate the impact of the applied drying conditions and techniques on time consumption, process energy consumption, and on the quality of the product obtained. In particular, the drying of kaolin clay, oak, pine and walnut wood, apple, carrots, kale, potatoes, raspberries and red pepper are presented. The results of the studies indicate that both variable drying conditions and hybrid techniques may result in improved drying kinetics, reduced process energy consumption, and increased product quality.