The influence of ultrasonic processing on the structure and electrophysical properties of fruit in combined drying

Abstract

The use of ultrasonic vibrations to intensify technological processes of processing agricultural products is becoming more and more widespread in the food industry. Because of the unique effect on raw materials, low-frequency ultrasonic waves are usually used to intensify the processes of freezing, thawing and drying. Studying the impact of ultrasonic treatment before drying raw materials is a particularly relevant issue, as it can lead to a decrease in energy consumption for the dehydration process. The purpose of the work is to study the influence of ultrasonic treatment on the change in electrophysical parameters and the structure of apple raw materials in the process of combined drying using direct electric heating. Ultrasonic processing of apples before drying was carried out in an ultrasonic bath filled with water for 5, 10 and 20 minutes. On the basis of the conducted experimental studies, the dependence of the magnitude of the current flowing through the sample in the process of combined drying using direct electric heating on the duration of processing of raw materials in an ultrasonic bath was obtained. The influence of ultrasound on the maximum values of the current during direct electric heating was determined. The dependence of changes in the specific electrical resistance of apple samples during their dehydration at different durations of preliminary ultrasonic treatment was investigated. The influence of ultrasound on the initial specific electrical resistance of apples, the duration of electroplasmolysis and the value of the specific electrical resistance at which the maximum values of the direct electric heating current are observed are determined. With the help of raster electron microscopy, pictures of the structure of the surfaces of dried apple samples were obtained with different combinations of the duration of ultrasound treatment and the methods of supplying heat to the raw materials during the drying process. The obtained results of experimental studies of the effect of preliminary ultrasonic treatment on the electrophysical parameters of raw materials in the process of combined drying and the surface structure of dried apples can become a prerequisite for the development of an energy-efficient technical means of ultrasonic treatment of fruit and vegetable raw materials before drying and the selection of optimal operating modes.