Application of High Power Ultrasound and Microwave in Food Processing: Extraction

Abstract

Ultrasound is defined as sound waves having frequency that exceeds the hearing limit of the human ear (~20 kHz). Ultrasound is one of the emerging technologies that were developed to minimize processing time, cost of processing, maximize quality and ensure the safety of food products [1]. Ultrasound is applied to improve positive effects in food processing such as improvement in mass transfer, food preservation, etc. High power (high energy, high intensity) ultrasound operates at frequencies between 20 and 500 kHz, and intensities higher than 1W·cm −2 which are disruptive and induce effects on the physical, mechanical or chemical (biochemical) properties of foods. The propagation of ultrasound through a material induces compressions and decompressions (rarefactions) of the medium particles, which imparts a high amount of energy. High power ultrasound with frequency higher than 20 kHz has mechanical, chemical and/or biochemical effects, which are used to modify the physicochemical properties and enhance the quality of various food systems during processing. High power ultrasound can be applied using sonication baths or ultrasonic immersion probes with different lengths, diameters and tip geometries depending on applications. These effects are promising in food processing, preservation and safety. This emerging technology has been used as alternative to conventional food processing operations for facilitating the extraction of various food and bioactive components, accelerated drying and modifying of textural characteristics of starch, fat products (sonocrystallization), emulsification, defoaming, modifying the functional properties of different food proteins, depolymerisation, inactivation or acceleration of enzymatic activity to enhance shelf life and quality of food products, microbial inactivation, freezing, thawing, freeze drying and concentration etc [1-5]. High power ultrasound has opportunity to be used as tool for extraction [6-10]. The first Soxhlet extraction assisted by ultrasound, named Ultrasound-Assisted Soxhlet (UASE) was developed in 2004 by Luque de Castro et al. Another innovative method for ultrasound assisted extraction was developed by Chemat et al. (2012–in press). System for oil extraction, named Sono-Soxhlet system was developed by inserting an ultrasonic probe directly into the extraction chamber, i.e. ultrasound is applied directly in the extraction reactor. The lipid extracts obtained from the Sono-Soxhlet process are qualitatively the same as conventional process, and time for extraction is significantly reduced, requiring 30 minutes vs. conventional 8h.