1 - Low-Frequency, High-Power Ultrasound-Assisted Food Component Extraction

Abstract

Extraction is one of the essential processes in the preparation of key ingredients in the food industry. Choosing the best technology and procedure has a significant impact on food and beverage quality. The development of green technologies for process intensification is a prerequisite to advancing the biorefinery concept and green extraction. The overall goal here is the cost-effective production of high-value food ingredients and the recovery of coproducts from food processing wastes, which sees ultrasound-assisted extraction (UAE) playing a pivotal role. The extraction enhancement provided by low-frequency, high-power ultrasound has been attributed to the propagation of sound pressure waves and resulting cavitation phenomena. High shear forces, generated by cavitation bubble implosion, cause increased extractant mass transfer thanks to intense turbulence, high-velocity interparticle collisions, and perturbation in microporous particles of the biomass, which accelerate both eddy and internal diffusion. Moreover, cavitation on the product surface leads to impingement by microjets that results in surface peeling, erosion, and particle breakdown. These effects expose new surfaces, further increasing mass transfer. The advantages that UAE furnishes include higher yields and a reduction in extraction time, energy consumption, and solvent amounts. Ultrasound energy may also favor extraction selectivity, while reducing thermal gradients and extraction temperature. Unlike some other nonthermal processes, such as high-pressure processing, pulsed electric field processing, and compressed/supercritical carbon dioxide extraction, ultrasound can be easily tested on a laboratory or benchtop scale, generating data suitable for scale up. Intensity and cavitation can be easily adapted to specific extraction processes in order to target specific objectives. Amplitude and pressure can be varied over a wide range and used to identify the most energy efficient extraction setup, while ultrasound can also act synergistically with temperature and pressure to achieve even further benefits. The optimization of UAE operational parameters (sample size, particles size, solvent type, ultrasonic power and frequency, extraction time and temperature, and liquid/solid ratio) is clearly crucial to achieving high efficiency. Optimal conditions can vary dramatically according to the material and analyte of interest. Industrial UAE provides a good return on capital investment, due to the availability of high amplitude/power units for large commercial operations, competitive energy consumption, and low maintenance costs. This long list of reasons makes ultrasound a clear improvement on existing food component extraction processes.