Critical Variables Influencing the Ultrasound-Assisted Extraction of Bioactive Compounds—A Review

Abstract

Ultrasound-assisted extraction (UAE) is a novel methodology, belonging to the so-called “Green Chemistry”, which has gained interest in recent years due to the potential to recover bioactive compounds, especially those from plant matrices. It is widely recognized that the extraction of molecules by UAE gives rise to higher or similar yields than those obtained by traditional extraction methods. UAE has certain advantages inherent to Green Chemistry extraction methods, such as short extraction time and low solvent consumption. The aim of this review is to critically present the different variables and parameters that can be modified in UAE, such as ultrasound power, time, temperature, solvent, and solid to solvent ratio that influence yield and extraction performance.

Application of Ultrasound as Clean Technology for Extraction of Specialized Metabolites From Stinging Nettle (Urtica dioica L.)

“…First, it should be highlighted that both the device and the solvent type used (EM × S) had the greatest influence on TCh and TCa ( p ≤ 0.0001). When considering solvent type, significantly higher pigment values were obtained when 80% v/v ethanol was used, regardless of extraction method and duration, which is consistent with other literature data that also suggest 80% v/v ethanol as an optimal solvent for pigment isolation ( 42 , 70 ). Furthermore, if we compare the efficiency of each of the devices used for UAE, we can see that the probe system was significantly more efficient even when using 50 and 80% ethanol for both TCh and TCa.…”

“…The main reason for this effect is the generation of strong shear forces, which are achieved to a much greater extent when using the probe and cup-horn systems (probes) compared to the bath system. In general, the higher power delivered (acoustic energy → cavitation energy) is the main advantage of using an ultrasonic probe system in the application of UAE processes compared to ultrasonic baths, where the main disadvantage is the lower power ( 41 , 42 ). In the combination of the equipment used in this study, the probe system (nominal output power 200 W) delivered higher ultrasonic energy when compared to the ultrasonic bath (output power 140 W), which is the main reason for the more effective extraction of AsA with the ultrasonic probe.…”

“…The efficiency of extraction assisted by high-intensity ultrasound depends mainly on several variables, some of which are related to the type of solvent or, in particular, to some of the properties, such as viscosity, density, surface tension (medium), and presence of solid particles (physical properties) ( 41 , 42 ). Density, viscosity, and acoustic impedance are the most important solvent properties that strongly affect extraction efficiency, as they have a major impact on the amount of acoustic power.…”

Efficiency of Supercritical CO2 and Ultrasound-Assisted Extraction Techniques for Isolation of Bioactive Molecules from Sea Buckthorn (Elaeagnus rhamnoides (L.) A. Nelson) Berry Oils and Cakes

“…Ultrasonic power is considered one of the critical parameters that need to be optimized, as the use of high values usually improves the extraction yield due to the generation of strong shear forces. In addition, a higher ultrasonic power shortens the extraction time [78]. As shown in Table 10, increasing the ultrasonic power from 30 to 60% increased the TPC and AA of SB cake extracts.…”