Ultrasound assisted extraction: A relook at solvent to material ratio, its effects on process efficiency and how it can be exploited for different uses

Ultrasound assisted extraction (UAE) is one of the preferred green extraction techniques widely used for the extraction of bioactive compounds from plant materials. It has attracted much attention and many studies have been done to understand its mechanism, effects and efficiency. However, no study has discovered and given enough attention to the superior role solvent‐to‐material ratio (SMR) plays in moderating UAE efficiency. This study therefore emphasizes the importance of SMR as the main determinant of UAE efficiency and further proves its mechanistic effects with ultrasound physics. It discusses SMR effects on extraction medium density, acoustic energy transfer, cavitation rate, power intensity attenuation and free hydroxyl radical generation during water‐based UAE. This understanding is needed to assist researchers in the design of their extraction experiments and optimizations. Without this insight, even optimization processes will be limited in giving the true conditions needed for the highest UAE efficiency. The study shows that low SMR increases acoustic energy scattering and absorption and attenuates ultrasound power intensity and vice versa. SMR can be controlled to either preserve bioactivity of compounds or produce free radicals for microbial inactivation and elimination and oxidative degradation of natural pigments in aqueous media. Practical application A comprehensive understanding of the mechanism and physics behind the effects of solvent‐to‐material ratio (SMR) during ultrasound assisted extraction (UAE) of bioactive compounds helps in fine‐tuning SMR purposely to ensure that ultrasound power attenuation is minimized. Ultrasound power defines UAE efficiency by virtue of acoustic cavitation. Due to the fact that UAE in aqueous media generates free hydroxyl radicals (*OH) from water autolysis, SMR can be deliberately tuned to induce controlled power attenuation to limit this phenomenon. This becomes a strategy to protect bioactive compounds that are prone to oxidative degradation. As ultrasound power is linked to energy consumption, fine‐tuning SMR to minimize power attenuation can significantly improve process efficiency and reduce treatment time, saving energy and enhancing profitability, especially during large scale industrial treatments.