Influence of frequency on ultrasound-assisted extraction of betalains from Stenocereus queretaroensis peel

Optimization of green extraction to obtain natural colorants is relevant as the stability of colors can be influenced by the energy and temperature of the extraction process. The influence of frequency on ultrasound-assisted extraction of betalains from Stenocereus queretaroensis peel in Opuntia ficus indica mucilage at room temperature is analyzed. Frequencies of 0.04, 2.25, 7.5, and 15 MHz, higher than those commonly used (0.02–0.5 MHz), were employed in this work. A dependence of extraction efficiency on frequency applied was found, being 2.25 MHz the optimal frequency with the highest extraction yields and with an 8°C increase in the temperature of the system, without requiring cooling systems, favored by the extraction sequence of nine ultrasonic pulses of 10 min, each pulse separated by a pause of 5 min. Practical Applications: Betalains (BTs) are a source of red to yellow natural colorants, as an alternative to synthetic ones. Because of their nature, BTs could be lost during the extraction process, requiring for research of optimal extraction methods. The green methodology herein proposed, using mucilage as extracting medium and applying a sequence of nine pulses of 10 min, each pulse separated by a pause of 5 min, allows for a faster extraction of bioactive compounds, without significantly increasing the system temperature, therefore avoiding the use of cooling systems, minimizing costs, without degrading the bioactive compounds, providing an alternative for utilization of waste materials, increasing profits and diminishing waste. The use of an optimal frequency for ultrasound-assisted extraction of bioactive compounds could be easily implemented for industrial or for communal purposes due to the feasibility of customizing ultrasonic transducers.