Ultrasonic-assisted extraction of betalains from red beet (Beta vulgaris L.)

In this work, ultrasonic-assisted extraction was evaluated for obtaining red beet extracts rich in betalains. Experiments evaluated the effects of operating variables (temperature, time, and ratio of ethanol to water) using a Box–Behnken experimental design, allowing the determination of conditions that maximize the removal of betacyanins and betaxanthins. The results indicate that the extracts obtained had higher betacyanins’ levels (0.11–4.24 mg/g) than betaxanthins (0.02–2.89 mg/g) for all experimental conditions evaluated. The concentration of ethanol in the extraction solvent had the greatest influence on extraction efficiency, and higher ethanol availability did not favor target compounds removal. Use of higher temperatures impaired betaxanthin extraction but did not affect the removal of betacyanins. The optimum conditions were then evaluated for betalain content, total phenolic compounds, and antioxidant activity, and results were compared with conventional extraction methods. The optimum conditions for the extraction of betacyanins and betaxanthins were determined to be at temperatures 52 and 37 °C, with an extraction time of 90 min, using 25% of ethanol in water as the solvent. Under these conditions, betacyanin (4.2 mg/g) and betaxanthin (2.80 mg/g) concentrations were higher than found in conventional extractions, as were phenolic compound concentrations and antioxidant activity.

Practical applications

An ultrasonic-assisted extraction method for obtaining red beet extracts rich in betalains is demonstrated to be more efficient than the extraction of these compounds by conventional methods. Extracts obtained by this technique had higher betalains and total phenolic contents and greater antioxidant activity.