The performance of combined ultrasound and nonsolvent precipitation for betalain encapsulation in different types of starches: thermal stability and antioxidant activity

In this study, betalain-enriched microparticles were produced from black sorghum, pearl millet landraces and domesticated quinoa starch. Response surface methodology was used to assess the encapsulation via nonsolvent precipitation method. The effects of starch type, ultrasound treatment (40 kHz, 120 W, 30 min) and starch concentration (5 and 1% (w/v)) on microparticles formation through a combined nonsolvent precipitation-ultrasound-assisted method, including thermal stability, betalain retention and antioxidant activity were evaluated. X-ray diffraction patterns revealed a V-type crystalline structure for microparticles and an A-type structure for starches. Scanning electron microscopy images showed that sorghum and millet starch granules were mostly rounded with polygonal geometry, whereas quinoa starch granules exhibited irregular forms and polygonal shapes. The formulated microparticles displayed an irregular morphology, were almost spherical with concavities and had no cracks on their external surfaces. The thermogravimetric analysis results revealed significant differences according to ultrasound treatment and the sonicated sample exhibited the lowest mass loss. Fourier-transform infrared spectra of loaded microparticles revealed new bands at 1364 cm⁻¹ and 850 cm⁻¹ corresponding to the carboxylic function of the betalains. The concentrations of betaxanthins and betacyanins recovered from microparticles ranged from 1.54 to 6.19 mg/L and 2.45 to 12.94 mg/L, respectively, and the antioxidant activities ranged from 36.58 to 73.49%. Quinoa starch-based microparticles exhibited highest betalain concentrations and antioxidant activity than pearl millet and sorghum. These findings suggest that the prepared microparticles are promising ingredients for healthy food and drug applications.