Optimization of ultrasound-assisted aqueous two-phase system extraction of carotenoid-allelochemicals from sweet potato roots by response surface methodology

Abstract

Orange sweet potato (Ipomoea batata L., Convolvulaceae) roots are an attractive source of β-carotene and other carotenoids. These compounds (allelochemicals) are used in the pharmaceutical, medicinal and food industries. In this study, the extraction of carotenoid-allelochemicals from roots of orange sweet potato cultivar ‘pushu 32’ was optimized by response surface methodology (RSM) in aqueous two-phase systems (ATPS) based on polymer/salt mixtures. Preliminary tests yielded higher contents of carotenoids in ATPS, based on sodium sulfate-PEG than on ammonium sulfate-PEG. Hence the effects of PEG-4000 concentration, sodium sulfate concentration, liquid-to-solid ratio and ultrasonic time were further investigated on carotenoids yield in single factor experiments. Four factors were used in a 3-level Box-Behnken design (BBD) of response surface model (RSM) to find the best conditions for carotenoid yield. Optimum carotenoids yield was obtained with 35.96 % (w/w) PEG-4000; 15.40 % (w/w) sodium sulfate; an ultrasonic time applied for 31.84 min and a liquid-to-solid ratio of 25.96:1 (v/w). Under these conditions, carotenoids yield was 0.594 mg/g which was very close to the predicted value (0.597 mg/g). The new proposed extraction method is promising for higher recovery of carotenoids from roots of orange sweet potatoes.