Ultrasonic impact on viscosity and extraction efficiency of polyethylene glycol: A greener approach for anthocyanins recovery from purple sweet potato

Purple sweet potatoes are known for its vibrant purple color due to high level of anthocyanins. A polyethylene glycol based ultrasonic-assisted green extraction (PEG-UAE) of anthocyanins from purple sweet potato was proposed. Different types of PEG were tested for anthocyanin extraction along with PEG concentration, liquid-to-solid ratio, ultrasonic temperature and time were investigated for its impact on viscosity and extraction efficiency. The optimum extraction condition, 42 mL/g of ratio, 83% of PEG 200 concentration, 64 °C of ultrasonic temperature and 80 min of sonication time, resulted in better extraction of anthocyanins (83.78 mg CE/100 g DW) and phenolics (994.88 mg GAE/100 g DW). Using UPLC-Triple-TOF/MS, ten anthocyanin and six non-anthocyanin compounds were identified and characterized, with the highest peak area for cyanidin-3-caffeoyl-p-hydroxybenzoyl sophoroside-5-glucoside (25.9%). Moreover, the anthocyanins and phenolics extraction yield along with antioxidant activity were negatively correlated with PEG viscosity, on which ultrasonication has profound effects.