Extraction flavonoids from peanut shell by dual-frequency ultrasound: Optimization of PLS-UD, impact of frequency combination and its mechanism

Flavonoids extraction from peanut shell was firstly investigated using dual-frequency ultrasound with various frequency combinations in three modes (Low + Low, Low + High, High + High). Based on the results of single-factor experiments, it focused on the parameters optimization by combining partial least squares with uniform design (PLS-UD). Additionally, the effects of different frequency combinations on flavonoid recovery were evaluated under the optimized parameters of liquid-solid ratio of 41 mL/g, ultrasonic power of 145 W, particle size of 0.263 mm, ethanol concentration of 70 % at 50 °C for 29.5 min. It was found that the combination of 40 + 40 kHz has obtained the highest flavonoids yield of 10.91 ± 0.07 mg/g, while 40 + 180 kHz achieved the lowest (only 9.18 ± 0.11 mg/g), indicating both Low + Low mode and smaller frequency difference between two frequencies are favorable for the extraction of flavonoids. Furthermore, numerical simulation was performed to evaluate the role of different frequency combinations in acoustic cavitation by monitoring the maximum expansion ratio (R max /R 0 ). Results showed that the maximum expansion ratio has a strong correlation with the flavonoids yields, and they both exhibited a similar variation trend in various frequency combinations. These findings may provide a valuable guidance for selecting the appropriate frequency combinations during the flavonoids extraction from peanut shell. • Dual-frequency ultrasound was used for the extraction of flavonoids from peanut shell. • Six extraction parameters were optimized by PLS-UD method with higher accuracy. • Impact of various frequency combinations in three modes were evaluated for the first time. • Low + Low mode obtained the highest value of yield, followed by High + High and Low + High. • Mechanism of flavonoids extraction was firstly revealed by simulation cavitation.