Stirring-assisted dead-end ultrafiltration for protein and polyphenol recovery from purple sweet potato juices: Filtration behavior investigation and HPLC-DAD-ESI-MS2 profiling

The potential of stirring assisted dead-end ultrafiltration (UF) to recover polyphenols from purple sweet potato (PSP) juices was evaluated. For this purpose, the effects of rotation speed (200–600 rpm), transmembrane pressure (TMP) (0.2–0.4 MPa), and membrane molecular weight cut-off (30–100 kDa) were investigated with a lab-scale filtration module. The results showed that the highest protein removal (86%) and polyphenol selectivity (12.2) were both obtained under higher rotation speed (600 rpm). Moreover, filtration flux was more important at 600 rpm due to the anti-fouling effect of shear rate generated by the rotation. The results also revealed that under TMP of 0.4 MPa, the cake resistance was the dominating fouling resistance. In addition, it was shown that the results obtained after fitting the data obtained for the filtration with 100 kDa membranes under the different TMP could be modeled by an exponential model. The optimum UF conditions in this study were found under rotation speed of 600 rpm, using a 100 kDa membrane and at TMP of 0.3 MPa. Six main anthocyanins were identified by HPLC-DAD-ESI-MS2 analysis in the unfiltered PSP juice and the permeate obtained under UF at the optimum conditions, being the intensities of the peaks lower in the filtrate obtained using UF. This study opens the doors of rotation-assisted UF as a promising anti-fouling technique, thus avoiding subsequent purification steps.