Effect of alternative physical pretreatments (pulsed electric field, high voltage electrical discharges and ultrasound) on the dead-end ultrafiltration of vine-shoot extracts

This work is devoted to the dead-end ultrafiltration of vine shoot extracts; these extracts were obtained after a previous step of solid-liquid extraction assisted by different physical pretreatments. Grinding, high-voltage electrical discharges (HVED), pulsed electric fields (PEF) and ultrasounds (US) were studied. The highest cellular damage (Z) was provoked by grinding (360 kJ/kg; Z = 1) then HVED (242 kJ/kg; Z = 0.71). The resulting protein and polyphenol concentrations were 0.097 and 0.4 mg/mL for grinding and 0.082 and 0.3 mg/mL after HVED pretreatment. A relationship between the extraction process and the unstirred dead-end ultrafiltration parameters was found. The highest cellular damage obtained with grinding (Z = 1) gave the greatest specific cake resistances (alpha c approximate to 4.8 x 10(13) m/kg). A correlation was therefore observed between cellular damage resulting in a higher polyphenol concentration and the membrane fouling phenomenon. HVED treatment (242 kJ/kg) gave a lower specific cake resistance (alpha c approximate to 4 x 10(13) m/kg) than grinding. Dynamic ultrafiltration was also conducted to decrease membrane fouling and study polyphenol purification and concentration in retentates. The experimental conditions leading to the highest filterability (highest flux J) and polyphenol retention conducted on HVED (242 kJ/kg) extracts were a stirring velocity of 150 rpm, a pressure value of 4.5 x 10(5) Pa and a nominal molecular weight cut-off equal to 50 kDa for the polyethersulfone membrane. Under these conditions, the filterability of HVED extracts (2.7 x 10(-6) m(3)/m(2) s) was higher than that of grinding (2 x 10(-6) m(3)/m(2) s). Up to 8% of polyphenols from the grinding extract were shown to deposit on the membrane. A lower percentage was found for HVED (7%). Polyphenols were therefore shown to be implicated in membrane fouling and pore blocking for unstirred and dynamic ultrafiltration processes. (C) 2015 Elsevier B.V. All rights reserved.