Purification of Grape Proanthocyanidins by Membrane Ultrafiltration

Abstract

The objective of this study was to maximize the permeate flux (J) in the purification by UF of a grape seed extract, by evaluating the effect of operating variables: transmembrane pressure and tangential velocity on J and on the extracts chemical characteristics. Concentrations of total phenols, mean degree of polymerization (mDP), and average molecular weights (aMW) were compared. Flat membranes of polyvinylidene fluoride (PVDF) with a molecular weight cut off (MWCO) of 10 (kDa) and 1 (kDa) were used in an Alfa Laval equipment LAbUnit M10. The pressure was tested at 2, 3, 4 and 5 (bar) at a constant speed of 0.9 (m/s) and the tangential velocity was evaluated at 1.2, 1.3 and 1.4 (m/s) at 5 bar pressure and constant temperature (20oC). The transmembrane pressure and tangential velocity tests confirmed a direct relationship of these variables with J for both membranes. The J for 1kDa membrane was more sensitive to changes in pressure, with a maximum J of 15.18 (L/mh), while that for 10 kDa membrane J reached a maximum value of 37.50 (L/mh), both at 20 °C, 5 bar and 1.3 (m/s). The purification by UF reduced the mDP of the extracts from 7.15 up to 1-3 units of flavan-3-ols, corresponding to dimmers and trimmers in the permeate. To maximize J, the phenolics concentration, and minimize the mDP, carrying out the UF process with 10kDa membrane to 5 bar and 1.3 m/s would be optimal.