The role of polysaccharides on the grape must ultrafiltration performance

This work addresses ultrafiltration of grape must and the understanding of the membrane/polysaccharides interactions due to the chemical composition of the soluble grape must polysaccharides. The performance of two laboratory-made cellulose acetate membranes was investigated. The membranes have molecular weight cut-off of 96 kDa (CA-400-32) and 31 kDa (CA-400-28). To identify the different polysaccharides in the fractions obtained by ultrafiltration, these molecules were isolated by dialysis, then concentrated, freeze-dried and the polysaccharide composition analysed by Gas-Chromatography with flame ionization detector after acid hydrolysis, reduction and acetylation. Polysaccharides adsorbed on the membranes were also identified and quantified by Gas-Chromatography, after hydrolysis, reduction and acetylation of the known mass of dehydrated membrane. The analysis of the membrane matrix, give evidence that mannoproteins were adsorbed on the matrix of CA-400-32 membrane, which has originated, in some extension, the clogging of the pores. It was concluded that the ramnogalacturonan type II crossed the CA-400-32 membrane easily, however its depletion in the retentate and permeate streams over time may be due to its accumulation on the membrane surface, probably caused by adsorption. Arabinogalactan-proteins and mannoproteins were found in the permeate stream of the CA-400-32 membrane, whilst in the CA-400-28 membrane, ramnogalacturonan type II and the majority of arabinogalactan-proteins and mannoproteins remained in the retentate.