Aqueous extraction of sunflower seeds and rapeseeds with mixtures of hydrolytic enzymes were carried out in 2-L reactor and uronic acid and reducing sugar concentrations were measured during digestion. The goal of the study was to determine if a correlation between those concentrations and free oil exists that would allow predicting free oil release from aqueous solution measurements. Similar concentrations of 4.5 and 4.7 g/L of reducing sugars and 43 and 55 g/L of uronic acid were found for sunflower and rapeseeds, respectively. The corresponding yields of free oil from the two seeds were 83% and 16% of total oil, and this difference was due to the formation of an emulsion in the rapeseed dispersion. Therefore, measurement of reducing sugars or uronic acid concentrations are not sufficient to predict a release of free oil from all oil seeds. (C) 2011 Elsevier Ltd. All rights reserved.