Seed proteins from Quercus suber

A study on the extraction and characterization of the cotyledonary proteins from cork oak (Quercus suber L.) seeds is reported. The seed proteins, which constitute approximately 5% of the seed weight, are glutelins on the basis of solubility criteria. They are readily solubilized in sodium berate buffer, pH 10, 50 mM, containing 1% (v/v) beta-mercaptoethanol and 1% (w/v) sodium dodecyl sulfate. This fraction is made up of a large number of polypeptides with molecular masses ranging from 10 to above 100 kDa and occurs in the form of large aggregates. The level of glycosylation is low, with two main glycopolypeptides present (43 and 65 kDa). However, the major polypeptides are not glycosylated. In vitro digestibility studies indicated that trypsin and cr-chymotrypsin produce a partial proteolysis of the cotyledonary proteins, particularly among the larger molecular mass polypeptides. The partial proteolysis seen in trypsin digests is not due to the presence of enzyme inhibitors in the seeds. On the other hand, pepsin almost completely digests the seed proteins. Taken together, these results may be considered as a good indication of the potential nutritional quality of the proteins from Q. suber seeds.