Maria A. Piçarra-Pereira

The wine proteins

Proteins are typically present in wines in low concentrations, contributing little to their nutritive value. However, they assume a considerable technological and economical importance because they greatly affect the clarity and stability of wines. Although exhibiting a large diversity, the majority of the wine proteins are structurally related and have been identified as pathogenesis related (PR) proteins. Thus, different wines are essentially composed by identical sets of polypeptides. They derive from the grape pulp, and survive the vinification process simply because they are highly resistant to proteolysis and to the low pH characteristic of wines. There is increasing evidence suggesting that although protein-dependent, the development of turbidity in wines is controlled by a number of factors of non-protein origin, such as polyphenols, the wine pH and the presence of polysaccharides. A variety of procedures has been developed and tested for the specific removal of proteins from wines. Even though bentonite fining is nonspecific and can impair the quality of wine, it remains the only effective method to stabilize wines.

Preparation of polyclonal antibodies specific for wine proteins

Immunology is an expanding area of research with potentially important applications in the analysis of many biological molecules. Polyclonal antibodies were raised in rabbits against specific proteins as well as against the total protein from a Portuguese wine. FPLC cation exchange chromatography was used to isolate the total protein fraction and, when in combination with denaturing electrophoresis, to purify individual wine polypeptides. To obtain a high titre, an injection of each antigen followed by three boosters were given in the immunisation of each rabbit. The titre of the antisera was measured by the ELISA technique and the specificity of the antibodies detected by immunoblotting. The antibodies produced were shown to be highly specific for the corresponding antigens. However, antibodies obtained specifically against a highly purified wine polypeptide seem to recognize the other major wine polypeptides, raising the possibility of structure similarity between different wine proteins. Neither the anti-total wine protein antibodies not the anti-specific wine protein antibodies originated a signal when used to probe thaumatin or chitinase. © 1999 Society of Chemical Industry