The adsorption of proteins in fermented aqueous food by silica gels

Fermented aqueous foods such as beer, wine, vinegar and soy sauce contain numerous types of enzymes and proteins. Those which have a high molecular weight can be removed easily, but lower molecular weight compounds are more difficult to remove, and stabilize these products. Adsorption techniques have been employed for the removal of these proteins in order to increase the stability. In this report, the adsorption behavior of proteins in aqueous foods is studied on colloidal silicas such as silica gels, ordinary xerogels and hydrogels. The adsorbed amount of proteins and the stability were measured by titration with ammonium sulphate and by turbidity determinations, respectively. Surface properties of the adsorbents, such as N2 isotherms, BET specific surface areas and pore-size distributions were measured, and the above properties of the hydrogels were measured after replacing the water with acetone and then drying. Among these silicas, mesoporous silica gels with 10% water were found to adsorb lower molecular-weight proteins, which cause turbidity, selectively from beer. Macroporous silica gels were useful for aqueous foods other than beer. The mechanism of adsorption will be discussed.