EFFECT OF ADSORBENT pK_a ON SELECTIVE REMOVAL OF GLUCOAMYLASE FROM UNPASTEURIZED SAKE MATERIALS

Abstract

& To selective adsorption of glucoamylase (GA) from the raw materials of the unpasteurized sake, various polymer beads were prepared by immobilization of cationic or anionic functional groups onto cellulose beads (Cellufine). Under conditions which mimic sake (GA 500 lg mL À1 , ethanol 20 vol%, pH 4), Aspergillus species GA (As-GA) (pI 3.5) was strongly adsorbed by cationic Cellufines with anion-exchange capacity (AEC) of 0.5-1.3 meq g À1 , but Rhizopus sp. GA (pI 6.5) was strongly adsorbed by anionic adsorbents with cation-exchange capacity of 0.3-1.1 meq g À1 . The As-GA selectivity of the cationic Cellufines depended on their apparent pK a (pK a,app ) but not necessarily on their AEC. The Cellufine-poly(ethyleneimine) (pK a,app 7.9, AEC 0.4 meq g À1 ) was effective at adsorbing As-GA (>99%) in a sake model solution (GA 250 lg ml À1 , ethanol 20 vol%, 0.016 M acetate buffer, pH 4), but it also adsorbed organic acid, such as acetic acid. By contrast, Cellufine-poly(e-lysine) (pK a,app 7.3-7.4, AEC 0.6-1.0 meq g À1 ) selectively removed the As-GA from the sake-model solution without adsorption of the organic acid; the residual As-GA concentration was lower than 1%, and the recovery of organic acid was more than 99% as total acidity.