A COMPARISON OF RAW STARCH-DIGESTING GLUCOAMYLASE PRODUCTION IN LIQUID AND SOLID CULTURES OF RHIZOPUS STRAINS

Maximum growth for Rhizopus sp, A-11 was obtained at a zinc ion concen tration of 0.7 ppm in a liquid medium, Glucoamylase (GA, EC 3.2.1.3) p roduction in Rhizopus sp, A-11 was maximized at 710 U/ml, at the prese nce of 75 ppm for calcium and 0.7 ppm of zinc ions in liquid medium, Z inc ion is known as an essential biometal for Rhizopus growth; however , growth was inhibited by the zinc ion concentration, not maximized, A lthough calcium ion was not necessary to Rhizopus growth, GA productio n using Rhizopus sp. A-11 was markedly stimulated by calcium ion conce ntration over 75 ppm in the liquid medium. The GA productivity of the present liquid culture was about 4.4 times higher than that of the sol id state culture, based on the unit starch amount in the liquid and so lid media carbon source, The characteristics of the GA produced by the Rhizopus sp, A-11 liquid culture were interesting; that is, almost al l the GA produced was classified as raw starch-digesting GA (GA-I). Se creted protein in the culture liquid after 30 h was nearly GA, and had a limited amount of impure protein. As a result, it was found that us ing a Rhizopus culture in a specified metal-ion regulated medium was a n effective method for producing GA, Thus the present culture method w as renamed the ''metal-ion-regulated liquid culture method.