EVALUATION OF THE FLOCCULANT STRAIN ZYMOMONAS-MOBILIS Z1-81 FOR THE PRODUCTION OF SORBITOL AND GLUCONIC ACID

The biological production of sorbitol and gluconic acid from glucose a nd fructose is normally performed with previously grown and concentrat ed Zymomonas mobilis suspensions, in reactions catalyzed by the enzyme s glucose-fructose oxidoreductase (GFOR) and glucono-delta-lactonase ( GL). By using the flocculent strain Z. mobilis Z1-81, mechanical metho ds for cell concentration are unnecessary. Flocculation of Z. mobilis Z1-81 is seriously affected by both stirring and initial glucose conce ntration (S-0). Under mild agitation conditions, with S-0 = 100 g.l(-1 ), up to 76% of the final biomass was recovered by settling. At any im peller speed tested, similar specific GFOR/GL activities (8.4 to 9.5 U .g(-1) cell) were measured. When S-0 was increased to 144 and 210 g.l( -1), however, enzyme activities above 14 U.g(-1) were found. Ideal pH and temperature values for GFOR/GL, in whole Z. mobilis Z1-81 cells, a re 6.4 and 39 degrees C, respectively. The K-m and the theoretical V-m ax are 250 g glucose.l(-1) and 26.6 g gluconic acid.g(-1) cell.h(-1). With the settled biomass, bioconversion of 300 g.l(-1) each of glucose and fructose led to gluconic acid and sorbitol yields between 91 and 92% of the theoretical maximum, with specific productivities of 1.09 a nd 1.00 g product.g(-1) cell.h(-1).