Effects of Water Activity on Biooxidation Kinetics
Krešimir Mihaljević, Stipe Gamulin, N. Pavlović, Nada Bošnjak and Marijan Bošnjak
PLIVA d.d., Research Institute, Prilaz baruna Filipovića 89, Zagreb, Croatia
Received January 27, 1995
Accepted February 28, 1995
The effects of D-sorbitol concentration on water activity and the other parameters which determine the oxidation rate of D-sorbitol to L-sorbose when applying Gluconobacter suboxydans S-22 as biocatalysl were studied. Oxygen solubility in sorbitol solutions, sorbitol solutions viscosity, water activity and diffusion permeability for different particles were determined. Water activity was defined on the basis of oxygen solubility. The effects of different parameters on kinetics of sorbose formation and microorganism growth were analyzed. The following was established: 1) The specific rate of sorbose formation is proportional to: a) specific rate of oxygen uptake, b) diffusion coefficient, c) reciprocal viscosity, d) difference between genuine and critical water activity; 2) Water activity affected microorganism growth more than sorbitol oxidation and critical water activity was found higher for groxoth than for bioconversion; 3) D-sorbitol can be converted into L-sorbose even when a part of sorbose crystallizes.
Presented at the 2nd Croatian Congress of Food Technologists, Biotechnologists and Nutritionists, Zagreb, June15-17,1994