AN IMMOBILIZED WHOLE YEAST-CELL BIOCATALYST FOR ENZYMATIC SUCROSE HYDROLYSIS

A novel granular immobilized biocatalyst with invertase activity was prepared by mutual covalent bonding of native bakers' yeast cells Saccharomyces cerevisiae with polyethyleneimine and glutaraldehyde without the use of any solid carrier. The specific invertase activity of the biocatalyst was 300-1500 Ug-1. The optimum pH value for the invertase activity was 4.6. The half-life of the invertase activity was 500-1000 h at reaction temperatures of 60-75-degrees-C. The activation energy of sucrose hydrolysis equaled 36.2 +/- 5 kJ kmol-1 at reaction temperatures below 65-degrees-C. The enzyme reaction was inhibited by substrate at concentrations above 1.0-1.5 mol 1-1, depending on the particle size. The biocatalyst was used for batch sucrose hydrolysis in laboratory-scale reactors at substrate concentrations of 10-70% (w/w), pH 4.6, and temperatures of 60-75-degrees-C. The specific productivity of the biocatalyst was 3-10 h-1. The total biocatalyst productivity over the period of its lifetime was 2000-10,000 kg of sucrose hydrolysed per kilogram of the biocatalyst. The mechanical stability of the biocatalyst particles was quite satisfactory even during long-term operation in stirred reactors. The biocatalyst was stored at temperature +4-degrees-C for 1 year without appreciable loss of the invertase activity. The results of the biocatalyst exploration confirmed its applicability for enzymatic hydrolysis of even highly concentrated sucrose solutions under industrial conditions, especially at a high reaction temperature.