Sunday, April 29, 2007

Multi-enzymatic conversion of sucrose into gluconic acid and fructose using a membrane reactor

Luiz Carlos Martins das Neves and Michele Vitolo. Department of Biochemical and Pharmaceutical Technology, School of Pharmaceutical Sciences, University of São Paulo, Av. Prof. Lineu Prestes, 580, B.16, 05508-900, São Paulo, Brazil

The fructose and gluconic acid are products of great application in chemical, pharmaceutical and food industry. Enzymatic conversion of sucrose increases the value added to the sugarcane, usually marketed as a commodity, because the fructose and gluconic acid are more valuable products. The use of membrane bioreactor (MBR), which operates under mild conditions regarding internal pressure, temperature and pH, has been growing along the years for enzyme catalyzed processes. The sucrose can be converted to the inverted syrup (an equimolar solution of fructose and glucose) by invertase (in this work was employed Bioinvert®, a commercial invertase) followed by the oxidation of glucose in gluconic acid by the glucose oxidase (GO).

The sucrose conversion was attained when carried out under initial substrate (20 to 100 mM) and invertase (3.0 to 24 U/mL), glucose oxidase (0.25 to 40 U/mL) and catalase (100 to 800 U/mL) concentrations in a membrane reactor operated in a fixed dilution rate (1.0 to 6.0 h-1), temperature (30°C to 50°C) and pH 5.5. The optimized operational conditions led to a conversion yield of 100% for sucrose hydrolysis and glucose oxidation when utilizing 50 mM of sucrose and resulting in enzymes productivities of 4.2 mmol/U.h, 0.60 mmol/U.h and 0.00062 mmol/U.h, respectively, to invertase, glucose oxidase and catalase. In regard to the glucose oxidation, the addition of catalase in the reaction medium was necessary, in order to minimize the inhibition of the GO by the hydrogen peroxide formed.