ENZYMATIC CONVERSION OF SUCROSE INTO GLUCONIC ACID BY A FED-BATCH PROCESS OPERATED IN THE CONSTANT FEEDING MODE

摘要

The biomass bio-refinery is a facility in which huge sugarcane crops as well as other agricultural rawrnmaterials are transformed into several types of commercial products through different integrated processes. This workrnis based on the use of invertase (KM = 40.2mM; Vmax = 0.064UI/mL) and glucose oxidase (KM = 15.6mM; Vmax =rn3.41x10-3UGO/mL), respectively, for hydrolyzing sucrose into glucose and fructose (inverted syrup containing bothrnsugars at 1:1 ratio) and for oxidizing glucose into gluconic acid. Catalase (KM = 1.1μM; Vmax = 1.2 Ucat/mL) was alsornused as an auxiliary enzyme. Both reactions were evaluated through a fed-batch process whose sucrose (64 g/L) orrnglucose (32 g/L) solution was added according to a constant feeding mode [φ = (Vf – Vo) ÷ θ; φ = feeding rate (L/h),rnVf = final volume (L), Vo = initial volume (L) and θ = filling-up time (h)]. The invariable assay conditions were: pHrn= 5.0, agitation = 100 rpm, 37℃, Vo = 0.1L and Vf = 0.4L, whereas θ was 1h and 4h for sucrose hydrolysis andrnglucose oxidation, respectively. The filling-up time (θ) was set at 4h when the sucrose conversion into fructose andrngluconic acid was carried out by the simultaneous action of invertase (780UI), glucose oxidase (7,000UGO) andrncatalase (230,000Ucat). Samples were taken at each 0.1h for analytical purposes. The yield of sucrose hydrolysis byrninvertase was 91%, whereas the yield of glucose oxidation by glucose oxidase was 60%. Nevertheless, the yield ofrnthe multienzymatic sucrose/(gluconic acid + fructose) conversion was 75%.