Design of immobilized enzyme reactors for the continuous production of fructose syrup from whey permeate

Abstract

Biocatalyst inactivation is inherent to continuous operation of immobilized enzyme reactors, meaning that a strategy must exist to ensure a production of uniform quality and constant throughput. Flow rate can be pro®led to compensate for enzyme inactivation maintaining substrate conversion constant. Throughput can be maintained within speci®ed margins of variation by using several reactors operating in parallel but displaced in time. Enzyme inactivation has been usually modeled under non-reactive conditions, leaving aside the effect of substrate and products on enzyme stability. Results are presented for the design of enzyme reactors under the above operational strategy, considering ®rst-order biocatalyst inactivation kinetics modulated by substrate and products. The continuous production of hydrolyzed-isomerized whey permeate with immobilized lactase and glucose isomerase in sequential packed-bed reactors is used as a case study. Kinetic and inactivation parameters for immobilized lactase have been determined by the authors; those for glucose isomerase were taken from the literature. Except for lactose, all other substrates and products were positive modulators of enzyme stability. Reactor design was done by iteration since it depends on enzyme inactivation kinetics. Reactor performance was determined based on a preliminary design considering non-modulated ®rst-order inactivation kinetics and confronted to such pattern. The new pattern of inactivation was then used to redesign the reactor and the process repeated until reactor performance (considering modulation) matched the assumed pattern of inactivation. Convergence was very fast and only two iterations were needed. List of symbolsA m 2 cross sectional area of reactor a kat/kg speci®c activity of catalyst D m reactor diameter d s total operation time for each reactor cycle E kat enzyme activity e kat/m 3 volumetric enzyme activity F m 3 /s total process¯ow rate F 0i m 3 /s initial feed¯ow-rate to each reactor H number of enzyme half-lives used in the reactor H b m catalyst bed height H R m reactor height K eq kg-mole/m 3 equilibrium constant of glucose isomerization to fructose ( V G K F aV F K G ) K F kg-mole/m 3 IGI Michaelis constant for fructose K G kg-mole/m 3 IGI Michaelis constant for glucose K L kg-mole/m 3 CIL Michaelis constant for lactose K P kg-mole/m 3 CIL competitive inhibition constant for galactose k cat catalytic rate constant for lactose hydrolysis k H cat catalytic rate constant for glucose isomerization k D s À1 ®rst-order inactivation rate constant under no modulation k DJ s À1 ®rst-order inactivation rate constant under modulation by J M kg catalyst mass N 1 ± CIL global modulation factor N 2 ± IGI global modulation factor N R ± number of reactors n L ± CIL modulation factor by lactose n P ± CIL modulation factor by galactose n G ± IGI modulation factor by glucose n F ± IGI modulation factor by fructose R F ± ratio of minimum to maximum ow rate s 0 kg-mole/m 3 feed lactose concentration t s time of operation t s s time interval between e...

Whey upgrading by enzyme biocatalysis

“…β-galactosidase has also been used in the upgrading of whey (and permeate) as ingredients of food and feed and in the production of sugar substitutes from permeate (Knopf et al 1979, Illanes et al 1990b). The production of high-fructose syrups by a sequential enzymatic process of hydrolysis and isomerization of whey permeate with immobilized β-galactosidase and glucose isomerase has been developed, obtaining a product of similar sweetening power than sucrose (Illanes et al 1999), which represents an option for sugar-importing countries (Marwaha and Kennedy, 1988). Hydrolysis of whey and their derivative expands their use as fermentation medium for the production of fodder yeast, (Mawson, 1988;Boze et al 1992), bioethanol (Coté et al 2004) and other commercially important microbial metabolites (Degeest et al 2001, Audic et al 2003Virtanen et al 2007).…”

Experimental and modeling study of catalytic reaction of glucose isomerization: Kinetics and packed‐bed dynamic modeling

“…9,23,24 Thus, the apparent kinetic parameters evaluated by batch experimental runs may be used in the packed-bed reactor, as the true effectiveness factor was taken into consideration. This assumption is valid when the concentration used for batch experimental runs is the same as those used for packed-bed reactors.…”

Application of modeling and simulation tools for the evaluation of biocatalytic processes: A future perspective

“…When the focus of the model is on reactor design, mass balances are also included to describe/compare various reactor configurations (batch or fed-batch vs. continuous). Moreover, mass transfer limitations are considered particularly when building models for immobilized enzyme systems 29 as well as biphasic systems (e.g., between organic and aqueous phases when organic solvents are used in the biocatalytic process 17,19,31 ). The effects of mixing and hydrodynamics in reactors have typically been neglected by assuming ideally mixed conditions (homogenous concentration throughout the reactor), which were described using the continuously stirred tank reactor (CSTR) concept.…”