Use of Immobilized Biocatalysts in Fluidized Bed Format

Ipsita Roy and Munishwar N. Gupta

Summary

In a fluidized bed reactor, the substrate solution is fed from the lower end of the bed at a velocity high enough to lift the biocatalyst containing beads. Such reactors are especially valuable when the substrate solution contains particulate matter. The mass transfer in a fluidized bed is better as compared with packed beds. For optimum interaction between the biocatalyst and the substrate, the fluidization velocity needs to be optimized. This illustrative protocol describes a somewhat novel concept in which preparations of glucoamylase and pullulanase were entrapped in different populations of calcium alginate beads. These two entrapped enzyme preparations were premixed in the desired ratio to form a fluidized bed reactor that was used for hydrolysis of starch to glucose. The approach is different from coimmobilization because it allows one to blend the two enzymes in different ratios for optimum bioconversion.

Key Words: Bioconversion; calcium alginate beads; coimmobilization; entrapment; expanded beds; glucoamylase; pullulanase; pullulan hydrolysis; starch hydrolysis.

1. Introduction

Immobilized biocatalysts can be used in various kinds of reactors. Some examples are the batch reactor, continuous-flow stirred tank reactor (CSTR), packed bed reactor, and fluidized bed reactor. For an overview of design, operation, and chemical engineering aspects of fluidized bed reactors, the review by Godia and Sola (1) may be consulted. In a fluidized bed reactor, the substrate solution is fed from the lower end of the bed at a velocity high enough to lift the particles (see Fig. 1). Such reactors are especially valuable when the substrate solutions contain particu-late matter. The mass transfer in a fluidized bed is better as compared with packed beds (2). The bed expansion during fluidization is dependent on the nature of support, the distributor design, the fluidization velocity, and the viscosity of the feed.

Packed Bed

Fig. 1. (A) Flow of liquid through a packed bed and a (B) fluidized bed column.

Fig. 1. (A) Flow of liquid through a packed bed and a (B) fluidized bed column.

For optimum interaction between the biocatalyst and the substrate, the fluidization velocity needs to be optimized.

Fluidized bed reactors utilizing both immobilized enzymes and whole cells have been reported (Table 1). Hydrolysis of tributyrin emulsion droplets by immobilized lipase in a fluidized bed bioreactor is perhaps one of the earliest reports of this approach (3). In the hydrolysis of phenylalanine methyl ester by chymotrypsin, fluidized bed reactor was found to give higher conversion rates than CSTR (4). The first pilot plant for whey hydrolysis used a fluidized bed consisting of Aspergillus niger lactase adsorbed on porous alumina and cross-linked with glutaraldehyde (5). More recently, whey lactose hydrolysis of Lactozym™ immobilized on cellulose beads in batch and fluidized bed modes were compared (6). The fluidized bed hydrolyzed whey lactose (<90% conversion) in 5 h as compared with 48 h required in the batch mode. The immobilized enzyme could be reused three times without any change in performance of the fluidized bed reactor. The fluidized bed could also hydrolyze milk lactose up to 60% within 5 h. Sun et al. (7)

Table 1

An Illustrative List of Reactions Catalyzed by Immobilized Systems on Fluidized Beds

Table 1

An Illustrative List of Reactions Catalyzed by Immobilized Systems on Fluidized Beds

Protein/cell

Matrix

Immobilization method

Reaction catalyzed

Ref.

ß-Galactosidase

Cellulose beads

Epichlorohydrin activation

Hydrolysis of whey lactose

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Responses

  • Ezio
    Why use immobilized enzymes in fluidised bed?
    8 years ago
  • simone
    Why use immobilised cells in the fluidised bed reactor?
    8 years ago
  • olli-pekka
    Why use immobilised cell in fluidised bed reactor?
    8 years ago

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