title: Configuration of a bioreactor for milk lactose hydrolysis.
abstract: Permeabilized microbial cells can be used as a crude enzyme preparation for industrial applications. Immobilization and process recycling can compensate for the low specific activity of this preparation. For biomass immobilization, the common support is alginate beads; however, its low surface area and the low biomass concentration limit the activity. We here describe a biocatalyst consisting of a paste of permeabilized Kluyveromyces lactis cells gelled with manganese alginate over a semicircular stainless steel screen. A ratio of wet permeabilized biomass to alginate of 50:4 (wt/wt) resulted in a paste with maximum immobilized beta-galactosidase activity and maximum gel biomass retention. The biocatalysts retained activity better when stored in milk at 4 degrees C than in 50% glycerol. The unused biocatalysts stored in milk did not lose activity after 50 d. However, repeated use of the same biocatalyst 40 times resulted in almost 50% loss of activity. A bioreactor design with two different conditions of operation were tested for milk lactose hydrolysis using this biocatalyst. The bioreactor was operated at 40 degrees C as packed bed or with recirculation, similar to a continuous stirred tank reactor. The continuous system with recirculation resulted in 82.9% lactose hydrolysis at a residence time of 285.5 min (flow of 2.0 ml/min), indicating the potential of this system for processing low lactose milk, or even in processing other substrates, using an appropriate biocatalyst.
mesh_terms: D000464:Alginates; D000818:Animals; D019149:Bioreactors; D004800:Enzymes, Immobilized; D005511:Food Handling / Q000295:instrumentation / Q000379:methods; D006868:Hydrolysis; D007716:Kluyveromyces / Q000201:enzymology; D007785:Lactose / Q000378:metabolism*; D008892:Milk / Q000737:chemistry*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D000464:Alginates; D004800:Enzymes, Immobilized; D001616:beta-Galactosidase; D007785:Lactose