Preparation and properties of β-galactosidase confined in cells of Kluyveromyces sp

Biotechnological approaches for the value addition of whey

Whey, the liquid remaining after milk fat and casein have been separated from whole milk, is one of the major disposal problems of the dairy industry, and demands simple and economical solutions. In view of the fast developments in biotechnological techniques, alternatives of treating whey by transforming lactose present in it to value added products have been actively explored. Whey can be used directly as a substrate for the growth of different microorganisms to obtain various products such as ethanol, single-cell protein, enzymes, lactic acid, citric acid, biogas and so on. In this review, a comprehensive and illustrative survey is made to elaborate the various biotechnological innovations/techniques applied for the effective utilization of whey for the production of different bioproducts.

Configuration of a bioreactor for milk lactose hydrolysis

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.

Stabilization of D-amino acid oxidase and catalase in permeabilized Rhodotorula gracilis cells and its application for the preparation of alpha-ketoacids*

The cellular D-amino acid oxidase (DAAO) and catalase activities of Rhodotorula gracilis were greatly increased upon the treatment of the cells with cetyltrimethylammonium bromide (CTAB). However, these enzymes, slowly leaks out from the permeabilized cells. The released DAAO was rapidly inactivated in the absence of ethylenediaminotetraacetic acid (EDTA), beta-mercaptoethanol, and glycerol. DAAO within the permeabilized cells did not require these stabilizing agents. Treating the CTAB-permeabilized cells with 0.2% glutaraldehyde (GA) at 4 degrees C for 10 min prevented the leakage of both DAAO and catalase. Alternately, stabilized whole cell DAAO and catalase was prepared by treating the whole yeast cells with 1% GA at 4 degrees C for 60 min, followed by permeabilization with CTAB, a method which was equally efficient but easy to scale up. CTAB-permeabilized cells converted D-phenylalanine to 97% phenylpyruvate and 3% phenylacetate, and these cells were reused up to 3 cycles in a batchwise reaction. On the other hand, GA-treated CTAB-permeabilized cells produced more than 99% phenylpyruvate and the cells could be reused up to 20 cycles.