Permeabilization of yeast cells (Kluyveromyces fragilis) to lactose by digitonin

Purified lactases versus whole-cell lactases-the winner takes it all

Lactose-free dairy products are in great demand worldwide due to the high prevalence of lactose intolerance. To make lactose-free dairy products, commercially available β-galactosidase enzymes, also termed lactases, are used to break down lactose to its constituent monosaccharides, glucose and galactose. In this mini-review, the characteristics of lactase enzymes, their origin, and ways of use are discussed in light of their potential for hydrolyzing lactose. We also discuss whole-cell lactase catalysts, which appear to have great potential in terms of cost reduction and convenience, and which are more natural alternatives to purified enzymes. Lactic acid bacteria (LAB) already used in food fermentations seem to be optimal candidates for whole-cell lactases. However, they have not been industrially exploited yet due to technical hurdles. For whole-cell lactases to be efficient, the lactase enzymes inside the cells must be made available for lactose hydrolysis, and thus, cells need to be permeabilized or disrupted prior to use. Here we review state-of-the-art approaches for disrupting or permeabilizing microorganisms. Lastly, based on recent scientific achievements, we propose a novel, resource-efficient, and low-cost scenario for achieving lactose hydrolysis at a dairy plant using a LAB whole-cell lactase.Key points• Lactases (β-galactosidase) are essential for producing lactose-free dairy products• Novel permeabilization techniques facilitate the use of LAB lactases• Whole-cell lactase catalysts have great potential for reducing costs and resources Graphical abstract.

β-Galactosidase: From its source and applications to its recombinant form

Carbohydrate-active enzymes are a group of important enzymes playing a critical role in the degradation and synthesis of carbohydrates. Glycosidases can hydrolyze glycosides into oligosaccharides, polysaccharides, and glycoconjugates via a cost-effective approach. Lactase is an important member of β-glycosidases found in higher plants, animals, and microorganisms. β-Galactosidases can be used to degrade the milk lactose for making lactose-free milk, which is sweeter than regular milk and is suitable for lactose-intolerant people. β-Galactosidase is employed by many food industries to degrade lactose and improve the digestibility, sweetness, solubility, and flavor of dairy products. β-Galactosidase enzymes have various families and are applied in the food-processing industries such as hydrolyzed-milk products, whey, and galactooligosaccharides. Thus, this enzyme is a valuable protein which is now produced by recombinant technology. In this review, origins, structure, recombinant production, and critical modifications of β-galactosidase for improving the production process are discussed. Since β-galactosidase is a valuable enzyme in industry and health care, a study of its various aspects is important in industrial biotechnology and applied biochemistry.

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.

Lactulose: production, purification and potential applications

Lactulose a "bifidus factor" is composed of galactose and fructose, which can be produced by the isomerization of lactose. It is a prebiotic carbohydrate which stimulates the growth of health-promoting bacteria in the gastrointestinal tract, such as bifidobacteria and lactobacilli and at the same time inhibits growth of pathogenic bacteria such as Salmonella. It can also be used for the treatment of constipation, hepatic encephalopathy, tumour prevention, and to maintain blood glucose and insulin level. This review provides comprehensive information on the different techniques used for the production of lactulose, purification and analysis. Besides this mechanism of action and its potential applications in food and pharmaceutical industries have also been discussed.

Potential Applications of Immobilized β-Galactosidase in Food Processing Industries

The enzyme β-galactosidase can be obtained from a wide variety of sources such as microorganisms, plants, and animals. The use of β-galactosidase for the hydrolysis of lactose in milk and whey is one of the promising enzymatic applications in food and dairy processing industries. The enzyme can be used in either soluble or immobilized forms but the soluble enzyme can be used only for batch processes and the immobilized form has the advantage of being used in batch wise as well as in continuous operation. Immobilization has been found to be convenient method to make enzyme thermostable and to prevent the loss of enzyme activity. This review has been focused on the different types of techniques used for the immobilization of β-galactosidase and its potential applications in food industry.

Silica hybrid biomaterials containing gelatin synthesized by sol-gel method

This work reports the sol-gel synthesis of silica hybrids. We determined the effect of the type and quantity of silica precursors and organic compounds on the resulting structure, surface area, nanostructure design and size, and potential applications. The structure of the synthesized hybrids was analyzed using FT-IR, XRD, BET-Analysis, SEM, and AFM. We demonstrate the immovilization of whole living thermophilic bacterial cells with cyanocompound degradation activity in the synthesized silica hybrid biomaterials by entrapment, chemical binding, and adsorption.

Microbial biosensors

A microbial biosensor consists of a transducer in conjunction with immobilised viable or non-viable microbial cells. Non-viable cells obtained after permeabilisation or whole cells containing periplasmic enzymes have mostly been used as an economical substitute for enzymes. Viable cells make use of the respiratory and metabolic functions of the cell, the analyte to be monitored being either a substrate or an inhibitor of these processes. Bioluminescence-based microbial biosensors have also been developed using genetically engineered microorganisms constructed by fusing the lux gene with an inducible gene promoter for toxicity and bioavailability testing. In this review, some of the recent trends in microbial biosensors with reference to the advantages and limitations are been discussed. Some of the recent applications of microbial biosensors in environmental monitoring and for use in food, fermentation and allied fields have been reviewed. Prospective future microbial biosensor designs have also been identified.

Preparation of high activity whole cell biocatalyst by permeabilization of recombinant flocculent yeast with alcohol

Flocculent yeast Saccharomyces cerevisiae YF234 (MATa ura3-52 trp1Delta2 his ade 2-1 can1-100 sta1 FLO8) cells overexpressing glyoxalase I and having strong flocculation ability were permeabilized with isopropyl alcohol and ethanol under various conditions. The treatment with 40% isopropyl alcohol significantly improves the initial reaction rates of recombinant flocculent yeast cells. Moreover, the reactivity of permeabilized flocculent yeast cells was similar to that of dispersed cells with EDTA. On the other hand, the flocculation ability of yeast cells was not affected by the treatment with alcohol solutions of various concentrations and treatment time length. Therefore, the recombinant flocculent yeast cells permeabilized with alcohol are very effective whole cell biocatalysts.

Production of S-lactoylglutathione by high activity whole cell biocatalysts prepared by permeabilization of recombinant saccharomyces cerevisiae with alcohols

The permeabilization of yeast cells with methanol, ethanol, and isopropyl alcohol under various conditions was studied to develop the preparation method of high activity whole cell biocatalysts. Recombinant Saccharomyces cerevisiae, which intracellularly overexpresses glyoxalase I and catalyzes the conversion of methylglyoxal to S-lactoylglutathione in the presence of glutathione, was used as the model system. The permeabilization treatments with alcohols significantly enhanced the activities of yeast cells. Especially, the initial S-lactoylglutathione production rates of cells permeabilized with 40% ethanol and isopropyl alcohol solutions for 10 min at 4 degrees C were high and were 364 and 582 times larger than those of untreated cells, respectively. These permeabilized yeast cells retained high activities during repeated batch reactions. Even in third batch reaction, they showed approximately 70-80% of the activity in the first batch. The plasma membrane of S. cerevisiae cells was damaged by the treatment with alcohol solutions in such a way that leakage of glyoxalase I from the cells is rather small and that both substrate and product show very high permeability. The initial S-lactoylglutathione production rates of these permeabilized cells were 1.5-2.5 times larger than those of glyoxalase I in cell extracts prepared by ethyl acetate method from the same amount of cells. These results demonstrate that the recombinant S. cerevisiae cells permeabilized with alcohol solutions under the optimum condition are very effective whole cell biocatalysts. Copyright 1999 John Wiley & Sons, Inc.

Heterologous Kluyveromyces lactis beta-galactosidase production and release by Saccharomyces cerevisiae osmotic-remedial thermosensitive autolytic mutants

The beta-galactosidase from Kluyveromyces lactis is a high molecular weight protein with commercial interest. A major drawback of its industrial production is the high cost associated with extraction and downstream processing due to its intracellular nature. In this work, the effectiveness of the utilization of Saccharomyces cerevisiae LD1 and LHDP1 strains, osmotic-remedial mutants which lyse at 37 degrees C, for the heterologous production and release into the extracellular medium of this protein has been proved. The highest absolute values of released beta-galactosidase have been obtained with the protease-deficient strain LHDP1 by osmotic shock.

Characterization of beta-glucosidase activity in yeasts of oenological origin

Three hundred and seventeen strains representing 20 species of yeasts were screened for the presence of beta-glucosidase activity. All of the strains of the species Debaryomyces castellii, Deb. hansenii, Deb. polymorphus, Kloeckera apiculata and Hansenula anomala showed beta-glucosidase activity, but only one of 153 strains of Saccharomyces cerevisiae. The other species behaved differently, depending upon the strain. The strains that hydrolysed arbutin were checked to localize the beta-glucosidase activity. A strain of Deb. hansenii exhibited the highest exocellular activity and some wall-bound and intracellular activity. The beta-glucosidase synthesis from this yeast was enhanced by aerobic conditions of growth, was repressed by high glucose concentration (9%) and occurred during exponential growth. The optimum conditions for enzymatic preparations of Deb. hansenii were between pH 4.0 and 5.0 and 40 degrees C. A high concentration of ethanol and glucose did not reduce the enzymatic activity. The enzymatic preparations of Deb. hansenii released monoterpenols and other alcohols from a grape glycoside extract.

Detergent permeabilized yeast cells as the source of intracellular enzymes for estimation of biomolecules

The feasibility of using permeabilized whole cells as a source of intracellular enzymes instead of isolated expensive enzymes for the estimation of biomolecules has been studied. Alcohol dehydrogenase (ADH), glucose-6-phosphate dehydrogenase (G6PDH), hexokinase (HK), and beta-galactosidase (beta-GAL) activities of cetyltrimethylammonium bromide (CTAB)-permeabilized whole yeast cells were employed to estimate ethyl alcohol, glucose, and lactose. The method using permeabilized cells was comparable to that of isolated enzymes and was applicable for the estimation of these analytes in complex samples such as blood, milk, and fermented samples. The usefulness of permeabilized cells as a single source of more than one enzyme required for coupled enzyme assays was demonstrated.