Nadia Krieger

The realm of microbial lipases in biotechnology.

In this review, a comprehensive and illustrious survey is made of the applied aspects of microbial lipases in modern biotechnological practices. Lipases are the most versatile biocatalyst and bring about a range of bioconversion reactions such as hydrolysis, interesterification, esterification, alcoholysis, acidolysis and aminolysis. After a brief description of the microbial sources of lipases, the pivotal role of lipases in the processes and products of the food and flavourings industry is illustrated. An illustration is presented of biomedical applications. The panorama of lipases in the manufacture of fine chemicals is depicted with special emphasis on pharmaceuticals, pesticides, cosmetics, biosensors and detergents. Widening applications such as those in waste management and improved tanning techniques are other novel aspects of lipase utilization that are discussed in this review.

Recent Developments in Microbial Inulinases Its Production, Properties, and Industrial Applications

Microbial inulinases are an important class of industrial enzymes that have gained much attention recently. Inulinases can be produced by a host of microorganisms, including fungi, yeast, and bacteria. Among them, however, Aspergillus sp. (filamentous fungus) and Kluyveromyces sp. (diploid yeast) are apparently the preferred choices for commercial applications. Among various substrates (carbon source) employed for their production, inulin-containing plant materials offer advantages in comparison to pure substrates. Although submerged fermentation has been universally used as the technique of fermentation, attempts are being made to develop solidstate fermentation technology also. Inulinases catalyze the hydrolysis of inulin to d-fructose (fructose syrup), which has gained an important place in human diets today. In addition, inulinases are finding other newer applications. This article reviews more recent developments, especially those made in the past decade, on microbial inulinases—its production using various microorganisms and substrates. It also describes the characteristics of various forms of inulinases produced as well as their applications.

A review of recent developments in modeling of microbial growth kinetics and intraparticle phenomena in solid-state fermentation

Mathematical models are important tools for optimizing the design and operation of solid-state fermentation (SSF) bioreactors. Such models must describe the kinetics of microbial growth, how this is affected by the environmental conditions and how this growth affects the environmental conditions. This is done at two levels of sophistication. In many bioreactor models the kinetics are described by simple empirical equations. However, other models that address the interaction of growth with intraparticle diffusion of enzymes, hydrolysis products and O2 with the use of mechanistic equations have also been proposed, and give insights into how these microscale processes can potentially limit the overall performance of a bioreactor. The current article reviews the advances that have been made in both the empirical- and mechanistic-type kinetic models and discusses the insights that have been achieved through the modeling work and the improvements to models that will be necessary in the future.

Recent developments in modeling of solid-state fermentation: heat and mass transfer in bioreactors

Abstract Mathematical models are important tools for optimizing the design and operation of solid-state fermentation (SSF) bioreactors. Such models must describe the transport phenomena within the substrate bed and mass and energy exchanges between the bed and the other subsystems of the bioreactor, such as the bioreactor wall and headspace gases. The sophistication with which this has been done for SSF has improved markedly over the last decade or so. The current article reviews these advances, showing how the various transport phenomena have been modeled. It also discusses the insights that have been achieved through the modeling work and the improvements to models that will be necessary in order to make them even more powerful tools in the optimization of bioreactor performance.

Biochemical Engineering Aspects of Solid State Bioprocessing

Despite centuries of use and renewed interest over the last 20 years in solid-state fermentation (SSF) technology, and despite its good potential for a range of products, there are currently relatively few large-scale commercial applications. This situation can be attributed to the complexity of the system: Macroscale and microscale heat and mass transfer limitations are intrinsic to the system, and it is only over the last decade or so that we have begun to understand them. This review presents the current state of understanding of biochemical engineering aspects of SSF processing, including not only the fermentation itself, but also the auxiliary steps of substrate and inoculum preparation and downstream processing and waste disposal. The fermentation step has received most research attention. Significant advances have been made over the last decade in understanding how the performance of SSF bioreactors can be controlled either by the intraparticle processes of enzyme and oxygen diffusion or by the macroscale heat transfer processes of conduction, convection, and evaporation. Mathematical modeling has played an important role in suggesting how SSF bioreactors should be designed and operated. However, these models have been developed on the basis of laboratory-scale data and there is an urgent need to test these models with data obtained in large-scale bioreactors.

Scale-up strategies for packed-bed bioreactors for solid-state fermentation

Abstract Two approaches are compared for scale-up of solid-state fermentation processes in packed-bed bioreactors, one based on a dynamic heat transfer model, and the other based on a modified Damkohler number. A critical bed height is proposed, being the maximum bed height which can be used without undesirable temperatures being reached in the substrate bed during the fermentation. It depends on the microbial specific growth rate, as well as the superficial velocity and inlet temperature of the air. The critical heights predicted by the two approaches are almost identical, suggesting that approaches to scaling-up packed-bed bioreactors based on the modified Damkohler number may be successful. The modified Damkohler number is then used to predict how simple rules of scale-up might perform. Superficial velocities will need to increase with scale, although for practical reasons, it is not possible to increase superficial velocity in direct proportion to height indefinitely. A strategy is proposed to guide experimental programs for scaling-up of packed-bed bioreactors.

FIRST EVIDENCE FOR THE SALT-DEPENDENT FOLDING AND ACTIVITY OF AN ESTERASE FROM THE HALOPHILIC ARCHAEA HALOARCULA MARISMORTUI

A gene encoding an esterase from Haloarcula marismortui, a halophilic archaea from the Dead Sea, was cloned, expressed in Escherichia coli, and the recombinant protein (Hm EST) was biochemically characterized. The enzymatic activity of Hm EST was shown to exhibit salt dependence through salt-dependent folding. Hm EST exhibits a preference for short chain fatty acids and monoesters. It is inhibited by phenylmethylsulfonyl fluoride, diethyl-p-nitrophenyl phosphate, and 5-methoxy-3-(4-phenoxyphenyl)-3H-[1,3,4]oxadiazol-2-one, confirming the conclusion from sequence alignments that Hm EST is a serine carboxylesterase belonging to the hormone-sensitive lipase family. The activity of Hm EST is optimum in the presence of 3 M KCl and no activity was detected in the absence of salts. Far-UV circular dichroism showed that Hm EST is totally unfolded in salt-free medium and secondary structure appears in the presence of 0.25-0.5 M KCl. After salt depletion, the protein was able to recover 60% of its initial activity when 2 M KCl was added. A 3D model of Hm EST was built and its surface properties were analyzed, pointing to an enrichment in acidic residues paralleled by a depletion in basic residues. This peculiar charge repartition at the protein surface supports a better stability of the protein in a high salt environment.

Overview of solid state bioprocessing

Solid-state fermentation has centuries of history, but it is only in the last two decades that there has been a concerted effort to understand the bioprocessing issues involved and to apply them to a wide range of new products. This article provides an overview of the knowledge of solid-state bioprocessing that has been gained over this time. It shows that, although significant advances have been achieved in understanding of what controls process performance, much research is still required.

Functional properties of yam bean (Pachyrhizus erosus) starch.

The study was carried out in order to determine and establish the functional characters of starch extracted from yam bean (Pachyrhizus erosus (L) Urban) compared with cassava starch. Yam bean is a tropical tuber legume easily grown and holds a great potential as a new source of starch. Yam bean starch shows functional properties which are peculiar to those of most starch root crops. Gelatinization temperature (53-63 degrees C) and the pasting temperature (64.5 degrees C) are less than those of cereal starch, however, the swelling power is high (54.4 g gel/g dried starch). Yam bean starch paste presents a high viscosity profile, high retrogradation tendency and low stability on cooking. The functional properties of yam bean starch, similar to those of cassava starch, allows yam bean to be used as a potential new source of starch.

An efficient system for catalyzing ester synthesis using a lipase from a newly isolated Burkholderia cepacia strain

The synthesis of ethyl-oleate by the lipase from the newly isolated strain Burkholderia cepacia LTEB11 in three different systems has been studied – immobilization on a hydrophobic support (Accurel EP 100®), encapsulation in reverse micelles, and direct addition of powdered free enzyme to the reaction medium. The immobilized enzyme performed best, giving a 70% ester yield in 10 h, this yield being five-fold greater than that obtained for reversed micelles, and two and a half times greater than that obtained for direct addition. An increase in the amount of immobilized enzyme preparation added gave a 100% ester yield in 3 h. The immobilized preparation was quite stable, giving a 100% yield of ethyl-oleate during 11 repeated reactions, and 50% yield after 24 reactions. These results suggest that the lipase of our strain of B. cepacia LTEB11 immobilized on Accurel has good potential for application in biocatalysis in organic media.