Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
10.1 INTRODUCTION
The diversity of possible structures of sugars corresponds to a multiplicity of their
roles in nature and diversity of enzymes involved in their synthesis and decomposition.
Practical applications of these enzymes range from hydrolysis of macromolecules
such as starch to the production of monomers and oligomers with precisely
defined structure to be used in cancer therapy.
Started in the 20th century, industrial conversions of polysaccharides involved
processes that employed harsh conditions, consumed enormous portions of energy,
and contributed to pollution of the natural environment. The increasing profitability
of “green” technologies and growing public concern about the environment, resulting
in stricter law regulations, have brought about the progressive dislodging of chemical
technologies with environment-friendly production strategies that lead to a higher
yield and quality of product and concomitantly reduce an input of energy and
chemicals.
The main drawbacks of earlier biotechnologies resulted from relatively poor
activity and stability of enzymes derived from natural sources. In some cases,
enzymes showing sufficient activity and stability under adverse conditions were
derived from extremophilic organisms, which thrive at extreme pH; very low or high
temperature; or elevated pressure, salinity, or concentration of various compounds.
Extremophiles such as thermo-, psychro-, baro-, acido- alkali-, or halophiles were
shown to be the best natural sources of stable catalytic proteins and their genes.
Studies on these organisms yielded an important insight into relationships between
protein structure and stability, and many genes encoding their enzymes of industrial
significance were cloned and expressed in hosts [usually generally regarded as safe
(GRAS)]. At present, approximately 90% of all commercial enzymes are derived
from genetically modified organisms (GMOs), due to advances in construction and
selection of industrial mutant strains.
Tremendous advances in improvement of such properties of enzymes as catalytic
efficiency, stereospecificity, and stability under diverse conditions and in various
media, including organic solvents, supercritical fluids, or ionic liquids, make their
industrial application more reasonable as compared to other technologies, and have
contributed to implementing of biotechnologies in virtually all branches of industry,
also those employing enzymes involved in conversions of saccharides. Immobilization
of biocatalysts and construction of modern bioreactors have also enhanced
production yield. An expansion of modified and improved enzymes or engineered
whole cells gave rise to rapid development of glycobiotechnology, a research area
focused on synthesis of various saccharides and their derivatives, with precisely
determined structures. The range of possible applications of these compounds
includes prevention of diverse infections, neutralization of toxins, and cancer immunotherapy.
Controlled enzyme-catalyzed depolymerization, transglycosylation,
isomerization, oxidation, and reduction of oligo- and polysaccharides lead to a
variety of high-value-added products with improved functional properties. A benign
effect can be also achieved by selective enzymatic degradation of some antinutritional
oligosaccharides, consumption of which causes malfunction of the alimentary
tract. The strictly enzymatic methods, termed as combinatorial biosynthesis, 1 have