Biomedical Engineering Reference
In-Depth Information
is largely limited by the high concentrations of lactose due to its poor
solubility and insuffi cient sweetness. Hydrolysis of lactose to glucose and
galactose by β-galactosidase would overcome some of these limitations
and permit greater use of whey permeates, e.g., as a substitute for corn
syrup in soft drinks, fermented beverages and confectionary products
(Szczodrak 2000).
Usually glycosidases such as β-galactosidase hydrolyze glycosidic
linkages but when reaction conditions are manipulated
in vitro
molecules
other than water can be accepted as nucleophiles and new glycosides are
obtained (Toone et al. 1989). This method is called transglycosylation. In
recent years, considerable attention has focused on the transglycosylation
activity of β-galactosidase based on the enormous potential for synthesis of
novel oligosaccharides in food, pharmaceutical and medical applications.
Non-digestible galacto-oligosaccharides (NDOs) are carbohydrates, which
are resistant to gastro-intestinal digestive enzymes, but are fermented by
specifi c colonic bacteria. These carbohydrates benefi cially affect the host
by selectively stimulating the growth and/or activity of one or a limited
number of bacteria in the colon and are recognized as prebiotics (Gibson
and Roberfroid 1995, Fuller and Gibson 1997). The microbial community
in the large intestine is extremely complex, both in terms of the number of
organisms and its diversity. This complex and highly adapted community
benefi ts the host by providing resistance to pathogens. It is diffi cult for
other organisms, including pathogens, to colonise in the lumen of the small
intestine. This generates colonization resistance or non-specifi c disease
resistance in the gut which acts as an important line of defence against
pathogens (Tannock 1995). In addition to their prebiotic activity, some
NDOs, including galacto-oligosaccharides, have also been investigated for
other health promoting properties. They have been shown to consistently
increase absorption and retention of several minerals, particularly calcium,
magnesium and iron and to improve mineralization of bone (Miniello
et al. 2004). Galacto-oligosaccharides are also used in pastry, jam and
bread-making because of their heat stability, allowing the sweetness of the
products to be controlled (Bhat 1998). Oligomate 50 is a heat stable (stable
at temperatures of 100°C), non cariogenic galacto-oligosaccharide that is
added to food products e.g., ice cream, to prevent lactose crystallization. This
galacto-oligosaccharide has water binding properties which is important in
maintaining a healthy gut, by assisting in the control of constipation and
decreasing blood NH
3
content.
Whilst a number of non-pathogenic, 'generally regarded as safe'
microorganisms are used as producers of enzymes, fi lamentous fungi
are signifi cantly important. Filamentous fungi are extremely effi cient cell
factories due to their secretion of a variety of enzymes at a high level (Punt et
