Biomedical Engineering Reference
In-Depth Information
results in increased viscosity therefore reducing fi ltration rate and yield in
beer processing. For that reason, β-glucanases, usually classical mixtures
of enzymes derived from
T. reesei
and
Ta. emersonii,
are applied in beer
production (Briggs et al. 2004).
Although the relative content of non-cellulosic and cellulosic
carbohydrates in wheat is rather low, cellulases (endo-β-glucanases,
cellobiohydrolase, β-glucosidase) do have effects in bread making. Usually,
the complex enzyme mixture of
Trichoderma
is used in combination with
xylanases, resulting in improved loaf volume and crumb softness, as
compared to the single use of xylanase (Hille and Schooneveld-Bergmans
2004).
Another type of hemicellulose that occurs in some plants is mannan or
glucomannan, which consists of β-(1,4)-linked mannose units or alternating
mannose and glucose units, respectively. Both types of mannan can also be
branched by single α-(1,6)-linked galactose units. Mannans occur in seeds
of some plants, such as in green coffee and in plants of the Leguminoseae
family. Glucomannans mainly occur in softwoods and to a minor extend
in hardwoods. In food processing endo-β-mannanases are not extensively
applied, but applications of interest are in coffee processing, to reduce the
viscosity of liquid coffee extracts or to increase the yield of coffee extract
and oligosaccharide production from coffee spent ground, konjac or guar
gum (van Zyl et al. 2010). Fungal mannanases available for such applications
may be derived from
Aspergillus
and
Trichoderma
species.
Pectinases
Pectins are present in cell walls of fl owering plants (dicots), such as fruits
and vegetables. Pectins are very complex polysaccharides, consisting of
various regions of differently branched sugar molecules, also build up of
different sugars such as rhamnose, galacturonic acid, arabinose, galactose,
sometimes methylated or acetylated. In processing of fruits and vegetables
pectin-degrading enzymes can be applied for improving extraction yield,
decreasing fi ltration time and juice clarifi cation; in vegetable oil extraction
to improve yield; in wine production to reduce grape must viscosity and
improve juice yield, color and aroma; in tea and coffee fermentation to
accelerate the process (Grassin and Fauquembergue 1996, Jayani et al.
2005). The most common fungal species commercially used for production
of pectin degrading enzymes are
A. niger
and
A. aculeatus
. Usually classical
enzyme mixtures are applied, in which the pectin degrading activities are
optimised. Pectin methyl esterase is, through overexpression, available as
pure enzyme and applied to deacetylate highly methylated pectins. As a
consequence of the removal of the methyl-groups the pectins can interact
with each other via divalent cations to form strong pectate gel structures.
