2009_Book_FoodChemistry

154 2 Enzymes
2.7.2.2.15 Tannases
Tannases hydrolyze polyphenolic compounds
(tannins):
(2.112)
For example, preparations from Aspergillus niger
prevent the development of turbidity in cold tea
extracts.
Fig. 2.51. Pectin esterase (orange) activity as affected
by inhibitors (according to Termote, 1977). 1 Without
inhibitor, 2 hepta- and octagalacturonic acids, 3 pectic
acid
juice (3.5). Negatively charged pectin molecules
form the outer shell of the particle. Partial pectinolysis
exposes the positive core. Aggregation of
the polycations and the polyanions then follows,
resulting in flocculation. Clarification of juice by
gelatin (at pH 3.5 gelatin is positively charged)
and the inhibition of clarification by alginates
which are polyanions at pH 3.5 support this suggested
model.
In addition, pectinolytic enzymes play an important
role in food processing, increasing the yield
of fruit and vegetable juices and the yield of oil
from olive fruits.
2.7.2.2.14 Lipases
The mechanism of lipase activity is described
under section 3.7.1.1. Lipase from microbial
sources (e. g. Candida lipolytica) is utilized for
enhancement of aromas in cheesemaking.
Limited hydrolysis of milk fat is also of interest
in the production of chocolate milk. It enhances
the “milk character” of the flavor.
The utilization of lipase for this commodity is
also possible.
Staling of bakery products is retarded by lipase,
presumably through the release of mono- and diacylglycerols
(cf. 15.4.4). The defatting of bones,
which has to be carried out under mild conditions
in the production of gelatin, is facilitated by using
lipase-catalyzed hydrolysis.
2.7.2.2.16 Glutaminase
This enzyme catalyzes the hydrolysis of glutamine
(Formula 2.113). For meat preparations, the
addition of an enzyme preparation from Bacillus
subtilis is under discussion. It increases the concentration
of glutamic acid, which substantially
contributes to the taste of meat.
2.7.2.3 Isomerases
(2.113)
Of this group of enzymes, glucose isomerse,
which is used in the production of starch syrup
with a high content of fructose (cf. 19.1.4.3.5), is
very important. The enzyme used industrially is
of microbial origin. Since its activity for xylose
isomerization is higher than for glucose, the
enzyme is classified under the name “xylose
isomerase” (cf. Table 2.4).
2.7.2.4 Transferases
Protein glutamine-γ-glutamyl transferase (transglutaminase,
TGase) catalyzes the acyl transfer
between the γ-carboxyamide group of peptidebound
glutamine (acyl donor) and primary
amines (acyl acceptor, I in Formula 2.114), e. g.,
peptide-bound lysine (II in Formula 2.114). Free