2009_Book_FoodChemistry

2.7 Enzyme Utilization in the Food Industry 153
sion in the confectionery or candy industry. Invert
sugar is more soluble and, because of the presence
of free fructose, is sweeter than saccharose.
2.7.2.2.9 α-L-Rhamnosidase
Some citrus fruit juices and purées (especially
those of grapes) contain naringin, a dihydrochalcone
with a very bitter taste. Treatment
of naringin with combined preparations of
α-L-rhamnosidase and β-D-glucosidase yields
the nonbitter aglycone compound naringenin
(cf. 18.1.2.5.4).
2.7.2.2.10 Cellulases and Hemicellulases
The baking quality of rye flour and the shelf life
of rye bread can be improved by partial hydrolysis
of the rye pentosans. Technical pentosanase
preparations are mixtures of β-glycosidases (1,3-
and 1,4-β-D-xylanases, etc.).
Solubilization of plant constituents by soaking
in an enzyme preparation (maceration)
is a mild and sparing process. Such preparations
usually contain exo- and endo-cellulases,
α- and β-mannosidases and pectolytic enzymes
(cf. 2.7.2.2.13). Examples of the utilization are:
production of fruit and vegetable purées (mashed
products), disintegration of tea leaves, or production
of dehydrated mashed potatoes. Some of
these enzymes are used to prevent mechanical
damage to cell walls during mashing and, thus, to
prevent excessive leaching of gelatinized starch
from the cells, which would make the purée too
sticky.
Glycosidases (cellulases and amylases from Aspergillus
niger) in combination with proteinases
are recommended for removal of shells from
shrimp. The shells are loosened and then washed
off in a stream of water.
2.7.2.2.11 Lysozyme
The cell walls of gram-positive bacteria are
formed from peptidoglycan (synonymous with
murein). Peptidoglycan consists of repeating
units of the disaccharide N-acetylglucosamine
(NAG) and N-acetylmuramic acid (NAM) connected
by β-1,4-glycosidic linkages, a tetrapeptide
and a pentaglycine peptide bridge. The NAG
and NAM residues in peptidoglycan alternate
and form the linear polysaccharide chain.
Lysozyme (cf. 11.2.3.1.4) solubilizes peptidoglycan
by cleaving the 1,4-β-linkage between NAG
and NAM. Combination preparations containing
both lysozyme and nisin (cf. 1.3.4.3) are recommended
for the preservation of meat preparations,
salad dressings and cheese preparations. They are
more effective than the components.
2.7.2.2.12 Thioglucosidase
Proteins from seeds of the mustard family
(Brassicaceae), such as turnip, rapeseed or
brown or black mustard, contain glucosinolates
which can be enzymatically decomposed into
pungent mustard oils (esters of isothiocyanic
acid, R−N=C=S). The oils are usually isolated
by steam distillation. The reactions of thioglycosidase
and a few glucosinolates occurring in
Brassicaceae are covered in section 17.1.2.6.5.
2.7.2.2.13 Pectolytic Enzymes
Pectolytic enzymes are described in section
4.4.5.2. Pectic acid which is liberated by
pectin methylesterases flocculates in the presence
of Ca 2+ ions. This reaction is responsible for
the undesired “cloud” flocculation in citrus
juices. After thermal inactivation of the enzyme
at about 90 ◦ C, this reaction is not observable.
However, such treatment brings about deterioration
of the aroma of the juice. Investigations
of the pectin esterase of orange peel have
shown that the enzyme activity is affected by
competitive inhibitors: oligogalacturonic acid
and pectic acid (cf. Fig. 2.51). Thus, the increase
in turbidity of citrus juice can be prevented by
the addition of such compounds.
Pectinolytic enzymes are used for the clarification
of fruit and vegetable juices. The mechanism of
clarification is as follows: the core of the turbidity
causing particles consists of carbohydrates and
proteins (35%). The prototropic groups of these
proteins have a positive charge at the pH of fruit