322 Chapter 12
two main substrates for the manufacture of
cheese fl avors. The use of enzyme - modifi ed
cheese (EMC)and lipid fl avors is discussed
later in this chapter.
A variety of proteases is commercially
available. The operational characteristics
(pH, temperature of stability, specifi city, etc.)
and amount and type of products vary, and
the variations result in different fl avor pro-
fi les in EMC. Twenty - three commercial
microbial proteinase preparations derived
from various Bacillus or Aspergillus spp. or
from Rhizomucor niveus were assessed for
proteolytic activity on azocasein at pH 5.5 or
7.0 or specifi city on sodium caseinate at pH
5.5. They were semi - quantitatively assessed
for esterase, lipase, trypsin, chymotrypsin,
general aminopeptidase, phosphatase, and
glycosidase activities using the API - ZYM
system. Selected preparations were further
assayed for peptidase, esterase, and lipase
activities at pH 7.0. The proteolytic activity
of the Bacillus preparations was greater at pH
7.0, while that of the Aspergillus and
Rhizomucor preparations was greater at pH
5.5. All of the Bacillus preparations con-
tained one of two main proteolytic activities,
thought to be either bacillolysin or subtilisin.
Most of the Aspergillus preparations con-
tained the same proteinase, thought to be
aspergillopepsin I, but two preparations
appeared to contain a different unidentifi ed
proteinase. The proteolytic specifi city of the
Rhizomucor preparation was different from
that of the Bacillus or Aspergillus prepara-
tions; this difference is thought to be due to
an enzyme called rhizopuspepsin.
According to the results of the API - ZYM
system, all preparations contained enzyme
activities in addition to their main proteolytic
activity, with the Aspergillus and Rhizomucor
preparations containing the highest levels
and widest range of activities. Generally,
preparations derived from Aspergillus con-
tained the highest level of general, proline,
and endopeptidase activities, with the
Bacillus preparations conspicuous by theexhibit both the elastic and viscous proper-
ties described by the term viscoelasticity.
The gelation process can immobilize a large
volume of liquid.
A classic example of gelation of milk
occurs in the cheese - making process wherein
the enzyme chymosin causes the formation
of a soft gel. This gelation occurs due to the
hydrolysis one specifi c peptide bond (Phe105 -
Met106) in κ - casein by chymosin. The scis-
sion of the glycomacropeptide causes the
casein micelle to become sensitive to ionic
calcium in the environment, leading to coag-
ulation or gel formation.
Any alteration in the native conformation
of a protein has the potential to induce gela-
tion. Thus, enzymes modify the conforma-
tion of proteins and the altered conformation
increases the propensity of the protein to
form gels under appropriate conditions.
Sometimes other enzymes, e.g., transgluta-
minase, are employed to increase the strength
of the formed gels. The exact nature of the
peptides that result in gelation is not easy to
understand. The processing pre - treatments
accorded to proteins pre - or post - modifi cation
confound the understanding of the gelation
process. In general, enzymatic modifi cation
results in a conformation of the protein that
can form aggregates, which have a propen-
sity to form gels under a variety of condi-
tions. Altering the environment by changing
pH, ionic strength, and type of ions, or by
physical treatments such as heat causes the
aggregates to form gels. Structural informa-
tion in this context is of limited use in delin-
eating the mechanism of gelation.
Flavor Production Resulting
from Hydrolysis
Commonly used hydrolyzed proteins for fl a-
vorings are derived from plant materials, and
milk proteins are not an economically viable
source for manufacturing such fl avorings.
However, enzymes are used to manufacture
cheese fl avors. Lipids and proteins are the