Chemistry Reference
In-Depth Information
intracellular enzymes although some extracellular glutaminases have been reported. The
main cellular function of glutaminases is proposed to be associated with the control of
intracellular concentration of glutamine, which is an essential nitrogen metabolite.
75
Many reported glutaminases work optimally at a temperature range of 40-50
◦
C and at
neutral pH.
70
High salt concentrations can markedly inhibit glutaminases. For example,
A. oryzae
glutaminase is inhibited at 3 M NaCl concentrations,
70
which can hamper the
use of the enzyme in applications requiring high salt concentration. Therefore salt-tolerant
glutaminases have been screened for. Some marine bacteria including
Micrococcus luteus
K-3 have been shown to tolerate up to 16% (w/v) concentrations of NaCl.
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12.4
MEAT TENDERIZATION WITH ADDED ENZYMES
Of all the attributes of eating quality, texture and tenderness are presently rated as most im-
portant by the average consumer. Methods to increase tenderness include, for example natural
aging, electric stimulation, mechanical blade tenderization and use of added proteolytic en-
zymes (see Section 12.3). The most widely used exogenous enzymes in meat tenderization
are the plant enzymes papain, bromelain and ficin. Plant proteases, especially papain and
bromelain, have been studied for tenderization purposes for decades. Some examples of the
use of plant proteases or protease-containing fractions in experimental meat tenderization
are given in Table 12.4.
The way of applying tenderizing enzymes in meat industry depends on the actual target.
If the aging time of high-grade meat parts has to be shortened, the main action of pro-
tein hydrolysis should be on myofibrillar proteins. If the tenderness improvement of lower
grade meat cuts or meat from, for example aged animals is desired, the connective tissue
proteins, mostly collagen, should be the target of proteolysis. The methods and challenges
to tenderize meat sold raw to consumers differ from those needed for cooked meat. Plant
proteases mainly used to tenderize meat act unfortunately more actively on other meat
proteins than on collagen. Therefore attempts to tenderize collagen-rich connective tissue
inevitably led to too extensive hydrolysis of non-collagen proteins, resulting in too soft
(mushy) meat. To tenderize meat pieces with a high connective tissue content it is evident
that an enzyme having pronounced activity against connective tissue but limited activity
against myofibrillar proteins should be used. Potential collagenases come mainly from mi-
crobial origins, but unfortunately up till now there are no commercial food-grade collagenases
available.
Although not suitable for food manufacturing purposes, some collagenases have been
studied in meat tenderization. Foegeding and Larick
17
studied
Cl. histolyticum
collagenase
in tenderization of beef steak but the results were not very promising. Clear positive effects
were achieved in the study where microbial collagenases were evaluated for their ability to
degrade collagen in a restructured beef product. Extreme thermophilic bacteria species have
been searched in order to find proteases which would be active against collagen during a
controlled cooking period of meat and show only limited activity during often uncontrollable
cold storage periods.
77, 78
Interesting new proteases from plant origin are cucumis and ginger extracts. Powdered
cucumis extract from the Kachri fruit as well as ginger proteases has successfully tenderized
meats from different species (see examples in Table 12.4). Ginger extract has proven to be
especially effective in increasing collagen solubilization.
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