Handbook of Meat Processing

178 Chapter 8

related to changes in protein solubility. The

matrix density decreases as temperature is

raised (Barbut et al. 1996 ). The major changes

in microstructure could be related to changes

observed in gel rigidity and the reduction in

extractable proteins.

Effect of Heat on Proteins and

Protein Structure

Although the exact nature of denaturation

and coagulation is not fully understood, there

are distinct and easily recognized physical

changes in meat proteins during cooking

(Table 8.4 ). Solidifi cation of the muscle and

color changes are readily observed and are

closely associated with the reduction in

solubility. Heating meat up to 45 ° C internal

temperature resulted in a slight decrease

in the amount of water - soluble fraction

extracted from meat (Laakkonen et al. 1970 ).

Between the temperatures of 45 ° C and

58.5 ° C, the water - soluble fraction decreased

rapidly, and only a slight decrease in water -

soluble fraction is seen during holding at

60 ° C (Laakkonen et al. 1970 ). Solubility of

the myofi brillar fraction also decreases

with increasing temperature (Hamm and

Deatherage 1960 ; Lyon et al. 1986 ; Barbut et

al 1996 ). The decrease in solubility is great-

losses. Beyond 70 ° C, drip losses rose rapidly.
These researchers suggest that drip loss can
be minimized if internal temperatures can be
kept below 65 ° C. Furthermore, evaporative
losses could be kept to a minimum by increas-
ing the relative humidity in the cooking
environment.
Hamm and Deatherage (1960) suggested
that the changes in water - holding capacity
during cooking, and thus cooking losses, are
due to changes in charges and unfolding of
proteins. This results in the shifting of the
isoelectric point to a more basic pH.
Palka (2003) reported increased cooking
losses when starting meat was aged for 7
days compared with 12 days postmortem.
Boles and Swan (2002b) also reported cook
yields decreased as refrigerated storage of
inside rounds and fl ats increased to 8 weeks
of storage. Furthermore, an increase in pH
was found during refrigerated storage of
inside rounds and fl ats, and was related to a
decrease in cook yield.
Cooking is responsible for the setting of
gels that make it possible to manufacture sau-
sages and restructured products. Increasing
internal temperature results in increased gel
strength (Barbut et al. 1996 ). Increased gel
strength is paralleled by a decrease in soluble
protein. Changes in gel structure can be

Table 8.4. Effect of cooking on meat proteins

Authors Temperature Effect on proteins

Laakkonen et al., 1970 45 – 58.5 ° C

Hold at 60 ° C

Rapid decrease in water soluble fraction of meat. No

further decrease in water soluble fraction when

held.

Hamm and Deatherage, 1960 ;

Lyon et al., 1986 ; Barbut

et al., 1996

40 – 60 ° C Reduction in solubility of myofi brillar fraction

Leander et al., 1980 63 ° C Slight disfi gurement of the myofi bril, some swelling

of the perimysial connective tissue

68 ° C Swelling of the A - band, connective tissue coagulated

73 ° C Sarcomeres contraction and breakage at Z - line,

Coagualtion of sarcolemma, increased loss of

sarcomeric structure

Bendall and Restall, 1983 40 – 90 ° C Decreased myofi ber diameter

Martens et al., 1982 53 – 63 ° C Denaturation of collagen, breaking up of fi brous

structure

Welke et al., 1986 Increased epimysial connective tissue with cooking