Interaction Of Milk Proteins With Meat Proteins

The results of application research indicate that there is a specific interaction between milk protein and meat proteins. To study this effect we have to make a classification of proteins present in meat. Meat protein can be divided

Final chopping temperature of the meat emulsion (°C)

Figure 6. Influence of Na-caseinate on the stability of a meat emulsion in dependence of the final chopping temperature.

No addition

Milk protein (%) Figure 7. Milk proteins in reformed cooked ham (60% injection).

No addition

Milk protein (%) Figure 7. Milk proteins in reformed cooked ham (60% injection).

into different groups according to their specific function and solubility in different solvents (Table 4).

To study the effect of interaction between milk protein and salt-soluble meat proteins, lean meat was extracted according to the extraction procedure shown in Figure 8. Sixty-three percent lean meat (M. semimembranosis) is extracted with 2% salt and 35% ice/water in the bowl chopper. After dilution with 200% brine (2% salt), the lean meat slurry is centrifuged.

After centrifugation there are three distinct layers in the centrifuge tube:

Upper layer: contains wsp (sarcoplasmic proteins) and the salt-soluble myofibrillar proteins.

K-fraction: contains nonsolubilized and swollen myofibrillar proteins, mainly actomyosin.

R-fraction: contains connective tissue materials.

The gellification of wsp/ssp proteins was tested in the following solution:

3% ssp/wsp proteins.

2% milk protein.

The equipment for these tests is the gelograph (Fig. 9).

The principle of this gelograph is as follows: A protein solution that is placed in a waterbath is slowly heated (1°C/ min). During this heat treatment the viscosity/gel strength of the solution is continuously measured by means of an oscillating needle; this equipment operates in a nondestructive way; this means the gel structure that is formed during the heating of the solution is not destroyed because of minimal oscillating of the needle. In this way it is possible to imitate the gelling of meat proteins in pasteurized meat products (eg, a cooked ham).

An example is a product containing 60% lean meat, which contains about 12% total meat protein. Roughly 50% of this protein is myofibrillar proteins. This is about 6%. Suppose that 50% of total myofibrillar proteins are extracted during massaging/tumbling. This means that the concentration of ssp will be around 3%. This is the same concentration as used in the model experiments. Results of gelograph experiments are presented in Figures 10 and 11.

Figure 10 shows the gel strength of a 3% wsp/ssp as a function of temperature. The temperature starts at 20°C (68°F) and is increased at a rate of l°C/min; during this temperature increase the gel strength is measured as mili-gels. At 44°C (110°F) there is a sudden increase in gel strength; this is caused by the aggregation of myosin molecules (24). At higher temperatures the viscosity decreases

63% Lean meat

2% NaCl 25% Ice/water

Communication

Dilution (200% brine)

Centrifugation

63% Lean meat

2% NaCl 25% Ice/water

Communication

Dilution (200% brine)

Centrifugation wsp/ssp

K - fraction R - fraction

Figure 8. Fractionation of meat proteins.

wsp/ssp

K - fraction R - fraction

Figure 8. Fractionation of meat proteins.

Oscilliating needle

Thermostatically J^ZZ^ controlled water bath

To recorder

Figure 9. The gelograph.

To recorder

Figure 9. The gelograph.

again. The reason for this phenomenon is not yet exactly known (23,26,27).

At a temperature of 57°C there is again an increase in gel strength. With further heating of the solution to 75°C the gel strength reaches a constant value of ± 150 m gels. Cooling down the solution results in a final gel strength of ± 200 m gels. The same experiments are done in the presence of 2% milk proteins and 2% soy protein isolate. The results are presented in Figure 12. A conclusion from this figure—addition of 2% milk protein (which has no gellify-ing capacity itself) results in a much higher gel strength of a heated meat protein solution.

This result supports the theory that there is a synergistic effect of milk proteins on the gellifying capacity of salt-soluble meat proteins, either milk proteins play a role in the cross-linking of myosin molecules or they absorb a significant amount of water, which results in a higher net concentration of myosin molecules. Other nonmeat proteins

Table 4. Classification of Meat Proteins

Protein

Percent

Role

Solubility

Gellifying properties

Emulsifying properties

Sarcoplasmic

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