Food Structure


String cheese samples ranging in pH from 5.0 to 5.9 were prepared by kneading Mozzarella curd and stretching it 2 to 80 times. Rheological properties were examined by compression, stress relaxation , and flow property tests. Stringiness was tested by a device specifically designed for this purpose: a standardized string was pulled from the sample at a direction perpendicular to the orientation of the curd and the amount of fibres resulting from this process was quantitated using digital image analysis.

Force-deformation curves implied that the curd prepared by kneading may be considered to be an incompressible viscoelastic body similar to rubber. Curd made at pH 5.0 flowed more easily then the other curds. Changes in pH had greater effects on rheological properties than the moisture content. The effect of temperature on the flow properties should be considered when pumping the curd through pipes , extruding from nozzles , and in stretch processing. Stringiness was low at 5 w 10 C but was markedly increased at 25 C, at which temperature string cheese should be consumed. Optimal stringiness was obtained in cheese curd samples having a pH of 5.4.

Light microscopy and electron microscopy revealed that stringiness is associated with a uniform longitudinal orientation of the protein matrix. Moderate stringiness occurred in a network of casein subunits having diameters equal to those of casein submicelles. CryoSEM showed that the state of water in string cheese was affected by kneading.

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