Rheological Behavior of Starch-Protein Dispersions

In many foods, both starch and protein can be encountered so that understanding interactions between them would be useful. The selectivity in interaction between proteins and starches is best seen in results of dynamic rheological studies. The results depend upon the molecular structure of protein, the starch state of the granules and the amylose/amylopectin ratio, the composition of protein and starch, as well as the phase transition temperatures are important factors influencing protein-starch interaction. Because proteins and starches are thermodynamically different polymers, their presence together may lead to phase separation, inversion, or mutual interaction with significant consequences on texture (Morris, 1990). 

Addition of gluten to 6.5-6.6% (w/w) dispersions of different starches at a 1% level ealeulated on dry stareh basis inereased the G of wheat and rye starches, lowered that of maize stareh but did not affeet the modulus of barley, triticale and potato starehes (Lindahl and Eliasson, 1986). G was also found to increase with increasing amounts of gluten (1-4%) added to the wheat starch. Studies on starches with different amylose/amylopectin ratios suggest that gelatinization of amylopectin and not amylose favors a synergistie interaetion with proteins leading to an increase in dispersion viscosity (Chedid and Kokini, 1992 Madeka and Kokini, 1992). 

The com starch-SP isolate dispersions displayed tme gel-like behavior. Table 4-12 contains magnitudes of the slopes ( and n ) and intercepts (K and K ) in the equations  

In the starch-SP isolate dispersions, the starch continuous network was formed first as a result of its lower transition temperature. Because the denaturation temperature of 7 S globulin was close to the gelatinization temperature of com starch, the diffusion and aggregation of amylose molecules and the swelling of starch granules was a little bit 

1997) G increased from an initial value, G q, to a maximum plateau value, that increased with the proportion of starch in the mixture. A slight decrease in G was observed during the later part of aging, probably due to weakening of starch granules. The rise in G up to the maximum value followed an apparent first order rate process, Equation 4.58. 

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