Starch-protein dispersions

Dynamic and flow rheological characteristics of heated mixed whey protein isolate (WPI) and cross-linked waxy maize starch (CWM) dispersions 5% solids, pH = 7.0, 75 mM NaCl, were examined at starch mass fractions (jcs) from 0 (pure WPI) to 1 (pure CWM) (Ravindra et al., 2004). The mixed dispersions had lower values of G than the pure WPI dispersion, primarily due to the disruptive effect of CWM granules on the WPI network. The point of phase inversion (minimum G value) was at about Xs = 0.65 (Figure 4-40). 

Ravindra, R, Genovese, D. B., Foegeding, E. A., and Rao, M. A. 2004. Rheology of mixed whey protein isolate/cross-linked waxy maize starch gelatinized dispersions. Food Hydrocolloids 18 775-781. 

Endosperm constitutes the main part of the corn kernel and consists of 85 to 90% starch, 8 to 10% protein, and a small amount of oil and other compounds. Corn endosperm can be divided into two distinct parts floury and horny endosperm. In floury endosperm, starch particles are round and are dispersed loosely in the protein matrix. In the horny endosperm, the protein matrix is stronger and starch particles are held more firmly. Starch granules are encased in the continuous protein matrix. The tighter setting in horny endosperm gives starch particles a polygonal shape. On average, the amount of horny endosperm in the corn kernel is twice that of the floury endosperm. However, this ratio is a function of the corn kernel protein content (Wolf et al., 1952). 

After spray drying, rice starch containing <0.5% protein is present as clusters of 10-2011 m. At 1.5% and again at 6.0% protein, increased formation of spheres of 30-70 qm is observed. The presence of these spheres is responsible for improved dispersibility and gel smoothness.26 It has also been suggested that the unique absorption properties of the sphere aggregates may have application in holding and dispersement of flavor material or pharmaceuticals.27... 

Starch for use in papermaking has to meet specific purity requirements in residual oil, protein, bran and ash content. Industrial starches have a protein content (N X 6.25), ranging from about 0.05% for potato starch to 0.3-0.6% for com starch, depending on separation efficiency during production. Excess protein content will induce foaming in dispersions of starch and affect the quality and strength of the coated surface. Starch for use in the paper industry should not contain more than 0.4% protein. Oxidized starches tend to have the lowest protein content. Residual oil will cause retrogradation due to complex formation with amylose. 

The classical thermodynamic and kinetic model is that of a rigid sphere impenetrable by water. A spherical geometry has been observed in many polysaccharide systems, notably hyaluronic acid-protein complexes (Ogston and Stainer, 1951), dispersed gum arabic (Whistler, 1993), and spray-dried ungelatinized starch granules (Zhao and Whistler, 1994). Spherulites of short-chain amylose were obtained by precipitation with 30% water-ethanol (Ring et al., 1987), and spherulites of synthetic polymers were obtained... 

Cakes essentially are emulsified slurries before baking. Considerable use is made of sugar (with corn sweeteners increasingly used), starch in low-protein content flours, and fat. Emulsifiers have three functions in cake systems to improve air incorporation to disperse shortening into smaller particles to maximize the number of air cells and to... 

Pure lipids can be combined with hydrocolloids such as proteins, starches or celluloses and their derivatives, either by incorporating the lipids in the hydrocolloid film-forming solution (emulsion technique) or by depositing the lipid layer onto the surface of the preformed hydrocolloid film to obtain a bilayer (Fennema and Kamper 1986 Krochta and De Mulder Johnston 1997). Multicomponent films have been extensively reviewed by Wu et al. (2002). The addition of nonlipid compounds (hydrocolloids, sugar solids, etc.) as dispersed components in fat materials permits forming fat dispersions (e.g., chocolate. Figure 23.2). 

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). 

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