Swelling capacity of starch and its relationship to suspension viscosity: effect of cooking time, temperature and concentration

Swelling capacity of starch and its relationship to suspension viscosity: effect of cooking time, temperature and concentration

1982

REP.G1937

A range of concentrations (c) of wheat starch granules dispersed in water were heated at 60, 65, 70 and 75°C for 15, 30, 45, 60 and 75 min. Viscosity (71)-shear rate plots for these cooked dispersions, determined with a Haake Rotovisco rotational viscometer at 60°C and 23°C, varied markedly, often showing dilatant behavior, particularly at the shorter cooking times but always becoming typically non-Newtonian shear thinning fluids at the longer cooking times. At the lowest temperature, 60°C, the viscosity increases very rapidly with concentration above 16%. As the cooking temperature is raised to 65, 70, and 75°C these rapid viscosity increases occur at progressively lower concentrations. These concentration curves for the longest cooking times could be superimposed on a master curve by plotting, instead of 71 versus c, 71/ cQ versus cQ, where Q is determined in a separate experiment and is the weight of the swollen starch granules after the specified time at cooking temperature divided by the dry weight of the starch prior to cooking. This method of reducing viscosity concentration data has been reported by Taylor and Bagley (1977) for highly swollen gel systems and by Urbanski (1981) for soy beverqges, and thus appears to be a general method for treating viscosity data for suspensions of deformable particles that sorb solvent. Where excess solvent is present, CQ is less than unity and is equivalent to volume fraction; for deformable particles, however, CQ can be greater than unity, and for our systems concentrations in this range represent doughs.

v.13(1):115-126, JOURNAL OF TEXTURE STUDIES

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