Voluminosity of some food proteins in aqueous dispersions at various pH and ionic strengths

Commercial casein and whey protein and laboratory preparation of soybean protein of various pH were dispersed in distilled water at the initial concentration of 4.0% w/v and then diluted with NaCl solutions of known ionic strengths (mu). Viscosity was measured and voluminosity (V-e = ml/g) was calculated using Lee's equation relating volume fraction (phi(v)) to relative viscosity: eta/eta(o) = 1 + 2.5 phi(v) + 7.031 phi(v)(2) + 37.371 phi(v)(3). The combined effects of pH and mu on V-e were determined from regression analysis. V-e was inversely related to mu between 0.005 and 0.07 M and increased with pH between 6 and 8 and decreased at higher pH. The results are discussed in terms of the relationship between the protein electrostatic charges and structure. It is concluded that in associative proteins V-e is controlled by the number of electrostatic charges and their strength. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.