Influence of NaCl on optical properties, large-strain rheology and water holding capacity of heat-induced whey protein isolate gels

The influence of NaCl (0-1000 mM) on the physical properties of gels formed by heating 10 wt% whey protein isolate (WPI) solutions (pH 6.9) at 80 degreesC for 15 min has been studied. Elastic modulus, elastic recoverability and water loss of gels were measured during uniaxial compression/decompression. Optical properties of gels were characterized by spectral reflectance and colorimetry measurements. Below 60 mM NaCl, no gels were formed and the WPI solutions remained optically transparent. From 60 to 150 mM NaCl, gel elastic modulus increased, elastic recoverability remained high, water loss remained low and lightness remained low. From 150 to 200 mM NaCl, gel elastic modulus decreased, elastic recoverability decreased, water loss increased, and gel lightness increased. Above 200 mM NaCl, the elastic modulus, elastic recoverability, water loss and lightness of the gels were relatively insensitive to salt concentration. Theoretical predictions indicated that the lightness (L) of dyed gels had a maximum value at protein particle radius of 100 nm and that L increased with protein particle concentration (especially from 0 to 1 wt%). Differences in gel physicochemical properties are interpreted in terms of differences in the microstructure and interactions of the protein molecules within the gel network. (C) 2002 Elsevier Science Ltd. All rights reserved.