Use of fibre optics to study the transition from clear to opaque whey protein gels

The transition from a clear whey protein isolate gel (25 mM Na) to an opaque gel (500 mM Na) was studied by a fast responding fibre optic probe. The gels, formed by gradually increasing Na concentration, showed a progressive decrease in water holding capacity (WHC) which plateaued at 300 mM. The fibre optic probe was able to detect the differences in the gel's WHC (r=0.89; P less than or equal to 0.001); whereas, a regular surface colour meter was not as useful (r=0.72). The gel's ability to deform (spread out during compression) also decreased with the increase in [Na] and was highly correlated with the probe readings (r=0.92; P less than or equal to 0.001); the surface colour meter only provided r=0.78. The specific design of the probe which made it sensitive to scattering light was used to explain the differences between the two light measuring systems. Overall, the probe will allow a rapid assessment of WPI gel quality in the transformation region. Copyright (C) 1996 Canadian Institute of Food Science and Technology.