Simple and Rapid Method for Measuring Turbidity in Gels and Sols from Milk Whey Protein

Protein isolates prepared from acid whey concentrate and cheese whey concentrate, and β-lactoglobulin were studied. Turbidity of samples was measured using a 96-well microplate and a microreader. This method allowed many (>100) small samples (< 250 μL) to be treated at the same time. At low ionic strength and at neutral to alkaline pH, samples were transparent after heating. Transparent gels could also be prepared in this region with a small amount of NaCl.     

Viscous Sol and Gel Formation from Process Whey Protein Below 25°C

The viscosity of process whey protein (PWP; whey protein preheated under salt-free conditions) solution increased and led to gel formation with incubation at ambient or lower temperature by NaCl addition. Viscosity of PWP solution (70 mg/mL, 38.3 sec^-1, 40 min incubation) either with NaCl up to 120 mM or without NaCl decreased with increasing temperature, viscosity gave straight lines in an Andrade plot below 25°C, whereas viscosity of PWP solution with NaCl sharply increased with increase in temperature above 25°C. This suggested that association of the aggregates of PWP molecules occurred above 25°C by addition of NaCl, and that network formation by such aggregates might cause gelation.