Effect of sodium level on the microstructure and texture of whey protein isolate gels

The effect of sodium level (25-500 mM, at pH 7.0) on the gelation of whey protein isolate (WPI) was investigated. At low sodium level clear gels were formed. They were composed of fine protein strands, which exhibited good water holding capacity (WHC). As sodium level increased gel clarity gradually decreased. At high sodium levels (> 200 mM) aggregated, opaque gels with poor WHC were formed. Scanning and transmission electron micrographs of the gel made with 500 mM NaCl resembled the gel formed in the presence of low calcium (25 mM) level. A progressive increase in the size of the protein strands was observed as sodium level was increased up to a point where aggregates were formed. The formation of aggregates was related to a significant decrease in WHC and gel strength, indicating that the fine gel structure can hold moisture much better than the aggregated structure.