Effects of calcium level on the structure of pre-heated whey protein isolate gels

Abstract

The effects of Ca level (10–360 mmol/L) on the gelation, at room temperature, of pre-heated whey protein isolate (100 g/L, pH 7.0) were investigated. At a low Ca concentration a clear gel was formed. Scanning and transmission electron micrographs (SEM, TEM) revealed the formation of a fine protein strand microstructure. As the Ca level increased, larger and thicker strands were formed. This was associated with a progressive reduction in the gel's clarity as was measured objectively with a colour meter. At 180 mmol/L Ca, TEM micrographs showed large aggregate formation which was associated with a significant reduction in water-holding capacity. Using 360 mmol/L Ca resulted in a gel similar to the 180 mmol/L treatment. Shear stress at fracture increased as the Ca level increased up to 180 mmol/L Ca and then levelled off. Shear strain decreased with the increase in Ca. The same was observed for water-holding capacity, indicating that the fine strand microstructure could hold moisture better than the aggregated structure. In a heat-induced gel (produced for comparison purposes) low Ca concentration (10 mmol/L) formed a typical opaque, aggregated gel. The water-holding capacity and shear stress values of the cold set gels were significantly higher than that of the heat-induced gels.