Rheological and structural characterization of agar/whey proteins insoluble complexes

•Insoluble complexes between whey proteins and agar molecules were obtained.•The composition and properties of the insoluble complexes were changed by citrate.•In the absence of buffer the behaviour of gels were governed by agar.•With citrate buffer the behaviour of flocculated complexes were governed by proteins.

Complex coacervation between whey proteins and carboxylated or highly sulphated polysaccharides has been widely studied. The aim of this work was to characterise a slightly sulphated polysaccharide (agar) and whey protein insoluble complexes in terms of yield, composition and physicochemical properties as well as to study their rheological behaviour for better understanding their structure. Unlike other sulphated polysaccharides, complexation of agar and whey protein at pH 3 in the absence of a buffering agent resulted in a coacervate that was a gel at 20 °C with rheological properties and structure similar to those of simple agar gels, reinforced by proteins electrostatically aggregated to the agar network. The behaviour towards heat treatment was similar to that of agar alone, with a high thermal hysteresis and almost full reversibility. In the presence of citrate buffer, the result was a “flocculated solid”, with low water content (75–81%), whose properties were governed by protein behaviour.