Rheology of acid-induced sodium caseinate stabilized emulsion gels

The storage modulus G', loss modulus G ", and phase angle delta of acid-indnced sodium caseinate emulsion gels were measured at; 25C for a certain period of time after the addition of glucono-delta-lactone (GDL). Comparison between pure protein gels and emulsion gels revealed that the presence of emulsion droplets greatly enhanced the gel strength. Acidification by mixing an emulsion with a GDL solution caused immediate gelation but the emulsion gel had similar mechanical properties to the gel formed by direct addition of GDL granules. The viscoelasticity of the gel was strongly related to the pH:value of the system. There was no evidence for a three-dimensional network when the pH value was higher than 5.8 or lower than 3.2. The largest,storage and loss moduli were observed for gels formed at pH values near the isoelectric point of sodium caseinate (pH 4.6). Rheological differences for gels made at different pH values:became distinguishable at low frequencies, where a much smaller phase angle was determined for a gel made at a pH value below the isoelectric point. Partial recovery of the three-dimensional gel network was observed for disrupted gels formed at a pH near the isoelectric point.