Effect of ι-Carrageenan on Mechanical and Swelling Properties of Heat-Induced WPI Gel

The effect of ι-carrageenan (ι-CG) on the rheological, textural, microstructural, and chemical properties of whey protein isolate (WPI) gel was studied. Gel formulations (12 or 15% total solid (TS)) containing 0, 0.2, and 0.4 wt.% ι-CG were prepared by heating method. Puncture tests demonstrated that both increasing the total biopolymer concentration (from 12 to 15 wt.%) and incorporating ι-CG enhanced the rigidity of the gels. The gel strength was also increased from 0.09 N in the 12% WPI control sample to 2.06 N in the gel composed of 14.6% WPI and 0.4% ι-CG. Normalized stress relaxation data indicated that the addition of ι-CG raised the magnitude of both k₁ and k₂ parameters. On the other hand, incrementing the total biopolymer and ι-CG concentration decreased swelling of the gels, although gel fraction did not change significantly. A rise in storage modulus (G^′) and a fall in time and temperature of gelation were observed for all samples by increasing the total biopolymer and ι-CG concentration. SEM images revealed that augmenting the ι-CG content led to the formation of larger pores with thicker walls in the gel network. FTIR spectra showed changes in the intensity of amide groups and conformational transition of WPI due to mixing with ι-CG.