Abstract

The effect of whey protein concentrate enrichment on the electrical and themophysical characteristics of pasteurized yoghurt was studied. Six samples consisting of control (unpasteurized yoghurt without whey) and yoghurt pasteurized at 50°C for 12 min and enriched with 0, 3, 6, 9 and 12% whey protein concentrate (WPC) were used. Results showed that electrical conductivity (G) increased with both temperature and whey protein concentrate. At 15 to 30°C and constant whey concentration of 3%, G ranged from 0.643 to 0.677 μΩ^‑1.cm^‑1. Similarly, at 12%, G ranged from 0.643 to 0.725 μΩ^‑1. cm^‑1 corresponding to the same temperature range. Specific heat of samples increased significantly (p < 0.05) with increase in WPC from 5.812 to 10.823 Jkg-¹K-¹corresponding to 0 to 12% WPC. At constant temperature of 25°C, density increased from 1645 to 1655 kgm^-3 corresponding to 3 to 12% WPC. Statistically, there was no significant difference (p ≥ 0.05) in density among samples. Rheological characteristics of samples indicated that the consistency index and apparent viscosity decreased generally with temperature but increased with whey concentration. Both apparent viscosity and consistency index decreased with shear rate indicating shear thinning. The flow behavior index did not show any defined trend with changes in temperature but was generally less than one (n<1) indicating that the samples are pseudoplastic. The activation energies of samples decreased with temperature and increased with shear rate.

Key words: Protein enrichment, yoghurt, protein concentrate.