The study evaluated the physical and sensory qualities of low fat yoghurt made by fortifying milk base with soy milk powder (SMP) instead of non-fat dried milk (NFDM) powder. Two batches of yoghurt were produced using 2% fat milk fortified with 1.0, 2.0, 3.0 and 4.0% of SMP or NFDM. One batch contained Maizena as stabilizer (MS). Yoghurts were produced from the fortified milk and a control without fortificant. Total soluble solids (TSS), pH, titratable acidity, viscosity, susceptibility to syneresis (STS), water holding capacity (WHC), color, whiteness index (WI) and consumer acceptability of the yoghurts were analysed. STS in SMP-fortified yoghurts without stabilizer was greater (p<0.05) than for NFDM-fortified and stabilized yoghurt. TSS, viscosity, WHC, STS and WI were higher for NFDM-fortified and stabilized yoghurts than yoghurt without stabilizer, at all the concentrations tried out. NFDM-fortified and stabilized yoghurt had higher sensory scores than that without stabilizer. SMP-fortified low fat yoghurts displayed poor physical quality compared to NFDM-fortified yoghurts. Yoghurt made using soymilk solids fortification exhibited weaker physico-chemical properties as compared to NFDM-fortified yoghurts. The fortification of yoghurt with soy solids using stabilizer is, however, recommended considering the isoflavones and mineral content in soymilk.
Key words: Yoghurt, fortification, soya solids, milk solids, syneresis, stabilizer.
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