ABSTRACT

The study investigated the effect of addition of soy protein isolates on the nutrient composition and rheological properties of soy yoghurt. Soybean seeds (1kg) were processed into liquid soy milk using conventional method. Soy protein isolates (procured from Jumia Nigeria) was mixed with the soy milk at 0% (SY2), 2% (SY3), 4% (SY4), 6% (SY5), 8% (SY6) and 10% (SY7); and the mixture processed into soy yoghurt using a commercial starter culture (Streptococcus thermopthilus and Lactobacilus bulgaricus). The yoghurts were analysed for quality characteristics. There were decrease in moisture content, fat, and carbohydrate contents as the soy protein isolate increased in the yoghurt samples. Moisture content ranged from 79.86 to 84.42%. Conversely, protein content increased and ranged from 4.81 in SY2 (soy yoghurt with 0% protein isolate) to 12.43 in SY7 (soy yoghurt with 10% soy protein isolates), but was 3.59 in SY1 (cow’s milk yoghurt, the control). Addition of soy protein isolate decreased syneresis from 42.75 in SY2 to 28.25 in SY7, pH from 4.58 in SY2 to 4.41 in SY7. But, increased viscosity from 406.36cP in SY2 to 501.97cP in SY7. Total solids (g/100g) and density (kg/cm3) improved. Total bacterial count (cfu/ml) varied indiscriminately at below acceptable minimum standard. But, no coliform was detected in the yoghurt samples. The control (cow milk yoghurt, SY1) had similar value of microbial load with the soy milk yoghurt. All the soy yoghurt samples were acceptable as the scores for all the sensory attributes ranged from 4.65 to 7.25, which were within dislike slightly to like moderately in the hedonic scale. The sensory scores were at most in SY4 (4% soy protein