Physiochemical composition, sensory properties and keeping quality of functional yoghurt produced from milk-soy flour blends

Present study was aimed to investigate the potential of utilizing milk powder in combination with whole soybean flour for the production of functional yoghurt. Yoghurt samples A (control), B, C, D and E were produced at 0%, 10%, 20%, 30% and 40% of milk (nunu) substitutions with whole soybean flour. The physico-chemical properties, sensory evaluation, and keeping quality of the different yoghurt samples were investigated using standard methods. All data were statistically analysed and significance difference was accepted at 5% probability level. The physico-chemical analyses results obtained showed a decrease in total solids (21.71-9.98%), total solids-not-fat (20.13-6.19%), titratable acidity (1.17-0.80%) and viscosity (10.65-0.97 Pa.S) with an increase in pH (4.10 - 5.01) and peroxide value (2.50 – 8.50meq/kg). Proximate values increase remarkably for moisture (78.20-86.23%), Ash (0.19-1.20), protein (2.98-9.14%), fat (1.02-3.42%) and fibre (0.00- 2.37%). A reverse trend was observed for carbohydrate (16.60-1.02%). pH, titratable acidity, viscosity and peroxide value of yoghurt samples evaluated during 19 days of storage at 50 C revealed a decreasing trend in viscosity throughout the storage period and in pH up to 16th day. Conversely, titratable acidity and peroxide value increased in all samples but higher titratable acidity values and peroxide value values were recorded for whole soybean enriched yogurts compared to the control (all milk yoghurt) after the 4th day and throughout the storage period respectively. The sensory evaluation result showed no significant difference (P > 0.05) between the control and sample B in aroma and appearance but a significant difference (P<0.05) between the control and the enriched samples was recorded for taste, mouth-feel and overall acceptability. It was concluded that the blend containing 90% milk powder and 10% whole soybean flour had the best potential for the production of yoghurt which would be acceptable.