Effect of partial substitution of cows milk by soymilk on the composition and sensory characteristies of yoghurt [Sudan]

This investigation was carried out to study the effect of partial substitution of cow's milk with soymilk on the quality substituted with 5, 10 and 20 (V/V) soymilk plus the control sample (whole cow's milk). The stater culture was added at the rate of 3 (V/V) (1:1 combination of streptococcus thermophilus and Lactobacillus bulgaricus) and stored for 7 days at 4 Daraja C. Chemical composition of milk as well as the final product was determined (fat, protein, total solids, soilds-non-fat, ash and acidity) at 0, 3 and 7-day intervals. Moreover, sensory evaluation (color, flavor, consistency, taste and overall acceptability) was carried out using untrained panelists at the same intervals. The results showed that yoghurt made from control sample had higher fat content (P0.001), protein (P0.01), total solids (P0.001) and solids-non fat (P0.01) cotents, while the lowest values were obtained by the product made from 20 soymilk. The ash content had the highest value in yoghurt made from 5 soymilk and lowest value in yoghurt made from 20 soymilk (P0.001). The acidity was high in 5 soymilk yoghurt while low in 10 soymilk sample (P0.001). The sensory evaluation showed that yoghurt made from control sample scored the highest in color (P0.05), taste (P0.01) and overall acceptability (P0.01), while that made from 20 soymilk scored the lowest. However, the flavor score was highest in 20 soymilk yohurt, although there was no significant difference between means (P0.05). The consistency did not show any significant difference (P0.05) although the highest score was obtained in yoghurt made from control sample and the lowest was in 20 soymilk yoghurt. The storage period affected the chemical composition of yoghurt, indicating that yoghurt analyzed at day zero (immediately after manufacture) had higher fat (P0.05), protein (P0.05), total solids (P0.01) and ash (P0.05) contents, followed by day 3 and the least values were obtained at day 7. The storage period did not affect (P0.05) the solids-non-fat content of yoghurt. The acidity increased with time (P0.01). The period of storage did not significantly affect (P0.05) the color, consistency, taste and overall acceptability of yoghurt, while there was significant variation (P0.05) betwwen the periods of storage in flavor. The interaction between concentration of soymilk and storage period did not significantly (P0.05) affect the chemical composition except the total solids content (P0.05). The sensory attributes were not significantly (P0.05) affected by the interaction