Effect of Storage period on the chemical composition and sensory characteristics of soy milk — made Yoghurt

Abstract

This study was carried out to investigate the effect of storage period 
on the chemical composition and sensory characteristics of Yoghurt 
made from milk partially substituted with soymilk. 
Yoghurt was made from cow's milk substituted with 5, 10 and 20% 
(v/v) soymilk plus the control sample (whole cow's milk). The starter 
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 °C. 
Chemical composition of milk as well as the final product was 
determined (fat, protein, total solids, solids-non-fat, ash and acidity) at 
0, 3 and 7 day intervals. Sensory evaluation (colour, flavour, 
consistency, taste and overall' acceptability) was carried out using 
untrained panelists at 0, 3 and 7 day intervals. 
The storage period affected the chemical composition of yoghurt, 
indicating that yoghurt analyzed at day zero (immediately after 
manufacture) had higher fat (P<0.05), protein (P<0.05), total solids 
(P<0.01) and ash (P<0.05) contents, followed-by day 3 and the least 
values were obtained at day 7. the storage period did not affect 
(P>0.05) the solids-non-fat content of yoghurt. The acidity increased 
with time (P<0.01). 
The period of storage did not significantly affect (P>0.05) the 
colour, consistency, taste and overall acceptability of yoghurt, while 
there was significant variation (P<0.05) between the periods of 
storage in flavour.