PRODUCTION OF COMPOSITE YOGHURT FROM BLEND OF SOY MILK AND COW MILK USING MIXED LACTIC STARTER CULTURES ISOLATED FROM AQUARAPHA YOGHURT

ABSTRACT
The need to improve our vegetable protein consumption in order to reduce the incidence of protein deficiency diseases cannot be over-emphasized. This research was premised on evaluating the appropriate levels of substitution of cow milk with soya milk to produce composite yoghurt. Eight hundred (800) grams of soya bean seeds after sorting out foreign materials and washing were used
to produce 4.0 liters of soya milk (20% total solids). Cow milk (20% TS) was blended with soya milk in the ratio of 1CM:1SM (sample A), 2CM: 1SM (sample B) and 3CM:1SM (sample C). One hundred percent (100%) whole cow milk solution (20% TS) was also prepared to serve as control (sample D). The blends were pasteurized at 85oC for ten minutes, cooled to 45oC and inoculated with 20mls each of mixed starter broth culture of Lactobacillus bulgaricus and Streptococcus thermophillus isolated from Aquarapha yoghurt using MRS agar medium. The samples were incubated for 24 hours and subjected to physicochemical and sensory evaluations. The results of physicochemical analysis showed that the pH of sample A, B, C and D was 5.0, 4.50, 4.0 and 3.8 respectively. The total acidity as lactic acid was 0.85, 0.92, 1.20 and 1.4 respectively. Microbiological analysis showed that there were no microbiological contaminants in
all the samples. The results of the sensory evaluation of the composite yoghurt samples using taste, aroma and texture as sensory attributes showed that there was significant difference between the control D and sample A while there was no significant difference between the control, sample B and C at 95% confidence level. Conclusively, composite yoghurts with acceptable qualities can
be produced from the blend of soy milk and cow milk up to 25-33% soya milk substitution.