Abstract

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This study was aimed at determining the nutritional and sensory evaluation of soy yoghurt produced by fermentation of soymilk with Lactobacillus plantarum isolated from fermented skimmed cow milk. Lactobacillus platarum which was randomly isolated, and identified with biochemical and molecular processes underwent fermentation for 9 hours, together with commercial yoghurt starter culture containing Streptococcus thermophilus and Lactobacillus delbreuckii subsp. bulgaricus, which served as control to produce two types of fermented soy yoghurts labeled A and B respectively. Samples of the soy yoghurts were collected at 3 hours interval, analysed for proximate and physicochemical parameters, and at the end of 9 hours fermentation period, sensory evaluation was carried out. Also there was an overall drop in pH from 7.13 to 4.3 in soy yoghurt A and from 7.1 to 4.2 in B, while the titratable acidity (Lactic acid equivalent) showed an overall increase from 0.51 to 0.92% in A and 0.74- 0.90% in B. However, total solids and viscosity increased in sample A from 9.02- 13.25%, 0.3-0.5PaS and in B from 3.66-5.86%, 9.56- 13.62%, 0.24 to 0.40 PaS between 0 – 9 hours respectively. The ash, moisture and crude fat content had an overall decrease in sample A from 0.85 - 0.61% , 92.4- 92.28% and 1.92 - 0.79%, respectively and Sample B from 0.85- 0.63%, 92.87- 92.06% and 1.87- 0.85%, respectively. The protein content increased from 3.72-5.54% in sample A, and 3.66-5.86% in sample B respectively. The carbohydrate content of the soy yoghurt samples decreased after 3-9 hours, from 1.20-0.78% in sample A and 0.80- 0.60% in sample B respectively. The microbiological analysis indicated that there was an increase in cell growth of sample A containing Lactobacillus plantarum, from 3.2 log cfu/ml to 4.6 logcfu/ml and from 3.7logcfu/ml to 5.0logcfu/ml in sample B. Sample B was most preferred in terms of aroma, taste, texture, colour and overall acceptability (70% acceptability), while sample A had a 64% acceptability. The result revealed that the use of isolates from fermented skimmed cow milk in the fermentation of soy milk produced soy yoghurt of acceptability and sensory attributes similar to that produced using commercially sold starter culture.

Keywords: Soy yoghurt, Starter culture, Milk, Sensory, Acceptability