ABSTRACT
Yoghurt is a fermented milk product produced by bacteria fermentation of milk which is consumed all over the world. This study investigated the physico-chemicals, sensory attributes and microbial analysis of yoghurt made from powder milk and tiger-nut milk. Powder milk-tigernut milk yoghurt was produced in the following ratio and coded. ABE (90:10), FBE (80:20), DCF (70:30), BDI (60:40), BEG (50:50) and EFE (100% powder milk as control sample). The results revealed that the protein, fat, ash and the total energy content of the yoghurt were all increased as the level of the tiger-nut milk in the yoghurt increased. The moisture content ranged from 84.24 to 92.15%. There were significant different (p ≤ 0.05) in the total carbohydrate content, the total carbohydrate ranged from 0.35 to 10.67%. The pH of the sample BEG and EFE was not significantly different (p ≤ 0.05), so also ABE and DCF. However, the EFE had the lowest pH value. The total solids ranged from 12.09 to 16.31% with sample EFE having the highest value of 16.31% total solids. Titratable acidity (TTA) ranged from 1.04 to 6.02% with EFE having the highest value of 6.02% TTA. The results of the colour parameters revealed that EFE had the highest value for lightness (L*) and colour intensity (∆C) of 85.58 and 87.88 respectively. There were significant different (p ≤ 0.05) in the hue angle (H*=tan b*/a*) as the level of the H* increased with the increased level of the tiger-nut milk. The value of a* (redness/greenness) decreased as the tiger-nut milk increased while the b* value (blueness/yellowness) was risen and fallen as the tiger-nut milk increased. The deltachroma value (∆C) of ABE had the highest value of 19.89. The microbial results under refrigeration temperature at 4oC showed that as the level of the tiger-nut milk increased, the microbial loads increased particularly on the total viable bacterial count (TVC). The total fungal counts (TFC) also showed a similar trend but the EFE had the highest count of 6.10 × 103 cfu/ml during the fourth week of the storage. The total coliform counts (TCC) was detected only on the sample BDI and BEG throughout the storage period below the limit of detection (LOD) of microbial count. However, the microbial loads of all the samples were within the acceptable limit. The sensory quality of the samples showed that there were significant different (p ≤ 0.05) in all the parameters analyzed. The highest taste, colour aroma and overall acceptability was recorded for ABE while, the mouth feel was recorded for FBE.
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