The physicochemical and sensory evaluation of commercial sour milk (amasi) products

The physicochemical and sensory properties of five commercially available sour milk (amasi) products- AoA, AoB, AoC, AoD and AoE were analyzed in 3 batches. Samples were collected from retail shops in Thohoyandou. The products were examined forEscherichia coli, lactic acid bacteria (LAB), total plate count (TPC), pH, titratable acidity (TA), colour, viscosity and sensory properties. Microbial analysis results for LAB ranged between 1.25 × 105 and 1.97 × 106cfu with sample AoA and AoB being the highest by 1.96 × 106 and 1.97 × 106 cfu, respectively. E. coli count ranged from 1.22 × 104 to 1.78×105 cfu with sample AoE and AoC being the lowest and highest (p < 0.05), respectively. TPC had the least number of counts with the values between 4.2 × 103 and 9.1 × 104 cfu. The pH values of the products ranged between 4.22 and 4.34 and TA ranged between 0.80 and 0.84. Colour measurements gave L* values of the products ranging from 33.77 to 40.19, while a* and b* values were 3.08 to 6.43 and 13.17 to 18.77, respectively. Differences existed in viscosities of the products that were not significantly different (p < 0.05). Sensory score for the overall acceptability indicated that consumers did like the sour milk, as the values ranged from 3.8 to 4.4. Although there were significant differences (p < 0.05) in terms of sweetness, smoothness and astringency, they did not affect the consumer acceptability of the products. Presence of E. coli in the sour milk products can be of health concern to consumers.                     Key words: Sour milk, amasi, physicochemical, microbial.