PHYSICO-CHEMICAL, SENSORY AND MICROBIOLOGICAL QUALITIES OF HOMEMADE YOGURT USING COMMERCIAL STARTER CULTURE

This research was initiated with the objectives of evaluating the physico-chemical, sensory and microbiological qualities of four homemade yogurt treatments. Fresh morning milk was collected from Andassa Livestock Research Center farm, thoroughly mixed, transported to Bahir Dar University for yogurt preparation. The milk samples were homogenized at 800rpm for three minutes and filled in to coded cups of 300ml capacity. The four yogurt treatments were pasteurized milk inoculated with starter culture containing thermophilic yogurt culture (YoFlex®) at 42oc (T1), pasteurized milk inoculated with plain yogurt at 42oc (T2), pasteurized milk inoculated with plain yogurt at room temperature (T3) and unpasteurized milk inoculated with plain yogurt at room temperature (T4). The treatments were subjected to physico-chemical and microbial count laboratory analysis and sensory evaluation, on the 1st, 7th, 14th and 21st day of storage. The analysis was done in duplicate and the design was a 4*4*2 factorial design. The results obtained showed that the mean moisture content of the treatment yogurt ranged between 86.52 and 88.26%, without showing significant difference between each other. The entire treatment yogurt seems to have a relatively long shelf-life because of the high acidity value of 4.3-4.5 recorded. Mean titratable acidity level of the yogurt ranged from 0.86 to 0.94 compare to the mean titrable acidity level of 0.67 - 0.95 recorded for good quality traditional yogurt in the area. The total solid content of the yogurt treatments ranged between 6.8 and 7.3. Relatively higher fat content of 9.88-10% was obtained from both yogurt treatments T1 and T2. The result of microbiological analysis indicated that the analysis ranged from <0.1 – 11420 (*10² cfu/ml) of Coliforms and 0 – 834 (*10² cfu/ml) of yeast and mold count. All the yogurt treatments studied fit into acceptable range set for good quality yogurt throughout the storage periods. Based on the panellist's sensory evaluation the yogurt treatment T4 ranked first in acceptance followed by T1. Testing different types of commercial starters in the area of, affordability and accessibility in the market seems to be the future direction of research.