NAME: POPOOLA, Ibijoke Ibironke
MATRIC NO: PG 13/0795
CENTRE: World Bank Africa Centre of Excellence in Agricultural Development and Sustainable Environment (CEADESE)
PROGRAMME: Food Processing and Value Addition
DEGREEAWARDED: M. Ag SE. Food Processing and Value Addition
Date of Oral Examination : 7th May 2018
Session:                                    2013 / 2014



Pasteurization temperature, incubation temperature and time are some of the important processing parameters for the development of fermented dairy products with desired qualities. This study investigated the effects of processing parameters on physico-chemical and microbiological qualities of West African Dwarf (WAD) goat milk yoghurt and also compared some sensory qualities and acceptability of the optimized milk yoghurt from goat and cow milk yoghurt as control. Response surface methodology (RSM) based on Box Behnken design was used to optimize the processing parameters; pasteurization temperature (PT; 80 – 85 °C), incubation temperature (IT; 40 – 45 °C) and incubation time (ITm; 2.5 – 4.5 h), while pH, titrable acidity, total solids, fat, protein, viscosity, total plate, fungal, lactic acid bacteria, and coliform count were determined using standard laboratory procedures. Aroma, taste and mouth-feel were monitored for the sensory qualities.  The acceptability of the products were evaluated using thirty untrained panelists. Data were analyzed using quadratic polynomial models and analysis of variance. Numerical optimization technique was used to obtain the optimum processing parameters for WAD goat milk yoghurt. The values for pH, titrable acidity, total solid, viscosity, fat, and protein content of goat milk yoghurt were in the range 4.35 – 5.97, 0.57 – 3.70%, 13.54 – 32. 64 mg/L, 130158 – 272712 mm2/s, 4.00 – 10.33% and 3.24 – 28.44% respectively. The total plate, fungal and lactic acid bacteria counts ranged from 5.0 × 104  to 3.5 × 105 cfu/ml, 1.0 × 104 to 2.4 × 105 cfu/ml and 2.0 × 104 to 5.50 × 106 cfu/ml respectively with no growth detected for coliform counts. Sensory assessment for the yoghurts showed that optimized WAD goat yoghurt had a sensory rating of 6.07 to 6.37 while cow yoghurt had a rating of 7.73 – 8.20. Significant (p<0.05) differences were observed among the optimized goat and cow milk yoghurts. The coefficient of determination (R2) of the quadratic models ranged between 0.60 and 0.97 while F-value was from 1.15 to 24.89. Also, pH was significantly (p<0.05) affected by IT and ITm while titrable acidity was significantly (p<0.05) affected by PT and ITm. PT significantly (p<0.05) affected the total solids. Viscosity and protein were significantly (p<0.05) affected by PT, IT and ITm (quadratic term), while fat was significantly (p<0.05) affected by IT and ITm (quadratic term) as well as PT and IT (interaction term). Total plate and fungal counts were significantly (p<0.05) affected by interaction of PT, IT and ITm in addition to the quadratic term of PT and IT. In conclusion, the optimum processing parameters for WAD goat yoghurt was found to be PT of 84.24 oC, IT of 44.22 oC and ITm of 3.8 h with optimized WAD goat milk yoghurt had a higher mean value for its protein content than cow milk yoghurt.



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