Özet:

Yoghurt is one of the most popular fermented dairy products with wide acceptance worldwide due to its nutritional and health benefits. However, the commercial production of yoghurt has been limited due to the poor quality stability in storage. The present study is concerned with development and characterization of value-added foam-mat dried yoghurt powder. The effects of different ingredient formulation and processing parameters on some selected nutritional and functional properties of the developed yoghurt were evaluated. A four-component, six-processing parameters, constrained D-optimal mixture-process experimental design, with 59 randomized experimental runs, was employed. The formulation design constraints were: raw yoghurt (80%), moringa seed extract (5% - 13%), ginger extract, (5% - 13%), and foaming agent (2% - 7%). The design constraints of the processing parameters investigated were: pasteurization temperature (50°C - 80°C), pasteurization duration (5min - 30min), fermentation duration (5hr - 10hr), mixing duration (2 min - 10 min), drying temperature (50°C - 80°C), and drying duration (2hrs - 5hrs). Quality properties evaluated include moisture content, ash content, crude protein, fat content, carbohydrate content, pH, total titer acid, total lactic acid bacteria and fungi counts. Data collected were analyzed using Design Expert 11.0.0 software package. Model equations were developed to adequately relate the quality indices to the mixture component proportions and processing parameters. The adequacy of the model equations were evaluated statistically. The effects of the components formulation proportions and processing parameters on the nutritional quality of the foam-mat dried powdered yoghurt were studied and the optimum conditions for the production of foam-mat dried yoghurt were obtained. Numerical optimization, via desirability technique was utilized to determine the optimum formulation conditions for the foam-mat dried yoghurt. The result of optimization of the formulated foam-mat dried yoghurt gave optimized foam-mat dried yoghurt with overall desirability index of 0.514, based on the set optimization goals and individual quality desirability indices. The optimal foam-mat dried yoghurt was gotten from 80 % raw yoghurt, 13 % moringa seed extract, 5 % ginger extract, and 2 % foaming agent. The optimized processing conditions were 800C pasteurization temperature, 30 minutes pasteurization duration, 10 hours fermentation duration, 10 minutes mixing duration, 800C drying temperature, and 5 hours drying duration. The quality properties of this optimal formulated foam-mat dried yoghurt are: 27.1 % moisture content, 10.1 % crude protein, 0.673 % ash content, 1.43 fat content, 58.4 % carbohydrate, 4.05 pH, 2.58 % total titre acid, 2.23E+05 CFU/g total lactic acid bacteria, and 3.81E+06 CFU/g fungi count. The result of the study showed that the optimized formulated foam-mat dried yoghurt was found to be of high quality.

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