Preparation and Quality Evaluation of Raw Milk and Yoghurt Sourced from Machine Milked Jersey Cows

摘要

In this study, there was preparation of yoghurt from the raw milk of machine milked Jersey cows. Physicochemical parameters, mineral composition, microbiological qualities and sensory evaluation of raw cow milk and yoghurt samples were examined. Correlations between the proximate parameters versus sensory perception attributes of yoghurt were analysed. The results showed that the pH, titrable acidity, moisture and ether extract contents were significantly (P<0.05) higher in the raw cow milk than in the yoghurt. However, the values recorded for specific gravity, viscosity, protein, ash, carbohydrates and mineral contents were higher (P<0.05) in the yoghurt than in the raw cow milk. The total viable bacterial counts were 8.2 x 10 2 cfu/ml for raw cow milk and 3.7 x 10 3 cfu/ml for yoghurt; total fungal counts were 3.1 x 10 2 cfu/ml for raw cow milk and 9.6 x 10 2 cfu/ml for yoghurt; while coliform was absent in both samples. The sensory attribute scores for the yoghurt samples were all very high and ranged between 7.17 and 8.17 on a nine point hedonic scale. There were significant (P<0.01) but negative correlations between moisture content versus taste, aroma and texture of yoghurt (r = - 0.7.28, - 0.541 and – 0.971 respectively). There were also, strong positive correlations between fat content versus aroma and texture (r = 0.574, 0.500 respectively). Based on the findings of this study, it was concluded that the raw milk and yoghurt sourced from machine milked Jersey cows were of good physicochemical, microbiological and sensory qualities and these could serve as prove that good hygienic practices were observed on the dairy farm. Also, the yoghurt was found to be more acidic, had higher specific gravity and viscosity, was higher in most of the nutrients such as protein, ash, carbohydrates and the minerals (calcium, phosphorus, magnesium, sodium and iron) than the raw cow milk from which it was prepared.