1.College of Food Engineering and Nutritional Science,Shaanxi Normal University,Xi’an 710119;2.China
To study the characteristics of differential scanning calorimetry (DSC) of freeze-dried goat milk and guide the production and processing of goat milk, the fractionation of raw goat milk was carried out by means of centrifugal separation, isoelectric point sedimentation and filtration. The fractionation components, such as skimmed goat milk, cream, whey and caseins, were turned into powder after vacuum freeze-drying for 48 hours. The freeze-dried samples were scanned by differential scanning calorimeter to obtain and analyze the DSC thermal phase diagram. The results from DSC thermal phase diagram of the goat milk and each fraction showed two endothermic peaks (a, b) related to fat melting, one endothermic peak (c) related to melted protein denaturation, one complex exothermic peak (d) produced by lactose melting, one glass transition temperature Tg" induced by lactose, one glass transformation temperature Tg" caused by casein. All above-mentioned thermal transformations were not isolate and could not be observed in a single component, which was due to the phenomena of mutual masking, superposition and delay existed among different components. After the whole milk powder was fractionated into cream and skimmed milk powder, the glass transition temperature of lactose and the endothermic melting of fat were changed. After the fractionation of skimmed milk powder into whey and casein, the glass transition temperature, protein denaturation, heat absorption and other indexes were also changed. The DSC could be used as a tool to study and evaluate the physical properties of freeze-dried goat milk powder and to identify the milk components, the crystal and content of cream, the types of milk protein, and skimmed or not. These results might provide theoretical support to explain the unique characteristics, functions and commercial value of freeze-dried goat milk powder products.