Application of differential scanning calorimetry to freeze-dried milk and milk fractions

The thermal profiles of whole freeze-dried raw milk, obtained by differential scanning calorimetry (DSC) upon heating, were compared to those of their concentrate fractions (cream, skimmed milk, acid casein and whey) in order to associate the thermal peaks with the related components. Two peaks associated with fat melting, a glass transition attributed to caseins and a complex exothermic peak associated with lactose and its interactions with the other milk components were observed, in a close relation to the values of water activity of the samples. Freeze drying is the least invasive technique for drying milk, thus the results of this study may be attributed to the thermal transitions of milk components in their native state, unlike what is observed on roller- or spray-dried milk. The DSC technique is confirmed as an effective tool for the evaluation of the thermophysical properties of milk, as modified by different industrial processes.