Characterization of commercial dried milk and some of its derivatives by differential scanning calorimetry

The comprehension of the thermal phenomena of milk powders is still object of investigation, being the result of complex interactions among their components as affected by composition, storage conditions and manufacturing. For a better understanding of the above-mentioned phenomena, the effect of the single milk component (proteins, casein, whey proteins and lactose) on the thermal behavior of whole and skim milk powders was investigated by means of DSC during heating. Whole milk powders exhibited two endothermic transitions related to the fat crystal melting at temperatures between 276 and 325 K. Glass transitions of lactose (309 K) and caseins (347-358 K) with their enthalpy relaxation phenomena were observed in the milk derivatives, being instead highly influenced from a (w) and composition in the dried milk. At higher temperature (353-473 K), different exothermic events, such as lactose crystallization, Maillard reaction and/or decomposition of carbohydrates and proteins, were recognized in the curves of milk and protein derivatives powders. A good explanation of the thermal properties of the milk powders was obtained from the comparison with the heating curves of the single components. Lactose resulted the key component of many thermal events, being the molecule more influenced by the environmental conditions. These results can lead to a better comprehension of the physical properties of the milk powders, fundamental for their functional and commercial quality.