## 3 Results and Discussion
### Differential Scanning Calorimetry--Phase Transitions and Crystallisation Curves
Figure 15 presents the DSC curves of the mixtures M1, M2, and M3 and agglomerates A1, A2, and A3 obtained from them after storage. Based on the observation of the DSC curve of the stored M1 mixture, it can be concluded that the temperature range (7-45 \({}^{\circ}\)C) of the peaks corresponding to the presence of fats did not change compared to the DSC curve of the fresh M1 mixture (Figure 13). A large endothermic peak was observed in the temperature range from 65 to 125 \({}^{\circ}\)C. The occurrence of this peak indicated water sorption by the powder. The state of the water in food and biopolymers was examined by evaporating it from a sample placed in a DTA (differential thermal analyser) or DSC [53]. In the initial studies, the endothermic surface area was taken as a measure of the amount  
Figure 16: DSC cooling curves of powdered infant formula mixtures M1, M2, and M3 and agglomerates A1, A2, and A3 after six months of storage. Figure 15: DSC curves of powdered infant formula mixtures M1, M2, and M3 and agglomerates A1, A2, and A3 after six months of storage. of free water in the material, while differences in the transformation temperature and changes in the heat of evaporation were considered as indicators of the bonding strength of water with the material [53; 54; 55]. DSC allows us to determine the thermal energy needed to evaporate water. [PERSON] et al. [56] studied the influences of the relaxation kinetics and ageing of whey protein concentrate on the solubility of these proteins. They observed that as the water activity of the protein concentrate increased, weak endothermic peaks appeared in the DSC curve. The main component of the M2 and M3 mixtures (Table 1) was lactose, and it presented a large impact on the DSC diagrams. Very weak peaks were observed in the DSC diagrams of the stored M2 and M3 mixtures in the temperature range 35-110 \({}^{\circ}\)C (Figure 15). This transformation was the result of an increase in the water content in the tested sample. The DSC diagram of the stored A1 agglomerate obtained from the M1 mixture was characterised by a weak endothermic peak in the temperature range 40-125 \({}^{\circ}\)C, indicating the transformation of the evaporated water (Figure 15). The DSC curves of the stored agglomerates A2 and A3 obtained from the M2 mixture (Figure 15) did not present significant differences from the DSC curves of the fresh powders (Figure 13). The DSC diagrams of the powders after storage were characterised by a weak endothermic peak in the temperature range 44-120 \({}^{\circ}\)C, which corresponded to the evaporation of water. The water content in the tested samples of the powdered infant formulas increased during the storage period, which can be determined based on the observation of the DSC diagrams of the stored powders. [PERSON] et al. [57] indicated that the high lactose content improved the stability of the mixtures. Lactose, which was partially in an amorphous form, prevented fat oxidation and protein degradation. [PERSON] et al. [58] studied the effects of the storage conditions (time, water activity, and temperature) on egg white powder. During storage, changes in the protein structure, the loss of free amino groups, and the initiation of the non-enzymatic browning reaction (Maillard reaction) were observed. Figure 16 presents the DSC cooling curves of the M1, M2, and M3 mixtures and agglomerates A1, A2, and A3 obtained from them. In the DSC diagram of mixture M1, containing whole milk powder, broad exothermic peaks and several single peaks were observed in the temperature range from 11 to \(-\)15 \({}^{\circ}\)C. The DSC cooling curve of the M1 mixture showed the presence of three small peaks. During storage, milk fat moved from the centre of the milk powder particle to its surface [47]. On the surface of the particle, fats have increased contact with factors causing their oxidation (air, water, temperature, and light).