## 3 Results and Discussion
### Sorption Isotherms  
Figure 4 presents the water adsorption isotherms for the mixtures of the powdered infant formulas. The course of the isotherms for all the mixtures was very similar.  
There were no statistically significant differences between the water contents despite the differences in the compositions of the mixtures. The amounts of water adsorbed by the M2 and M3 mixtures were at a similar level. In the M2 and M3 mixtures, the main ingredient was lactose (Table 1). The statistical differences were insignificant in the course and shape of the isotherms for all the mixtures. For all the mixtures, after reaching a water activity of 0.75, there was a sharp increase in the amount of adsorbed water (Figure 4). The lowest level of the water content at a water activity of 0.75 was observed in the M3 mixture, amounting to 6.6 g of H\({}_{2}\)O/100 g of DM, and the highest was observed in the M1 mixture, amounting to 10.35 g of H\({}_{2}\)O/100 g of DM (Figure 4).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Water Content (g H\({}_{2}\)O/100 g Product)**} & \multicolumn{3}{c}{**Water Activity (-)**} \\ \cline{2-5}  & \multicolumn{3}{c}{**Storage Duration (Months)**} \\ \cline{2-5}  & **0** & **6** & **0** & **6** \\ \hline M1 & 3.62 \({}^{\text{a}}\)\(\pm\) 0.03 & 4.07 \({}^{\text{b}}\)\(\pm\) 0.04 & 0.215 \({}^{\text{a}}\)\(\pm\) 0.002 &  
Figures 5 and 6 present the influences of agglomerations using water, lactose, and maltodextrin on the courses of the water vapor adsorption isotherms for the powdered infant formulas. There was no significant effect of the wetting liquid on the amount of water absorbed by the agglomerates. At a water activity of 0.75, the A2 agglomerate (water wetting liquid) reached a level of absorbed water of 7.2 g of H\({}_{2}\)O/100 g of DM (Figure 6). At a water activity of 0.75, the A1 agglomerate (lactose wetting liquid) reached a level of absorbed water of 9.8 g of H\({}_{2}\)O/100 g of DM (Figure 5), while the powder agglomerated with maltodextrin, A3, reached a level of absorbed water of 7.0 g of H\({}_{2}\)O/100 g of DM (Figure 6). [PERSON] et al. [20] obtained sorption isotherms for three types of infant formulas with contents of lactose above 50%. The sorption isotherms for all the powders were characterised by a similar shape and course.  
Figures 5 and 6 show the influence of the agglomeration on the course of the powders' isotherms. No significant differences were found in the course and shape of the sorption isotherms for both mixtures and their agglomerates in the water activity range from 0.0 to 0.903.  
The analysis of the sorption isotherms of the agglomerated products indicated a greater influence of the powders' composition than the agglomeration process itself. A  
Figure 5: Sorption isotherms of mixture M1 and agglomerate A1.  
Figure 6: Sorption isotherms of mixture M2 and agglomerates A2 and A3.  
difference was observed in the amount of water absorbed by the agglomerates below and above aw = 0.75, which was considered as a limit value. [PERSON] et al. [35] determined the isotherms and kinetics of the water sorption of powder mixtures, glucose, whey proteins, maltose syrup, and soy isolate. They stated that mixing components with different sorption properties resulted in uniform values of the equilibrium water content that was obtained. A large amount of protein in the mixtures increased the water sorption capacity; however, the high carbohydrate content resulted in its lowering. [PERSON] et al. [36] determined the sorption isotherms, among others, for powdered cream with fat contents of 56 and 72% at various temperatures (4, 20, 37, and 50 \({}^{\circ}\)C). It was concluded that the content of the milk fat did not influence the course of the powdered cream's isotherms.