# Valorization of Spent Osmotic Solutions by Production of Powders by Spray Drying
## 3 Results
### Bulk Density and Flowability  
DL of powders ranged from 0.45 \(\pm\) 0.02 (MAN) to 0.88 \(\pm\) 0.02 g/mL (ACH) (Table 2). This range is typical for spray dried powders and is similar to that reported by [PERSON] et al. [60] for black mulberry juice powder, and [PERSON] et al. [20] for cranberry juice powder. Bulk density was significantly correlated with particle size (Table 3); higher density was observed for larger particles. The typical correlation presented by many researchers is usually the opposite--smaller particles typically tend to have higher bulk densities because of the arrangement of the particles; the particles are in close form, and there are fewer spaces between them [75; 76]. Such a correlation was presented for spray dried pitaya fruit powder [76] or spray dried microcapsules containing fish oil [77]. However, in the current work, high DL was observed for samples characterized by high stickiness during drying. The stickiness effect, leading to problems with evaporation and the formation of particles, could also affect the low internal porosity of particles and easy bed packing, both of which result in high bulk density. In contrast, MAN powder of very low particle size and SUC had the lowest bulk density. HR--the indicator of powder flowability--varied from 1.00 \(\pm\) 0.04 (APP) to 1.34 \(\pm\) 0.06 (MAN). According to the flowability criteria presented by [PERSON] et al. [78], some of the powders were in the range of excellent flowability (HR \(<\) 1.11 for samples ACH, APP, CHO, CHE), while some of them were in the range of passable flow (HR 1.26-1.34 for SUC, BWH, MAN). Contrary to the previous correlation--the correlation between HR and particle size was typical, as described in the literature--powders with smaller particles had worse flowability owing to higher cohesiveness [79]. Such a correlation was previously reported for pitaya fruit powder [76] and sugarcane juice powder [61]. According to [PERSON] et al. [80], particles larger than 250 \(\upmu\)m flow freely, whereas those less than 10 \(\upmu\)m are considered cohesive. This was explained by the fact that larger particle sizes have a smaller number of points at which particles can combine and interact with each other, which results in lower cohesiveness of the powders and thus better flow properties [81]. Additional reasons for the excellent flowability of samples ACH, APP, CHO, and CHE can be the morphology of particles (smooth surfaces) and lower PDI (more uniform particle size reduces the number of interparticle interactions) [82]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **MC** & \(\mathbf{a_{w}}\) & **H** & **DL** & **DT** & **HR** & **WSI** & **D50** & **PDI** \\ \hline Y & \(-\)0.38 & \(-\)0.75 & \(-\)0.09 & \(-\)0.53 & \(-\)0.29 & 0.68 & \(-\)0.14 & \(-\)0.72 & 0.86 \\ MC & & \(-\)0.19 & 0.70 & 0.73 & 0.68 & \(-\)0.75 & \(-\)0.50 & 0.74 & \(-\)0.71 \\ \(a_{w}\) & & & \(-\)0.44 & \(-\)0.13 & \(-\)0.36 & \(-\)0.05 & 0.17 & 0.18 & \(-\)0.32 \\ H & & & & 0.79 & 0.89 & \(-\)0.66 & \(-\)0.49 & 0.60 & \(-\)0.52 \\ DL & & & & & 0.16 & \(-\)0.57 & \(-\)0.04 & 0.19 & \(-\)0.57 \\ DT & & & & & & 0.38 & \(-\)0.12 & 0.79 & \(-\)0.71 \\ HR & & & & & & & \(-\)0.01 & 0.52 & 0.19 \\ WSI & & & & & & & 0.01 & 0.00 \\ D50 & & & & & & & & 0.05 \\ \hline \multicolumn{8}{l}{negative significant correlation} \\ \hline \multicolumn{8}{l}{-0.50} & 0.50 & 0.70 \\ \multicolumn{8}{l}{positive significant correlation} \\ \hline \hline
0.70 & 0.80 & 0.70 \\ \hline \end{tabular}
\end{table} 
Table 3: Pearson correlation matrix between the yield of drying (Y) and physical properties of the powders: moisture content (MC), water activity (aw), hygroscopicity (H), loose bulk density (DL), tapped bulk density (DT), Hausner ratio (HR), solubility (S), median particle size (D50), and polydispersity index (PDI).