# Valorization of Spent Osmotic Solutions by Production of Powders by Spray Drying
## 3 Results
### Yield
However, the results are difficult to compare because in the research cited above, the yield of SD was not presented. Recently, inulin was tested by [PERSON] et al. [16] as a carrier for SD of spent osmotic solution--tomato concentrate used for garlic dehydration. They concluded that the properties of inulin as a carrier are worse than for MD--Y values were as low as 2.75-14.12% (depending on the level of addition and the inlet air temperature), while with MD, it was in a range from 13.52 to 28.83% (thus it was also lower than the limit of 50% of successful SD). Figure 1: The yield of spray drying and SEM pictures (mag. 500\(\times\)) of powders obtained from different raw materials—spent osmotic solutions: sucrose (SUC), honey buckwheat (BWH), acacia honey (ACH), apple juice concentrate (APP), chokeberry juice concentrate (CHO), cherry juice concentrate (CHE), mannitol (MAN). a–e: Different letters indicate statistically significant differences between mean values (HSD Tukey, \(p<0.05\)). Figure 2: PCA biplot diagram. Vectors are dependent variables: drying yield (\(\gamma\)) and physical properties of the powders: median particle size (D50), polydispersity index (PDI), moisture content (MC), water activity (aw), hygroscopicity (H), solubility (WSI), loose bulk density (DL), tapped bulk density (DT), and Hausner Ratio (HR). Points are experimental variants; powders obtained from different raw materials—spent osmotic solutions: sucrose (SUC), honey buckwheat (BWH), acacia honey (ACH), apple juice concentrate (APP), chokeberry juice concentrate (CHO), cherry juice concentrate (CHE), and mannitol (MAN). Mannitol is a compound from a different group than the rest of the OSs. It is not a sugar-rich material, but a sugar alcohol, characterized by low hygroscopicity, high water solubility, and low toxicity [51]. It is approved for pulmonary drug delivery and has been investigated as an alternative carrier for dry powder inhalers [52; 53; 54], diluent in tablet formulations [55], and was also tested as a superior anticaking agent for spray dried hydroxopropyl-beta-cyclodextrintrin microcapsules [51]. Mannitol is commercially available in spray dried form [55]; thus, it is not a problematic material to be spray dried, in contrast to sugar-rich materials. Even though there can be some issues during the SD of mannitol, they relate to the final form of the particles. Mannitol can exist in different polymorphic forms or mixtures of polymorphs, as well as amorphous materials. [PERSON] et al. [52] reported that pure mannitol does not normally exist in the amorphous state after SD or freeze-drying. This was also confirmed by [PERSON] et al. [55], who reported that after SD, there was no amorphous material within the samples. However, mannitol may crystallize in three different polymorphs during SD, with slightly different crystal habits, possibly leading to different surface topographies [52]. Because polymorphism, particle size, and surface roughness can affect the final suitability of mannitol as a carrier for dry powder inhalers, the SD of mannitol is still a topic of interest, but none of the available papers on mannitol SD concern the yield of SD. Therefore, it was expected in the current study that Y of MAN should be high. However, on the other hand, it is known that Y can be affected, for example, by particle size, moisture content, or bulk density, because they can also affect the cyclone efficiency. MAN had the smallest particle size (Figure 3, Table 2), the lowest moisture content, and bulk density (Table 2) among all samples; thus, this could be the reason for the decreased Y--the smallest and lightest particles were probably unable to separate in the cyclone, being easily blown out of the cyclone in the outlet air [56].