# Valorization of Spent Osmotic Solutions by Production of Powders by Spray Drying
## 3 Results  
### Yield  
The yield (Y) of SD was dependent on the type of raw material and varied from 6 to 92% (Figure 1). According to the criteria presented by [PERSON] et al. [31], successful SD at the laboratory and pilot scales should have a Y above 50%; therefore, only two materialscould be classified as efficient: SUC and BWH. This was strongly related to the chemical composition of the OSs and the relationship between the carbohydrate profile and \(T_{g}\). It is well known that sucrose has a higher \(T_{g}\) (62 \({}^{\circ}\)C) than the low-molecular-weight sugars glucose (31 \({}^{\circ}\)C) and fructose (5 \({}^{\circ}\)C) [32]. Thus, SUC, characterized by a higher \(T_{g}\), could be dried without stickiness, which is usually observed for fruit juices or honey. This stickiness results from the difference between the outlet air temperature (OAT) and \(T_{g}\) of the material when the OAT is higher than \(T_{g}+20\)\({}^{\circ}\)C [33; 34]. The feed solution is not transformed into a powder form, or the formed particles adhere to each other and to the internal wall of the drying chamber [18; 31], which results in low drying yields. Such behavior is typical for fruit juices, concentrates, and honey, and has been presented by numerous researchers [35; 36; 37; 38; 39; 40; 41; 42]. As far as honey spray drying is concerned, in some cases, it is easier than in the case of fruit concentrates, which is also a consequence of the sugar profile. Usually, the fructose/glucose (F/G) ratio in honey varies from close to 1 (rape honey) to 1.5 (acacia honey) [43], while for various fruit concentrates, this ratio can be much higher. A much higher amount of fructose than glucose, typical for apple concentrate (F/G ratio from 2 to 6) [44], also creates higher stickiness owing to the lower \(T_{g}\) of fructose than glucose. This resulted in a low Y value of the APP variant. Similar results of lower \(T_{g}\) and powder recovery of apple powder than honey dried with the same carrier and under the same conditions were presented by [PERSON] et al. [45]. For honey powder spray dried with MD, nutriose powder recovery was 74-75%, while for apple concentrate it was 44-55%. Among different types of honey, the yield of SD can also be different because buckwheat honey contains higher amounts of proteins [46], which have higher \(T_{g}\) than sugars and can prevent stickiness due to surface activity. Protein-rich surface films can decrease particle-to-particle cohesion and particle-to-surface adhesion, as previously described by [PERSON] et al. [47] and [PERSON] et al. [32]. PCA illustrated as a biplot (Figure 2) was used to evaluate the relationship between Y, the physical properties of the powders, and the type of dried OS. According to this analysis, it can be stated that Y was the main variable which discriminated SUC and BWH powders--points SUC and BWH are located close to the Y vector. These two principal components explained 88.97% of the total variance. The first component (F1) explained 62.15% of the variance, whereas the second component (F2) explained 23.50%. A clear discrimination between the powders based on the type of OS was observed. When comparing Y of APP and ACH (honey) with the previous study cited above [45], it can be noticed that values obtained in the current work were lower. Previously, MD and nutriose were applied as carriers, while in the current study, inulin was used. Y below 20% indicates much worse properties of inulin as a carrier. Previously, other researchers also suggested inulin as an SD additive, which is effective when applied as a wall material for the encapsulation of different extracts such as green tea extract [48], anthocyanins extracted from Jussara pulp [49], or as a single carrier for sugar-rich materials, such as cranberry juice [20], orange juice [50], and blueberry juice [35]. According to [PERSON] et al. [35], inulin presents a \(T_{g}\) of 105 \({}^{\circ}\)C, which is appropriate for spray drying microencapsulation of sugar-rich juices.