## 3 Results
### Physicochemical Properties of Powders
#### 3.5.2 Moisture Content and Water Activity  
The MC of obtained buckwheat honey powders did not exceed 5% (0.9 \(\pm\) 0.2-5.0 \(\pm\) 0.4%), which in combination with water activity (\(a_{w}\)) well below 0.3 (0.088 \(\pm\) 0.005-0.190 \(\pm\) 0.005) (Figure 4), indicates good storage stability due to low free water availability for potential microbial growth and biochemical reactions [31; 43]. It can be observed that the MC of powders spray dried with MD as a carrier was significantly lower than powders with MP as a carrier, and \(a_{w}\) was higher. This phenomenon was related to proteins' ability to hold water in the amorphous matrix, resulting from the formation of a film on the particle surface; this was noted as well by [PERSON] et al. (2014), who spray dried tamarind pulp powder with whey protein concentrate (WPC) as a carrier [36]. [PERSON] and [PERSON] (2016) studied honey powders with different carrier agents, including MD and WPC, noting significantly higher moisture content when WPC was used a carrier than when MD was applied [15].  
Variants SDMD50 and SDMP50, which were spray dried at high drying temperatures, had lower MC than corresponding DASD variants due to higher heat transfer. The MC values of spray dried buckwheat honey powders were in compliance with results noted by other authors. [PERSON] et al. (2013) reported an MC of honey powders spray dried traditionally at 150 \({}^{\circ}\)C with MD and whey protein isolate as carriers (WPI) (honey solids to MD solids and WPI solids was 40:60 and 70:30, respectively) that ranged from 3.1 \(\pm\) 0.5% to 5.0 \(\pm\) 0.9% [31]. [PERSON] et al. (2015) recorded an MC of rapeseed and buckwheat honey spray dried at 180 \({}^{\circ}\)C with sodium caseinate and/or Arabic gum as a carrier (honey solids to carrier solids 50:50) varying from 3.7 \(\pm\) 0.1% to 5.8 \(\pm\) 0.3% [12]. However, it should be highlighted that in this work the drying temperature and carrier content were lower than in the present literature. Nevertheless, it was possible to obtain stable honey powders that were characterized with a WC below 5% as a result of the application of dehumidified air.  
Obtained results for \(a_{w}\) are also consistent with the literature, i.e., the results of [PERSON] et al. (2019), who spray dried rapeseed and honeydew honey with the application of dehumidified air and NUTRIOSE(r) as a carrier agent and noted \(a_{w}\) values from 0.074 \(\pm\) 0.003 to 0.178 \(\pm\) 0.006 [20]. Powders where MP was used as a carrier and its content was the highest (SDMP50 and DASDMP50) were characterized with lower \(a_{w}\) than variants where MD was applied. This phenomenon might be the result of the high water capacity of protein-based carriers in an amorphous state, which in turn lowers the \(a_{w}\) of obtained powders [44]. Moreover, it can be observed that powders spray dried with MP had the lowest \(a_{w}\), but at the same time the highest MC (thus, there was no significant Pearson correlation between these two parameters, as presented in Table A1). This phenomenon points to the likelihood that water present in the powder was bound in the structure, being unavailable for microbial growth and thus ensuring stability. Furthermore, milk proteins form a protective membrane on the particles' surface, which lowers water availability and results in lower \(a_{w}\). There was no statistically significant difference observed for powders with the lowest carrier content (DASDMD75 and DASDMP75). Obtained results point to the usefulness of MP as a carrier for buckwheat honey spray drying with regard to \(a_{w}\), which results in better storage stability.