# Impact of Atmospheric Pressure Microwave Plasma Treatment on Quality of Selected Spices
## 3 Results and Discussion  
### Dry Matter Content and Water Activity  
Dry matter content and water activity of plasma treated spices is presented in Figures 3 and 4. Both dry matter content and water activity changed with treatment time, and the changes depended on the type of raw material that was subjected to treatment. The highest changes of both water activity and dry matter content were found for the longest plasma application times regardless of the type of spice. For example, allspices berries after 60 s of treatment contained 0.91 kg d.m./kg of dry matter, which was around 7% more than the dry matter content obtained for untreated samples. The increment of dry matter content registered for juniper berries and black pepper seeds was equal to 2 and 3.5%, respectively. The changes of dry matter content were related to evaporation of water after the plasma treatment, since the temperature of the samples after radiation were raised (Figure 5). Similar findings were reported by [PERSON] et al. [35] who studied plasma treatment of grain and [PERSON] et al. [36] who studied impact of plasma on grain and legumes. Moreover, all the changes were significantly (\(p<0.05\)) different in comparison to control samples.  
Figure 3: Dry matter content changes after plasma treatment. The significant differences between investigated samples, based on the Tukey test results, are indicated by different small letters (a, b, c... ), capital letters (A, B, C... ) or capital letters in brackets ([A], [B], [C]... ) for different spice species (black pepper seeds, juniper berries and allspices berries, respectively). \(n=3\).  
Water activity of untreated raw materials was equal to 0.45, 0.66 and 0.74 for juniper berries, black pepper seeds and allspices berries, respectively (Figure 4). Water activity changes followed a pattern opposite to the changes of dry matter content, which was also related to the changes of temperature and enhanced water evaporation. Samples with higher dry matter content were characterized by lower activity. The lowest water activity levels were found for samples subjected to the longest treatment. Among all samples, black pepper seeds and juniper berries treated for 60 s of plasma radiation exhibited the lowest water activity, which was equal to 0.34. At the same time, allspices berries treated for the same time had water activity level of 0.56. In almost all cases, even the lowest treatment time differed significantly from the material in control samples. Only in the case of allspices berries did plasma irradiation lasting 15 s not cause any significant decrease of water activity. In fact, materials subjected for the longest plasma treatment differed significantly from all other samples regardless of the type of spice. The lowering of water activity by means of plasma application was also reported by [PERSON] et al. [37] for red pepper powder treated by microwave-powered cold plasma. The decrease of water activity was strongly related to the dry matter content and water evaporation during the treatment. It is also worth emphasizing, that the kinetics of water activity decrease was different for each raw material subjected to treatment. The fastest changes were noted for the black pepper seeds, followed by allspices and juniper berries, as indicated by the parameters of linear equations appended to Figure 4.  
Figure 4: Water activity changes after plasma treatment. Significant differences between investigated samples, based on the Tukey test results, are indicated by different small letters (a, b, c... ), capital letters (A, B, C... ) or capital letters in brackets ([A], [B], [C]... ) for different spice species (black pepper seeds, juniper berries and allspices berries, respectively). \(n=3\).  
Figure 5: Changes of samples surface temperature directly after plasma application. \(n=3\).