## 3 Discussion  
All four drying methods investigated in this study led to an almost complete removal of moisture from fresh chopped sea fennel leaves, with a reduction in \(\mathrm{a_{w}}\) below 0.6. Undoubtedly, \(\mathrm{a_{w}}\) is one of the most important factors affecting microbial growth and toxin production, and its reduction is the main goal of food dehydration [2,27]. More specifically, an \(\mathrm{a_{w}}\) value of 0.6 conventionally represents the threshold for growth inhibition of both bacteria and cumycetes [28]. Hence, it guarantees the protection of dehydrated foods, including spices, against microbial spoilage during their shelf-life. As far as microbial viable counts are concerned, the dried samples were characterized by comparable or even higher microbial loads than fresh sea fennel. Exceptions to this trend were the samples subjected to OD at 45 \({}^{\circ}\)C, which resulted in a significant reduction in yeasts, and the samples subjected to MD, which caused a significant reduction in all microbial groups, except for spore formers. For RTD and FD, the trends observed can be easily explained by the mild and low temperatures applied, corresponding to 18-20 \({}^{\circ}\)C and \(<\)0 \({}^{\circ}\)C, respectively, which are unable to exert a microbicidal effect [29; 30; 31]. For OD, the reduction in the yeast population could again be ascribed to the specific temperature applied [32]. Finally, the reduction in the microbial loads of mesophilic aerobic bacteria, yeasts, and molds in the microwave-dried samples could be explained by the sterilizing capability of microwave treatment, which, in turn, is attributable to a combination of thermal and non-thermal effects [33]. Despite the documented capability of microwave treatment in killing bacterial spores [34; 35], some authors reported a higher resistance of bacterial endospores to microwave radiation than vegetative cells [36; 37]. This evidence might explain the microbial counts of spore formers observed in the microwave-dried sea fennel samples. Furthermore, the increase in the microbial loads of some microbial groups might be ascribed to the apparent weight loss registered in all the dried samples. Spices are foods with low water activity (\(\mathrm{a_{w}}<0.7\)), which inhibits microbial growth; however, microorganisms that survive the drying process can remain viable during storage, thus representing a potential hazard when dried spices are added to ready-to-eat or cooked foods [38; 31]. In recent years, foodborne outbreaks related to the consumption of dried herbs and spices, mainly caused by _Bacillus cereus_, _Salmonella sinfenberg_, and _Clostridium perfringens_, have been reported by the European Food Safety Authority (EFSA) [39]. As suggested by the EFSA, microbial contamination of fresh plants represents one of the main factors affecting the microbiological quality of spices; hence, proper cleaning procedures, including the use of sanitizing solutions, could enable the production of dried spices of high microbiological quality [40]. The metataxonomic analysis performed in this study revealed a higher yeast than bacterial diversity in terms of number of identified taxa. Regarding bacteria, members of the family Methylobacteriaceae prevailed in both the fresh sea fennel and dried samples. Methylobacteriaceae are a large family of _Alphaproteobacteria_ within the order _Rhizobiales_, which currently includes three genera, namely _Meganema_, _Microviga_, and _Methylobacterium_[41]. The last genus currently contains 44 validated species that are ubiquitous in the natural environment, as free-living organisms in water and soil, on the phylloplane, and in plant leaf, stem, and root tissues [41]. Further bacterial families that are generally found in soil were also identified in a few samples of dried sea fennel spices, including Caulobacteraceae [42], Gailellaceae [43; 44], and Microbacteriaceae [45]. For the identified genera, ubiquitous (_Bacillus_ spp., _Propionibacterium_ spp., and _Pseudomonas_ spp.)