## 2 Results and Discussion
### Application of the HS-SPME/GC-MS Method to Strawberry Fruit Samples  
Food aroma is an important parameter to evaluate the sensory quality of fruit products and fruits. Fruit aroma production is dependent on many factors, such as cultivar, maturity, and storage conditions [7]. Aroma is characterized by a complex composition because of the presence of a wide variety of volatiles with different chemical and sensory nature. These volatile chemical compounds fall into several categories, including esters, terpenes, aldehydes, alcohols, and furanones, which are considered to be the most important aroma perception indicators for fresh fruits [18]. Particularly in commercial strawberry fruit, only 15 odor-active compounds contribute to the strawberry flavor [19], with the esters being the most important group [20]. SPME analysis of berries is a good method to understand the volatile composition of the intact fruit, and it decreases the development of byproducts; however, analysis of headspace compounds is dependent upon their individual vapor pressure. Thus, the more volatile analytes might be more easily extracted and appear at comparatively higher concentrations. This reflects the compound's contribution to the fruit aroma, but does not give its true concentration in the tissue. Thus, volatiles present in the analyzed samples are presented as relative percentage [21; 22]. In this study, our newly developed and optimized HS-SPME/GC-MS method was successfully applied in the analysis of the volatile fraction of 11 samples of fresh, frozen, and dried strawberry fruits and some commercial jams using the selected DVB/CWR/PDMS fiber. A total of 165 volatile compounds were identified in the analyzed samples (Table 1), accounting for 85.03-96.88% of the total headspace composition. The identification of all compounds was based on comparison of retention index (RI) and mass spectra with those reported by NIST 17 (National Institute of Standards and Technology), [PERSON] (2007) and Wiley library spectra [22]. The chemical classes detected in the analysed strawberry samples were esters (52 compounds), terpenes (31 compounds), aldehydes (19 compounds), alcohols (16 compounds), ketones (15 compounds), lactones (eight compounds), furanones (four compounds), and acids (four compounds) (Table 1, Figure 1). Many compounds appear to be primarily responsible for strawberry characteristic flavor such as esters (e.g., methyl butanoate, ethyl lexanoate, methyl butanoate), furanones (2,5-dimethyl-4-hydroxy-3(2\(H\))-furanone (DMHF) and its derivative), and terpenoids (e.g., linalol and meridold) [3; 18; 23; 24], all of which were detected in our samples. According to the differences in volatile composition between strawberry powders and frozen samples, it was possible to infer that each drying and freezing process affected volatile composition in a different way, and some chromatograms are reported in Figure 2. The variation in ester content, as well as that of terpenoids, furanones, lactones, alcohols, and others, is listed in Table 1. Moreover, the influence of drying treatments (oven-drying at 45 \({}^{\circ}\)C and 60 \({}^{\circ}\)C, freeze-drying, microwave-drying, or shade air-drying) and freezing on the volatile profile of strawberry fruits with respect to fresh fruits (control) and a comparison of their detected aroma volatiles are discussed below in detail.