## 2 Results and Discussion
### Application of the HS-SPME/GC-MS Method to Strawberry Fruit Samples
#### 2.2.4 Terpenes  
Terpenes are of particular interest in strawberries since these compounds have characteristic sensory properties and are known to exert antimicrobial activity [28]. Among these compounds, volatile monoterpenes (C10) and sesquiterpenes (C15) were identified in most soft fruits. The monoterpene linalol and the sesquiterpene neerhold are the main and most important volatile terpen in cultivated strawberry fruits, whereas \(\alpha\)-pinene, \(\beta\)-myrcene, \(\alpha\)-terpineol, \(\beta\)-phellandrene, and myrtenyl acetate have been identified in wild strawberries [3; 20]. In the current study, a total of 33 terpenoid compounds were detected in all the analyzed strawberry samples, accounting for 41.57%, 39.89%, 23.32%, 19.48%, 16.14%, and 15.14% of total volatiles in frozen, freeze-dried, microwave-dried, oven-dried (60 \({}^{\circ}\)C), oven-dried (45 \({}^{\circ}\)C), and shade air-dried strawberry samples, respectively, with respect to 18.28% in fresh samples. It is noticeable that total terpene percentage increased after freezing, freeze-drying, microwave-drying, and oven-drying (60 \({}^{\circ}\)C), whereas oven-drying (45 \({}^{\circ}\)C), and shade air-drying decreased this percentage. As for the effect of temperature on volatile terpenes, a previous report revealed that the terpene content in the \"Akihime\" strawberry cultivar after 9 days of storage at low temperature declined less than that at room temperature [38], whereas another study found that, in white \"Sweet Charlie\" fruit cultivar, after storage at 15 and 25 \({}^{\circ}\)C, terpene level increased with elevation in temperature [3; 39]. In this study, linalod was the major terpene in the fresh strawberry fruit followed by meridolod, and it was reported that linalod is present in large amounts in some strawberry cultivars [32]. Interestingly, the intensity of meridolod in all treatments was much greater than in the fresh strawberry; while linalod intensity decreased in all samples except in the freeze-dried sample. In a previous study, terpenes were reported as the least intense aroma components contributing to floral aroma notes of strawberries [32]. Linalod was classified as a citrus, floral [32], or lemon-like aroma note [11], and meridolod was categorized as a fir/pine-like aroma [11]. In addition to the reasonably high amounts of the monoterpene linalod and the sesquiterpene meridolod, these two compounds were accompanied by small or trace amounts of other terpen, such as \(\alpha\)-terpineol, D-limonene, caryophyllene, _cis-\(\beta\)-farmesene, myrtenol, myrtenyl acetate, and terpinolene, and these results are consistent with the literature [26; 28]. \(\alpha\)-Terpineol has been reported as a potential off-flavor metabolite in strawberry juice [28; 34]. In general, esters were the major class and were found in high contents in fresh strawberry fruit (36.96% of total volatile fraction); however, after freeze-drying and freezing (1 week), terpenes became the major class, corresponding to 39.89% and 41.57% of the total volatile fraction, respectively (Table 1). Relatively high concentrations of terpenes could be used to distinguish among genotypes such as Senga, Senga, Bounty, and Jonsok, whereas other compounds related to the class of esters and acids might also be used for classification purposes [28; 40].