## 2 Results and Discussion
### Application of the HS-SPME/GC-MS Method to Strawberry Fruit Samples
#### 2.2.2 Furanones  
Strawberries contain very low amounts of volatile furanones. However, compared to their threshold values, the furanones as a small group of aroma volatiles significantly contribute to the overall strawberry aroma [3; 28]. 2.5-Dimethyl-4-hydroxy-3(\(2H\))-furanone (furaneol, DMHF) and 2,5-dimethyl-4-methoxy-3(\(2H\))-furanone (mesifurane, DMMF) are considered the two most important furanones in strawberry, and both of them characterized by a caramel-like and sweet aroma and flavor impression [3]. These compounds have a strong \"strawberry-like\" aroma with extremely low aroma threshold values; thus, they are also termed strawberry furanone (DMHF) and berry furanone (DMMF) [25; 32]. Mesifurane is more stable than furanenol; although it resembles the typical aroma of wild strawberry, a much higher concentration of this compound has been found in some cultivated varieties [25]. In the current study, four furanones, namely, mesifurane, furnaceol, 2,4-dihydroxy-2,5-dimethyl-3(\(2H\))-furan-3-one, and dihydro-5-methyl-5-vinyl-2(\(3H\))-furanone were detected in the analyzed samples, accounting for 0.15%, 0.94%, 1.99%, 3.27%, 10.77%, and 11.44% of total volatiles in frozen, oven-dried (60 \({}^{\circ}\)C), microwave-dried, freeze-dried, shade air-dried, and oven-dried (45 \({}^{\circ}\)C) strawberry samples, respectively, compared to 0.10% in fresh samples. Mesifurane and furanenol were found in all samples, while 2,4-dihydroxy-2,5-dimethyl-3(\(2H\))-furan-3-one was only detected in oven-dried (60 \({}^{\circ}\)C) and oven-dried (45 \({}^{\circ}\)C) strawberry samples, and dihydro-5-methyl-5-vinyl-2(\(3H\))-furanone was only present in microwave- and shade air-dried samples. Mesifurane was the most abundant furanone, followed by furanenol. It has been reported that mesifurane levels increase during fruit ripening while furanenol simultaneously decreases [25], but both show similarly low odor threshold values [28; 33]. The highest percentage of mesifurane was present in oven-dried (45 \({}^{\circ}\)C) (9.30%), followed by shade air-dried (8.47%) samples, and the lowest percentage was detected in fresh strawberry (0.08%). The highest percentage of furnaceol was found in shade air-dried strawberry (1.92%), followed by oven-dried (45 \({}^{\circ}\)C) (1.89%), freeze-dried (0.04%), oven-dried (60 \({}^{\circ}\)C) (0.02%), frozen (0.02%), and fresh (0.02%) samples. Interestingly, furanone levels were increased in all drying methods especially heat-drying treatments at low (oven-drying, 45 \({}^{\circ}\)C) or room temperature (shade air-drying) and freeze-drying; consequently, the \"strawberry-like\" note or aroma would be increased or at least maintained and retained in these powders because it was reported that the abundance of furaned and mesifurane strongly contributed to \"fresh strawberry\" sensory attributes [28; 34]. Furaneol was detected in trace amounts in oven-dried (60 \({}^{\circ}\)C) and was not detected in microwave-dried samples due to the high microwave temperature, and this is consistent with other authors who reported that furaned is not stable and its destruction depends on temperature and pH [25; 35; 36]. Furthermore, due to its sensitivity in aqueous solutions, furaned detection is affected by the conditions of extraction or isolation and detection technique [25].