## 3 Results and Discussion
### Quality Evaluation  
Chromatographic separation of phenolic compounds identified nine phenolic compounds, including four hydroxybenzoic acid derivatives (gallic, salicylic, chlorogenic,  
Figure 11: Contribution of solar and electrical energy during the drying process. Figure 12: Energy efficiency for drying the _Arbutus unedo_ L. fruits at different air-drying temperatures. and coumaric acids) and five flavonoids (quercetin, kaempfer, catechins, naringin, and epicatechin) (Table 5). This phenolic profile is similar to those reported by [71]. The total phenolic compounds of _Arbutus unedo_ L. was 63.22 mg/100 g dry solids (Table 5). Total phenolic compounds of dried fruits were less compared to fresh ones. Higher temperature resulted in a decrease from 15.54% (60 \({}^{\circ}\)C) to 62.78% (80 \({}^{\circ}\)C) in total phenolic compound content. Likewise, in a study conducted on cherry laurel fruits, a significant decrease was noticed in both total phenolic and total flavonoid content of dried samples at 50, 60 and 70 \({}^{\circ}\)C when compared with fresh fruits [72]. The degradation of phenolic compounds observed after drying can be attributed to the activation of some enzymes, such as peroxidase and polyphenol oxidase, which can catalyze the oxidation of phenolic compounds. It can also be noticed that the total phenolic content decreased as the temperature elevated. Similarly, an increase in the drying temperature from 25 to 60 \({}^{\circ}\)C was linked to a decline in the total phenolic content of dried strawberry _Fragaria vesca_ L. fruits [73]. This loss in the phenolic compounds content may be attributed to oxidation, thermal degradation and polyphenol oxidase activity [72]. However, these outcomes are quite different from those reported in a study conducted by [PERSON] and co-workers on _Citrus lemon_ (L.) waste [74]. Drying lemon residues at different temperatures ranging between 40 and 110 \({}^{\circ}\)C induced an increment in total phenolic content at higher temperatures (from 90 to 110 \({}^{\circ}\)C). An eventual explanation of this trend is that higher temperatures may enhance the solubility of phenolic compounds through the breakdown of cellular structures and thereby the release of these compounds [75]. In another investigation, the total polyphenols content of sweet cherries was not affected by drying temperatures at 60 \({}^{\circ}\)C, 70 \({}^{\circ}\)C, and 80 \({}^{\circ}\)C [38]. Focusing attention on individual phenolic compounds, gallic acid and chlorogenic acid were the most abundant phenolic acids in the studied samples and quercetin was by far the main flavonoid. Increasing the drying temperature from 60 to 80 \({}^{\circ}\)C was responsible for the substantial loss of all phenolic compounds except gallic acid which was enhanced from 14.41 at 60 \({}^{\circ}\)C to 17.66 g/100 g of dw at 70 \({}^{\circ}\)C then decreased to 15.29 g/100 g of dw at 80 \({}^{\circ}\)C. These findings are in a good agreement with those reported by [PERSON] and co-workers (2020) as there was a significant decline in the contents of individual phenolic compounds in dried cherry laurel fruits [76]. [PERSON] et al., (2020) explained that in dried matrices, the extraction is challenging due to the fact that the components in the cells are more attracted to each other [77]. However, [PERSON] and co-workers found that phenolic compounds behave differently regarding drying temperatures [74]. Indeed, while the content of some compounds increased linearly with drying temperature, other compounds