## 3 Results and Discussion
### Determination of the Antioxidant Potential of the Extracts and Correlation Analysis
In order to link the antioxidant capacity to the presence of a particular phytochemical, a Pearson correlation analysis was applied (Figure 6). This analysis provided evidence of the strong and highly significant correlation between both HAT-based in vitro assays as well as cellular antioxidant assay and TPC of the extract, in particular with the presence of chlorogenic acid, protocatechuic acid, and \(p\)-hydroxybenzoic acid (Figure 6, Table S1). The presence of \(p\)-coumaric acid was significantly correlated with a DPPH assay only. On the contrary, none of these phytochemicals, here analyzed, were significantly correlated with the in vitro ET-based antioxidant CUPRAC assay. Figure 5: (**a**) hierarchical clustering analysis (HCA) showing the relation between the phytochemical composition and antioxidant activity of each extracts from AOR of Eastern Morocco obtained by USAE; (**b**) principal component analysis (PCA) showing the discrimination of the different extracts from AOR of Eastern Morocco obtained by USAE. Altogether, these results showed a higher antioxidant activity, expressed in \(\upmu\)M TEAC/g DW, determined with the ABTS and DPPH assays as compared to the CUPRAC assay. Therefore, these results suggested the prominence of the HAT- over the ET-based mechanism for the antioxidant action of these extracts. In good agreement, several authors have reported an antioxidant activity of extracts from various almond products based on HAT mechanism [18; 44; 46; 42]. Similarly, a higher relation between HAT assay and phenolic acids as compared to flavonoids have been previously reported [57; 52]. This observation is also in line with the results of [PERSON] and [PERSON] [58] that reported a relatively stronger scavenging capacity of radicals generated by the ABTS and DPPH assays for chlorogenic acid, the main phenolic acid of our AOR extracts, and its derivatives. The authors attributed this observation to the available hydroxyl groups of these compounds. The presence of flavonoids has been also reported in almond products [13; 18; 44; 46; 42]. Here, we cannot exclude the presence of flavonoids potentially linked to the ET-based antioxidant activity evidenced by the CUPRAC assay. [PERSON] et al. [13]) have reported in the presence of flavonoids in almond skin (i.e., isorhamnetin derivatives). Future works will be conducted to study in detail the flavonoid fraction of our AOR extracts. The cellular antioxidant assay using yeast further confirmed the interest of this system to study natural antioxidant from plant extracts [34; 52] as also previously reported for other natural antioxidants such as thiamine and/or melatonin [55; 56]. Natural antioxidants have aroused increasing interest over the past decade due to their possible use as an alternative to potentially dangerous synthetic antioxidants such as butylated hydroxyapatite (BHA) or butylated hydroxytoluene (BHT) in various food or cosmetic formulations [6; 7; 8]. Some natural antioxidant phenolics have already been shown to be as efficient in stabilizing nonpolar systems such as bulk oil or various types of emulsions as these synthetic antioxidants [7; 9; 10; 11]. These preliminary results indicate a potential use as natural antioxidants of our AOR extracts generated by the present validated USAE.