## 3 Results and Discussions
### Polyphenols
#### 3.1.4 Quantification of Phenolic Compounds in Almond Skin  
Flavanols occurred as monomers, oligomers, and polymers, the latter also called procyanidins (A-type and B-type dimers, trimers, tetramers and pentamers), which are the main compounds in almond skin. Monomeric units include mainly Catechin and Epicatechin. Various procyanidins were identified despite the Ultra Scan mode with _m/z_ 1500 as a maximum. Procyanidin quantification was performed after phloroglucinolysis. In addition to the concentration of procyanidins, this reaction allows to determine the mean degree of polymerization (mDP). Catechin and Epicatechin were also observed linked to hexoses [10]. Small amounts of non-flavonoids such as vanillic acid and chlorogenic acid were identified. Vanillic acid was linked to two hexoses, probably glucose and/or galactose. Flavonols are either linked or not linked to sugars (glucose and/or rhamn and/or galactose). Two main flavonoids were quantified: isorhamnetin and kaempfer. Compounds identified belonging to flavanones include Naringenin its 7-O-glucose. Table 2 summarizes the content of phenolic compounds in (ug/100 g of almond) identified in natural skin (NS), non-Ultrasonicated almonds (NUA), Ultrasonicated almonds (UA) and blanched almonds (BA) extracts. Procyanidins content in the four samples is remarkably the highest, followed by Isorhamnetin-3-O-rutinoside. Analysis of the products formed in the presence of phloroglucinol revealed that three major products were formed: phloroglucinol-catechin + phloroglucinol-epicatechin (A), catechin (Cat) (B), and epicatechin (epicat) (C) (Figure S3). Procyanidin concentration (PC) in almond skin was calculated as shown in the Equations (3) and (4) [19]. Considering NS as a reference, UAE is the most efficient technique to extract phenolic compounds (33.45%) comparing to other extractions (4.1% and 8.3% for NUA and BA, respectively). Using solvents (methanol in this case for natural skins) appears to be more efficient for polyphenol extraction compared to ultrasonication, but this latter is certainly eco-friendlier and better environmentally speaking since water was used as a solvent, and no heating is necessary. UAE could be a very interesting substitute for polyphenol use in cosmetic and pharmaceutical industries. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **NS (ug/100 g of** & **NUA (ug/100 g of** & **UA (ug/100 g of** & **BA (ug/100 g of** & **Almond)** \\  & **Almond)** & **Almond)** & **Almond)** \\ \hline Vanillic acid di-hexoside & \(1078.8\pm 34.9\) & \(66.5\pm 5.4\) & \(423.5\pm 49.4\) & \(245.0\pm 13.7\) \\ \hline Catechin & \(648.6\pm 13.8\) & \(72.7\pm 21.5\) & \(493.0\pm 245.1\) & \(335.9\pm 24.1\) \\ \hline Epicatechin & \(263.9\pm 18.2\) & \(37.6\pm 10.4\) & \(152.7\pm 44.7\) & \(220.0\pm 4.0\) \\ \hline (Epi)Catechin-hexoside & \(198.4\pm 19.9\) & \(11.0\pm 3.1\) & \(136.4\pm 19.9\) & \(146.9\pm 44.1\) \\ \hline Chlorogenic acid & \(34.413\pm 2.1\) & \(5.2\pm 1.5\) & \(33.3\pm 6.8\) & \(12.7\pm 0.5\) \\ \hline Isorhamnetin & \(262.3\pm 2.4\) & \(9.1\pm 2.0\) & \(60.7\pm 0.75\) & \(28.3\pm 2.2\) \\ \hline Isorhamnetin-3-O-rutinoside & \(2399.9\pm 118.0\) & \(161.5\pm 36.4\) & \(957.4\pm 66.7\) & \(522.5\pm 20.8\) \\ \hline Isorhamnetin-3-O-glucoside & \(1571.9\pm 62.94\) & \(87.1\pm 19.9\) & \(487.3\pm 32.0\) & \(317.0\pm 15.0\) \\ \hline Kaempfer-3-O-glucose & \(72.0\pm 3.5\) & \(5.9\pm 1.4\) & \(29.5\pm 3.4\) & \(23.1\pm 1.4\) \\ \hline Kaempfer-3-O-rutinoside & \(228.9\pm 23.5\) & \(16.3\pm 3.1\) & \(105.1\pm 6.5\) & \(61.6\pm 3.4\) \\ \hline Naringenin & \(23.8\pm 0.2\) & \(1.6\pm 0.2\) & \(10.7\pm 1.5\) & \(13.2\pm 1.0\) \\ \hline Procyanidins & \(64636.8\pm 2670.1\) & \(2438.4\pm 617.4\) & \(21003.5\pm 3086.2\) & \(3994.0\pm 77.2\) \\ \hline Total & \(71419.8\) & \(2912.9\) & \(23893.0\) & \(5920.0\) \\ \hline  & \(100.0\) & \(4.1\) & \(33.5\) & \(8.3\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Content (ug/100 g of almond) of phenolic compounds in NS, NUA, UA, and BA extracts.