## 1 Introduction  
Almond (_Prunus dulcis_, Rosaceae family) is one of the most consumed drupes in the world, appreciated for its pleasant taste and its abundance in nutritional compounds (proteins, polyphenols, omega 6, omega 9), and known for its hypercholesterol reduction [1,2]. The United States of America, especially California, dominates the global production of almonds, followed by the European Union, Maghreb countries, and Japan. Almond fruits are dehiscent drupes. The ovary wall becomes a pericarp with a leathery mesocarp (also called hull), a woody endocarp (shell) that contains and protects almonds (kernels) covered by a brown skin [3]. During industrial food processing, kernels are separated from skins by blanching [4] and then discarded. Almond skin represents an average of 4% of the total almond weight but covers 70-100% total polyphenols present in the drupe [5,6]. By-products derived from the almond processing (skins, shells, hulls, blanching water) are generally used for livestock feed and raw material for energy production [7]. Nevertheless, over the past years, research had been led to assess the possible use of these by-products as sources of extracts rich in polyphenols which can be used as an ingredient for food, pharmaceutical, and cosmetic applications [7, 8, 9, 10, 11].  
According to [PERSON] et al. 2010 [12], blanching at water boiling point has a negative impact on polyphenols initially present in natural almond skin. This blanching technique is used worldwide but involves a decrease of almond polyphenols, a large consumption of energy (heating), and a denaturation of almond proteins. As reported by [PERSON] et al. 2016 [13], ultrasound technique is a key-technology in achieving the objective of sustainable \"green\" chemistry and extraction. By using ultrasound, full extractions can be completed in minutes with high reproducibility, reducing the consumption of solvent, simplifying manipulation and work-up, giving higher purity of the final product. It also allows the damage of the cell wall, thus releasing bioactive compounds in the aqueous solution. The efficiency of ultrasound has already been proven in the extraction of substances of interest such as polyphenols and can be considered as an alternative to the conventional methods [14]. Ultrasound mechanisms can be explained as follows: cavitation phenomena lead to high shear forces in the media, causing the implosion of cavitation bubbles on a product's surface and releasing micro-jetting which generates several effects such as surface peeling, erosion and particle breakdown. Furthermore, implosion of cavitation bubbles in a liquid media leads to macro-turbulences and to a micro mixing [15].  
The aim of this study is to use ultrasound to combine almond skin separation and polyphenol extraction. Our purpose is to obtain a rapid, environmentally friendly process for a scale-up involving skin separation and requiring a cell breakdown to improve intracellular compounds extraction efficiency using Ultrasonic Assisted Extraction (UAE). Extracts will be analyzed to quantify polyphenol composition in ultrasonicated almonds and compared with natural almonds, blanched almonds, and non-ultrasonicated almonds. Another purpose of this paper is to explore ultrasound effect on almond skin cells integrity with SEM observations, and finally to evaluate its action on skinless almond proteins and lipids (Figure 1).  
Figure 1: Graphical illustration of the experiment’s design.