# Advanced and Potential Methods for Extraction of Bioactive Compounds from Avocado Peel--A Review
## 1 Introduction  
The use of bioactive compounds extracted from various plants in the food and pharmaceutical industries has gained high interest recently. The incorporation of phenol-rich plants and extracts in food generally aims at improving its health-promoting properties [1, 2]. Over the years, numerous methods have been developed to recover bioactive molecules from different agricultural products. An appropriate extraction method is essential for desorbingcompounds of interest from the plant matrix's active spots. This is because the extract's yield and quality are strongly linked to the effectiveness and selectivity of the extraction methods used [3; 4].  
Nowadays, scientists are making tremendous efforts to extract bioactive compounds from food by-products. In the context of sustainability and the circular economy, food by-products have been an emerging issue because 30-40% of the total food produced annually is wasted worldwide. About 40-50% of the food waste is from fruits, vegetables, and root crops [5]. The global consumption of fruit results in a vast quantity of solid waste, including peel, skin, and seeds. These materials still contain valuable, economically viable constituents.  
Avocado (_Persea americana_ Mill.) is a tropical fruit with economic significance in many countries [6]. Avocado has been used in several industries, including food and cosmetics. Thus, using avocado on an industrial scale brings a consequence in which the process generates a considerable number of by-products, such as peels and seeds. According to [PERSON] et al. [7], the avocado peel is about 13% of the fruit weight. Avocado peel is a source of bioactive compounds. In their report, about 53 compounds were detected from the avocado peel, including phenolic content, and some of the compounds exhibited antioxidant activity. This implies that avocado peel is potentially further processed by appropriate extraction methods for retrieving its bioactive constituents.  
Some established methods to obtain bioactive compounds from various plants include maceration, Soxhet extraction, solvent-solvent extraction, and decoction. The aforementioned techniques are effective in retrieving bioactive compounds from avocado peels (Table in Section 4.7). The techniques, however, are considered traditional or conventional extraction methods because they are time-consuming and tedious and require large amounts of environmentally unfriendly organic solvents with low extraction yields. In recent decades, alternative environmentally friendly techniques have received more attention. Moreover, the advanced methods are faster, more selective, and automated, and they are able to preserve the quality of the extract. The advanced, so-called non-conventional methods include microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), enzyme-assisted extraction, supercritical fluid extraction, and subcritical water extraction (SWE) for the quality of extracted molecules [8; 9; 10; 11]. For this reason, developing a technique that aims to preserve the nature, quality, and quantity of molecules of interest and, thus, the success of the following steps is promising. This paper, therefore, discusses the advantages of the emerging techniques for extracting bioactive compounds from avocado peel. This paper also covers the advanced extraction techniques that have yet to be applied in avocado peel but may be interesting to conduct in future studies.