Vegetable sources and agro-industrial residues represent an important source of phenolic compounds that are useful in a wide range of applications, especially those with biological activities. Conventional techniques of phytochemical extraction have been associated with a high consumption of organic solvents that limits the application of bioactive extracts, leading to the implementation of novel extraction technologies using mechanisms such as Ultrasound Assisted Extraction (UAE). In the present review, an analysis of the involved variables in the extraction yield of phenolic compounds through UAE is presented, highlighting the advantages of this technology based on the results obtained in various optimized studies. A comparison with other technologies and a proposal of its possible application for agro industrial residues as raw material of phenolic compounds is also indicated. Finally, it is concluded that UAE is a technology that is placed within the area of Sustainable Chemistry since it promotes the use of renewable raw materials through the extraction of phenolic compounds, implementing the substitution of organic solvents with solvents that do not present toxic effects, lowering the energy consumption when compared to conventional methods and minimizing process times and temperatures, which is useful for the extraction of thermo-labile compounds.

Tangerine (Citrus reticulata. CRP) and grapefruit (Citrus paradisi. CPP) pectins obtained by ultrasound-assisted extraction (UAE) and conventional extraction (CE) using citric acid were characterized to establish their potential uses as an alternative source of commercial pectin. The pectins obtained by UAE and CE presented a pseudoplastic fluid characteristic with shear thinning behavior, a high esterification degree (CRP 82.30–71.81% and CPP 84.25–72.15%) and were of commercial quality based on galacturonic acid content (CRP 76.03% and CPP 76.03–71.01%). CPP presented greater viscosimetric molecular weight than CRP. Meanwhile, CRP presented greater polyphenol and protein content with respect CPP. The functional properties were influenced by citrus source and extraction method. UAE favored greater yields in a shorter time (CPP: 26.05%, 30 min; CRP: 13.46%, 15 min) compared to CE. UAE combined with the use of citric acid offers an effective alternative for obtaining high-quality pectins with lower polluting effluent, time and energy requirements.