The avocado (Persea americana Mill.) is a tree native to Mexico and Guatemala. Avocado consumption, fresh or in the form of processed products, is growing everywhere and it has caused a large number of countries to invest heavily in avocado production. The industrialization of avocado gives as a result a huge amount of waste, not only the peel and stone but also that waste generated by the pruning practices and oil extraction. These biomasses could be converted into raw materials to obtain different types of co-products, but this implies changes in the use of these resources, the design of efficient production systems, and integration to take full advantage of them, e.g., by developing biorefinery models. Therefore, this review firstly gives a snapshot of those residues generated in the avocado industry and provides their chemical composition. Secondly, this review presents updated information about the valorization ways of avocado-derived biomass to obtain bioenergy, biofuels, and other marketable products (starch, protein, phenolic compounds, and biosorbents, among others) using a single process or integrated processes within a biorefinery context. Green technologies to obtain these products are also covered, e.g., based on the application of microwaves, ultrasound, supercritical fluids, etc. As a conclusion, there is a variety of ways to valorize avocado waste in single processes, but it would be promising to develop biorefinery schemes. This would enable the avocado sector to move towards the zero-waste principle.

Avocado has become fashionable due to its great organoleptic and nutritional properties. It is consumed as a fresh product and it is also processed to obtain salad oil and guacamole. In all cases, the only usable portion is the pulp. Therefore, to be a more sustainable and profitable agribusiness, it is important to recognize which compounds from the peel and the stone waste can be converted into valuable bio-products. Therefore, their chemical composition was determined according to the National Renewable Energy Laboratory, the total phenolic content by the Folin-Ciocalteu method and the antioxidant properties by the FRAP and TEAC assays. The main components of the peel and stone were acid-insoluble lignin (35.0% and 15.3%, respectively), polymeric sugars (23.6% and 43.9%, respectively), and the aqueous extractives (15.5% and 16.9%, respectively). Both biomasses contain lipids and protein, but a minor proportion (<6%). The valorization of lignin and sugars is of interest given the high content; stones are a rich source of glucose (93.2% of the polymeric fraction), which could be used to obtain biofuels or derivatives of interest. The extractive fraction of the peel contained the highest number of phenolic compounds (4.7 g/100 g biomass), mainly concentrated in the aqueous fraction (i.e., 87%) compared to the ethanol one, which was subsequently extracted. It correlated with major antioxidant activity and, therefore, the peel can be applied to obtain antioxidants and water can be used as an environmentally friendly extraction solvent.

Since ancient times, plants have been used as preservatives, spices, flavorings and as natural remedies to prevent or treat diseases owing to the biological activity correlated with the bioactive compounds they contain. The avocado fruit (Persea americana), native to Mexico and Guatemala, has been traditionally used for its pleasant organoleptic characteristics, high nutritional value and health benefits, but its residual biomass (seeds, skin and tree leaves) is also valuable in therapeutic terms. For this reason, the present investigation reviews the pharmacological potential of avocado waste. It can serve as a source of antioxidants, as well as hypotensive, anti-analgesic, photoprotective, antibacterial, and anti-inflammatory agents, and can be used to treat skin disorders. The main active components seem to be phenolic compounds. The content of phenolic compounds in waste extracts varied from 6 to 307 g/kg dry weight, depending on the waste type and extraction conditions, among others. In particular, our results suggested that using water as a solvent, a high amount of phenolic compounds can be obtained from the peel (266 g/kg dry weight), and this was correlated with major antioxidant activity. Therefore, the peels can be applied to obtain antioxidants, and water can be used as an environmentally friendly extraction solvent to obtain various valuable compounds of its chemical composition for food and pharmacological applications.