## 6 Valorization Technologies for Avocado-Derived Biomass through Obtaining Bioactive Compounds  
### Phenolic Compounds  
Besides the latter applications based on the use of the major chemical components, this tropical fruit can be better exploited if the residual parts are also used as alternative sources of bioactive substances with different industrial purposes. In particular, research on sources of natural antioxidants, such as phenolic compounds, for the food industry has increased because consumers prefer products that contain few or no synthetic compounds. So, the avocado by-products could be used to obtain extracts with high antioxidant power to replace synthetic antioxidants [78; 79; 80]. As a preliminary study, we showed that the peel is richer in phenolic compounds than the stone using Soxhlet extraction, with the water and the peel extract also showing a higher purity. Water can be used for extraction as a green solvent since the major part of the total phenolic content (TPC) (87%) and antioxidant activity (>90%) remained in the water extract [12] (Table 5). In another work, [PERSON] et al. [81] extracted the bioactive compounds from the peel and stone with the ultrasound technique and the solution consisted of ethanol/water (80/20, _v/v_). It enabled the authors to reduce the  
Figure 8: Enzymatic hydrolysis yield in terms of the glucose of the avocado waste. processing time, cost, and thermal damage and to improve the total bioactive compounds recovered. Their results also indicated that the peel extracts have a higher phenolic content than those from the stone. Nonetheless, other studies have obtained extracts from avocado stone with high antioxidant capacity. For comparison, Table 5 shows some examples of the technologies applied to assist the extraction process or to recover phenolic compounds; it also depicts the TPC and the antioxidant activity determined by two common in vitro assays. In general, there is a high variation between the results in terms of the solubility (avocado waste weight) and purity of the extracts (extract weight), even when in most studies the cultivar 'Hass' was used. The different biomass types, preconditioning and extraction methods, and solvents used, in addition to the place of origin, among others, can explain these differences. Concerning the technology, some authors have investigated the feasibility of microwave-assisted extraction [82; 83] and accelerated solvent extraction [84] as thermal-type extractions, and ultra-sound assisted extraction [79; 83] and supercritical CO\({}_{2}\) extraction (with ethanol as co-solvent) [85] as non-thermal procedures (Table 5). These techniques require shorter processing times, less energy, and considerably lower amounts of chemicals or solvents. They also tend to generally provide higher extraction efficiencies. Among them, supercritical CO\({}_{2}\) extraction and microwave-assisted extraction seem to have a higher efficiency to solubilize the phenolic compounds from the peel and stone, while the highest purity of the extracts were reached using Soxhet extraction with water for the peel and microwave-assisted extraction with 70% acetone for the stone. The latter is characterized to be a fast and efficient extraction method due to the rapid heat generation by the microwaves energy, which causes destruction of the cellular matrix to release phenolic compounds, with extraction times lower than 20 min [82; 83]. Furthermore, in a recent work, another strategy was followed to recover phenolic compounds from the pomace part, i.e., using aqueous two-phase systems, based on two immiscible liquid phases. It can avoid thermal treatments and has a high potential to be scaled-up due to its simplicity [86]. These authors used polyethylene glycol and magnesium sulfate or sodium citrate as the polymeric material and salt, respectively, for extraction that is based on a salting-out phenomenon. Having the biorefinery concept on one's mind, greener extraction trends should be considered for further deployment.