## 2 Avocado Processing and By-Products  
Throughout the avocado value chain, from tree planting to industrialization, there are stages where different types of biomass are generated and they can be recycled as resources in a biorefinery. The activities prior to industrialization are planting, harvesting, selection, cooling, washing/brushing, packing, and temporary storage [1] (Figure 3). In the traditional plantation system, trees are planted with distances of \(10\times 10\) m between them, so that the tree grows up to 8 or 10 m high and the density is around 117 trees per hectare. In the orchards, the tree grows up to a maximum height of around 3 m to facilitate the practices of phytosanitary control, harvesting, foliar fertilization, and cutting. This enables plantation distances of \(6\times 3\) m or up to \(3\times 3\) m, increasing the density to 300 and up to 1000 trees per hectare [1; 19]. Accordingly, maintenance pruning practices results in a big amount of biomass (branches and leaves) that must be removed from the fields to avoid propagation of plant diseases. One sustainable alternative is to use it for compost, although in most occasions these residues are burned. Figure 2: (**a**) Parts of the avocado fruit; stone split in half before (**b**) and after (**c**) partial oxidation, in the latter appearing the orange color. In addition to the market of avocado fruit as a fresh food product, avocado is processed into several types of foods, as commented before, and the associated by-products are generated. Because the pulp is the only part of the fruit that is used as raw material, a significant amount of peel and stone are generated. The percentage of this waste depends on the cultivar of the fruit; for example, the proportion of avocado by-products (peel and stone) in the cultivar 'Fuerte' was higher than in 'Hass', i.e., 31% vs. 24%, respectively [13]. Even, some differences can be found in the same cultivar, e.g., 24% and 27% of avocado waste have been reported for the Hass cultivar [12; 13]. If the processing of avocado is intended to recover oil from the pulp, a by-product rich in pulp is obtained, as commented on next. Avocado oil and guacamole are the most conventional processed products. In order to extract avocado pulp oil, several processes have been suggested, some industrially consolidated (Figure 4) and others only used on a laboratory scale: (i) chemical extraction by organic solvents, which is the most widespread, using mainly hexane; and (ii) physical methods like mechanical extraction (the traditional method) and centrifugation, also known as cold-pressing. Many other combination methods have been tested, including microwave + pressing, oven-drying + pressing, or solvent extraction, aided or not by enzymes, sonophysical processes, supercritical CO\({}_{2}\) extraction, etc. [11]. During chemical extraction (Figure 4a), the shell and bone are totally removed to obtain the pulp that is dried with hot air, and then the oil is extracted with an organic solvent, such as hexane; an up to 95% extracted oil content is obtained [20; 21]. The mechanical extraction of avocado oil (Figure 4b) is obtained by peeling and destoning the fruit, crushing the pulp, and finally drying it. Then, the paste is heated with hot water with CaCO\({}_{3}\)/CaSO\({}_{4}\) or NaCl, and rotated, pressed or skimmed (by natural decantation) to obtain the oil phase. In both methods the oil is refined for most applications [21]. Considering the oil content of avocado, the generated residual pulp fraction can be around 46% of the avocado weight. Figure 3: Activities prior to commercialization of avocado and by-products/waste generated in the field (yellow squares). Figure 4: Chemical (a), mechanical (b), and cold-pressing extraction (c) of avocado oil and the by-products/waste obtained (yellow squares). At the end of the last century, a New Zealand food producer, in collaboration with a market-leading food producer, began to extract avocado oil by cold pressing (CPAO), which does not require refining (Figure 4c).