## 3 Chemical Composition of Avocado Waste  
The moisture content and the chemical characterization of the aforementioned by-products are shown in Table 1. All residues were characterized by high moisture; the stones presented the lowest value (up to 57%) and the wastewater the highest value (88%). This is one of the main limitations since dried samples are required for some technologies before processing. If it cannot be used as fresh biomass or there is a shortage in time to process, a drying step can transform this waste into storable commodities, but the energy cost will depend not only on the technology but also on the moisture content, as well as on the type of avocado by-product. Some authors have applied air-drying, convective drying, freeze-drying, and microwave drying before further application of the stone, peel, and avocado pomace [12; 20; 27; 28], and freeze-drying and spray-drying for wastewater [20]. Alternatively, to be used as a biofuel for heating, [PERSON] et al. [29] recommends a cheap drying system that is used in other industries, such as making wood chips, in order to achieve around a 10% moisture content.  
In all cases, the higher components are the sugar fraction (glucans + hemicellulose sugars), the extractives fraction (non-structural components), and lignin, but a high variability has been found in the literature [12; 27; 30; 31; 32; 33] (Table 1). The variety/cultivar, ripeness, pedoclimatic conditions, and fertilizer used may affect the chemical composition of these residues, as well the methodology applied. Moreover, among the avocado waste, a large part of the carbohydrates from the stone are available (69%), making it an unconventional, yet viable starch source [20].  
Moreover, the elemental analysis (%, dry weight) of some of these by-products is shown in Table 2. These values are similar to that of olive stones, an agro-industrial by-product used as a biofuel, but the carbon content is lower than vegetable coal. Both products were added in Table 2 for comparison and as references for Section 4.1.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**By-Product** & **Moisture** & **Ash** & **Lipids** & **CP** & **Ext** & **Hem 3** & **Cel/Glu 4** & **L Lignin** \\ \hline Exhausted pulp/pomace & 81.4–82.8 & 4.5–7.0 & 9.3 & 14.7–12.8 & 18.2 1 & 8.5 & 29.8 & 26.9 \\ Peel & 70.9–75.3 & 1.0–8.7 & 6.3–10.4 & 6.0–9.3 & 43.7 1/20.5–34.4 2 & 11.5–25.3 & 12.1–27.6 & 4.4–35.3 \\ Stone & 35.2–57.0 & 0.9–2.9 & 2.3–6.0 & 3.7–5.3 & 21.0–35.9 2 & 3.0–47.9 & 6.5–40.9 & 1.8–15.8 \\ Wastewater & 88.3 & 17.9 & 53.8 & 10.3 & ND & ND & ND & ND \\ \hline \end{tabular}
\begin{tabular}{c c c c c c c c} \hline
**CP, crude protein; Cel/Glu, cellulose/glucans; Ext, extractives; Hem, hemicellulose; ND, not determined; PC, phenolic content. 1 Ether extract. 2 Aqueous-ethanolic extractives, which refer to non-structural material determined using the standard method reported by the National Renewable Energy Laboratory (NREL). 3 As xylan, arabian, galactan, and/or mannan. 4 In some studies, cellulose was determined on the basis of the glucose content as glucans, and so starch can contribute to this value. Other studies determined the available carbohydrate content (free sugars, dextrins, and starch), which was pomace (0.6%), peel (1.2%), stone (69.1%), and wastewater (0.9%).**  
\end{table}
Table 1: Moisture (%, fresh weight) and chemical composition of some avocado residues (%, dry weight) [12; 20; 27; 29; 30; 31; 32; 33].