## 4 Valorization Technologies of Avocado-Derived Biomass through Obtaining Bioenergy and Biofuels
### Fermentable Sugars and Bioethanol
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Sample Type** & **Conditioning** & **Oil Extraction** & **Procedure \({}^{\ast}\)** & **Heating Value (M/kg)** & **Density at 15 \({}^{\circ}\)C** & **Viscosity at 40 \({}^{\circ}\)C** & **Flash** & **Ester** & **Content** & **Ref.** \\ \hline Biodiesel (stone oil) & Size reduction (120 mesh) and drying & Hexane & Methanolysis with NaOH (60 \({}^{\circ}\)C; 60 min; r, 6.1 1\% catalyst) & 41.3 & 877.7 & 5.0 & 184.0 & 84.6 & [60] \\  & (110 \({}^{\circ}\)C) & & & & & & & \\ \hline Biodiesel (peei (2.6 mm) and air drying & Hexane (Soxhel) & Methanolysis with NaOH (60 \({}^{\circ}\)C; 67.5 min; r: 6.1; 1.21\% catalyst) & 40.0 & 910.0 & 4.2 & 161.0 & 95.2 & [61] \\ \hline Biodiesel (invocado oil) & - & - & Ethanolysis glycerol-enriched CaO (75 \({}^{\circ}\)C; 1 hr: r: 91.7 \% catalyst) & ND & ND & 4.9 & ND & 91.2 & [62] \\ \hline Biodiesel (invocado oil) & - & - & Methanolysis with NaOH (65 \({}^{\circ}\)C; 2 hr: r: 6.1 1\% catalyst) & 40.1 & ND & 3.8 & 148.0 & ND & [63, 64] \\ \hline Biodiesel (invocado oil) & Size reduction and drying (85 \({}^{\circ}\)C) & Hexane (Soxhel) & Methanolysis with KOH (60 \({}^{\circ}\)C; 2 hr: r: 6.1 5\% catalyst) & ND & ND & ND & 61.2 & [66] \\ \hline Biodiesel (invocado oil) & Size reduction and drying (85 \({}^{\circ}\)C) & Hexane (Soxhel) & Dimethyl carbonate with KOH (85 \({}^{\circ}\)C; 2 hr: r: 91.8 5\% catalyst) & ND & ND & ND & ND & 7.3 & [66] \\ \hline Biodiesel (invocado oil) & Size reduction and drying (85 \({}^{\circ}\)C) & Hexane (Soxhel) & Methanolysis non-catalyzed (380 \({}^{\circ}\)C) & & & & & 90.1 & [66] \\ \hline Biodiesel (invocado oil) & Size reduction and drying (85 \({}^{\circ}\)C) & Hexane (Soxhel) & Dimethyl carbonate non-catalyzed & & & & & 93.0 & [66] \\ \hline Avocado oil & & & 39.5 & 34.0 & 186.0 & & [63] \\ \hline  & & & 45.3 & 3.0 & 58.0 & & [63] \\ \hline  & & & & & & & & \\ \hline \hline \end{tabular} \({}^{\ast}\) r the solventol ratio.  
\end{table} 
Table 4: Methods applied to obtain biodiesel from avocado stone and peel oils and avocado oil, as well as the characteristics of the biodiesel. In this regard, to obtain bioethanol, different process configurations, including the aforementioned pretreatments, enzymatic hydrolysis, and fermentation conditions, are applied (Figure 7). Concerning fermentation, _Saccharomyces cerevisiae_ is mainly utilized to convert glucose into ethanol, while microorganism such as _Pachysolen tannophilus_ can ferment pentoses to ethanol and xylitol [71]. In co-fermentation approaches, some ethanologenic _Escherichia coli_ strains and _Pichia stipitis_ can ferment xylose and glucose to ethanol, while the combination of microorganisms is also plausible [41; 67; 70]. However, the production of sugars and bioethanol (butanol, etc.) from avocado waste is still in its initial stage and few examples have been found in the reviewed literature. Milling, milling + steam-NaOH (1%) at 140 \({}^{\circ}\)C for 10 min, and milling + microwave-assisted fractionation (1% NaOH; 300 W for 25 min) of avocado stones (pre-dried at 105 \({}^{\circ}\)C) were recently compared by [PERSON] et al. [52]. Using sequential hydrolysis and fermentation, the yield of sugars was high using the second pretreatment with a hydrolysis rate of 75% using the enzymatic cocktail Cellic CTec2. However, the yield of bioethanol was the lowest (102 mL/kg or around 8%). This was explained by the presence of a higher level of inhibitors.