## 5 Other Vaporization Ways through Obtaining Starch and Protein  
In addition to the aforementioned applications, avocado by-products contain other macrocomponents that can be used in the food sector or for bioenergy purposes. In this sense, the avocado stone presents starch, as commented on before. Although some authors reported values up to 30% [10], specific enzymatic methods should be applied to determine its content in future studies (e.g., [[https://permanent.fdlp.gov/LPS94088/42624.pdf](https://permanent.fdlp.gov/LPS94088/42624.pdf)]([https://permanent.fdlp.gov/LPS94088/42624.pdf](https://permanent.fdlp.gov/LPS94088/42624.pdf))).  
In a recent work, starch was isolated from the avocado stone by sodium tripolynphosphate (STPP) at different concentrations, with the best results obtained after 1 h of reaction and at a concentration of 6% STPP. This led to a modified starch that improves the stability of the stickiness in the cream soup and prevents viscosity breakdown [72]. Microwaves were also applied to assist the extraction of starch at 161.1 \({}^{\circ}\)C for 56.2 min, with an extraction yield of 49.5%. The yield using this technology was higher than using conventional methods and the properties of the starch were adequate. Some differences were found since the former starch showed high solubility, a low water absorption capacity, and a non-granular structure with small particle size (lower than 2 \(\upmu\)m), with potential to be applied in biotechnological and food applications [73]. Alternatively, other authors have applied a wet extraction method to obtain starch with a yield of 64% [74].  
Moreover, the application of avocado stone starch for second generation bioethanol is interesting after its conversion into free glucose [26], but limited works are available, as commented on before.  
Figure 7: Summary of the steps followed to produce liquid biofuels.  
Our preliminary results show that avocado stone (dried and milled), can release glucose in relatively high amounts (>40% of the initial glucose in the raw biomass) by enzymatic hydrolysis with Cellic(r) CTec2 and \(\beta\)-glucosidase for 72 h (Figure 8; see also Supplementary Files). This value is higher than that for the peel and other agri-food residues [75; 76], probably due to its starchy or highly available characteristics.  
Avocado waste also contains protein, whose content depends on the type of biomass. The highest values are found in defatted avocado waste (up to 15%) (Table 1). Therefore, in a recent work, this residue was chosen to obtain protein, which was separated by water adjusted to a pH of 8.5 with 1.0 M NaOH and acid-precipitated to an isoelectric point of 4.5 with 1.0 M HCl. This was a high-quality protein since it contained all the essential amino acids and provided higher water and oil absorption capacities as well as a higher radical scavenging capacity than soy protein, the latter used as the reference. Nonetheless, avocado protein showed a lower in vitro digestibility. Moreover, as an emulsifier, it enhanced the stability of the oil-in-water emulsion system and it also showed a greater emulsifying stability than soy protein, even with a lower interfacial tension and emulsifying activity [77]. Due to these promising results, future studies could be addressed to recover edible protein from avocado pomace for human nutrition or as a feed and new technology can be applied for this purpose. In this regard, besides alkaline extraction, a plethora of possibilities have been applied to recover protein from agri-food by-products, including novel trends like electro-based techniques and those using ultrasounds, microwaves, and subcritical water conditions [16]. As far as we know, none of them has been applied to avocado waste or used in an avocado-based biorefinery.