## 4 Discussion  
Considering the different possible accessions of kurugua in the region, [PERSON] et al. (2015) reported _S. odorifera_ fruits with similar characteristics of weight (2510 g), longitudinal diameter (36.91), and latitudinal diameter (9.72 \(\pm\) 0.88), although slightly more elongated. However, another species, _S. sphaerica_, reported by the same authors is lighter (1550 g) and of similar proportions (23.70 cm \(\times\) 11.20 cm, respectively) [42]. In this work, a hydroalcoholic extraction of anthocyanins from the peel of kurugua fruit was evaluated by UAE. This process is highly studied for the recovery of valuable compounds from different raw material sources, such as fruit and vegetables [13]. Among the variables chosen in this work to evaluate the performance of the process for anthocyanin extraction, the solvent concentration, the liquid-solid ratio (L-S), and the pH were significant, whereas the temperature and the time of extraction were not significant. For the Box-Behnken design, the temperature was set at 20 \({}^{\circ}\)C and the time at 15 min. As can be seen in Figure 2, lower temperatures are more efficient for anthocyanin removal. Regarding time, even though longer times imply a higher operational cost, in this work, this time was chosen to allow for enough exposure time of the solute to the solvent. In the literature, extraction times of phenolic compounds from 10 to 90 min are reported [13]. Ethanol was chosen in this work due to its categorization as GRAS (generally recognized as safe), allowing it to be used for food applications [26]. Moreover, this solvent could be considered ecofriendly [10]. Based on the screening design, higher concentrations of ethanol, as well as higher L-S, were tested using the Box-Behnken design. The pH was adjusted between 3.5 and 6. The increment in the concentration of ethanol allows for achieving a high TMA concentration until reaching a maximum concentration value, above which there is a negative effect. It has been reported that a very high concentration (near to the pure solvent) could cause plant tissue dehydration [13], which explains the low concentration of TMA obtained using the pure solvent as shown in Table 5. This was also observed by other authors using other raw materials [9,10]. Regarding the liquid-solid ratio, this also has a positive influence on anthocyanin extraction due to the principles of mass transfer, since the driving force during the mass transfer process is the concentration gradient between the peel and the solvent, which shifts into a higher mass transfer rate [42]. However, an indiscriminate increase in the liquid-solid ratio would lead to economic problems, since increasing this ratio would increase the amount of solvent required for extraction. Concerning the pH, this parameter is understudied in the literature despite its importance for the color stability of anthocyanins. It has been reported that a pH around 4-5 induces a change in the structure, decreasing the concentration of the red-colored flavylium cation and increasing the concentration of the colorless carbonl pseudo base. At pH 6, the extract color trends to be blue or violet due to the presence of hydroxyl groups and the increment of the concentration of the quinoidal base [32]. In this work, the best conditions for anthocyanin extraction were achieved at t = 15 min, T = 20 \({}^{\circ}\)C, pH = 6, S = 60% ethanol \(v\)/\(v\), and L-S of 80 mg/L, obtaining a concentration of 61.908 mg C3G/100 g DW. It is important to mention that although the final anthocyanin concentration might be higher due to the inherent limitations of the pH differential method, correlation (R) values equal to 0.925 or higher among the results obtained by this method and HPLC measurements have been presented. Therefore, the optimal extraction conditions would remain the same regardless of the quantification method [18,26,43].