OPTIMIZATION OF THE HYDROTHERMAL PROCESS FOR THE RECOVERY OF FLAVONOIDS AND FERMENTABLE SUGARS FROM COCONUT HUSK

The exploitation of agro-industrial residues as alternative sources of valuable molecules is a strategic approach within the biorefinery concept. Coconut husk (Cocos nucifera L.), characterized by a lignocellulosic matrix rich in cellulose, hemicellulose, lignin, and phenolic compounds, represents a promising renewable feedstock for the recovery of fermentable sugars and flavonoids, contributing to the integral valorization of agro-industrial residues. In this study, the efficiency of hydrothermal technology for valorizing coconut husk as a renewable feedstock to recover flavonoids and fermentable sugars was evaluated, along with the effects of temperature and flow rate on process performance. The experiments were carried out in a continuous-flow system using temperatures of 60, 90, and 120 °C and flow rates of 2 and 6 mL min⁻¹. Flavonoid content was determined by a spectrophotometric method, while reducing sugars were quantified using the Somogyi–Nelson method. The influence of these operational parameters on the solubilization of the lignocellulosic matrix and the selective recovery of the target fractions was investigated. The results demonstrated that flow rate significantly influenced compound recovery, with higher flow rates improving mass transfer and reducing the residence time of extracted compounds under hydrothermal conditions. The highest fermentable sugar yield was obtained at 90 °C and 6 mL min⁻¹, reaching approximately 190 mg glucose g⁻¹. This condition provided a favorable balance between biomass hydrolysis and reduced sugar degradation, maximizing sugar recovery. In contrast, higher temperatures favored flavonoid extraction, with the highest yield obtained at 120 °C and 6 mL min⁻¹, reaching approximately 27 mg catechin g⁻¹. The enhanced flavonoid recovery at higher temperatures was attributed to changes in the physicochemical properties of pressurized water, particularly the reduction in solvent polarity, which improves the solubilization of less polar phenolic compounds and facilitates their release from the lignocellulosic matrix. However, more severe thermal conditions also promoted secondary degradation reactions, resulting in lower sugar recovery and highlighting the importance of selecting operating conditions according to the desired target products. The results demonstrate that the hydrothermal process using pressurized water is an efficient and sustainable technology for coconut husk valorization, enabling the selective recovery of flavonoids and fermentable sugars. This approach contributes to the development of integrated biorefinery platforms by converting agro-industrial residues into value-added fractions with potential applications in biotechnology, food, and bio-based industries. The authors acknowledge financial support from CNPq, Brazil (Grant No. 302451/2021-8) and CAPES, Brazil (Finance Code 001). This study was funded by FAPESP, Brazil, under Grant Nos. 2024/06628-6, 2021/04096-9, 2023/02064-8, and 2018/14938-4.