Sunflower by-products valorization: Chemical characterization, modeling, and thermodynamic study

Considering a circular economy, this study explores the valorization of sunflower by-products. Extraction kinetics of chlorogenic acid (CGA) were investigated from sunflower meal (SM) and hulls (SH) using pressurized water extraction (PWE) at different temperatures (120-160 °C). Chemical characterization, kinetic modeling (reaction, diffusion, and coupled extraction-transformation-based models), and thermodynamic analysis elucidated the mass-transfer mechanisms involved. The optimal conditions (120 °C, S/L 1/100, 15 min) yielded 33.61 and 11.56 mg/g dry matter for SM and SH, respectively, whereas an S/L ratio of 1/30 was identified as the most advantageous from a process perspective.For SM, extraction kinetics profile revealed a rapid increase in CGA yield within the first 12 min, reaching a plateau at 15 min, followed by thermal transformation after 25 min. High temperatures and extended extraction time favored CGA isomerization into NeoCGA and CryptoCGA, and CGA hydrolysis into caffeic acid (CFA) in SM. This phenomenon was not detected in SH, highlighting the matrix effect. The coupled extraction-transformation model successfully described CGA release and transformation in SM, whereas pseudo-second order models described extraction in SH. The extended Fick's law model indicated that over 70 % of CGA was solubilized during the washing phase. Thermodynamic and Damköhler analyses confirmed diffusion-controlled extraction and revealed distinct activation behaviors for SM and SH, reflecting the strong influence of matrix structure on CGA release and transformation. This work is the first to demonstrate that PWE not only enables the green extraction of CGA from sunflower by-products but also reveals its thermal transformation.