Adsorption of flavonols from onion (Allium cepa L.) processing residues on a macroporous acrylic resin

• Effects of temperature and pH on adsorption of onion flavonols are determined.
• Evaluation is conducted by statistical design of experiments.
• Adsorption kinetics are modeled using the pseudo-second order model.
• Structural features of the flavonols decisively influence their adsorption kinetics.
• The findings contribute to the value-added utilization of plant residual materials.

Adsorption behavior of six flavonols derived from onion processing residues was evaluated using statistical design of experiments. Adsorption experiments were conducted at temperatures varying between 25 and 65 °C and pH-values of 2 to 6. Adsorption capacities and adsorption rates of the individual flavonols were determined by fitting the pseudo-second order model to concentration-time curves of adsorption. Evaluation of these kinetic parameters showed that structural features of the phenolic compounds, such as polarity and molecular size, considerably affect their kinetic behavior during adsorption. While pH exerted no significant effect, temperature decisively influenced adsorption kinetics. The effect of temperature varied in dependence of the individual compound's affinity towards the adsorbent resin. This work provides fundamental knowledge for the efficient and economic purification of flavonols from onion processing residues and contributes to the value-added utilization of plant residual materials.