Melanoidin Removal Mechanism in An Aqueous Adsorption System: An Equilibrium, Kinetic and Thermodynamic Study
Diego L. Nunes,
Leandro S. Oliveira,
Adriana S. Franca.
Melanoidins are colored products that can be found in food and drinks, formed by Maillard
reactions. Sometimes these compounds are considered undesirable in certain food products, because
they impart a brownish color and must be removed. An overview of recent patents related to melanoidin
removal indicates that it can be performed by chemical/biological degradation or by adsorption processes. Therefore,
in the present study, the adsorption mechanism for synthetic melanoidin removal from aqueous solutions was studied
using different Raphanus sativus press-cake sorbents, with the precursor material being carbonized in a microwave oven,
either with direct heating or after a chemical activation process with phosphoric acid, nitric acid or potassium hydroxide.
Physical and chemical modifications were evaluated by FTIR, pHPZC, thermogravimetry and BET. The adsorption kinetics
was better described by a pseudo-second order model for all activated carbons (ACs). Evaluation of the diffusion process
showed dependence on the initial melanoidin concentration due to the wide range of sizes of the adsorbed molecules. The
equilibrium data were best fitted by the Langmuir model for the acid-treated AC and by the Freundlich model for the
base-treated and non-chemically treated ACs. Melanoidin adsorption was characterized as a spontaneous, favorable and
endothermic process involving hydrogen bonds and π-π interactions between the adsorbents surfaces and the adsorbed
Keywords: Activated carbon, adsorbents, adsorption mechanism, melanoidin, microwave carbonization.
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