Estudio del proceso de extracción de compuestos fenólicos a partir residuos de mazorca maíz

Abstract

Corn is currently one of the most cultivated cereals in the world, obtaining many agricultural solid residues. Corncob residue can be considered as a subproduct due to the presence of a phenolic fraction rich in flavonoids, which could be used as a substitute of synthetic antioxidant additives for different food and pharmaceutical applications. This work was focused on studying different extraction processes and operating conditions aimed at the recovery of the phenolic fraction from corncob, as well as an identification study in order valorise the final extracts. Experiments were performed by using bath extraction with rotary agitation, ultrasound-assisted extraction, and microwave-assisted extraction. The effects of contact time, temperature (40 and 70ºC) and solvent (ethanol, water, and different ethanol-water mixtures) were also examined. Throughout the work it was possible to verify that with the use of the temperature of 70 ºC better results of extraction of polyphenolic compounds and flavonoids were achieved; Like the ethanol:water mixtures, they are more effective than the use of pure solvents, the 70% mixture being the most effective. Thanks to the extractions in which mixtures are used as solvents, better results were achieved for the percentage of total polyphenolic compounds with respect to the total dry solids. It was verified that by means of the 70% ethanol-water mixture, the reducing capacity of the extract was correlated with the flavonoid fraction, in extraction with ethanol with the polyphenols and if water was used, a very poor correlation was obtained. Regarding the identified compounds, both in the ethanol:water mixtures and in the ethanol the same compounds were identified, although all of them in greater quantity in the mixtures, being the 70% where the most was obtained. In the extraction with water it was also possible to identify gallic acid, p-hydroxybenzoic acid and vanillinic acid. The compound that was identified in the greatest amount was ethyl ferulate, followed by p-coumaric acid, syringic acid and kaempherol. Regarding the extraction techniques, the ultrasound-assisted one turned out to be the most effective, since compared to the agitated bath, it was possible to extract more polyphenolic compounds and flavonoids in less time. With the use of microwaves, extraction results were obtained that were very similar to those obtained by means of a bath, but using only a few minutes of extraction compared to hours in the bath, thus resulting in being more efficient.

El maíz es actualmente uno de los cereales más cultivados en el mundo, generándose gran cantidad residuos sólidos que suelen desecharse. En este sentido, la mazorca de maíz es un residuo potencialmente valorizable debido a que presenta en su estructura celulosa, lignina y una fracción fenólica rica en flavonoides, que podrían proporcionar productos con diferente aplicación en el sector químico y alimentario. El objetivo de este trabajo fue estudiar la recuperación de compuestos fenólicos a partir de residuos de mazorca utilizando diferentes técnicas de extracción y condiciones de operación. Se examinó el efecto del disolvente (etanol, agua y mezclas), de la temperatura (40 y 70 ºC), y del tipo contacto (agitación rotatoria, ultrasonidos y microondas) en la cinética de liberación de fenólicos totales y flavonoides a la fase extracto. Se recogen también los resultados del perfil de ácidos fenólicos y flavonoides recuperados bajo las diferentes condiciones de extracción utilizadas.