Extraction of bioactive compounds from cob and pericarp of purple corn (Zea mays L.) by sequential extraction in fixed bed extractor using supercritical CO2, ethanol, and water as solvents

Abstract

Purple corn (Zea mays L.) is traditionally used in Peru in the preparation of desserts and juices. Purple corn cob and kernel extracts have intense color and are rich in anthocyanins and phenolic compounds. Purple corn cob, whole grain, ground grain, and pericarp extracts were obtained by supercritical fluid technology in a fixed bed at 50 °C and 400 bar in a sequential extraction process using supercritical carbon dioxide (scCO₂) as a solvent in the first step, ethanol in a second step, and water in a third step, in order to determine the composition of the extracts. The curves from the initial extraction kinetics of each raw material were used to determine the best overall yield and extraction time. The two matrices with higher yield (cob and pericarp) were selected and triplicate extraction curves of these matrices were performed in a predetermined period of time. Each point of the extraction curve was chemically analyzed, except the extract from the scCO₂ extraction, due to its low yield. The extracts were characterized for yield, total monomeric anthocyanins by differential pH, total phenolics, total flavonoids, major anthocyanins by HPLC, and antioxidant activity by DPPH. Color measurements of the purple corn pericarp extracts were performed by the CIEL* a^* b^* system. Overall, the aqueous extraction presented the best overall mass yield, higher yield of the components monitored analytically, and higher antioxidant activity, while the ethanol extracts were more concentrated only in anthocyanins.