Metabolomic profiling of purple corn pericarp phytochemicals and their efficient recovery in deep eutectic solvents with ultrasound-assisted extraction

Authors: KUMAR, RAVINDER - University Of Missouri; WAN, CAIXIA - University Of Missouri; Flint Garcia, Sherry; VARDHANABHUTI, BONGKOSH - University Of Missouri; KUEHNEL, LUCAS - University Of Missouri; MUSTAPHA, AZLIN - University Of Missouri; SOMAVAT, PAVEL - University Of Missouri

Submitted to: Sustainable Chemistry and Pharmacy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2025
Publication Date: 3/4/2025
Citation: Kumar, R., Wan, C., Flint Garcia, S.A., Vardhanabhuti, B., Kuehnel, L., Mustapha, A., Somavat, P. 2025. Metabolomic profiling of purple corn pericarp phytochemicals and their efficient recovery in deep eutectic solvents with ultrasound-assisted extraction. Sustainable Chemistry and Pharmacy. 44. https://doi.org/10.1016/j.scp.2025.101978.
DOI: https://doi.org/10.1016/j.scp.2025.101978

Interpretive Summary: Many plants contain bioactive compounds that can be extracted using industrial processes to create high value phytochemicals including natural food dyes and polyphenolic compounds such as anthocyanins, condensed tannins, and flavonoids. The outside layer of the kernel, called the pericarp, is often removed from yellow dent corn in the first step of many processes and is a low value byproduct. In the case of some maize (corn) varieties, the pericarp can contain high levels of purple and red pigments and other phytochemicals of potentially high value. There are numerous industrial methods and technologies to extract these phytochemicals, and the goal of our research is to find the best combination of methods and technologies to extract high yields of high quality phytochemicals, all while minimizing the negative environmental impacts common in industrial processes using organic solvents. In this study, we investigated the extraction potential of so called “green solvents” that are renewable, non-toxic, biodegradable, and economically viable. We paired a group of 19 green solvents called deep eutectic solvents (DESs, liquids created from mixing two solids) with ultrasound-assisted extraction to extract various anthocyanins, condensed tannins, and flavonoids from purple corn pericarp corn. We found that different combinations of constituents in the deep eutectic solvent resulted in differing abilities to extract specific phytochemicals, but that some combinations were consistently better than others. We have demonstrated that deep eutectic solvents combined with ultrasound can offer an environmentally friendly method to extract high value phytochemicals that can add value to the corn crop, thus supporting agricultural communities.

Technical Abstract: There is a growing demand for solvents that are renewable, non-toxic, biodegradable, and economically viable for value-added phytochemical extraction. Purple corn pericarp, a cellulosic corn processing industry byproduct, has been documented to be an exceptionally rich source of polyphenolic compounds with potential agro-industrial applications. Nineteen different deep eutectic solvent (DES) formulations were prepared and used in conjunction with ultrasound-assisted for the extraction of anthocyanins, condensed tannins, and flavonoids present in purple corn pericarp. The DESs formed strong intermolecular bonds, and dominant stretching of O–H and C–H bonds was observed during the FTIR analysis. Metabolomic profiling using a UHPLC-MS system identified 36 distinct polyphenolic compounds in pericarp. The ultrasound-assisted extraction of polyphenols in DESs was found to be a highly efficient extraction methodology. Within a short duration of 10 min, 27.41 mg of anthocyanins, 240.37 mg of condensed tannins, and 25.52 mg of flavonoids per g of pericarp, respectively were extracted in DES 13, composed of glycerol and lactic acid (2:1). Extracts retained their bioactivities, demonstrating significant antioxidant potential (Trolox equivalent antioxidant activity) during the DPPH, ABTS and CUPRAC assays. HPLC quantification for distinct anthocyanin forms identified cyanidin-3-glucoside, delphinidin, cyanidin chloride, and peonidin. Caffeic acid, ferulic acid, gallic acid, hesperidin, and chlorogenic acid were the main phenolic acids, whereas the major flavonoids present were epicatechin, naringin and kaempferol. Solvent dependent extraction of individual polyphenols was observed, which was further validated through principal component analysis. An efficient and green extraction methodology for phytochemical recovery from colored corn pericarp has been proposed.