Sonoprocessing improves phenolics profile, antioxidant capacity, structure, and product qualities of purple corn pericarp extract

Authors: BOATENG, ISAAC - University Of Missouri; KUMAR, RAVINDER - University Of Missouri; DAUBERT, CHRISTOPHER - University Of Missouri; Flint-Garcia, Sherry; MUSTAPHA, AZLIN - University Of Missouri; KUEHNEL, LUCAS - University Of Missouri; AGLIATA, JOSEPH - University Of Missouri; LI, QIANWEI - University Of Missouri; WAN, CAIXIA - University Of Missouri; SOMAVAT, PAVEL - University Of Missouri

Submitted to: Ultrasonics Sonochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2023
Publication Date: 5/1/2023
Citation: Boateng, I.D., Kumar, R., Daubert, C.R., Flint Garcia, S.A., Mustapha, A., Kuehnel, L., Agliata, J., Li, Q., Wan, C., Somavat, P. 2023. Sonoprocessing improves phenolics profile, antioxidant capacity, structure, and product qualities of purple corn pericarp extract. Ultrasonics Sonochemistry. 95: Article 106418. https://doi.org/10.1016/j.ultsonch.2023.106418.
DOI: https://doi.org/10.1016/j.ultsonch.2023.106418

Interpretive Summary: Corn is an extremely valuable commodity crop in the United States, and is used primarily as animal feed and in industrial processes such as fuel ethanol production. Each structure of the corn kernel is composed of different chemical components (starch, protein, oil, fiber, etc.) that are used in various industrial processes. The fibrous outer layer of the kernel is called the pericarp and is generally a low value by-product in fuel ethanol processing. Some corn varieties produce pigments in the pericarp layer which can be extracted and used as high-value nutraceuticals and plant-based replacements for synthetic food dye. Various methods have been tested to efficiently extract these phytochemicals, but these had low product yield or quality. In this study, we investigated ultrasound technology as a method to extract phytochemicals from purple corn pericarp, and compared the product yield and quality extracted by the ultrasound method to a microwave-based method. The new ultrasound method was 30% faster than microwave extraction method and resulted in higher phytochemical yields for nearly all compounds examined, especially the anthocyanin compounds which were adversely affected by the microwave method. The quality of the product was also higher for the ultrasound method compared to the microwave method. This new ultrasonic method will be used by processors and food chemists who extract phytochemicals from corn pericarp in order to add value to the US corn crop.

Technical Abstract: For the first time, purple corn pericarp (PCP) was converted to polyphenol-rich extract using two-pot ultrasound extraction technique. According to Plackett-Burman design (PBD), the significant extraction factors were ethanol concentration, extraction time, temperature, and ultrasonic amplitude that affected total anthocyanins (TAC), total phenolic content (TPC), and condensed tannins (CT). These parameters were further optimized using the Box-Behnken design (BBD) method for response surface methodology (RSM). The RSM showed a linear curvature for TAC and a quadratic curvature for TPC and CT with a lack of fit > 0.05. Under the optimum conditions (ethanol (50%, v/v), time (21 min), temperature (28 °C), and ultrasonic amplitude (50%)), a maximum TAC, TPC, and CT of 34.99 g cyanidin/kg, 121.26 g GAE/kg, and 260.59 of EE/kg, respectively were obtained with a desirability value 0.952. Comparing UAE to microwave extraction (MAE), it was found that although UAE had a lower extraction yield, TAC, TPC, and CT, the UAE gave a higher individual anthocyanin, flavonoid, phenolic acid profile, and antioxidant activity. The UAE took 21 min, whereas MAE took 30 min for maximum extraction. Regarding product qualities, UAE extract was superior, with a lower total color change ('E) and a higher chromaticity. Structural characterization using SEM showed that MAE extract had severe creases and ruptures, whereas UAE extract had less noticeable alterations and was attested by an optical profilometer. This shows that ultrasound, might be used to extract phenolics from PCP as it requires lesser time and improves phenolics, structure, and product qualities.