Novel two-pot microwave extraction of purple corn pericarp’s phenolics and evaluation of the polyphenol-rich extract’s product quality, bioactivities, and structural properties

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

Submitted to: Food and Bioprocess Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2023
Publication Date: 11/1/2023
Citation: Boateng, I.D., Mustapha, A., Daubert, C.R., Kuehnel, L., Kumar, R., Flint Garcia, S.A., Agliata, J., Wan, C., Somavat, P. 2023. Novel two-pot microwave extraction of purple corn pericarp’s phenolics and evaluation of the polyphenol-rich extract’s product quality, bioactivities, and structural properties. Food and Bioprocess Technology. 16:2668-2691. https://doi.org/10.1007/s11947-023-03072-7.
DOI: https://doi.org/10.1007/s11947-023-03072-7

Interpretive Summary: Corn is a valuable crop in the United States and is used primarily as animal feed and in industrial processes including fuel ethanol production. Portions of the corn kernel are waste products in processing, including the fibrous outer layer of the kernel called the pericarp. Some corn varieties have pigmented pericarps that contain valuable phytochemicals that can be extracted to add value to the corn crop. Phenolic compounds are a class of phytochemicals that have a wide range of biological activities including antioxidants, anti-obesity, anti-cancer, and anti-inflammation properties. Numerous extraction protocols are available, but many are time-consuming, require large volumes of solvents, or negatively affect the product quality. In this study, an innovative technology called microwave-assisted extraction was explored and the protocol was optimized in order to reduce waste and extraction time while maintaining high product quality. The optimized microwave extraction protocol was compared to the optimized conventional extraction protocol in the lab for a number of product characteristics such as yield, metabolite profiles (anthocyanins, flavonoids, and phenolics) and anti-oxidant activity. The microwave-based protocol reduced extraction time from 8.6 hours to about 0.5 hour, with improved product quality. Overall, the product yields for the microwave extraction protocol was 38% higher than the conventional protocol; specific individual anthocyanin yields were reduced compared to conventional extraction protocols, but yields of other phytochemicals such as phenolic acids, antioxidants, and proanthocyanins were increased. Thus the cost-effective microwave extraction protocol will improve extraction of many but not all phytochemicals from corn pericarp, thereby expanding the industrial application of corn.

Technical Abstract: Corn pericarp is a low-value byproduct of the processing industry. However, due to a disproportionately higher concentration of phytochemicals, colored corn pericarp could be a source of nutraceuticals and food additives. For the first time, purple corn pericarp (PCP) was converted to a polyphenol-rich extract containing anthocyanins, phenolic acids, and proanthocyanins using a two-pot microwave extraction technique. Besides, the microwave extraction (MAE) conditions were optimized, and response surface methodology was used to understand the association between independent variables and their responses and used further to decipher the underlying mechanisms through visualization. Plackett–Burman design (PBD) was used to screen significant extraction parameters, and further optimization was done using Box-Behnken design (BBD). Under the optimum conditions (ethanol (42.4% v/v), temperature (75 °C), and time (29 min)), total anthocyanin content (TAC), total phenolic content (TPC), and condensed tannins (CT) to the tune of 38.73 g/kg, 138.62 g/kg and 279.48 g/kg pericarp, respectively were obtained with a desirability function value of 0.838. Monomeric anthocyanins degraded and polymerized to 3-deoxyanthocyanin, whereas phenolic acids such as chlorogenic acid, caffeic acid, ferulic acid, and hesperidin increased as the microwave temperature and time increased. The MAE’s extraction yield was 38.11% higher than the conventional extraction (CE). The CE process took'~'8.6 h, whereas MAE took'~'0.5 h to extract the phenolics. The MAE samples had a higher TAC, TPC, CT, phenolic acids (chlorogenic acid, caffeic acid, ferulic acid, and hesperidin), total flavonoid content (TFC), and antioxidant activities than CE samples. Therefore, the valorization of PCP could contribute to the circular economy model.