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

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. Graphical Abstract