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 (ΔE) 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.

Purple corn pericarp, a processing waste stream, is an extremely rich source of phytochemicals. Optimal polyphenol extraction parameters were identified using response surface methodology (RSM) by combining a deep eutectic solvent (DES) and ultrasound-assisted extraction (UAE) method. After DES characterization, Plackett–Burman design was used to screen five explanatory variables, namely, time, Temp (temperature), water, Amp (amplitude), and S/L (solid-to-liquid ratio). The total anthocyanin concentration (TAC), total polyphenol concentration (TPC), and condensed tannin (CT) concentration were the response variables. After identifying significant factors, the Box–Behnken design was utilized to identify the optimal extraction parameters. The experimental yields under the optimized conditions of time (10 min), temperature (60 °C), water concentration (42.73%), and amplitude (40%) were 36.31 ± 1.54 g of cyanidin-3-glucoside (C3G), 103.16 ± 6.17 g of gallic acid (GA), and 237.54 ± 9.98 g of epicatechin (EE) per kg of pericarp, with a desirability index of 0.858. The relative standard error among the predicted and experimental yields was <10%, validating the robustness of the model. HPLC analysis identified seven phytochemicals, and significant antioxidant activities were observed through four distinct assays. Metabolomic profiling identified 57 unique phytochemicals. The UAE technique combined with DES can efficiently extract polyphenols from purple corn pericarp in a short time.

A comparative evaluation of cellulosic biomass from colored corn varieties including twenty cobs and seven tassels was performed to quantify their polyphenolic contents and corresponding antioxidant activity. Spectrophotometric analysis and antioxidant screening with four distinct protocols identified five polyphenol-rich cob varieties, whereas the quantified amounts in tassels were relatively lower. Variety V2458-1 contained the highest phytochemical content with total anthocyanin, condensed tannins, total phenolics, and total flavonoid concentrations of 61.22, 530.14, 111.56, and 35.90 mg per g of cob powder, respectively. HPLC and UHPLC-MS analyses were performed and 31 phytochemicals including 11 anthocyanins, 9 phenolic acids, and 11 flavonoids were identified. Ultrasonic-assisted microencapsulation with gum arabic (1%) as a coating material was used to formulate shelf-stable freeze-dried powders. Due to the higher concentrations of xylan, gum arabic was required as a coating material for producing free-flowing extracted powders. The developed powders were systematically analyzed for phytochemical retention, antioxidant capacity, and microstructural characteristics. Morphological analysis confirmed the formation of stable microcapsules, indicating effective encapsulation and protection of sensitive phytochemicals. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) revealed hydrogen-bond interactions between carrier materials and the extract, contributing to structural stability of the encapsulation matrix. The resulting powders had improved physicochemical stability, higher phytochemical content, and strong antioxidant potential, validating their application as natural red colorants and functional food ingredients in line with the circular bioeconomic paradigm.