Enhancing Nutritional Potential: Plasma-Activated Water Treatment on Sweet Orange Peel Powder—Polyphenols, Flavonoids, Antioxidants, and Anti-Nutrients Optimization

The immense waste generated from sweet orange (Citrus sinensis) peel during processing poses significant challenges in waste management, contributing to environmental pollution and health hazards. This study explores the impact of plasma-activated water (PAW) on sweet orange peel, focusing on polyphenols total phenol content (TPC), total flavonoid content (TFC), total terpenoid content (TTC), flavonoids (hesperidin, naringin), limonin, antioxidant activity 1, 1-diphenyl-2-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and anti-nutritional factors (tannin, phytic acid, and saponin), with an emphasis on optimization. The central composite rotatable design (CCRD) was employed, resulting in 13 experimental runs with independent parameters set at 7–13 kV (voltage) and 60–180 min (soaking time). PAW treatment significantly enhanced total polyphenols [112.52- ± 4.63- to 170.56- ± 5.78-mg gallic acid equivalent (GAE)/100 g], total flavonoids (621.26- ±25.15- to 972.69- ±80.29-mg QE/100 g), and antioxidant activities (DPPH 37.59% ±3.71% to 79.61% ±1.83% and FRAP 96.34- ±2.13- to 256.01- ±11.8- $\mu $ g AA/g) in sweet orange peel powder (SOPP). Conversely, TTC, naringin, limonin, and anti-nutrients decreased compared to control samples. Fourier transform infrared (FT-IR) analysis revealed characteristic peaks, confirming the alteration of polyphenolic functional groups. This study presents strategies for valorizing SOPP, enhancing its polyphenols and antioxidant properties for potential applications in nutraceuticals and novel functional foods.