Effect of Glow Discharge Cold Plasma Treatment on the Physicochemical Properties and Antioxidant Capacity of Maize

Abstract

This study evaluated the effect of cold plasma (CP) on the physicochemical properties and antioxidant capacity of maize. CP treatments were performed using a glow discharge, applying argon and/or nitrogen at 50 W, with different working pressures (75, 100, and 125 Pa) and exposure times (1, 5, and 10 min). The maize samples were analyzed before and after treatments for color, fatty acid value (FAV), malondialdehyde content, superoxide dismutase and catalase activities, total phenol content (TPC), ascorbic acid content, reduced glutathione content, and antioxidant activity. The antioxidant activity was further evaluated during storage (25 °C for 180 days). After treatments, color parameters (brightness, yellowness, and saturation) showed measurable enhancement, while FAV and malondialdehyde content were significantly reduced by 14.95-56.37% and 11.38-43.71%, respectively. The optimal treatment conditions (100 Pa working pressure and 5 min exposure) maximized antioxidant enzyme activities and bioactive compound levels, accompanied by substantial increases in TPC. Under these conditions, maize samples had the highest organic radical scavenging capacities (DPPH), reaching 1.31-fold (argon plasma) and 1.25-fold (nitrogen plasma) that of untreated sample. During storage, all samples subjected to the optimal combined treatment exhibited higher DPPH radical scavenging capacity and ferric reducing antioxidant potential, along with lower FAVs and malondialdehyde contents compared to the untreated sample. Additionally, the DPPH radical scavenging capacity exhibited statistically inverse correlations with both FAV (r² = -0.49) and malondialdehyde content (r² = -0.15), as quantified through Pearson correlation analysis. These findings indicated that glow discharge cold plasma is a potentially effective non-thermal processing technique to enhance bioactive compound accumulation and antioxidant enzyme activity for preserving maize's physicochemical properties, with possible use in the food industry for sustainable grain preservation strategies, particularly in delaying oxidative deterioration.

Keywords: antioxidant enzymes; bioactive compounds; color property; enhancing effect; fatty acid; malondialdehyde; storage.

Figure 1

Effect of CP treatments on overall appearance of maize kernels.

Figure 2

Effect of CP treatments on FAV (A,B) and MDA content (C,D) in maize kernels. Different colored letters indicate significant differences (p < 0.05) between samples at each working pressure.

Figure 3

Effect of CP treatments on SOD (A,B) and CAT (C,D) activity in maize kernels. Different colored letters indicate significant differences (p < 0.05) between samples at each working pressure.

Figure 4

Effect of CP treatments on the contents of total phenols (A,B), AA (C,D) and GSH (E,F) in maize kernels. Different colored letters indicate significant differences (p < 0.05) between samples at each working pressure.

Figure 5

Effect of CP treatments ((A) Ar plasma; (B) N₂ plasma) on DPPH radical scavenging activity in maize kernels. Different colored letters indicate significant differences (p < 0.05) between samples at each working pressure.

Figure 6

Effect of CP treatments on DPPH radical scavenging activity (A), FRAP (B), FAV (C), and MDA content (D) in maize kernels during storage for 180 d at 25 °C. */*/* represent comparisons between all treated samples with Ar plasma and the untreated control, comparisons between all treated samples with N₂ plasma and the untreated control, and comparisons between samples treated with different gas plasma at each time, respectively (p < 0.05).

Figure 7

Correlations between changes in color, FAV, MDA, antioxidant enzyme activity, antioxidant compounds, and DPPH scavenging activity in maize kernels. * and ** indicated significant differences at the p ≤ 0.05 and p ≤ 0.01 levels, respectively. Red (+1) and blue (−1) colors show the positive and negative correlations between different indexes, respectively.