Enzyme Activation via Ionizing Radiation: Gamma Irradiation Effects on Laccase Activity and Antimicrobial Potency in Mango (Mangifera indica) Peel Extract

Gamma irradiation, a common practice in pharmaceutical and food industry, is used to remove harmful organisms from food and plants. Despite this, the scientific community still does not understand why and how irradiated plant extracts not only change in chemical composition, but also their response to bacteria. Thus, this research study investigates how gamma radiation changes the chemical composition and antimicrobial properties of Carabao mangoes (Mangifera indica) in its peel. Freeze-dried (lyophilized) mango peels were irradiated at 5 doses (0 (control) 0.5, 1, 1.5, 2 kGy) at the Philippine Nuclear Research Institute and tested for its (a) total phenolic content, (b) antioxidant activity, and (c) total oxidoreductase activity using an Ultraviolet-Visible (UV-Vis) spectrophotometer. Antimicrobial activity was tested against Pseudomonas aeruginosa. All quantified data were statistically analyzed using a One-Way Analysis of Variance (ANOVA), Tukey's Honest Significant Difference (HSD) post hoc analysis, Pearson-R correlation, linear regression using GraphPad Prism. Results show that gamma irradiation significantly affected total phenolic content, antioxidant activity, and guaiacol-oxidizing activity of mango peel extracts (p < 0.05). Total phenolic content was highest at 1.0 kGy, while DPPH radical-scavenging activity and guaiacol-oxidizing activity were lowest at the same dose. Guaiacol-oxidizing activity decreased by approximately 51.6% at 1.0 kGy compared with the unirradiated control, followed by partial recovery at 1.5 kGy. Pearson correlation showed no significant linear relationship between irradiation dose and guaiacol-oxidizing activity (r = −0.4619, p = 0.0831). No detectable zones of inhibition were observed against Pseudomonas aeruginosa across all treatments, but an inhibition of growth in mold was observed.