Effect of germicidal light and ozone gas on the preservation and bioactive potential of papaya (Carica papaya)

Papaya (Carica papaya L.) is a tropical climacteric fruit with high nutritional value but a short postharvest shelf life. Its rapid deterioration is associated with increased metabolic activity, microbial growth, and changes in antioxidant compounds. Given the substantial losses during transportation and storage, sustainable preservation strategies are urgently needed. This study aimed to evaluate the effects of ultraviolet-C (UV-C) radiation, ozone gas, and their combination on microbial load and quality preservation in papaya fruits stored in a biochemical oxygen demand (BOD) incubator at 24 °C.The experimental design was based on a central composite design, including control and treated groups subjected to different exposure times. The factorial design comprised four treatment combinations: Factorial 1 (10 min UV-C and 5 min ozone); Factorial 2 (30 min UV-C and 5 min ozone); Factorial 3 (10 min UV-C and 30 min ozone); and Factorial 4 (30 min UV-C and 30 min ozone). Treatments were performed using UV-C radiation with a predominant emission wavelength of 254 nm and ozone gas at a constant concentration of 0.03 ppm. Following treatment, microbiological analyses were conducted using Sabouraud agar plates to enumerate molds and yeasts. Fruit appearance was documented weekly through photographs over seven days of storage at 24 °C. Data were analyzed using two-way factorial analysis of variance (ANOVA) and effect size calculations in JASP, with microbial counts expressed as log₁₀ CFU/g.Descriptively, ozone treatment alone yielded the lowest mean microbial count (0.27 ± 0.84 log₁₀ CFU/g), followed by UV-C radiation alone (0.64 ± 0.82 log₁₀ CFU/g). The combined UV-C and ozone treatment resulted in a mean count of 0.89 ± 0.25 log₁₀ CFU/g. However, inferential analysis revealed no statistically significant main effects of UV-C radiation [F(1,19) = 0.548; p = 0.468], ozone [F(1,19) = 0.354; p = 0.559], or their interaction [F(1,19) = 2.240; p = 0.151]. Therefore, no treatment significantly reduced microbial load compared with the control under the evaluated storage conditions. Although ozone alone presented the lowest descriptive mean, the significant heterogeneity of variance detected by Levene's test (p < 0.001) limits interpretation and highlights the need for improved experimental replication. Future investigations will include total phenolic content, total flavonoid content, and total antioxidant capacity to provide a more comprehensive assessment of fruit quality.