Laser light as a novel postharvest strategy to suppress chlorophyll degradation and oxidative stress in pakchoi (Brassica rapa subsp. Chinensis)

Short-term diode laser light irradiation is an emerging physical treatment for preserving quality and enhancing oxidative stress resilience in postharvest commodities. Rapid deterioration, including leaf yellowing, is a major factor limiting the postharvest shelf life of pakchoi. This study investigated the effects of short-term exposure to blue (450 nm) and red (660 nm) diode laser light on quality maintenance, oxidative stress mitigation, and chlorophyll metabolism in pakchoi stored at 20 °C for 5 days. The results demonstrated that 660 nm red laser irradiation significantly maintained visual quality and green coloration while reducing weight loss more effectively than 450 nm blue laser light and the untreated control. Both laser treatments reduced respiration rates and ethylene production and induced partial stomatal closure. Additionally, both treatments regulated oxidative stress responses by lowering malondialdehyde (MDA) content, lipoxygenase (LOX) activity, and reactive oxygen species (ROS) accumulation (H₂O₂ and O₂⁻), while enhancing both enzymatic and non-enzymatic antioxidant systems. The red and blue laser treatments also preserved total chlorophyll content by suppressing the expression of chlorophyll degradation genes (BcPAO, BcNYC1, BcPPH1) and upregulating chlorophyll biosynthesis genes (BcCAO, BcCHLH). Among the treatments, the 660 nm red laser exhibited the strongest effects, as confirmed by higher maximum quantum efficiency of PSII photochemistry (Fv/Fm) values and principal component analysis (PCA). Overall, these findings demonstrate that 660 nm laser irradiation synergistically modulates chlorophyll metabolism and antioxidant defense, offering an effective and practical physical strategy to extend the postharvest shelf life of leafy vegetables.