The effect of ε-poly-l-lysine treatment on molecular, physiological and biochemical indicators related to resistance in longan fruit infected by Phomopsis longanae Chi

Acidic Electrolyzed Water Maintains the Storage Quality of Postharvest Wampee Fruit by Activating the Disease Resistance

Harvested wampee fruit is susceptible to disease, resulting in postharvest losses. Acidic electrolyzed water (AEW), a safe and innovative sterilization technology, plays a role in enhancing disease resistance in harvested produce. In this study, the efficacy of AEW in delaying wampee disease development was assessed, along with its association with disease resistance metabolism. Wampee fruit was treated with AEW (pH 2.5) at different available chlorine concentrations (ACCs) (20, 40, 60, and 80 mg/L) and subsequently stored at 25 °C for 8 days. Results revealed that 40 mg/L ACC in AEW (pH 2.5) was most effective in improving the postharvest quality of wampee fruit. Compared with control wampee fruit, those treated with 40 mg/L ACC in AEW exhibited lower incidence of fruit disease, higher pericarp lignin content, and higher activities of pericarp disease resistance enzymes (DREs), such as cinnamate-4-hydroxylase, phenylalanine ammonia-lyase, chitinase, β-1,3-glucanase, polyphenol oxidase, 4-coumarate CoA ligase, and cinnamyl alcohol dehydrogenase. These results suggested that AEW elevated DRE activities, promoted lignin accumulation, and ultimately enhanced disease resistance, suppressed disease development, and improved storage quality in harvested wampee fruit. Consequently, AEW emerged as a safe technology to mitigate the disease development and enhance the storage quality of harvested wampee fruit.

Epsilon-poly-l-lysine alleviates brown blotch disease of postharvest Agaricus bisporus mushrooms by directly inhibiting Pseudomonas tolaasii and inducing mushroom disease resistance

The natural antimicrobial peptide, epsilon-poly-l-lysine (ε-PL), is widely acknowledged as a food preservative. However, its potential in managing bacterial brown blotch disease in postharvest edible mushrooms and the associated mechanism remain unexplored. In this study, concentrations of ε-PL ≥ 150 mg L-1 demonstrated significant inhibition effects, restraining over 80% of growth and killed over 99% of Pseudomonas tolaasii (P. tolaasii). This inhibition effect occurred in a concentration-dependent manner. The in vivo findings revealed that treatment with 150 mg L-1 ε-PL effectively inhibited P. tolaasii-caused brown blotch disease in Agaricus bisporus (A. bisporus) mushrooms. Plausible mechanisms underlying ε-PL's action against P. tolaasii in A. bisporus involve: (i) damaging the cell morphology and membrane integrity, and increasing uptake of propidium iodide and leakage of cellular components of P. tolaasii; (ii) interaction with intracellular proteins and DNA of P. tolaasii; (iii) inhibition of P. tolaasii-induced activation of polyphenol oxidase, elevation of antioxidative enzyme activities, stimulation of phenylpropanoid biosynthetic enzyme activities and metabolite production, and augmentation of pathogenesis-related protein contents in A. bisporus mushrooms. These findings suggest promising prospects for the application of ε-PL in controlling bacterial brown blotch disease in A. bisporus.

Hydrogen peroxide induced changes in the levels of disease-resistant substances and activities of disease-resistant enzymes in relation to the storability of longan fruit

The influences of hydrogen peroxide (H2O2) on the storability and metabolism of disease-resistant substances in fresh longan were investigated. Compared to the control samples, H2O2-treated longan exhibited a higher index of fruit disease, pericarp browning, and pulp breakdown, a higher rate of fruit weight loss, but lower chromaticity values (L*, a* and b*) in pericarp appearance, and a lower commercially acceptable fruit rate. Additionally, H2O2-treated longan showed a lower lignin content, lower activities of enzymes including phenylalnine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumaryl coenzyme A ligase (4-CL), cinnamate dehydrogenase (CAD), peroxidase (POD), chitinase (CHI), and β-1,3-glucanase (GLU). These data collectively suggest that H2O2 negatively impacted the storability of fresh longan. This can be attributed to H2O2's role in reducing the levels of disease-resistant substances and suppressing the activities of disease-resistant enzymes, implying that H2O2 reduced the postharvest storability of longan by compromising its disease resistance.

Fatty acid metabolism and C9 aldehyde biosynthesis are involved in ε-poly-l-lysine-induced citrus fruit resistance to Penicillium digitatum

Citrus fruit were easily infected by Penicillium digitatum, and caused green mold rapidly, resulting in enormous post-harvest losses. ε-poly-l-lysine (ε-PL) was generally regarded as a safe (GRAS) substance. Besides, it was proved to have a dual effect on harming fungi and triggering fruit defense responses. Fatty acid metabolism is closely related to fruit defense response. However, little is known about how ε-PL affected fatty acid metabolism in citrus fruit. Here, we found that ε-PL increased the expression of CsFATA, CsACSL, CsFAD2, CsFAD3, CsLOX2S, and CsHPL in fatty acid metabolism, decreasing oleic acid levels and enhancing linoleic and linolenic acid levels. Additionally, ε-PL enriched the activities of LOX and HPL during the oxidative decomposition of fatty acids, and activating C9 aldehyde biosynthesis. Interestingly, ε-PL combined with (2E,4E)-nonadienal (C9 aldehyde) would improve the inhibitory effect against Penicillium digitatum. And the combined bio-fungicide significantly delayed the citrus green mold compared to single concentrations of the individual components. These results suggested that ε-PL improved citrus fruit defense responses through fatty acid-mediated defense responses. Combined bio-fungicide consisting of ε-PL and (2E,4E)-nonadienal have an excellent prospect for controlling citrus green mold.

Synergistic Effects of 1-MCP Fumigation and ε-Poly-L-Lysine Treatments on Delaying Softening and Enhancing Disease Resistance of Flat Peach Fruit

Flat peach, a predominant fruit consumed in China, is highly susceptible to softening and perishable. The impact of 1-methylcycloproene (1-MCP) fumigation combined with ε-poly-L-lysine (ε-PL) on softening and postharvest reactive oxygen species (ROS) and phenylpropanoid pathway metabolisms in peaches and its relationship to disease resistance were investigated. Findings revealed that a combination of 1 µL L-1 1-MCP and 300 mg L-1 ε-PL effectively suppressed the activity of cell-wall-degrading enzymes and the disassembly of cell wall structure, thus maintaining higher firmness and lower decay incidence. Compared to the control group, the synergistic approach bolstered enzymatic responses linked to disease resistance and ROS-scavenge system, consistently preserving total phenolics, flavonoids, ascorbic acid, and glutathione levels. Concurrently, the accumulation of hydrogen peroxide and malondialdehyde was significantly diminished post-treatment. These results show that there is good synergistic effect between 1-MCP and ε-PL, which could effectively maintain the quality of flat peach fruit by modulating cell wall metabolism and enhancing the resistance.