β-Aminobutyric Acid Induced Resistance against Alternaria Fruit Rot in Apple Fruits

Preventing Fungal Spoilage from Raw Materials to Final Product: Innovative Preservation Techniques for Fruit Fillings

Spoilage fungi are a significant cause of financial loss in the food and beverage industry each year. These fungi thrive in challenging environments characterized by low acidity, low water activity and high sugar content, all of which are common in fruit fillings used in pastry products. Fruit fillings are therefore highly susceptible to fungal spoilage. Fungal growth can cause sensory defects in foods, such as changes in appearance, odor, flavor or texture, and can pose health risks due to the production of mycotoxins by certain mold species. To reduce food loss and waste and extend product shelf-life, it is critical that we prevent fungal spoilage. Synthetic chemicals such as sorbic acid and potassium sorbate are commonly used as preservatives to prevent fungal spoilage. However, with consumer demand for 'natural' and 'chemical-free' foods, research into clean-label preservative alternatives to replace chemical preservatives has increased. The objectives of this review are (i) to provide an overview of the sources of fungal contamination in fruit filling production systems, from pre-harvest of raw materials to storage of the final product, and to identify key control factors; and (ii) to discuss preservation techniques (both conventional and novel) that can prevent fungal growth and extend the shelf-life of fruit fillings.

Characterization of Fungal Species Isolated from Cankered Apple Barks Demonstrates the Alternaria alternata Causing Apple Canker Disease

Apple canker disease, also named as apple Valsa canker, is one of the most destructive diseases for apples (Malus domestica Borkh.). Cytospora/Valsa spp. are the dominant causal agent of this disease, but many studies have revealed that fungi from some other genus can also cause typical apple canker symptoms. In this study, we performed fungal pathogen isolation from cankered 'Fuji' apple barks. Six representative morphologically different fungi (Strain 1-6) were further subjected to ITS sequencing and evolutionary analysis. Molecular identification results revealed that Strains 1-6 are Cytospora mali, Fusarium cf. solani, Alternaria alternata, C. mali, Diplodia seriata and F. proliferatum, respectively. All these fungi have been reported to be causal agents of apple diseases. By inoculating fungal plugs onto trunks of 'Fuji' apple trees, the pathogenicity of the six fungi were accessed. Only the inoculations of the two C. mali strains (Strain 1 and Strain 4) and the A. alternata strain (Strain 3) resulted in typical apple canker symptoms in trunks. It is worth noting that Strain 1 caused much more severe canker symptoms and higher pathogenicity incidence than the other two fungi. A. alternata has been identified as a pathogen causing diseases on apple fruits and leaves. By further assessing its pathogenicity on apple fruits and leaves, we verified that it can also cause typical fruit rot and leaf spot symptoms. To the best of our knowledge, this is the first report on apple canker disease caused by A. alternata in China. Our present study can provide a theoretical foundation for the prevention and control of apple canker disease.

Emerging Trends in Non-Protein Amino Acids as Potential Priming Agents: Implications for Stress Management Strategies and Unveiling Their Regulatory Functions

Plants endure the repercussions of environmental stress. As the advancement of global climate change continues, it is increasingly crucial to protect against abiotic and biotic stress effects. Some naturally occurring plant compounds can be used effectively to protect the plants. By externally applying priming compounds, plants can be prompted to trigger their defensive mechanisms, resulting in improved immune system effectiveness. This review article examines the possibilities of utilizing exogenous alpha-, beta-, and gamma-aminobutyric acid (AABA, BABA, and GABA), which are non-protein amino acids (NPAAs) that are produced naturally in plants during instances of stress. The article additionally presents a concise overview of the studies' discoveries on this topic, assesses the particular fields in which they might be implemented, and proposes new avenues for future investigation.

Inhibitory Effect of L-Methionine on Alternaria alternata Based on Metabolomics Analysis

Alternaria alternata is the main pathogenic fungus of postharvest black spots in fruits and vegetables. This study aimed to explore the antifungal activity of methionine on A. alternata in vitro and to reveal related antifungal mechanisms through a metabolomics analysis. The results showed that the inhibitory effects of L-methionine (Met) treatment on mycelium growth, spore germination, and the germ tube elongation of A. alternata were enhanced with an increase in the Met concentration, but the inhibitory effects decreased when the Met concentration was higher than 50 mmolL-1. The results of propidium iodide staining and scanning electron microscopy showed that the Met treatment damaged the plasma membrane integrity of the A. alternata spores and caused an irreversible deformation of mycelium. In addition, after the Met treatment, the leakage of electrolytes, nucleic acid, and proteins in the A. alternata cells was significantly higher than that in the control group, indicating that the Met treatment increased the permeability of the cell membranes. Eighty-one different metabolites, divided into seven categories, were identified through the metabolomics analysis, including forty-three downregulated metabolites and thirty-eight upregulated metabolites. Among them, these differential metabolites were mainly involved in amino acid synthesis and metabolism, the pentose phosphate pathway, and the TCA cycle. Therefore, the antifungal effect of the Met treatment on A. alternata was mainly to damage the integrity of the cell membranes, make nucleic acid and protein contents leak, and affect the TCA cycle, carbohydrate metabolism, amino acid synthesis metabolism, and the metabolic pathways associated with cell membrane biosynthesis. Thus, the growth and development of A. alternata were inhibited. The research enriched the investigation of the effect of the antifungal mechanism of Met treatment on A. alternata and provided a theoretical basis for the application of Met to prevent and treat postharvest black spots in fruits and vegetables.