Kiwifruit bacterial canker is a highly destructive and invasive disease, primarily affecting the stems and leaves of kiwifruit plants, and is caused by the Pseudomonas syringae pv. actinidae (Psa) (Li et al., 2020). Psa is highly virulent and can rapidly reproduce and spread within infected plants, leading to a decline in tree vigor and death within a short period of 1–2 years (Donati et al., 2020). Previous studies have shown that Psa can be detected in tissues such as pollen and fruit samples of kiwifruit (Barrett-Manako et al., 2021). Stefani and Giovanardi demonstrated that Psa could be detected in kiwifruit fruits at the 3rd, 9th, and 15th weeks by PCR after pollination with Psa-contaminated pollen (Stefani and Giovanardi, 2011). Gallelli et al. tested 32 kiwifruit fruit samples for Psa using real-time PCR technology, and 22 samples were positive (Gallelli et al., 2011). Zhu et al. used nested PCR technology to detect Psa on the surface of Hayward kiwifruit during storage in Zhouzhi County, Shaanxi Province, and the results showed that Psa was found in eight of 40 kiwifruit samples (Zhu et al., 2017). In 2020, China imported a total of about 116,800 t of kiwifruit and exported a total of 12,600 t. As Psa will adhere to the fruit surface and spread with the transportation and sales of kiwifruit, international trade may become the main way for Psa to spread over a long distance in the world (Vanneste et al., 2014). Consequently, studying effective methods to eradicate Psa from the surface of kiwifruit is crucial in preventing the pathogen’s spread and reducing the incidence of kiwifruit canker, while also ensuring the overall quality of the fruit (Cao et al., 2019).

As a natural substance in plants, plant polyphenols are a type of secondary metabolic compounds containing phenolic groups, which are divided into five compounds (Meng et al., 2023), namely phenolic acid, stilbene, flavonoid, coumarin and tannin. Plant polyphenols and their active components have become natural bactericides to control fruit postharvest diseases (Gao et al., 2018; Li et al., 2019; Jia et al., 2021; Cheng et al., 2022). In addition, plant polyphenols are also natural antioxidants that have an important effect on the color, flavor and oxidative stress of fruits (Dróżdż and Pyrzynska, 2018). Vanillin, derived from the seeds of the Vanilla fragrans orchid plant, is a polyphenolic compound widely recognized as one of the most extensively employed food flavoring agents globally (Chen et al., 2014). In addition to its role as a flavor enhancer and fixative, vanillin also has antibacterial, antioxidant, and stabilizing effects (Zabka and Pavela, 2013; Lv et al., 2015; Wei et al., 2021). According to Pei et al. (2021), vanillin was observed to effectively inhibit the growth of fungi in milk, resulting in prolonged spore germination time, reduced growth rate, and decreased mycelia growth. A concentration of 100 mg/mL of vanillin was found to reduce the colony growth rate of Actinomyces elegans by 88.45%, increase the lag phase by 8.60 times, and inhibit hypha growth by 85.93%, leading to damaged hypha morphology. Safari et al. (2020) adopted the combination of vanillin and chitosan for tomato storage and fresh-keeping and concluded that the treatment with 15 mM vanillin, in combination with a 1.5% chitosan coating, can significantly reduce the disease incidence rate and severity during tomato storage, by 74.16 and 79% respectively, and that the coating treatment of “vanillin+ chitosan” can also reduce the rot rate, fruit firmness and respiratory rate of tomatoes, and extend the shelf-life of fruits for 25 d. Li et al. (2020) adopted the compound coating treatment of 2 mg/mL vanillin and 1% chitosan, which could prolong the shelf-life of frozen turbot for 6–7 days.

Currently, there is limited research on the use of vanillin to kill Psa on the surface of kiwifruit and regulate post-harvest physiology. In this study, various concentrations of vanillin solutions were employed to perform indoor antibacterial experiments on Psa, which revealed a substantial inhibitory effect of vanillin on the pathogen. Furthermore, the impact of vanillin solution treatment on the shelf-life quality of kiwifruit was analyzed to develop efficient, safe, and environmentally friendly plant-based preservatives, and to provide scientific and effective references for controlling the spread of Psa on kiwifruit and for the application of storage and preservation technology.

Although various copper compounds and antibiotics are widely used in China and abroad to prevent and control Psa, long-term and excessive use can lead to the development of drug resistance in the pathogen and also affect the safety and quality of fruit. Thus, the development of safe, efficient, and plant-based Psa bactericides has become an urgent priority, considering the challenges posed by conventional bactericides (Lin et al., 2020). Plant polyphenols, because of their diverse types, non-polluting nature, and absence of pesticide residue, are an effective alternative to copper-based and antibiotic pesticides (Pei et al., 2022). Previous studies have shown that plant polyphenols can enhance the antioxidant capacity of horticultural products, thus achieving the goal of controlling postharvest fruit diseases (Valverde et al., 2015; Chen et al., 2019). Kiwifruit is a climacteric fruit, and various factors such as postharvest diseases accelerate fruit ripening and senescence, leading to rapid decline in fruit quality during storage and shelf life. Therefore, there is an urgent need for safe and efficient preservatives to control postharvest diseases in kiwifruit. However, there are currently almost no reports on the antimicrobial effects of vanillin on Psa in postharvest kiwifruit, nor any reports on the impact of vanillin on fruit quality during the storage period of postharvest kiwifruit. In this study, it was shown that treatment with an 8.0 mg·mL⁻¹ solution of vanillin on the surface of kiwifruit for 12 h resulted in a 100% killing rate of Psa on the surface of the fruit. Furthermore, vanillin can also regulate the postharvest physiology and quality of kiwifruit, enhancing fruit storage performance and preservation effects.

Not only does vanillin contain an aldehyde group, but it also possesses a phenol structure with eight carbon atoms, indicating its strong antibacterial activity (Lv et al., 2015). The main targets of vanillin’s antibacterial activity are primarily located at three sites: acting on cell membranes to disrupt their integrity, acting on enzymes to deactivate essential enzymes, and acting on DNA to render them inactive or structurally damaged (Fitzgerald et al., 2004). Vanillin exhibits broad-spectrum antibacterial effects and has been applied in the preservation and storage of fruits such as papaya, pineapple, cantaloupe, and apple (Rupasinghe et al., 2006; Sangsuwan et al., 2008; Wang et al., 2012). Studies by Moon et al. (2006) have demonstrated that the antibacterial activity of vanillin in apple juice is influenced by its concentration and pH value, with higher vanillin concentrations and lower pH values favoring increased antibacterial activity. Additionally, the antibacterial effects of vanillin vary among different bacterial species, with better efficacy against Escherichia coli compared to other strains. In vitro antibacterial assays have shown that the antibacterial efficacy of vanillin against Psa is concentration-dependent, with higher concentrations of vanillin enhancing its antibacterial effects (Figures 1, 3). This study indicates that when the concentration of vanillin is 8.0 mg·mL⁻¹, it achieves a 100% bactericidal effect against Psa on the surface of kiwifruit, suggesting a potential correlation between the targets of vanillin’s antibacterial action and its effectiveness.

The storage properties and preservation effects of fruits are mainly evaluated through indicators of post-harvest physiology and quality changes (Xue et al., 2015). It is widely believed that important quality attributes affecting consumer acceptance of kiwifruit include fruit weight, hardness, color, aroma, and sweetness, etc. This study demonstrates that compared to the control, kiwifruit treated with vanillin showed a significant reduction in weight loss rate (Figure 4A) and decay rate (Figure 4B), inhibited the increase in respiration rate (Figure 5A), and improved fruit hardness (Figure 5B), thus delaying the ripening and senescence of kiwifruit after harvest and enhancing its storage tolerance. We believe that the vanillin-treated kiwifruit forms a thin layer of vanillin coating on the fruit surface, which enhances the structural integrity of the fruit surface, restricts the spread of pathogens, and helps maintain cell wall integrity against fungal attacks, thereby slowing down pathogenic infections and maintaining a lower decay rate. Respiration rate is an important parameter for evaluating postharvest metabolism and fruit quality. We speculate that the thin layer formed after vanillin treatment inhibits the respiration rate of fruit by blocking the stomata on the fruit peel and reducing water vapor and gas exchange, thus maintaining fruit hardness, restraining the increase in weight loss rate, and consequently delaying the postharvest senescence of kiwifruit. Previous studies using exogenous methyl jasmonate (MeJA) (Pan et al., 2019), citral (Wei et al., 2021), 2,4-epibrassinolide (Wang et al., 2020), and other treatments on kiwifruit have shown similar results, with reduced weight loss rate, decay rate, and controlled increase in respiration intensity, thereby extending fruit storage.

The process of plant maturation is considered as an oxidative phenomenon accompanied by reactive oxygen species (ROS) load (Xia et al., 2016). High levels of ROS can lead to oxidative stress-mediated damage in plant tissues. This study suggests that treatment with vanillin in kiwifruit resulted in lower O₂⁻ generation rates, indicating that vanillin treatment can protect kiwifruit from ROS-mediated oxidative damage. The elimination of ROS is related to the activity of antioxidant enzymes such as SOD, CAT, and POD in fruits and vegetables (Goffi et al., 2020). SOD plays a key role in the conversion of O₂⁻ to H₂O₂, while CAT clears H₂O₂, making CAT indispensable for detoxifying ROS (Zhu et al., 2014). POD is a key enzyme in the synthesis and oxidation of phenolic compounds (Foyer et al., 1994). Therefore, higher antioxidant enzyme activity and their synergistic effects may be potential mechanisms for reducing lipid peroxidation and delaying aging in fruit. Exogenous treatment with vanillin helps induce increased SOD, POD, and CAT activity in kiwifruit, thereby reducing oxidative damage and enhancing fruit storage performance.

Some studies have also reported an inseparable relationship between the content of phenolic compounds and the antioxidant capacity of postharvest fruits. Jin et al. (2012) found that yangmei (Myrica rubra) treated with linalool and cinnamaldehyde exhibited higher antioxidant capacity, primarily associated with higher phenolic compound content. High levels of antioxidants can delay physiological deterioration, thus slowing down the senescence of fruits. Tai et al. (2011) evaluated the antioxidant properties of vanillin using various methods and found that vanillin exhibited stronger antioxidant activity compared to vitamin C (Vc) and water-soluble Trolox (vitamin E analog). This indicates that vanillin also possesses a higher level of DPPH radical scavenging ability, thereby reducing damage caused by ROS. Therefore, the research results suggest that vanillin treatment effectively induces antioxidant enzyme activity, helping to balance the levels of ROS in kiwifruit. The interaction among these antioxidant enzymes triggers higher antioxidant activity, thereby maintaining the quality of postharvest kiwifruit and extending its storage time.

In summary, treatment of “Cuiyu” kiwifruit with vanillin at a concentration of 8.0 mg·mL⁻¹ not only eliminates Psa on the fruit surface but also maintains the nutritional quality and commercial value of the fruit. Vanillin, as a secondary metabolite in plants, is a natural phenolic compound with safe and non-toxic biological characteristics. Taking advantage of this, we can explore its potential as a novel fruit preservative. The next step will focus on studying the antibacterial mechanism of vanillin against Psa, optimizing the optimal treatment concentration and duration of vanillin, investigating the synergistic antibacterial effects of vanillin in combination with other substances, and assessing the impact of vanillin on the quality of kiwifruit during cold storage.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.

WLL, WL, and CY contributed to the motivation, the interpretation of the methods, the data analysis and results, and provided the draft versions and revised versions, references. TH, FL, and KH provided the data and results. BG, FX, and SY helped with the revised versions and references. FB, FT, and JC provided the related concepts and minor recommendations, and extracted the conclusion and discussion. All authors contributed to the article and approved the submitted version.

This project was supported by Natural Science Foundation of Hunan Province, No. 2020JJ4050; Fruit plant protection position of Hunan Fruit Industry Technology System in 2022 and 2023; National citrus industry technology system, kiwifruit Changsha comprehensive experimental station.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.