Investigation of the inhibitory effects of levulinic acid on citrus fruit fungi
Fruits are one of the most consumed foods and are highly complex to store and transport as they are highly perishable, with limited shelf life, and consequently correspond to a significant portion of waste in the supply chain. The main losses occur during harvesting and post-harvesting in the storage, processing, and packaging stages. Because they have high amounts of sugars and high moisture in their composition, fruits are susceptible to deterioration, mainly of microbial origin (Facchini et al., 2023; Obuobi et al., 2022).Among the most consumed are citrus fruits, such as oranges, lemons, limes, and tangerines. They are the 26th largest crop in the world in terms of cultivated area and are mainly produced by China, Brazil, India, and the USA (Granone et al., 2022). They are popular due to their high nutritional value; however, they are easily infected by post-harvest pathogens during their storage until final consumption (Guo et al., 2023; Vu et al., 2023; Zhang et al., 2023).Producing and identifying new antimicrobial active ingredients with high efficiency, low toxicity, low environmental pollution, and high safety for human consumption becomes essential. Delaying the onset of fungal diseases in fruit can increase shelf life, decreasing waste and waste generation. New sustainable strategies for preserving fruits and vegetables have been studied, such as treatment with ozone, high hydrostatic pressure, ultraviolet light, and electrolyzed water. However, the search for new disinfecting or sanitizing agents obtained from renewable resources is also a promising alternative and has been highlighted (Mendoza et al., 2022).Levulinic acid is an organic acid obtained from cellulose degradation or acid synthesis of hexoses present in biomass. Like most organic acids, the FDA recognizes LA as safe (GRAS) and has antimicrobial action. Combined with sodium dodecyl sulfate or electrolyzed water, it has already been used as a sanitizer in organic lettuce, in strawberries, in the decontamination of spinach by E. coli, in the inactivation of Listeria monocytogenes in tomatoes, in the reduction of contamination by Salmonella in melons and used gloves for harvesting products, and LA was exploited to inhibit Salmonella. However, there is a limitation of studies regarding the sanitizing effect of LA for the preservation of fruits to combat the appearance of fungi, such as the green mold responsible for significant losses in citrus fruits (Erickson et al., 2018; Mnyandu et al., 2015; Pyatkovskyy et al., 2017; Webb et al., 2013; L. Zhao et al., 2019, 2022; P. Zhao et al., 2020).LA can be obtained from different biomasses, and in this study, LA was obtained from watermelon residue using hydrochloric acid as a catalyst. The reaction was conducted in synthesized microwaves. The final product contains a mixture of LA and formic acid (FA). Therefore, this study aims to explore the inhibitory effect of this mixture obtained from watermelon waste. The investigation will first consist of evaluating the sensitivity of fungi isolated from organic lemon to LA, in different concentrations, through the diffuse disc technique. Subsequently, the preventive effect of the LA and FA solution and formic acid on citrus fungi will be investigated through in vivo tests.