Abstract
Consumers demand the use of eco-friendly fungicides to treat fruit and vegetables and governmental authorities have unauthorized the application of chemical antifungals for the efficient control of sour rot. In the present research, the microwave irradiation (MW) method was used to encapsulate thymol into 2-hydroxylpropyl-beta-cyclodextrin (HP-β-CD) and the effect of these HP-β-CD on controlling sour rot in citrus fruit, caused by Geotrichum citri-aurantii, was evaluated. Amounts of 25 and 50 mM of HP-β-CD-thymol were used, and compared with propiconazole, to control the decay of inoculated lemon fruit. The treatments were performed in curative and preventive experiments. The incidence and severity of Geotrichum citri-aurantii in 25 and 50 mM HP-β-CD-thymol-treated fruit were reduced in both experiments. The preventive 50 mM HP-β-CD-thymol treatment showed the best effect, reducing the sour rot, respiration rate and fruit weight loss during storage at 20 °C. HP-β-CD-thymol increased polyphenol concentration and the activity of antioxidant enzymes, such as catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD) in lemon peel, and the highest effects were found with the 50-mM dose. In conclusion, the results show that the use of thymol encapsulated by MW into HP-β-CD could be an effective and sustainable tool, a substitute to the synthetic fungicides, for G. citri-auriantii control in citrus fruit.
Highlights
Sour rot disease, occasioned by the fungus Geotrichum citri-aurantii (G. citri-aurantii), is one of the main rot types of citrus fruit [1]
We found that the microwave encapsulation method (HP-β-CD-thymol-microwave irradiation (MW)) was the best to encapsulate the essential oils and to control G. citri-aurantii growth and its sporulation and bacteria growth
Given the known role of HP-β-CD-thymol-MW in suppressing G. citri-aurantii by in vitro experiments, the goal of this research is to assess the in vivo antifungal effect of the HP-β-CD-thymol encapsulated by the microwave method by using lemons inoculated with G. citri-aurantii
Summary
Sour rot disease, occasioned by the fungus Geotrichum citri-aurantii (G. citri-aurantii), is one of the main rot types of citrus fruit [1]. This decay is the second cause of post-harvest citrus decay after Penicillium spp. G. citri-aurantii involves the secretion of extracellular endopolygalacturonases (PG) which quickly macerate the tissues of the fruit and the contact between fruit cells and the secreted juices of the infected area can reach the healthy areas propagating the rot during storage [2]. The ideal conditions for infection to occur are turgid fruit skin with free water, ambient temperatures between 12 and 36 ◦ C, pH ranging from 2.0 to 8.5, high relative humidity (92% to 98%) and availability of sugars, acids and starch. The aggressiveness of the fungus increases over degreening and fruit maturation [3]
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