Elaboração de revestimentos comestíveis, avaliação das atividades antifúngica e inseticida de óleos essenciais e compostos-padrão

Abstract

The application of essential oils in food to reduce the use of insecticides and fungicides has been increasingly promising. The aim of this study was to extract and chemically characterize the essential oils of cumin (CEO), laurel (LEO) and tangerine (TEO), as well as to evaluate the insecticidal and antifungal activity of these oils and their principal compounds, cuminaldehyde, 1,8-cineole and limonene, by direct application or by inclusion in edible coatings. The standard compounds were purchased commercially, whereas the essential oils were extracted by hydrodistillation and characterized by gas chromatography coupled to a mass detector. The insecticidal activity was determined in vitro through the acetylcholinesterase inhibition test and in vivo on D. suzukii. The toxicity of CEO and its principal compound cuminaldehyde were evaluated by incorporation into edible coatings applied to strawberries. The coatings contained different concentrations of CEO or cuminaldehyde, a control treatment involving the addition of the coating without the essential oil and another without the addition of a coating were also performed. The coatings were evaluated for their ability to prevent or reduce the birth rate of D. suzukii flies. The antifungal activity against Rhizopus stolonifer was evaluated by the contact method, and the samples used were CEO, LEO, TEO and their respective standard compounds. The antifungal and antiocratoxigenic activity of CEO, LEO and their respective standard compounds against the Aspergillus fungi A.carbonarius, A.niger, A.ochraceus and A. westerdijkiae was also evaluated. Scanning electron microscope (SEM) images were taken to suggest possible modes of action of the compounds analyzed. Antiocratoxigenic activity was determined by HPLC, after the fungi grew in specific culture media. Cuminaldehyde was the principal component in the CEO; 1,8-cineole in the LEO and; limonene in TEO. Acetylcholinesterase inhibition was greater for the CEO sample than for the cuminaldehyde sample. Regarding the toxicity to the D. suzukii fly, good results were obtained for both evaluated samples, CEO and cuminaldehyde, when they were incorporated into the coatings. These coatings did not prevent oviposition in any of the treatments evaluated; however, the natality of D. suzukii flies decreased. Regarding the antifungal activity against R. stolonifer, the mycelial growth of the fungus was completely inhibited by all evaluated samples at the highest concentration tested, with emphasis on the CEO and CPC, for which the lowest minimum inhibitory concentrations were observed. Better results were obtained for CEO for the inhibition of the growth of fungi of the Aspergillus genus and for the inhibition of the synthesis of ochratoxin. Deformations, morphological changes in fungal structures and spore inhibition were observed in the SEM images. Thus, it is inferred that edible coatings incorporated with CEO or CPC can be used as a good management strategy for D. suzukii and R. stolonifer in strawberries. The antifungal and antiocratoxigenic effects of essential oils and standard compounds on fungi of the genus Aspergillus were demonstrated, and these results indicate that they can be promising constituents of antifungals based on natural products.