Caracterização e aplicação de revestimento de quitosana e óleo essencial de Cymbopogon citratus (D. C.) Stapf. para o controle da qualidade pós-colheita de goiabas

Abstract

Guava (Psidium guajava L.) is a tropical fruit much appreciated for its slightly acid sweet taste and its important nutritional value. In the postharvest period, guava has a fast ripening process characterized by accelerated yellowing of the peel, weight loss and firmness, and degradation of compounds, generating losses and impacting their acceptability. Chitosan (Chi) is low toxicity, biodegradable polymer that has film-forming properties and antimicrobial activity. The use of edible coatings based on Chi has been proposed as a postharvest technology for fruit preservation. It has been suggested that the incorporation of essential oils (EO) improves the effectiveness of Chi coatings in the preservation of guavas. However, the surface characteristics of Chi coatings incorporated or not with EO remain unknown. This study aimed to characterize the physical, chemical and surface properties of an antifungal coating formulated with Chi (5 mg / mL) and Essential oil of Cymbopogon citratus (DC) Stapf (CCEO) (0.6 μL / mL) and to evaluate its effectiveness in maintaining postharvest quality in guavas cv Paluma during cold storage (12 ºC ± 1). The Chi-CCEO coating was characterized in terms of water solubility (WS), water activity (aw), identification of organic functional groups by Fourier Transform Infrared Spectroscopy, thermal properties through Differential Scanning Calorimetry and surface by 3D Optical Profilometry. Tests were also carried out to evaluate the effectiveness of the Chi-CCEO coating on the physical-chemical aspects (weight loss, firmness, color, titratable acidity, pH, total soluble solids, sugars, organic acids and phenolic compounds), microbiological, enzymatic, and sensorial in guavas cv. Paluma stored at 12 ºC. The Chi-CCEO coating showed low WS (22.56 ± 0.15) and aw (0.22 ± 0.01), good thermal resistance (1st peak at 136 ºC, 2nd peak at 260 ºC), flat surface, smooth and of low roughness (Sa = 0.005 μm). The application of the Chi-CCEO coating delayed losses in weight and firmness, changes in total soluble solids, titratable acidity, pH and color in guavas during storage. Guavas coated with Chi-CCEO showed lower (p <0.05) fructose content and higher (p <0.05) contents of citric and succinic acids compared to uncoated guavas after 10 days of storage. Phenolic acids (syringic acid and chlorogenic acid) decreased and flavonoids (hesperidin, cis-resveratrol, catechin, procyanidin B1 and myricetin) increased in both groups of fruits, but these changes were delayed in guavas coated with Chi-CCEO. Uncoated guavas showed higher (p <0.05) activity of polyphenol oxidase and pectin methylesterase and lower (p <0.05) peroxidase activity than those coated with Chi-CCEO, after 5 days of storage. Guavas coated with Chi-CCEO were preferred by the panelists and received higher scores (p <0.05) for texture, color and overall impression, but lower scores for the odor attribute than uncoated guavas during storage. The results indicate that the tested Chi-CCEO coating proved to