Espectroscopia Raman aplicada ao estudo de pigmentos de vegetais (legumes e frutas)

Abstract

In this work, Raman spectroscopy was used to identify compounds present in different stages of ripening of the exocarp of scarlet eggplant, two banana cultivars (‘prata’ and ‘nanica’), bell peppers, various varieties of peppers from the Solanaceae family, pink pepper (Anacardiceae), and white and black pepper (Piperaceae). Raman spectroscopy was also used to characterize the substances present in bracts of Euphorbia pulcherrima. Raman spectral analyses of j scarlet eggplant and banana exocarps showed bands attributed to phenolic acids, flavonoids, carotenoids, and fatty acids. scarlet eggplant ripening, changes in the spectral profile were observed mainly in the carotenoid content. Naringenin chalcone and β-carotene were suggested to be responsible for the redorange color of ripe scarlet eggplant. In bananas, variations in chemical composition were more evident in the ‘prata’ cultivar, mainly regarding the content of flavonoids and phenolic acids. In situ analysis of peppers from the Solanaceae family revealed characteristic bands of phenolic compounds, carotenoids, fatty acids, and alkaloids such as capsaicin. In malagueta, habanero, biquinho, and red karneval peppers, a shift of the ν(C=C) stretching bands of carotenoids to lower wavenumbers and band intensification was observed during ripening. In bell peppers, the ripening stage significantly impacted the spectral profile, regardless of the cultivation method. In pink pepper, analyses of the peel and seeds at different ripening stages did not show significant changes. However, bands attributed to anthocyanins, such as pelargonidin, were observed, suggesting that these flavonoids are responsible for the color of the peel. Analyses of black and white pepper revealed characteristic bands mainly attributed to piperine. The assignment of Raman bands was proposed by comparison with literature data and with spectra obtained by the Density Functional Theory (DFT) method. The sum of the theoretical spectra was used to simulate the spectral profile and the contribution of each substance in the experimental spectra. In Euphorbia pulcherrima bracts, characteristic bands of polyphenols, carotenoids, and fatty acids were identified. Green bracts showed a higher intensity of bands attributed to carotenoids, while red, pink, and yellow bracts showed more intense polyphenol bands. White bracts showed the absence of characteristic bands of carotenoids. Cyanidins and pelargonidins were identified as the main anthocyanins, responsible for the variation in bract color. Furthermore, the chemical composition of the crude extracts of green and red bracts interfered with the efficacy of synthesized silver nanoparticles (AgNP), highlighting the importance of Raman spectroscopy in the detection of bioactive compounds for the development of sustainable and innovative methodologies in nanotechnology.