Influência da adição de ácido cítrico como agente reticulante nas propriedades de filmes de galactomanana de Prosopis juliflora (Sw.) Dc

Abstract

The bioplastics synthesized from polysaccharides have low physical and mechanical properties compared to synthetic polymers. The use of citric acid as a crosslinking agent has been investigated as a strategy to improve the properties of these biopolymers. In this context, the objective of this study was to evaluate the influence of citric acid on biodegradable films made from Prosopis juliflora (Sw) DC galactomannan. Initially, the galactomannan (GAL) was obtained by ethanol extraction and characterized in terms of yield, granulometry, and nuclear magnetic resonance (NMR). Then, the gum was used as a polymeric matrix in the production of biodegradable films, along with corn starch (AM), glycerol (GLI), and citric acid (CA), resulting in seven formulations: F1 (80% AM, 20% CA), F2 (70% AM, 10% CA, 20% GLI), F3 (80% GAL, 20% GLI), F4 (70% GAL, 10% CA, 20% GLI), F5 (60% GAL, 20% CA, 20% GLI), F6 (40% AM, 30% GAL, 10% CA, 20% GLI), and F7 (40% AM, 30% GAL, 20% CA, 20% GLI). GAL and the films were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-VIS) spectrophotometry, tensile strength, contact angle, rheology, zeta potential, roughness, and thermal analysis (TG/DSC). They were then used in the preservation of acerola fruits. The yield of GAL was 11.68%, and it showed a polydisperse particle distribution system with a mannose:galactose ratio of 1.81, which indicates the difficulty of gum solubility. The films showed a semi-crystalline nature, and the addition of citric acid as a crosslinking agent in formulations F4, F5, F6, and F7 was confirmed by the formation of ester bonds, characterized by the spectral band around 1720 cm-1 in the FTIR. Additionally, these films showed low ultraviolet absorption intensity, increased elongation rate, higher hydrophilicity, roughness, and thermal stability. When applied as a coating on acerolas, formulations F4, F5, F6, and F7 reduced the mass loss rate, increasing the fruit's shelf life. The results obtained confirm the positive influence of citric acid as a crosslinking agent on the properties of Prosopis juliflora (Sw) DC galactomannan films.