Desenvolvimento e caracterização de filme polimérico produzido a partir de gelatina de pele detilápia (Oreochromis niloticus) contendo lignina encapsulada

Abstract

The development of biodegradable films from agro-industrial waste represents an alternative to conventional synthetic polymers. This study aimed to develop and characterize films based on gelatin obtained from Nile tilapia (Oreochromis niloticus) skin, containing lignin encapsulated by pectin (LP). The gelatin showed an extraction yield of approximately 16%. The films were produced via casting using formulation M4, composed of 5% gelatin, 1% glutaraldehyde, and 0.6% glycerin, as well as formulations M4 + LP 0.2% and M4 + LP 1.0%. Colorimetric and mechanical properties, solubility, biodegradation, and spectroscopic characteristics (UV-Vis diffuse reflectance, fluorescence, and FTIR) were evaluated. Quantitative data were analyzed using descriptive statistics, ANOVA, and Tukey's test, with a significance level of 5%. Tensile strength was 8.00 MPa for M4, 7.68 MPa for M4 + LP 0.2%, and 10.04 MPa for M4 + LP 1.0%, demonstrating an increase of approximately 25.5% in the formulation with the highest LP concentration. Conversely, elongation decreased from 87.04% to 40.88% and 16.75%, respectively, indicating increased rigidity and reduced matrix mobility. The average mass gain in the permeability test was 0.1579, 0.1549, and 0.1212 g·day⁻¹ for M4, M4 + LP 0.2%, and M4 + LP 1.0%, respectively. Water vapor permeability decreased from 4.0062 to 3.9301 and 3.0758 g·mm·m⁻²·day⁻¹·kPa⁻¹, corresponding to a reduction of approximately 23.2% for M4 + 1.0% LP. Average solubility showed a slight decrease, from 18.83 ± 1.78% to 18.27 ± 2.07% and 17.94 ± 0.83%, with no significant difference according to ANOVA (F = 0.374; p = 0.695). In the soil burial test, the films lost integrity before a complete mass curve could be obtained, with disintegration and the presence of mycelium observed by the sixth day. Regarding diffuse reflectance, the average value in the UV region dropped from 6.12% to 4.87% and 2.05%. The maximum Kubelka–Munk function increased from 9.02 to 11.22 and 28.42, representing a 214.9% increase for the formulation with 1.0% LP and indicating greater ultraviolet radiation attenuation. In fluorescence analysis, peak maxima remained between 495.5 and 497.0 nm, but intensity decreased from 3198 a.u. to 1859 and 1301 a.u., corresponding to quenching rates of 41.87% and 59.32%. The full width at half maximum (FWHM) ranged from 76.6 nm for the control to 84.1 nm for M4 + 1.0% LP. FTIR analysis confirmed characteristic bands for gelatin, lignin, and pectin without the formation of new detectable functional groups, suggesting predominantly intermolecular interactions. The pectin exhibited an estimated degree of methylation between 40% and 46%, classifying it as low-methoxyl pectin. It is concluded that M4 + 1.0% LP exhibited the best performance regarding barrier properties, mechanical strength, and optical protection, albeit with a marked loss of flexibility.