Chemical structure, morphology, and physicochemical properties of highly methylated pectin functionalized by amidation in homogeneous and heterogeneous medium

The present study explores the amidation of highly methylated pectin in a homogeneous medium. N-alkylpectinamide derivatives were synthesized at room temperature over 24–72 hours using various pectin/alkylamine mass ratios. The prepared derivatives were subjected to various physicochemical analyses, including solubility tests, Fourier-transform infrared (FTIR) spectroscopy, determination of degrees of esterification (DE) and amidation (DA), surface tension measurements, and emulsifying activity assessments. In addition, the surface and morphological characteristics of both native and modified pectins were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The findings revealed that most amidated pectin derivative exhibited reduced water solubility, with the appearance of new bands around 1650 cm⁻¹ and 1550 cm⁻¹, indicating the presence of substituted CONHR groups. SEM and AFM analyses showed that amidation in a homogeneous medium resulted in irregular morphologies, characterized by rough surfaces and short, individualized chains. Elemental analysis indicated a high nitrogen content (3.97 %) in the modified pectins. Furthermore, this study demonstrated that amidation in homogeneous medium was an effective method for producing highly substituted N-alkylpectinamide derivatives (DA = 30 %) with great surfactant properties (∼47.4 mN/m) and important emulsifying activity (59 % - 62 %).