Ficus awkeotsang Makino pectin in acidic environments: Insights into pectin structure, gelation behavior, and gel properties

Abstract

This study demonstrated the gelation capacity, gelation behavior, and mechanism of Ficus awkeotsang Makino pectin (JFSP) in acidic media (pH 3.4–4.5). JFSP exhibited an extraordinary ability to spontaneously form a gel at a low polymer concentration (0.3 %, w/v) within the pH range of 3.75–4.05 at room temperature, without the need to introduce exogenous metal ions or co-solutes. Analysis of zeta potential and carboxyl dissociation extent revealed the protonation of free carboxyl groups within JFSP under acidic conditions. Atomic force microscopy and small angle X-ray scattering elucidated the aggregation morphology and folding conformation of JFSP. At pH 3.8, the correlation length (ξ) of JFSP chains decreased to around 1.67 nm. Rheological experiments confirmed the formation of a stronger gel network at pH 3.8 and 4.0, with good thermal and freeze-thaw stability. Isothermal Titration Calorimetry (ITC), temperature sweeps, and gelation force analyses emphasized the pivotal role of hydrogen bonds in JFSP gels at pH 3.8 and 4.0. Further reducing the pH to 3.4–3.6 disrupted the dynamic equilibrium of gel-driving forces, leading to the formation of a flocculated gel network. These findings deepen our understanding of JFSP behavior in low-acid conditions, which may be useful for further food formulations at these conditions.