Lactoferrin-low methoxyl pectin (LMP) composite hydrogels: Mechanical and structural properties tailored by LMP and calcium

Abstract

Lactoferrin (LF)-low methoxyl pectin (LMP, 0–0.2 %, w/v) composite hydrogels with great mechanical properties were fabricated with calcium ions (Ca²⁺, 50 and 100 mM). Incorporation of LMP induced changes in mechanical properties by increasing steric hindrance and altering the structure of LF. These changes contributed to denser microstructure of hydrogels with 50 and 100 mM Ca²⁺, leading to superior texture profiles (hardness increased by 22 %–152 % and 50 %–251 %), viscoelastic properties (G′ increased by 25 %–286 % and 6 %–175 %), and water holding capacity (increased by 15 %–26 % and 19 %–30 %), with 0.1 % LMP being the optimal. Hydrogels with 100 mM Ca²⁺ exhibited less homogeneous and compact networks compared to those with 50 mM Ca²⁺, resulting in suboptimal gel properties. Independent of LMP and Ca²⁺ level, all hydrogels contained bound water (∼5 %) and immobilized water (∼95 %), and manifested amorphous structures. Fluorescence spectra elucidated the tertiary structure changes caused by LMP and Ca²⁺. Non-covalent interactions, especially hydrophobic interaction, maintained the LF-LMP hydrogels. Intermolecular force analysis implied the strength of interactions was related to LMP and Ca²⁺ concentrations. Pearson's correlation analysis confirmed that a dense and uniform gel network favors the hydrogel's mechanical properties and water holding capacity. Data suggest that LMP and Ca²⁺ altered the microstructure of LF hydrogel by modifying the conformation and intermolecular forces, thus regulating the mechanical properties.