Intermolecular interactions and gel properties of composite agglomerative networks based on oppositely charged polymers: Effects of pH and ionic strength

Abstract

The effects of pH and ionic strength on the intermolecular interactions and gel properties—textural and mechanical properties, water holding capacity, and color— of kidney-bean-protein-isolate–sodium-alginate (KPI-SA) composite gels were investigated. According to the zeta potentials of KPI, SA, and KPI-SA in the pH range of 2.0–7.0, pH values of 3.0, 4.0, 5.0, and 7.0 were selected as the experimental conditions. Protein solubility and ATR-FTIR analysis results indicated that the forces for the formation of KPI-SA gels were different under different conditions. Specifically, under neutral conditions (pH 7.0), hydrogen bonding was the most significant force, but when the pH (5.0) approached the isoelectric point (pI), hydrophobic interactions became dominant. Furthermore, as the pH (4.0, 3.0) became lower than the pI, electrostatic association became the main force. With an increase in Ca2+ concentration (20–80 mg/mL), the hydrophobic interactions were gradually enhanced while the electrostatic association was first enhanced and then weakened. When the pH decreased or the ionic strength increased, the KPI-SA gel network gradually formed a uniform and dense honeycomb structure, and the gel texture and mechanical and water-holding properties improved accordingly. The obtained results suggest that moderate acidification and increased ionic strength are promising conditions to produce composite gels for use in the food industry and other fields.