Investigation of the influence of pH on the properties and morphology of gelatin hydrogels

Abstract

The behavior of gelatin hydrogels is influenced by the charges located on the amino acid side chains throughout the gelatin molecules. The presence and distribution of ionisable side chains influences the surface activity of gelatin and ultimately determines the material properties. Herein, we report the influence of pH on mechanical properties as studied by texture analysis supported by data from polarimetry, zeta potential, pH titrations and NMR experiments. When adjusted to more extreme pH values (pH 2 and 12), softer gelatin blocks were observed. However, at pH values close to the isoelectric point (pH 5–10), the material is firmer. This behavior is related to the helical content. At pH 2 and pH 12 the surface of the gelatin carries a net charge, positive and negative, respectively, that inhibits the formation of tight helices and lowers the physical crosslink network density. Chemical shift perturbations were observed for the acidic amino acids glutamic and aspartic acid, under acidic pH, where their peaks shifted to higher ppm. Intense amide signals were observed at acidic pH but diminished with increasing pH. This was due to an increase in the rate of chemical exchange between the solvent and peptide amide protons as the pH increases.

Liquid and Pressure-Sensitive Adhesives Based on Cassava Starch and Gelatin Capsule Residue: Green Alternatives for the Packaging Industry

“…Likewise, the authors pointed out that in a composite matrix, the pH value influences the degree of compatibility and the nature of the interactions established between the biopolymers, which affects the microstructure and viscoelastic properties of the resulting gel. In accordance with Goudie et al [22], a dense and compact structure was promoted at a pH close to the isoelectric point, where the interactions within the gelatin network are equilibrated.…”

Physicochemical Properties of Mixed Gelatin Gels with Soy and Whey Proteins

“…A similar result was previously found by Noh et al [3], who noted that the inclusion of soy protein isolate (pH 7.30)/egg-white protein (pH 7.39) mixture increased the pH value of gelatin gels. Fundamentally, the gelation strength of gelatin is affected by the electronic environments surrounding the gelatin molecule, and the cross-linkage between gelatin molecules could be strengthened with predominant positive or negative charges at extreme acid and alkali pH, respectively [17]. Thus, the pH shifted into a neutral region due to the addition of globular proteins, which might be a chemical condition allowing the cross-linkage between gelatin molecules to be weakened.…”

Drug Delivery of Gelatin Nanoparticles as a Biodegradable Polymer for the Treatment of Infectious Diseases: Perspectives and Challenges

“…Gelatin has an IEP around pH 5, at which the gelatin molecules carry no net electrical charge and tend to aggregate, leading to larger nanoparticles. Similarly, temperature can affect the solubility and conformation of gelatin molecules, which in turn influences the size and stability of the resulting nanoparticles [79].…”