Mesquite gum/chitosan insoluble complexes: relationship between the water state and viscoelastic properties

Abstract

The aim of this work was to form polyelectrolyte complexes (PECs) mesquite gum (MG) and chitosan (Ch), as a function of the biopolymer mixing ratio (R_MG/Ch). The water state during PECs formation was monitored as a way of assessing its effect on the viscoelastic properties. The maximum difference of zeta potential values for polyelectrolyte solutions as a function of pH was found in the range from 4.0 to 5.0. PECs were obtained with zeta potential values of ∼ |< 10 mV| between R₇ – R₁₂ at a pH of 4.5. This condition was favorable for producing high insoluble-PECs yield (92.16 ± 0.56%). The viscoelastic properties and water state assessed the insoluble-PECs interactions. The insoluble-PECs exhibited a liquid-like behavior, typical of concentrated solutions. Similar loss modulus was observed independently of the R_MG/Ch. (G” ∼ 20 Pa, ω = 1 rad/s). DSC analysis showed that the water content influences the water state of insoluble-PECs. Freezing water increased exponentially with the increase of the water content independently of the R_MG/Ch. Nonfreezing water reached a maximum value of 37% around of 50% of water content, showing the hydrophobic nature of insoluble-PECs. This work will support futures studies to use PECs for foods and pharmaceutical applications.

Graphical Abstract

Keywords:

• Polyelectrolyte complexes
• zeta potential
• viscoelasticity
• freezing water
• nonfreezing water

Acknowledgments

We would like to thank the “Consejo Nacional de Ciencia y Tecnología de México” (CONACyT) for financing this study through grant CB-2015-01-258118.