Interactions Of Carboxymethyl Modified Polysaccharide With ε-Polylysine

The interaction between ε-polylysine (ε-PL) and anionic polysaccharides has gained considerable attention recently because of its scientific impact on the stability and appearance of liquid food systems. Carboxymethyl modified polysaccharides (carboxymethyl starch and carboxymethyl cellulose) and ε-polylysine were the major researching objective in this paper. First, we analyzed the nature of the thermodynamic properties, electrical properties, polymerization characteristics, apparent phenomena of the complex solution which was formed from ε-polylysine and anionic carboxymethyl polysaccharide. We also studied the feature of ε-PL/anionic carboxymethyl polysaccharide complex solutions under different anions carboxymethyl modified polysaccharide or different environments. Results are as follows:(1) The interactions between ε-PL and carboxymethyl sweet potato starch (CSS) characterized by using isothermal titration calorimetry (ITC), electrical charge and turbidity measurements. The results showed that the interaction between ε-PL and CSS was electrostatic and mainly depends on the molar ratio of amino groups in ε-PL to carboxyl groups in CSS. The interaction between ε-PL and CSS were also associated with degree of substitution (DS) of CSS, pH, ionic strength of the system and mixing mode of the two solutions. For the interaction of ε-PL with high DS (>0.225) CSS, three status of ε-PL/CSS mixture were observed as transparent, turbid and precipitated with successive increase in amino/carboxyl molar ratio. Distinguishingly, a transparent mixture could obtain for CSS with low DS (0.114) at sufficiently high amino/carboxyl molar ratio. The higher the pH. the higher the degree of ionization of the carboxyl group in the CMC solution, the system is more stable, and it is easy to precipitate. The NaCl containing in the solution will hinder the electrostatic attraction of CSS and ε-PL. Using an manner of equal volume mixed, ε-PL/CSS composite particles formed through CSS with ε-PL is more easily dispersed at sufficiently high amino/carboxyl molar ratio after binding in solution and achieve a steady state.(2) The interactions between ε-PL and carboxymethylcellulose (CMC) characterized by using electrical charge, turbidity and size measurements. The results showed that the interaction between ε-PL and CMC was electrostatic and mainly depends on the molar ratio of amino groups in ε-PL to carboxyl groups in CMC.The interaction between ε-PL and CSS were associated with degree of substitution (DS), viscosity and concentration of CSS, and pH, ionic strength of the system. A transparent mixture could be obtained for CSS with low DS (0.9) at sufficiently high amino/carboxyl molar ratio. Large concentration or viscosity of the CMC will increase the size of the ε-PL/CMC composite particles and lead to the particles precipitate in the solution easily. The lower the pH, the more unstable of the system, which is relevant with the degree of ionization of the carboxyl group in the CMC solution. The sodium ions in solution will hinder the electrostatic attraction of CMC and ε-PL.Hence, this study provided basic guidance in designing liquid food systems containing both ε-PL and CSS (CMC), and the conclusions also can apply to containing carboxymethyl-modified polysaccharides and ε-polylysine in the food system.