Complexation Kinetics, Dissociation, and Interaction Mechanism of Cationic Peptide ε-Poly-L-Lysine Complexed with Negatively Charged Polysaccharides

ε-Poly-L-lysine (ε-PL) is a polycationic antimicrobial peptide with a high positive charge density, widely used as a natural preservative in the food industry. However, ε-PL is susceptible to the influence of negatively charged polysaccharides and other components in food matrices. In order to investigate the kinetics of complexation kinetics between ε-PL and negatively charged polysaccharides [PS(-)], including sodium alginate (NaAlg), sodium carboxymethyl cellulose (CM C-Na), and κ-carrageenan (Carra), and explore the dissociation effects of temperature, pH, ionic strength, and food ingredients (sucrose) on the ε-PL/PS(-) complexes, the interaction mechanism between PS(-) and ε-PL was analyzed with infrared spectra. The results showed that the mass ratio of NaAlg or CM C-Na to ε-PL had a significant effect on the formation of complexes. There was no interaction at the mass ratio of NaAlg or CM C-Na/ε-PL at 1:1, and the rapid formation of complexes was observed at mass ratio of 8:1 or above. While for Carra, the complexation process was slower than that of NaAlg and CM C-Na with ε-PL. Temperatures above 40 ℃ caused the dissociation of the ε-PL/NaAlg and ε-PL/CM C-Na complexes, but had no effect on the complexation of ε-PL/Carra. All three ε-PL/PS(-) complexes were dissociated under alkaline conditions. The ε-PL/NaAlg and ε-PL/CM C-Na complexes were dissociated by NaCl, and the complete dissociation was achieved at the NaCl concentration of 30 mg/mL and 25 mg/mL, respectively. There was no dissociation effect of NaCl on the ε-PL/Carra complexes. Sucrose at 50 mg/mL led to the complete dissociation of ε-PL/NaAlg complexes, and 90 mg/mL sucrose induced the complete dissociation of ε-PL/CM C-Na complexes, while sucrose was ineffective for the ε-PL/Carra complexes. The infrared spectra indicated that the electrostatic forces and hydrogen bonds were responsible for the interactions between NaAlg, CM C-Na and Carra with ε-PL. This study aimed to provide a scientific guideline for the practical application and functional regulation of ε-PL in the food industry.