Measurement of the Water Relaxation Time of ε -Polylysine Aqueous Solutions

ε -Polylysine is an effective food preservative. In this paper, the β -relaxation time of ε -polylysine aqueous solutions, which represents the rotational speed of a single water molecule, was measured by broadband dielectric spectroscopy at various temperatures and concentrations. The broadband dielectric spectrum of each sample containing water ranging from 35 wt% to 75 wt% at temperatures ranging from 0∘C to 25∘C was measured using a co-axial semirigid cable probe. The measured dielectric spectra of the samples were composed of several Debye relaxation peaks, including a shortest single molecular rotational relaxation time of water, the β -relaxation time, longer than that of pure water. This result represents that ε -polylysine suppresses the molecular kinetics of water. It is also found that the β -relaxation time of an ε -polylysine solution that contained more than 35 wt% water showed a typical Arrhenius plot in the temperature range from 0∘C to 25∘C. The activation energy of each sample depends on the water content ratio of the sample. As indicated by its long β -relaxation time, ε -polylysine is expected to possess high abilities of suppressing freezing and ice coarsening.