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<p>Poly(γ-glutamic acid) (PGA), a naturally occurring biopolymer, is a highly viscous polyamide. PGA is nontoxic and biodegradable and is employed as a safe material in industrial applications. However, reductions in its molar mass and viscosity have been observed upon storage for long periods, even at temperatures of 4–25 °C. Although a decrease in the molar mass of PGA was observed after treatment at 100 °C for 24 h in aqueous solution, this reduction was suppressed upon increasing the pH from 7.0 to 11.0 in the analyses of agarose gel electrophoresis and size exclusion chromatography with multiangle light scattering. The morphology and particle size of PGA treated at 4 and 100 °C were compared using atomic force microscopy (AFM) and dynamic light scattering, respectively. The structure of the PGA treated at 4 °C was similar to that of anionic polysaccharides with fibril networks. Heat treatment induced the loss of the reticular structure and the appearance of spherical particles. Meanwhile, alkaline conditions restricted the spheroidization of PGA to maintain a fibril network structure according to the AFM images. The findings of this study can be applied to the development of novel technologies to prevent PGA deterioration.</p>

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Heat-induced structural changes in poly(γ-glutamic acid) and the effects of alkaline conditions on its thermal stability and morphology in aqueous solution

  • 期刊论文

  • 发表日期：

    2026年2月10日

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  • Akari Mizushima,
  • Kazuki Kobayashi,
  • Yuki Matsumoto,
  • Yoshihiro Yamaguchi,
  • Ryoji Masui,
  • Akira Ogita,
  • Shinichi Kitamura,
  • Masao Inoue,
  • Ken-ichi Fujita

摘要

Poly(γ-glutamic acid) (PGA), a naturally occurring biopolymer, is a highly viscous polyamide. PGA is nontoxic and biodegradable and is employed as a safe material in industrial applications. However, reductions in its molar mass and viscosity have been observed upon storage for long periods, even at temperatures of 4–25 °C. Although a decrease in the molar mass of PGA was observed after treatment at 100 °C for 24 h in aqueous solution, this reduction was suppressed upon increasing the pH from 7.0 to 11.0 in the analyses of agarose gel electrophoresis and size exclusion chromatography with multiangle light scattering. The morphology and particle size of PGA treated at 4 and 100 °C were compared using atomic force microscopy (AFM) and dynamic light scattering, respectively. The structure of the PGA treated at 4 °C was similar to that of anionic polysaccharides with fibril networks. Heat treatment induced the loss of the reticular structure and the appearance of spherical particles. Meanwhile, alkaline conditions restricted the spheroidization of PGA to maintain a fibril network structure according to the AFM images. The findings of this study can be applied to the development of novel technologies to prevent PGA deterioration.