Luis Fernando Arau, Celia Flores, Gabriel Ascanio, Leobardo Serrano‐Carreón, Enrique Galindo
Knowledge of the rheological properties of biopolymers, such as viscosity, viscoelasticity, flow behavior, and shear, is fundamental because it determines how these materials deform and flow under external forces during processing and thus meet specific requirements that define their applications. Poly-γ-glutamic acid (PGA) is an edible, biodegradable, non-toxic, and non-immunogenic biopolymer with very important applications. In the present study, the PGA from Bacillus velezensis 83 was characterized in detail in rheological terms, highlighting its ultra-high molecular weight (5,900 kDa), high consistency index (27.22 Pa·sⁿ), flow behavior index (0.29), and a yield stress of 34.7 Pa, as well as the high viscosifying power (up 8-fold higher, compared to other PGA polymers reported), for 31 g/L of PGA. Normal stress measurements indicated that this property is a function of polymer concentration, reaching a maximum value of 2,760 Pa at 31 g/L and a shear rate of 1,500 s⁻¹. Amplitude sweep tests showed that at 13 g/L the PGA exhibited a viscoelastic fluid behavior, while at 24 g/L and 31 g/L, it showed the behavior of a viscoelastic solid at rest. In addition, the stiffness of PGA increased as polymer concentration increased reaching values up to 800 Pa for 31 g/L. PGA produced by Bacillus velezensis 83 showed remarkable rheological properties, making this polymer a unique and valuable product for high-value applications. • Bacillus velezensis 83 synthetizes Poly-γ-glutamic acid with high molecular weight • Poly-γ-glutamic acid from Bacillus velezensis 83 shows high viscosifying power • Poly-γ-glutamic acid from Bacillus velezensis 83 is a viscoelastic polymer • Poly-γ-glutamic culture broths from Bacillus velezensis 83 shows high yield stress • Poly-γ-glutamic acid presents an elastic solid recovering structure after deformation