Сhitosan/Manganese(II) Complexes: Synthesis and Effect on Fermentation and Post Acidification of Fermented Milk by <i>Streptococcus thermophilus</i>

Post-acidification is a common challenge for fermented dairy products, which can significantly reduce the shelf life. Herein, we developed metal nanoparticles based on chitosan and Mn(II) ions that can slow down post-acidification and stimulate the milk fermentation process. By systematic characterization and optimization using dynamic and electrophoretic light scattering, X-ray diffraction, SEM, FTIR, and thermal analysis, we obtained nanoparticles with progressively decreasing zeta potential and sedimentation instability in aqueous medium. In addition, the obtained systems reduced the milk fermentation time, thereby demonstrating the effectiveness in accelerating the fermentation process by the gram-positive Streptococcus thermophilus bacterium. They also contributed to ~2 times longer shelf life of fermented milk products by inhibiting the undesirable post-acidification process. The study offers a promising approach to improving the quality and stability of fermented milk products.