Multifunctional Chitosan/Mn(II) Complexes: Preparation, Catalytic Activity in Imine Synthesis and Aldol Reaction, and Effect on Milk Fermentation/Post-Acidification.

Herein, we prepared nanoparticles of chitosan-manganese(II) complexes in different molar ratios (1:2, 1:1, and 2:1) and fully characterized them using dynamic and electrophoretic light scattering, X-ray diffraction, SEM, FTIR, and thermal analysis. Nanoparticles Chitosan + Mn2+ (1:1) have a high catalytic activity in the oxidative coupling of benzylamine, resulting in the imine formation and also in selective aldol reaction. Chitosan + Mn2+ (1:1) catalyze the reactions in the greenest solvents: water and water/ethanol mixture. Moreover, Chitosan + Mn2+ (1:1) is very easy to prepare and convenient to use. The catalyst is separated from the reaction mixture by a simple nanoporous filter or centrifugation and does not lose catalytic activity after at least ten uses. The chitosan-manganese(II) complexes reduce the milk fermentation time, demonstrating the effectiveness in accelerating the fermentation process by Streptococcus thermophilus. They also contribute to increasing the shelf life of fermented milk products by inhibiting the undesirable post-acidification process. We found that the optimal ratio of chitosan and Mn2+ to manifest the apogee of the desired effects (acceleration of milk fermentation and increase in the shelf life of the fermented product) is 1:2.