Long-term stabilization of living bacterial formulations using a biodegradable chitosan-based composite hydrogel
Description
Maintaining the viability and functional stability of living microorganisms during prolonged storage and transport remains a major challenge. In this study, we evaluated the potential of immobilization in a carboxyethylchitosan-based gel for four different probiotic bacterial strains (E. faecium L3, E. fae-calis, B. subtilis, and E. coli ) over a storage period of up to 12 months at +22 °C and +4 °C. We measured bacterial growth curves, optical density values, titer values, and growth kinetics using seven kinetic models at time points of 0, 2, 4, 6, and 12 months. For each kinetic model, we determined the goodness-of-fit metrics (R2, RMSE, AIC) and estimated parameters (y0, ymax, µmax, λ). Bacterial cultivation was performed in a bioreactor, and the data analysis was conducted using the R programming language with the minpack.lm library. During the storage of liquid controls under both temperature regimes, a significant decrease in bacterial titer was observed, whereas the gel carrier maintained a high initial bacterial titer over one year. The observed increase in the B. subtilis titer to 1010 CFU/mL, compared to other strains (typically 107 CFU/mL), is apparently due to the production of chitinases and chitosanases, which allow the bacterium to utilize chitin and chitosan as carbon and energy sources. Over the 12-month observation period, the maximum specific growth rate (µmax) varied within ranges typical for the studied species; ymax values were higher in the immobilized samples, while the lag phase (λ) was shorter than in the controls. Overall, this research highlights the potential of natural polymer hydrogels as versatile platforms for probiotic storage and encapsulation.