Chitosan and its derivatives regulate lactic acid synthesis during milk fermentation

The results of the study showed that when <i>L. bulgaricus</i> was cultured in the presence of 25.4 kDa oligochitosans at concentrations of 0.0025%, 0.005%, 0.0075% and 0.01%, the average rate of LA synthesis over 24 hours was 11.0 × 10^-3 mol/L/h, 8.7 × 10^-3 mol/L/h, 6.8 × 10^-3 mol/L/h, 5.8 × 10^-3 mol/L/h, respectively. The 45.3 kDa oligochitosans had a similar effect, while the average rate of lactic acid synthesis in the control sample was only 3.5 × 10^-3 mol/L/h. Notably, 350 kDa chitosan did not affect the rate of lactic acid synthesis compared with the control sample. Interestingly, interaction of chitosan with <i>L. bulgaricus</i> led to a slowdown in the synthesis of propanol, an increase in the content of unsaturated and saturated fatty acids, and a change in the composition and content of other secondary metabolites. The quantity of <i>L. bulgaricus</i> in a sample with 0.01% chitosan exceeded their content in the control sample by more than 1,700 times. At the same chitosan concentration, the fermentation process was slowed down, increasing the shelf life of the fermented milk product from 5 to 17 days while maintaining a high content of <i>L. bulgaricus</i> (6.34 × 10⁶ CFU/g).