2.6. Bacterial Zeta Potential

Changes in the surface groups of the bacteria were indirectly measured by determining the surface charge of the fresh and rehydrated freeze-dried Lp. plantarum HAC03 cells with or without the food additives incorporated into the mix. The assay was carried out by mixing the previously rehydrated bacteria with 9 mL of double-distilled water (DDW) at pH 2.0 to reach a final concentration of 1 × 10⁸ CFU/mL. The pH was measured and corrected to pH 2.0 by adding 0.1 N HCl or 0.1 N NaOH, and 800 μL samples were loaded in DTS1070 cuvettes. The samples were measured on a Zetasizer Nano ZEN 3600 after 2 min equilibration time (Malvern Panalytical, Malvern, UK) and the Smoluchowski model was used to convert electrophoretic mobility data to zeta potential values [34], which were considered as the average of three reads.