2.6.1. Monosaccharide Composition Analysis of Kefir EPS

The monosaccharide composition of EPS of K1 and K2 was determined as our previous method with minor modifications [24]. 5 mg of EPS was hydrolyzed with 2 mL of 2 M trifluoroacetic acid (TFA) at 120 °C for 2 h. The residual TFA was removed through rotary evaporation. Subsequently, the residue was dissolved in deionized water and mixed with 0.5 M 3-methyl-1-phenyl-2-py-razolin-5-one (PMP) solution and 0.3 M NaOH solution, and then reacted at 70 °C for 30 min. After neutralization with 0.3 M HCl, the solution was added to 2 mL of deionized water and 4 mL of chloroform followed by the vortex. The upper aqueous phase was analyzed by Waters 2695 HPLC system equipped with a photo-diode array (PDA) detector and a C₁₈ column (250 mm × 0.4 mm i.d., 0.5 μm) at a flow rate of 0.8 mL/min at 25 °C. The mobile phase consisted of 0.1 M ammonium acetate, acetonitrile and tetrahydrofuran at the volume ratios of 81:17:2.