The Gal A content in hawthorn pectin was determined using the carbazole-sulfuric acid method according to Chen [21 ]. In total, 0.5 mL of D-Gal A standard solution (20, 40, 60, 80, 100 mg/L, respectively) was placed in a stoppered test tube. Then, 3 mL of borax sulfuric acid solution (5 mg/mL) was added under ice-water bath conditions and mixed with a vortex mixer. The resulting mixture was kept in a boiling water bath for 5 min, then immediately cooled. After that, a 0.1 mL aliquot of the carbazole solution (0.1%) was added to the mixture, boiled for 5 min, cooled to room temperature, and the absorbance was measured at 530 nm. A total of 0.5 mL of sample solution was used instead of the standard solution and the absorbance value was measured.
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