Derivatization of hydrolysates with 1-phenyl-3-methyl-5-pyrazolone (PMP)
The monosaccharide composition of the samples was determined by PMP derivatization following a previous method (B. Zhao et al., 2020). The mixture of 2 mL 2 M trifluoroacetic acid was mixed, and the samples were kept in an oven at 100 °C overnight for hydroxylation. After drying, 1mL of methanol was added to the residue, which was then dried using a nitrogen stream. The hydrolyzed sample was dissolved in 10 mL water for derivatization. The hydrolyzed sample was mixed with 5 mL 0.3 M sodium hydroxide. After 70 °C and 1 h incubation, the reaction mixture was neutralized with 5 mL of 0.3 M hydrochloric acid. The resulting solution was extracted thrice with chloroform and the aqueous layer was filtered and analyzed by HPLC (1260, Agilent, USA) equipped with Diamonsil C18 column (250 × 4.6mm, 5μm).