Method for detecting glycosidic bonds of plant polysaccharides

A method for detecting glycosidic bonds of plant polysaccharides, comprising steps of:

• (a) performing methylation of the plant polysaccharides;
• (b) derivatizing glycosidic residues of the methylated plant polysaccharides with PMP reagent (1-phenyl-3-methyl-5-pyrazolone);
• and
• (c) performing mass spectrometry analysis by LC-MS;
• and wherein the steps (a)-(c) comprise steps of:
• (1) dispersing the plant polysaccharides in 100 μL of NaOH-DMSO suspension to a concentration of 1 mg/mL and shaking at room temperature for 30 minutes, and adding 40 μL of iodomethane and shaking for 1 hour;
• repeating three times to obtain the methylated and substituted polysaccharides;
• (2) placing the methylated and substituted polysaccharides in an ice bath, adding 500 μL of water of 0° C. to terminate reaction, and standing for 10 minutes;
• (3) adding 800 μL of dichloromethane and shaking for 30 seconds, and removing supernatant;
• (4) repeating steps (2) and (3) three times;
• then drying a lower organic layer with nitrogen to obtain partially methylated glycoside residues;
• (5) adding 100 μL of 2 M trifluoroacetic acid to a product resulted from step (4), hydrolyzing at 100° C. for 8 hours, and blow drying with nitrogen after hydrolysis;
• (6) adding 100 μL of 0.2 M PMP methanol solution to a product resulted from step (5), and heating in a 70° C. water bath for 30 minutes to obtain partially methylated PMP-derived glycoside residues;
• and
• (7) taking a product resulted from step (6) out, cooling at room temperature, drying in vacuum, dissolving in 1 mL of 70% methanol aqueous solution, and analyzing qualitatively and quantitatively by LC-MS in MRM mode, and wherein the plant polysaccharides are citrus pectin or araban.