Changes in Lignin Structure after Rumen Degradation from Different Forage Using High Boiling Solvent by Fourier-Transformed Infrared Spectroscopy
The lignin structure of 22 species of grasses and legume forage which were commonly used as roughage for dairy cows in northeast of China were characterized before and after 16 h rumen degradation. The present study aimed to compare the Fourier-transformed infrared (FT-IR) spectra changes of high boiling solvent lignin structure of the 22 feedstocks especially on syringyl/guaiacyl unit ratios of all the materials. In this paper, average ADL absolute contents of forage samples for in situ nylon bag trial were in the range of 0.15 ± 0.011 g (rice straw) to 0.96 ± 0.014 g (red bean straw) per nylon bag. The spectral feature bands around 830 cm-1 and 1120 cm-1 and 1165 cm-1 indicated that lignin of all the forages in this research was H-S-G type lignin. All the spectra of high boiling solvent lignin showed absorption around 1320 cm-1 (syringyl) and 1260 cm-1 (guaiacyl) and lower intensity of absorption at 1320 cm-1 than 1260 cm-1. The variation on lignin’s syringyl/guaiacyl ratios of raw and rumen-degraded materials for most species had the same trend that the ratio of lignin decreased after 16 h rumen degradation. The syringyl/guaiacyl ratios of the 22 species of forage were at the value of 0.81 in raw materials and 0.78 in rumen-degraded materials on average.