# Enzymatic Degradation of _Gracilariopsis lemaneiformis_
## 2 Results and Discussion
### Fourier Transform Infrared Spectra (FT-IR) Analysis  
FT-IR analysis was used in studying the structures of the polysaccharides (GLP and its enzymatic degradation products) according to the characteristic absorption feature. Figure S1 showed that GLP, GPP, GGP, GCP, GXP, and GDP had the typical absorptive peaks of glycosidic structures. The broad, strong absorptive peak at 3363.25-3403.74 cm\({}^{-1}\) indicated that the presence of many intramolecular and intermolecular hydrogen bonds featuring hydroxyl stretching vibration. The absorption peak at approximately 2901.38-2936.09 cm\({}^{-1}\) was a C-H stretching vibration peak, and the relatively strong absorption peak at 1594.84-1648.84 cm\({}^{-1}\) was caused by the asymmetric and symmetric stretching vibrations of COOH [18]. All samples had absorption bands near 1373.07-1413.57 cm\({}^{-1}\) due to the variable angle vibration of C-H. The characteristic absorption peaks at 1245.79-1255.43 cm\({}^{-1}\) were attributed to the S=O vibration of the sulfate groups in GLP and its degradation products, which was consistent with the results in Table 1. The peaks at 1036.55-1075.12 cm\({}^{-1}\) were assigned to glycosidic linkage C-O stretching vibration. The stretching vibration of C=O at 931.45-933.38 cm  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Samples** & **Total Sugar/\%** & **Sulfate/\%** & **Uronic Acid/\%** & **Mw/kDa** \\ \hline GLP & 69.33 \(\pm\) 0.61 & 18.71 \(\pm\) 1.31 & 5.55 \(\pm\) 0.20 & 106 \\ GPP & 74.29 \(\pm\) 1.48 * & 13.91 \(\pm\) 0.89 ** & 6.40 \(\pm\) 0.08 ** & 66 \\ GGP & 78.21 \(\pm\) 4.21 ** & 18.91 \(\pm\) 1.12 & 5.32 \(\pm\) 0.38 & 93 \\ GCP & 74.29 \(\pm\) 2.86 * & 4.56 \(\pm\) 0.48 ** & 4.13 \(\pm\) 0.09 ** & 89 \\ GXP & 72.68 \(\pm\) 2.35 & 7.33 \(\pm\) 0.10 ** & 6.01 \(\pm\) 0.11 * & 95 \\ GDP & 79.13 \(\pm\) 0.91 ** & 10.11 \(\pm\) 0.56 ** & 5.46 \(\pm\) 0.14 & 81 \\ \hline \end{tabular}  
* \(p\) + 0.05 and ** \(p\) + 0.01.  
\end{table}
Table 1: Physicochemical properties of the samples.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Monosaccharide** & **GLP** & **GPP** & **GGP** & **GCP** & **GXP** & **GDP** \\
**Composition (mol \%)** & & & & & & \\ \hline Fucose (Fuc) & - & - & - & - & 0.2 & - \\ Rhamnose (Rha) & - & 14 & 1.2 & - & - & 0.7 \\ Arabinose (Ara) & - & 0.2 & 0.5 & - & - & 0.1 \\ Galactose (Gal) & 89.7 & 58.8 & 68.0 & 20.0 & 70.9 & 41.9 \\ Glucose (Glu) & 2.3 & 33 & 13.8 & 74.5 & 23.4 & 42.1 \\ Xylose (Xyl) & 1.2 & 1.5 & 1.0 & 0.1 & 0.6 & 0.8 \\ Mannose (Man) & - & - & 10.9 & 4.2 & 0.8 & 11.1 \\ Galacturonic acid (GalA) & 3.4 & 2.2 & 2.6 & 0.4 & 1.6 & 1.3 \\ Glucuronic acid (GluA) & 3.4 & 2.1 & 1.3 & 0.6 & 1.4 & 0.6 \\ Mannuronic acid (ManA) & - & - & - & - & 0.7 & 0.5 \\ \hline \end{tabular}  
\end{table}
Table 2: Monosaccharide composition of the samples.  
indicated the existence of 3.6-endo-galactose in GLP and its degradation products. The peak at 845.63-894.81 cm\({}^{-1}\) indicated the existence of a \(\beta\)-glycosidic bond [26]. Moreover, most of the absorption bands of GLP were retained in the degradation products of the GLP, indicating that the structures of the GLP were not destroyed after enzymatic degradation. However, the infrared spectra of the degradation products were slightly different from those of the GLP, and the stretching and variable angle vibration peaks of C-H moved to higher wave numbers, indicating that the intramolecular and intermolecular hydrogen bonds of the degradation products were enhanced.