## 3 Results and Discussion
### Analysis of Bio-Functional Characteristics  
#### 3.5.1 FT-IR Analysis  
The infrared spectra of the CS, CSC and CSS are shown in Figure 5. CS was analyzed by FT-IR spectroscopy as a reference. The results showed that the FT-IR spectra of CS, CSC and CSS exhibited similar tendencies, but the peak positions were slightly shifted. Characteristic peaks located at 1664 cm\({}^{-1}\), 1597 cm\({}^{-1}\) and 1325 cm\({}^{-1}\) in CSC were assigned to the amides I, II and III band, but 1660 cm\({}^{-1}\), 1592 cm\({}^{-1}\) and 1321 cm\({}^{-1}\) in CSS were observed respectively [44]. The fundamental frequency of the alcohol hydroxyl group was around 3600 cm\({}^{-1}\), and the stretching vibration absorption peaks of hydrogen bond (O-H and N-H) moved to a low frequency direction due to the role of the hydrogen bond in the chitosan molecular chain. The broad peak around 3417-3442 cm\({}^{-1}\) was attributed to O-H and N-H starching vibration on the chitosan molecular chain. It can be observed that the O-H absorption strength of chitosan increased and the absorption peak of CSS became sharper by comparing the absorption peak of CSC and CSS at 3432 cm\({}^{-1}\) and 3417 cm\({}^{-1}\), respectively. According to the M\({}_{\rm W}\) of chitosan as determined above, the M\({}_{\rm W}\) of CSS was much lower than that of CSC, which indicated that the decrease in M\({}_{\rm W}\) may lead to an increase in the amount of hydroxyl in the product. The intramolecular and intermolecular hydrogen bonds were enhanced, and the molecular structure was improved. This is because with the decrease in M\({}_{\rm W}\), the entanglement between the molecules decreases, which is conducive to the orderly arrangement of molecules. The characteristic absorption peaks of C\({}_{6}\)-OH primary alcohol hydroxyl and C\({}_{3}\)-OH secondary alcohol hydroxyl were noticed at 1026 cm\({}^{-1}\) and 1166 cm\({}^{-1}\) in CSC, but 1023 cm\({}^{-1}\) and 1160 cm\({}^{-1}\) in CSS, respectively. The microscopic differences of the above infrared spectra may be related to the antiparallel and  
Figure 4: Thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTG) curves of commercial chitosan (CS) (**A**), crab chitosan (CSC) (**B**), squid chitosan (CSS) (**C**) and differential scanning calorimetry (DSC) spectra of chitosan (**D**).  
parallel arrangement of the molecules, explaining the difference in molecular structures between \(\alpha\)-chitosan and \(\beta\)-chitosan. \(\beta\)-chitosan has higher physiological activity than \(\alpha\)-chitosan due to the simpler molecular structure and weaker intermolecular force.  
FT-IR is based on the composition of molecular groups and sensitive to polar groups of chitosan, which is closely related to the biochemical characteristics of chitosan. Hydroxyl and amino groups are the main active functional groups of chitosan. So the eigenvalue of its PS is defined as the ratio of hydroxyl and amino groups. The FT-IR spectra of chitosan were fitted with sub peaks, and the results in Table 4 show that the PS values of CS, CSC and CSS were 0.28, 0.30 and 0.31, respectively. PS values of the three kinds of chitosan showed an increasing trend, which was attributed to the exposure of more active amino groups with the increase in DD and the decrease in M\({}_{\text{W}}\).  
The value in the figure is the peak area calculated by peak fitting, and the hydroxyl and amino values are the sum of the fitting peak areas at CS (3442 cm\({}^{-1}\), 1173 cm\({}^{-1}\), 1030 cm\({}^{-1}\)), CSC (3432 cm\({}^{-1}\), 1166 cm\({}^{-1}\), 1026 cm\({}^{-1}\)) and CSS (3417 cm\({}^{-1}\), 1160 cm\({}^{-1}\), 1023 cm\({}^{-1}\)) respectively.