| Lipid peroxidation is a typical free radical chain reaction.Its effect is generally manifested in the oxidative deterioration of unsaturated fatty acids and lipids.The oxidation of lipids on cell membrane is accompanied by the changes of cell function and morphology,which leads to the harm to the body.Chitosan oligosaccharide（COS）is degraded by chitosan deacetylated by chitin in the shell of shrimp and crab.Because of its good water solubility,great function and high biological activity,cos is widely used in biology,medicine,light industry and other fields.In this paper,cos was oxidized by green chemical method to prepare oxidized chitosan oligosaccharide（C-COS）and its anti lipid oxidation ability was studied.In this experiment,c-cos was prepared by selective oxidation of COS in laccase/tempo system.The structure was characterized by Fourier infrared spectroscopy（FT-IR）and nuclear magnetic resonance carbon spectroscopy(13C NMR).The carboxyl content of c-cos was calculated by acid-base conductometric titration.The results show that a new C=O asymmetric stretching vibration absorption peak of c-cos at 1600 cm-1 is found in the FT-IR spectrum;In the 13C NMR spectrum,it is found that there is a new resonance peak in the range of chemical shift 170-190 of C-COS,which is consistent with the resonance peak of carboxyl（-COO-）,and the corresponding carboxyl content is calculated according to conductivity titration.The above characterization jointly proved that after the oxidation of Laccase/tempo system,new carboxyl functional groups would be produced in the structure of chitosan oligosaccharide,marking the successful preparation of C-COS.Then,unsaturated fatty acids lecithin and linoleic acid were selected as the experimental objects for free radical induced oxidation in vitro.The anti lipid oxidation ability of COS and C-COS was detected according to the content and peroxide value of conjugated diene and malondialdehyde produced by oxidation.At the same time,the effects of different sample concentration,reaction time and carboxyl content on the inhibition effect were explored.The experimental results show that the maximum inhibition rate of C-COS is 87%,and the maximum increase is 55%compared with COS.In the concentration range of 0-5 mg/ml,the inhibition performance increased with the increase of concentration;After the reaction time was 1 h,the inhibition performance decreased slightly,but the decrease was small;The carboxyl content of C-COS increased greatly in the range of 0-1.60%.It can be seen that C-COS has better anti lipid oxidation ability than COS.The concentration of C-COS,reaction time and carboxyl content all affect its inhibition effect.Finally,we detected the structure of two fatty acids before and after adding C-COS samples during oxidation by FT-IR and 1H NMR,and speculated their anti lipid oxidation mechanism.The results showed that after C-COS was added,the damage of double bonds of two unsaturated fatty acids was reduced.It can be seen that COS can initially resist lipid oxidation because the amino group on the sugar ring can provide electrons to capture free radicals.However,C-COS can chelate metal ions and avoid the formation of free radicals because the hydroxyl group on C6 becomes carboxyl group;At the same time,more amino groups are exposed to the outside of the sugar chain to capture free radicals.These two functional groups play a synergistic role,which can more effectively protect the double bond on unsaturated fatty acids from free radical damage and oxidation.The anti lipid oxidation ability of C-COS is much higher than that of COS before modification,which makes it have potential application value and good development space in cosmetics,medicine and other fields. |
