| Acetyl content is one of the important factors affecting the gelation,rheological properties and biological activity of polysaccharides.The effects of acetyl groups in Dendrobium officinale Kimura et Migo（DOP）polysaccharides on its gelation,rheological properties and bioactivities have not been reported.In this study,DOPs with different degrees of deacetylation were prepared by heterogeneous deacetylation,and then the rheological properties,texture properties and effects of sols and gels of acetylated polysaccharide in hemostasis and wound healing were analyzed,and the influence of acetyl content on the physicochemical properties and biological activities of DOP was also explored.The main conclusions are as follows:（1）DOP with different degrees of deacetylation was prepared by heterogeneous alkali method.The reaction conditions were as follows:ethanol concentration was 90%,base concentration was 50%,reaction temperature was 40℃,and reaction time was 4 h.DOP0（deacetylation degree was 0%）,DOP1（deacetylation degree was 11.8%）,DOP2（deacetylation degree was 24.4%）,DOP3（deacetylation degree was 66.0%）,DOP4（deacetylation degree was 88.0%）,DOP5（deacetylation degree was 100.0%）were prepared by changing the amount of alkali addition to regulate the deacetylated amount,and the acetyl content in each sample was determined.（2）The basic structural characteristics of deacetyl DOP were analyzed by UV-vis,FT-IR and SEM,and its solubility was determined.UV-vis results showed that there were almost no free nucleic acids or proteins in DOP after deacetylation.FT-IR results showed that the wavenumber of C=O asymmetric telescopic vibration in acetyl or carboxylate was 1735.14cm-1absorption peak from DOP0 to DOP4,and completely disappeared in DOP5,and the degree of deacetylation was proportional to the intensity of the absorption peak,while the absorption peak of other characteristics did not change significantly.SEM analysis found that DOP was amorphous,mainly in the form of sheets,and there were many closely connected pores on the surface of deacetyl DOP,forming a network structure and bonded tightly.The solubility experimental results showed that there may be a turning point in the solubility of DOP at a deacetylation degree of 66.0%but all acetyl groups could not be dissolved,and it was also found that salts and hydrogen bond breakers had the effect of promoting dissolution,among which sodium chloride made DOP dissolve faster.Solubility experiments show that the solubility of DOP begins to increase when the degree of acetylation（DD is 88.0%）,guessing that 88.0%is a vertex point,but all acetyl groups can not be dissolved,in order to improve the application range of DOP,it is found that salts and hydrogen bond breakers have a dissolution promoting effect,of which sodium chloride makes DOP dissolve faster.Moreover,DOP1 and DOP2 were observed to be transparent sols,DOP3 and DOP4 had less turbidity,and DOP5 was layered,and this solubility was considered to be related to the presence of acetyl groups.（3）The rheology of different acetylated Dendrobium dendrobium polysaccharides was analyzed by rheometer,and the results showed that the viscosity of the sample weakened with the increase of shear rate,among which DOP0<DOP1<DOP2<DOP3<DOP4.With the increase of shear rate and the decrease of viscosity,the shear stress of the sample showed a rapid growth trend,among which DOP2>DOP1>DOP0>DOP3>DOP4.The angular frequency variation curve shows that with the increase of frequency,G’>G’is converted into G’<G’,and with the progress of deacetylation,the intersection point moves in the direction of low frequency,which is conducive to the early formation of the gel.The temperature change curve found that with the increase of temperature,G’>G’’was converted to G’<G’,and the intersection points of deacetylated DOP gels were higher than those of natural DOP gels,indicating that when some acetyl groups in DOP were lost,higher temperatures were required to form gels.（4）The texture characteristics of different acetylated Dendrobium dendrobium polysaccharide gels were analyzed by texture analyzer.The results of TPA experiments showed that,the gel hardness gradually increased with the increase of DD,reaching a maximum when the degree of deacetylation was 88.0%.The elasticity of the gel first decreased and then increased,and when the degree of deacetylation was 88.0%,the elasticity increased in reverse.The cohesion of the gel gradually increases,and the network structure becomes more and more dense;The adhesion of the gel gradually increases;The chewing properties of the gel gradually increase;The restorative effect increased,indicating that the deacetyldop gel was better than the natural DOP gel.The results of water-holding experimental results showed that with the decrease of acetyl group content,the WHC of the gel gradually decreased,and the higher degree of deacetylation could reduce the WHC of the gel.The swelling experiments showed that with the decrease of acetyl group content,the gel evolution water first decreased and then increased,and when the degree of acetylation reached 66.0%,the gel had a more uniform and dense gel network structure with smaller pore size.The freeze-thaw stability experiments showed that the DOP gel hardness remained basically unchanged after soaking in 2.0%citric acid solution,the gel hardness decreased slightly after deionized water immersion,and the gel network after 2.0%citric acid immersion was looser,and the pores were larger and larger.Finally,the texture characteristics of DOP1and DOP3 gels at different concentrations were used to verify that acetyl groups significantly affect the texture characteristics of DOP gels.The results of hemostasis performance showed that in vitro hemostasis experiments showed that DD had the lowest BCI at 66.0%,and the BCI value was also the lowest compared with the sample without deacetylation（DOP0）,indicating that only properly deacetylated DOP had better in vitro procoagulation performance,and its coagulation time was significantly shortened by 27.7%.Prolonged clotting time for other deacetylated DOPs relative to undeacetylated DOPs;The hemolysis rate results showed that both deacetylacyl DOP and DOP had good hemocompatibility,while fully deacetylated DOP did not have hemocompatibility.In vivo hemostasis experiments showed that only an appropriate range of acetyl-removal degree had a stopping effect,which was consistent with the results of in vitro hemostasis,indicating that the acetyl content had a smaller range in hemostatic performance;The results also showed lower blood loss in the deacetyldop group,with the largest blood loss in total deacetyl DOP（0.0397 mg）,indicating that the hemostatic effect of deacetyl DOP was enhanced（except DOP5）and better than undeacetylated DOP.（5）The coagulation performance in vitro and in vitro hemostasis experiments of different acetylated DOP was analyzed.In vitro results showed that the BCI had the lowest BCI at a deacetylization degree of 66.0%and was lower than that of non-deacetylated samples,with a significantly shorter clotting time of 27.7%,while other deacetylated DOPs had a longer clotting time.The results of hemolysis rate showed that except for fully deacetylated DOP,both deacetylated DOP and DOP had good hemocompatibility.In vivo hemostasis experiments showed that the hemostatic effect of deacetyldop gel was better than that of powder,because the hemostasis time was short and the amount of blood loss was less,indicating that the hemostatic effect of deacetyl DOP（except DOP5）was better than that of undeacetyldop,indicating that only the appropriate range of deacetylation degree has a hemostatic effect,which is consistent with the in vitro hemostatic results.（6）The results of wound healing effect of mice showed that the effect of deacetyl DOP on sand and frostbite in mice was not obvious.In the scald model,with the increase of administration time,the wound skin of mice in the deacetyl DOP group gradually turned dark brown from the pink state,the wound gradually hardened,there was a tendency to scab,and the skin elasticity increased,and part of the scab began to slowly fall off,until the 14th day after the scald,the wound area of the deacetyldop group was significantly reduced,the tissue was flat,the hair growth rate was faster,and the wound healing rate of the DOP group and the deacetyl DOP group was significantly improved,and the difference was significant.The water content gradually decreased at each time point of the scald,but it was still higher than that of the normal group,but the more the water content of the wound tended to be flatter,the less the amount of decrease.The results of wound hair growth showed that with the increase of administration time,a little hair grew out of the acetyldop mice,and the skin of the deacetyl DOP mice had more hair than in the DOP group.Total antioxidant experiments showed that the total antioxidant capacity of deacetylated DOP was better overall than that of natural DOP,and increased with the increase of concentration,and the total antioxidant capacity was the best when the acetyl group was completely removed.In this study,the role of acetyl content in the structure-activity relationship of Dendrobium dendrobium polysaccharides was analyzed preliminarily,and the results could provide new ideas for the in-depth development and application of DOP in food,medicine and chemical industry. |
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