| Dendrobium officinale is a valuable Chinese herb in China,which is loved by consumers because of its various nutrients and biological activities.Dendrobium officinale polysaccharide(DOP)is one of its important active ingredients,which has a variety of biological activities such as immune regulation,lowering blood sugar,improving lung function,and antioxidants,among which the most important is the immunomodulatory activity.Relevant studies have shown that molecular weight and acetylation are important factors affecting the immunological activity of DOP,but their structure-activity relationships are still unclear,which greatly restricts the development and application of DOP in the food industry.In this paper,DOP was modified by ultrasonic degradation and deacetylation to obtain DOP with different molecular weights and degrees of deacetylation,and its physicochemical properties and structure were characterized;meanwhile,an immunosuppressed mice model was established with cyclophosphamide,and its immunerelated indexes and intestinal immunity were measured,and then the structure-activity mechanism of DOP based on immunomodulatory function in mice was explored to provide some theoretical basis for its application in functional foods.The main results of this study are as follows:1)The physicochemical properties and structures of the different components were determined using ultrasonic degradation for 390 min and 80 min to obtain UDOP-1 and UDOP-2,respectively,and deacetylation treatment for 3 min and 25 min to obtain DADOP-1 and DADOP-2,respectively.The molecular weights of DOP were 649 k Da,and the molecular weights of UDOP-1,UDOP-2,DADOP-1 and DADOP-2 were 134 k Da,279 k Da,536 k Da and 616 k Da,respectively;the degrees of deacetylation were 11.32 ± 2.73%,58.41 ± 2.98%,57.62 ± 4.92% and 86.74 ± 2.73%.In addition,the longer the sonication time,the higher its solubility;the higher the degree of deacetylation,the lower its solubility.The monosaccharide and methylation results showed that all fractions consisted of glucose and mannose and were all linked as T-Manp,1,4-Manp,1,4-Glcp,1,3,4-Manp,1,2,4-Manp and 1,4,6-Manp,but their ratios differed.2)The results of immunoreactivity showed that the fractions of DOP were able to reduce the spleen and thymus indices of immunosuppressed mice and had a restorative effect on organ damage,as well as increased the phagocytic activity of abdominal macrophages,promote the proliferation of splenic lymphocytes and improve the killing ability of NK cells,and also increase the levels of immune cytokines and immunoglobulins.The results of intestinal immunization revealed that DOP and its components were able to restore intestinal damage to varying degrees,promote the production of short-chain fatty acids,and improve the diversity and overall structure of the microbial community,with the relative abundance of Bacteroidetes,Lactobacillus and Akkermansia increasing,and the relative abundance of Firmicutes and Proteobacteria decreasing.3)The structure-activity relationships analysis revealed that the immunomodulatory activities were from high to low: UDOP-2>DADOP-1>DOP>UDOP-1>DADOP-2,indicating the appropriate reduction of molecular weight and acetyl group could improve the immune activity of DOP.These results further suggest that molecular modification of DOP has great potential in the development of prebiotic or functional foods and provide a theoretical basis for its application as an immune restorative agent in foods. |
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