Structure Modification, Characterization Of Polysaccharides From Flowers Of Abelmoschus Esculments And Their Influence On Short Chain Fatty Acids In E.Coli BL21 Fermentation Liquiors

Okra [Abelmoschus esculentus(l.) Moench] is malvaceae okra annual herbaceous plant, which is rich in pectin, protein, vitamins, unsaturated fatty acid, polysaccharide and flavone. Polysaccharide, as one of the main active components from Okra, has various activities such as immunity, antioxidation, anti-fatigue and antitumorand hypoglycemic etc.. Recent studies revealed that polysaccharide can influence the host health by promoting the formation of short chain fatty acids(SCFAs) in gut. However, little had been reported on structure modification and effect on SCFAs in E.Coli BL21 fermentation liquors of okra polysaccharide. Based on our previous study, the structure modification of polysaccharide from okra flower, including carboxymethylation, sulfuric acid esterification, acetylation and structure characterization were studied. The modified polysaccharides on the influence of SCFAs in E.Coli BL21 fermentation liquiors were also researched. The main research contents were as follows:(1) The carboxymethylated, sulfated, acetytated polysaccharide were systhesized by polysaccharide in floweres of Abelmoschus esculentus. The structure of polysaccharide in floweres of Abelmoschus esculentus and its modified polysaccharides were analyzed by IR, Raman, CD, AFM, SEM and TEM. The results showed that the degree of substitution(DS) of carboxymethylated, sulfated, acetytated polysaccharide were 0.636, 1.265 and 0.168 respectively. The structure of modified polysaccharide was established as existence of-OCH2-COOH,-OSO3 and-COCH3. In addition, the molecular asymmetry, chain conformation, molecular thickness, molecular spacing and surface morpoology changes were observered in modified polysaccharides.(2) The pretreatment and analysis method of SCFAs in fermentation liquors of E.Coli BL21 by gas chromatography(GC) were studied. The optimal extraction condition was that the extraction solvent was ethyl acetate and pH value of fermentation liquors was 2. Chromatographic analysis was carried out by using a fused-silica capillary column with free fatty acid phase(DB-FFAP). The flow rate of hydrogen and air were 37 and 370 mL/min. The flow rate of carrier gas(N2) was 2 mL/min with a split ratio of 1:10. The temperature increasing procedure was as follows: 100-180 °C at 10 °C/min and kept for 1.0 min, then 180-230 °C at 20 °C/min and kept for 1 min. The total analysis time was 12.5 min. The injector and detector heater temperatures were 230 and 250 °C, respectively. The SCFAs(acetic, propionic, isobutyric, butyric, isovaleric, valeric, caproic isocaproic and heptanoic) were well separated and analyzed by GC with high linearity(R2≥0.99), low quantification limit(0.011-0.070 mM)(S/N≥3) and low limit of detecrion(0.037-0.233 mM)(S/N≥10). The intra- and inter-day reproducibility of each SCFA in the standard were from 0.07 to 0.70% and from 0.44 to 2.3%(n=6). The intra- and inter-day reproducibility of each SCFA in the samples were from 0.58 to 1.44% and from 1.19 to 2.67%(n=6). The stability of standard and samples was good(RSD% <6%)(n=6). Recoveries of SCFAs were from 82.65 to 104.17%, but the recovery rate of acetic acid was 70.22-87.83%. Thus, the GC analyses method was simple, stable and precise, which can be applyed to the analysis of SCFAs in E.Coli BL21 fermentation liquiors.(3) The influence of original polysaccharide and modified polysaccharids on SCFAs in E.Coli BL21 fermentation liquors was studied. Results showed that, when compared with the control group, polysaccharide in flowers of Abelmoschus esculentus can significantly promote the concentrations of acetic acid and caproic acid by E.Coli BL21, but there was no significant influence on the concentrations of propionic acid, isobutyric acid, butyric acid, isovaleric acid and valeric acid. When compared with the polysaccharide in flowers of Abelmoschus esculentus, the modified polysaccharids could significantly inhibit the concentrations of acetic acid, butyric acid and caproic acid by E.Coli BL21, while there were no significant effects on the concentrations of propionic acid, isobutyric acid, isovaleric acid and valeric acid.