| Mesona chinensis also named Hsian-tsao,Herb Jelly and Mesona chinensis benth,is an annual herbaceous plant from Lamiaceae family.In China,it has been used as a medical and edible plant resource for many years.In recent years,domestic and foreign scholars have done extensive studies on active ingredients and biological activities of Mesona chinensis.It has reported that the main constituents isolated from Mesona chinensis are polysaccharides,flavonoids,terpenoids polyphenols,and it has biological activities such as antioxidant,antidiabetics,antilipidemic,antihypertension,antiviral and anti-hypoxic.Mesona chinensis polysaccharide(MCP)has good gelling properties,it can form good bean jelly by mixing with starches.The aim of this paper is to investigate the optimization of extraction conditions,physicochemical characterizations,antioxidant activities,rheological properties and gelling behavior of polysaccharide from Mesona chinensis.The main contents of this paper are as follows:1.Optimization of the extraction conditions of MCP.To confirm the variation range of extraction parameters,single factors(eg.extraction time,extraction temperature,sodium carbonate concentration,ratio of extraction solvent to raw material)were carried out.Based on the single factor experimental results,a four-variable,three-level experiments coded +1,0 and-1 for high,middle and low value,respectively,and 29-run Box–Behnken design(BBD)were adopted for optimization,and Design-Expert software was used to analyze the experimental results.Results indicated that the highest yield of MCP was gained and the optimal variables were extraction time 2.03 h,extraction temperature 91.74 °C,sodium carbonate concentration 3.12 mg/m L,and ratio of extraction solvent to raw material 20.71 mL/g,and under these optimized conditions,the highest yield of MCP was 7.05%.2.After gaining the optimized extraction conditions,extraction procedure was conducted to obtain the dried MCP for latter investigation.Briefly,after extraction,centrifugation,alcohol precipitation and lyophilized in vacuum freeze dryer,the dried MCP was obtained.The total sugar,uronic acid,total phenols and protein contents of dried MCP were measured as 19.52%,29.3%,4.9% and 10.4%(w/w),respectively.The peaks in UV-spectrum were the results of protein bound to the polysaccharide of Mesona chinensis and the polymer is a proteoglycan.The average Mw of MCP was calculated to be approximately 1.45×106 Da,and MCP was composed of Gal and Glc in a molar ratio of 1.00:1.38,which were the mainly monosaccharides constructing the backbones sugar forms in MCP.It can be seen that Ara was also detected in MCP with a very small amount.FT-IR showed that the MCP was a heteropolysaccharide containing uronic acid.SEM verified MCP had a unique lotus leaf-like shape with some small irregular round-like rods surface morphology.Furthermore,MCP exhibited considerable antioxidant potential on scavenging hydroxyl(53.87±0.44%),superoxide anion(58.42±1.17%)and DPPH radicals(55.59±0.69%).3.The rheological properties,gelling behavior and texture characteristics of MCP were investigated.The rheological properties of MCP at different concentrations,temperature,pH values,salts,sucrose and freeze-thaw variation were studied.The rheological properties of MCP exhibited pseudoplastic characteristic and ‘‘gel-like” behaviour by the flow behavior detection.A closed hysteresis loop was formed when MCP concentration reached 4%.The phase angel(tan?)was less than 1,indicating MCP was a weak gel in linear viscoelastic region.In particular,at a 5% MCP content the gel was generated,and it exhibited favourable textural properties.4.The gelling effects of MCP with wheat starch were investigated,and only the wheat starch to MCP ratio(9.0:1.0,w/w)could form solid gel,other ratios(10.0:0,9.5:0.5,8.5:1.5,8.0:2.0,w/w)were just mashes.The texture results showed that the solid gel of the wheat starch to MCP ratio(9.0:1.0,w/w)had the highest hardness,adhesiveness and chewiness.The wheat starch to MCP ratio(8.5:1.5,w/w)could form the highest thixotropic loop area.The phase angel(tan?)of wheat starch to MCP ratios were all less than 1.0,the storage modulus(G?)were all higher than the loss modulus(G?),G? and G? were showed a dependence on the frequency,indicating the mixtures(10.0:0,9.5:0.5,8.5:1.5,8.0:2.0,w/w)of wheat starch to MCP were weak gels.The results of rapid visco analyser(RVA)showed that MCP had retarding effects on short-term retrogradation of wheat starch.The results of differential scanning calorimetry(DSC)showed that MCP could reduce the Enthalpy of gelatinization(?H1)of wheat starch.SEM observation exhibited the microstructure of different ratios of MCP with wheat starch showed smoother surface,less holes compared with wheat starch. |
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