| Starch plays an indispensable role in human diet,but starch gelatinization is often accompanied by poor water retention,retrogradation,fragile,soft and other problems.In the process of making starch based food,some non-starch polysaccharides were often added to make starch get better gel texture after gelatinization and retrogradation,so as to improve the sensory properties of starch based food.In this paper,two kinds of Mesona chinensis polysaccharides(MCP)were extracted by dietary alkali and cellulase from Mesona chinensis.With the help of physical and chemical analysis,rheometer,thermogravimetric analyzer,fourier transform infrared spectroscopy(FT-IR),X-ray diffractometer(XRD)and scanning electron microscopy(SEM),through the measure of monosaccharide composition,molecular weight,apparent viscosity and storage modulus,decomposition temperature,peak strength and surface microstructure and other indicators to compare the two kinds of MCP extracted by different methods.In order to comprehensively and objectively understand the role of the crude MCP in rheological and gelation properties of tapioca starch,it provides new ideas for tapioca starch-based food.The main research contents were list as follow:1.Dietary alkali and cellulase were used to extract polysaccharides from Mesona chinensis herb,the contents of uronic acid,total sugar and protein in Mesona chinensis polysaccharide extracted by dietary alkali(MCP-S)were 29.52%,32.28%and 31.35%,respectively,and the contents of uronic acid,total sugar and protein in Mesona chinensis polysaccharide extracted by cellulase(MCP-C)were 23.21%,29.37%and 22.37%respectively.The monosaccharide composition of MCP-C includes Ara,Fuc,Gal,Glc and Man,and the molar ratio was 0.24:0.92:0.55:10.7:0.32.The monosaccharide composition of MCP-S includes Ara,Fuc,Gal,Glc,Rha and Xyl,molar ratio was 0.32:0.87:0.82:6.24:0.11:0.34.The fluid behavior of MCP-C and MCP-S were pseudoplastic fluid,and the apparent viscosity,storage modulus(G’)and composite viscosity(η*)of the MCP-S were higher than that of MCP-C solution under the same concentration.The decomposition model of MCP-C and MCP-S under the action of temperature were three-stage decomposition modes,and MCP-S has a higher initial decomposition temperature(Ti)than MCP-C.SEM observed that the surface morphologies of the two kinds of MCP were different.Due to the erosion of cellulase,there were many "papules" on the surface of MCP-C.The surface of low concentration(0.1%)of MCP-S had some pores due to freeze-drying,and the surface of high concentration(0.3-0.5%)of MCP-S was very smooth.However,FT-IR and XRD results showed that the two kinds of MCP had typical infrared spectral characteristics of polysaccharides and were amorphous.2.The composition of different concentrations of two kinds of Mesona chinensis polysaccharides(0.1%、0.3%and 0.5%,w/v)with tapioca starch(6%,w/v)was studied.The expansion degree of starch granules,pasting viscosity,hardness,and the amount of amylose leached of TS were decreased after adding MCP-C and increased after adding MCP-S.Compared with the pure tapioca starch system,the addition of two kinds of MCP improved the storage modulus(G’)and short range order(DO)of the system,and give the tapioca starch more fine microstructure.The addition of MCP-C and MCP-S can reduce the content of rapidly digestible starch(RDS)of tapioca starch.Among them,adding 0.5%MCP-C has the most significant effect on reducing RDS content.In addition,correlation analysis showed that the contents of slowly digested starch(SDS)and resistant starch(RS)in the tapioca starch-crude MCP system were positively correlated with G’ and DO,indicating that the strong and orderly gel network had an inhibitory effect on the starch digestion.3.The effect of urea and NaCl on rheological and gelation properties of complex gels of MCP-S(0.5%,w/v)-tapioca starch(6%,w/v)were studied.In the urea-complex gel system,the pasting viscosity(peak viscosity,trough viscosity,and final viscosity)of all samples decreased with the increase of urea concentration,and urea showed significant inhibition on starch rearrangement during cooling.In the NaCl-complex gel system,the addition of 0.05%NaCl made the complex gel system obtain the maximum peak viscosity,and the addition of 2%NaCl obtained the minimum peak viscosity.The addition of urea and NaCl leads to the destruction of hydrogen bond in the system,and the storage modulus(G’)of the complex gel system is reduced.differential scanning calorimeter(DSC)analysis found that the peak temperature increased from 69.08℃ to 75.54℃ and ΔH increased from 11.70 j/g to 13.90 j/g after adding 0.5%NaCl to complex gel system.The results of texture showed that urea and NaCl had no effect on the springiness and cohesiveness of the composite gel,and the hardness and gumminess of the composite gel were reduced.The results of granules sizes and SEM showed that the addition of NaCl made the granules sizes increased and the microstructure were compact,while the addition of urea made the granules sizes decreased and the structure loose and porous.4.The effects of single factor analysis,orthogonal test and sensory analysis on the new Mesona chinensis sorbet were evaluated.The results showed that the order of the influence of five single factors on the new Mesona chinensi sorbet was the ratio of frozen storage time>starch concentration>sugar content>milk content>ratio of material and water.Among them,frozen storage time is a significant factor affecting the sensory evaluation of Mesona chinensis sorbet.The results showed that when the ratio of material to liquid was 1:40,the starch concentration was 6%,the sugar content was 8 g,the milk content was 50 mL and the freezing time was 6 h,it was the best formulation process of the new Mesona chinensis sorbet and the sensory score of the Mesona chinensis sorbet was 93. |
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