| Carboxymethyl corn starch-Stearate starch (CMCS-SS) was synthesized under certainconditions when carboxymethyl corn starch (CMCS) was used as raw material, stearic acid asesterification agent, lipase as catalyst. And then, stearate corn starch (SCS) was also preparedby the same method. In this paper, physicochemical properties and structure of CMCS-SS wasstudied. CMCS-SS was used in oyster sauce as thickener.Firstly, process conditions of CMCS-SS which was synthesized by lipase method wereresearched. Through single parameter experiments, mass fraction of stearic acid, addition oflipase, DS of CMCS, reaction temperature, reaction time, water content of system, stirringrate and pH of extra water were studied, which had effect on degree of esterification（DE）andreaction efficienc（yEF）of CMCS-SS. Based on single parameters, orthogonal experiment wasdesigned. Take DE as evaluation index, the optimum process conditions（measured by drybasis）were that: DS was0.2081, water content of system was8.5%, mass fraction of stearicacid was5%, addition of lipase was121u/g, reaction temperature was55℃, reaction timewas4h, stirring rate is220r/min, pH of system was9.0. And then, DE of CMCS-SS was0.02821, efficiency of reaction was89.7%.Secondly, structure of CMCS-SS was researched. FTIR spectrometer, X-ray diffractioninstrument, polarization microscope and atomic force microscope (AFM) were used toinvestigate functional group and surface and internal structure of crystal. From infraredspectrum, stretching vibration of C-O can be seen at1749.15cm-1, which indicated that groupof stearoyl were linked with carboxymethyl starch. From XRD spectrum, structure of crystalwas not broken. Compared with CMCS, degree of crystallization was decreased from9.49%to7.16%, and angle of diffraction moved a little. From pictures of polarization microscope,cross of starch granule still existed. From pictures of AFM, it was showed that, with extensionof storage time, bumps on granules of CMCS were increased; relative height was alsoincreased. And CMCS-SS was the opposite.Thirdly, compared with CMCS and SCS, rheological properties of CMCS-SS weremainly researched. It was showed that, rheological properties were better than the other twomodified starches. Viscosity of CMCS-SS was higher than CMCS, and this modified starchcould resist some disadvantageous factors such as shearing force, salt, acid and so on. Andthen, compared with CMCS, other properties of CMCS-SS such as solubility, emulsibility andemulsion stability, surface tension, retrogradation character and stability of freeze-thaw wereresearched. It was showed that, solubility was decreased, emulsibility and emulsion stabilitywas increased, and surface tension, retrogradation character and stability of freeze-thaw weredecreased.Lastly, based on properties, application of CMCS-SS was researched, which was used asthickener in oyster sauce. Three oyster sauces and soy sauce were bought from the market,and then ingredients were analyzed. Texture, liquidity and viscosity of three oyster sauceswere tested, and then, basic recipe of homemade oyster sauce was made. Through adjustingaddition and DE of CMCS-SS, measuring viscosity and liquidity, the optimum recipe of homemade oyster sauce was assured to suit for the market products. At the end of thisexperiment, texture, liquidity and viscosity of the optimum oyster sauce were texted; Andcompared with three market products, storage stability was studied. The results was showedthat, the optimum recipe of homemade oyster sauce was: soy sauce66.7%, sugar7.0%,soybean oil0.3%, monosodium0.27%, CMCS-SS6%(DE=0.01538, water content12.20%),water18.90%. After30days, this oyster sauce was still similar to which in the market, sohomemade oyster sauce had storage stability. |
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