Synthesis And Physicochemical Properties Of Carboxymethyl Chestnut Starch

Carboxymethyl chestnut starch was prepared with chestnut starch as material, and monosodium chloroacetate as etherifying agent. The preparation technology was optimized and the physicochemical properties were studied. The main results are as follow:(1) Carboxymethyl chestnut starch (CMCS) was synthesized by the reaction of chestnut starch and monosodium chloroacetate (MSCA) in an alkali environment. The Box-Behnken response surface method was carried to optimize the CMCS preparation after single factor experiment. The maximum degree of substitution (DS) of 0.68 was obtained as follows:80 mL of ethanol-water (4:1, v/v),10 g of chestnut starch, molar ratios of NaOH and MSCA to the anhydroglucose unit (AGU) of 2.0, alkalization reaction time 45 min at 30℃, etherification reaction time 3 h at 45℃. This mixture was reacted at for 3h.(2) Based on the optimum preparation condition, three starched with different DS (0.22,0.42,0.63) were prepared by changing the reaction condition. Fourier transform infrared spectroscopic analysis showed that the carboxymethyl starch derivative showed new bands at 1607 cm-1 which indicated the hydroxyl groups of starch were etherized through carboxymethyl groups. The absorption peak increased along with the increasing of DS. Native chestnut starch (NCS) has smooth granule surface while cracks and concave in the carboxymethyl starch granule surface were observed by scanning electron microscope (SEM). Wide-angle X-ray diffraction analysis indicated that the native chestnut starch was crystalline type C, and the crystallinity was reduced after carboxymethylation. The amyloglucosidase hydrolysis results suggested the substitution of carboxymethyl groups gradually occurred from the reducing end to non-reducing end of the starch chains in the CMCS starch other than evenly distributed.(3) Physicochemical properties of modified starch with different DS were studied. The differential scanning calorimetry (DSC) results revealed the absence of a transition peak in all CMCS samples. CMCS paste showed significant higher light transmittance and solubility than those of NCS. The syneresis results revealed that CMCS paste had no water release after 24 h storage at room temperature, while NCS paste lost 8.1% water. CMCS with middle DS showed higher viscosity than NCS at high shear rate. Compared with native starch, the freeze-thaw stability and retrogradation of carboxymethyl starch were improved, and the freeze-thaw stability was enhanced with increasing degree of substitution. In the high temperature resistance, salt resistance and acid resistance studies, CMCS paste also showed better characteristics. The results demonstrated that CMCS can be applied in the industrial processing of paste foods and frozen food as a thickening agent and a stabilizing agent.(4) According to the characteristics of the CMCS, the starches with different DS were added in the noodles. The sensory evaluation and texture analysis on the quality of noodles were analyzed. The noodle characteristics including hardness, chewiness and elasticity were significantly improved.