Comparative Study On Physicochemical Properties Of Sweet Potato Starch Obtained From Sour Liquid Processing And Centrifugation And Their Application On Noodle Products

The aim of this manuscript is compare and study the proximate composition, structure, andphysicochemical properties of starch made from sour liquid processing(SLPS) and centrifugation,(CFS),obtained from laboratory-prepared and commercial grades, and their application in noodles products.Furthermore, the proximate composition, structure and physicochemical properties of SLPS prepared bysour liquid processing with different fermenting time （0,12,18,24,48,72h, respectively）in thelaboratory, were examined and compared. The total amylase activities (α-, β-amylase) of the sour liquidand starch supernatant were also determined. Finally, studied on the effect of different pH and differentfood additives on starch pasting properties and gel strength. The results were as follows:The granule size, apparent amylose, Al, Mg, Fe, Zn content, crystalline peak, gelatinization enthalpy,peak viscosity and setback ratio of SLPS were lower than that of CFS, while protein, lipid, ash,phosphorous, K, Ca content, L*value, swelling power (55-95℃), solubility (55-95℃), and stability ratioof SLPS were higher than that of CFS. Scanning electro micrographs(SEM) showed that the addition ofthe sour liquid caused the smooth surface lost of native starch granules, and the results of Fouriertransform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and Differential scanning calorimetry(DSC) showed the hydrolysis of the amorphous and crystalline region in the granules, which weaken thestability of the intermolecular structure, lower the crystalline peak intensity and gelatinization enthalpy.The protein, lipid, ash, phosphorous, K, Ca content, L*value and gelatinization temperature ofSLPS0-72were higher than that of SLPS0(CFS), and increase with the time of precipitation increases.The apparent amylose content, granule size peak viscosity and setback ratio of SLPS12-72were lowerthan that of SLPS0with an upward trend after first the lower. Compared to SLPS0, SEM showed that thesurface of SLPS12-72granules has pits and fissures,which were more obvious with the fermentation timeincreases. Our study showed that cracks of the surface of SLPS48granules can be observed clearly.Compared to SLPS0, FT-IR showed the intramolecular binding force of SLPS12-72were weakened.XRD shows that all the starches were A-type, but crystallinity peak of SLPS12-72were lower than thatof SLPS0. DSC show that the gelatinization enthalpy and gelatinization temperature range of SLPS0-72lower with the fermenting time increased. In addition, there are amylases activity (α-,β-amylase) exit insour liquid, and the total amylase activity (α-,β-amylase) was51.23-214.8units/100mL sour liquid (pH5.3) during72h of fermention. The results suggest that sweet potato starches were degraded by theamylase during isolation with sour liquid solution, which could be the main reason that structure, andphysicochemical properties of SLPS differ from the CFS.The lightness and swelling index of CFS noodles were lower than those of SLPS noodles.Furthermore, the retrogradation rate, tensile strength and shear stress of CFS noodles were significantlyhigher (p<0.05) than those of SLPS noodles. It was found that increase the pH, Na2HPO4, sucrose and NaCl content to different levels wouldhigher the starch gelatinization temperature. In addition, added1.5-5%of the sucrose starch gel strength,rather than neutral pH, NaCl, soy protein, Na2HPO4and lipid varying degrees of reduction of starch gelstrength. Especially, soy protein is the most effective additives in lower starch gel strength.