| Resistant starch is the floorboard of the starch and its degradation products, which can escape enzyme digestion in the small intestine. Resistant starch has many excellent processability and physiological functions. Preparation of resistant starch by enzymatic and physical methods is a current research focus because it is safe and reliable. Grey color of sweet potato starch, poor stability of starch paste, easy to enzymatic browning in the production process limiting its application, sweet potato modified starch prepared by modification can better meet industrial requirements because it have a variety of physiological functions. Taking sweet potato starch as raw material, resistant starch was prepared by enzymatic method combined with ultrasonic treatment, and then the physicochemical properties and application of resistant starch was studied in the present study. The main research contents and results were as follows:1. Based on single factor experiment, the optimum process parameters of starch suspensions concentration17.3%, isoamylase amount5×103U/g starch, enzymolysis time14.09h, ultrasonic processing time40min, drying temperature46℃were obtained for resistant starch preparation by response surface optimization. Predictive value of resistant starch content was21.28%, while measured value was21.33%.2. The part physicochemical properties of the sweet potato resistant starch were studied, taking sweet potato starch as reference. The main conclusions were listed as follows:Sweet potato starch granules were complete, average diameter of17.59microns after through120mesh sieve, spherical or polyhedron in shape with smooth surfaces. The height difference was about10nm. Compared with sweet potato starch, average diameter of sweet potato resistant starch through120mesh sieve was measuredl23.3μm. The starch particle shape almost disappeared, presenting highly irregular lumps or clumps. With very rough particle surface, the height difference was about24nm. The sweet potato resistant starch was physical modified starch. X-ray diffraction results showed that the crystalline structure of sweet potato starch was C type, and crystalline structure of sweet potato resistant starch was B type. Thermal analysis found that the thermal stability of the resistant starch was significantly enhanced. The water binding capacity and emulsifying ability of resistant starch reduced, but the emulsion stability increased slightly, and the resistance enzyme digestion of sweet potato resistant starch increased. Within40～70℃, the expansion ability of the resistant starch was always stronger than the sweet potato starch. Whiteness of sweet potato resistant starch dropped, but the transparency of the starch paste increased.3. The specific rheological parameters of resistant starch were obtained through comparing rheological curve of sweet potato starch with rheological curve of resistant starch paste.The static rheological behaviors of sweet potato resistant starch were studied. Sweet potato starch pastes were significantly affected by the shear number, but the shear stress recovery of sweet potato resistant starch pastes was better. Apparent viscosity of starch paste decreased with the increase of shear rate. With the increase of temperature, the area of hysteresis curve gradually decreased. Compared with sweet potato starch paste at the same concentration, the viscosity of sweet potato resistant starch paste was low, and the downlink was under the uplink. The dynamic rheological behaviors of sweet potato resistant starch were studied. Compared with sweet potato starch paste, the sweet potato resistant starch paste had higher composite modulus.During the frequency scanning process, viscosity increasing speed is greater than the elastic increasing speed; Compared with sweet potato starch, the elastic solid and viscous liquid of sweet potato resistant starch gel significantly decreased, but the elastic and viscous were in balance.The rheological law of starch paste under the continuous heating scan was studied. In20～90℃temperature scanning process, Arrhenius equation can be used to fit the temperature sensitivity of two types of starch pastes. Modified starch paste had lower sensitivity to temperature changes. Stirring sweet potato resistant starch paste with high stirring rate, could counteract the effects of temperature on the apparent viscosity to some extent.4. The application of sweet potato resistant starch in biscuits was studied, and the conclusions were listed as follow:With the increase of resistant starch content, yellow value and color saturation of the biscuits reduced. With the increase of resistant starch content, compared with the control group, total aberrations of the biscuits increased gradually. The yellow of the biscuits containing resistant starch was paler than the control group, and the difference was easily observed by human eyes. Compared with control group, the moisture content of biscuits with resistant starch was relatively low. Moreover, with the increase of resistant starch content, the water content and water activity of the biscuits gradually reduced.The texture parameters of fresh biscuits with different RS content were compared. The hardness of biscuits named15RS and30RS was significantly greater than the control group. Compared with control group, the chewiness, cohesiveness, and resilience of biscuits being added RS increased. With the increase of the RS content, the elasticity of the biscuits decreased, but there was no linear relationship.The texture changes of biscuits during storage were studied. The hardness of fresh biscuits with RS was larger than the control group. But stored to the7th day, the hardness of fresh biscuits with RS was smaller than the control group. But in three weeks later, the hardness of fresh biscuits with RS was larger than the control group. During the storage, the elastic of biscuits with RS was almost always less than the control group. The chewiness of biscuits named15RS reduced, but still larger than other biscuits with RS and control group. The chewiness of biscuits named30RS was close to biscuits named45RS. The resilience of biscuits with RS was in slowly weakening trend, but the resilience of biscuits named15RS was larger than other biscuits.The sensory analysis results showed that sensory evaluation score contours of various biscuits were put in bigger differences. Texture score of biscuits added RS was lower than the biscuits in control group, but the appearance, color, taste and total score of biscuits with RS were higher than control group, especially the biscuits named15RS. |
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