| As a kind of traditional food, sweet potato starch vermicelli is deeply liked by people, and the properties of sweet potato starch play a decisive role in its quality. However, because of the difference of molecular structure between sweet potato starch and bean starch, which lead to the quality of sweet potato starch vermicelli is worse than bean starch vermicelli, and how to improve the quality of sweet potato starch vermicelli is a hot issue in starch vermicelli research. The heat moisture treatment refers to the relative lower humidity and temperature in a certain time, and make a physical modification methods of starch properties change. This method costs lower and avoid the pollution by chemical modification, and achieve the purpose of improving starch specific features, which has been showing a good application prospect in modified starch. This paper systematically studies heat moisture treatment on structure and properties of sweet potato starch, explores the heat moisture treatment on the effect of sweet potato starch vermicelli quality improvement, and illuminates the influence mechanism of improvement quality of sweet potato starch vermicelli by heat moisture treatment. Research papers can provide valuable ideas and basic data for heat moisture treatment regulation application properties, and offer a green and efficient technology solution to improve sweet potato starch vermicelli quality. Therefore, this thesis study has a great academic value and practical significance, which refers to heat moisture treatment technology applied in the field of starch vermicelli processing real fundamental key scientific problems.The main content and results are as follows:1、Relationship between gelatinization and gel properties of different starch and their vermicelliIn order to explore the key index between sweet potato starch and its vermicelli, this paper comparative study the relationship between the gelatinization and gel properties of starch and the texture and cooking qualities of their starch vermicellivermicellis by studying the correlation of the gelatinization and gel properties of five original starch and their vermicellis qualities, exploring the effect of properties of starch on the quality of starch vermicellis parameters. The five starch materials are from mung bean, sweet potato, potato, rice and corn. The results showed that five starch vermicellis have different qualities by evaluating the starch vermicellis cooking and texture qualities, the mung bean is the best, followed by the potato and sweet potato, rice and corn are the worst. The results indicated that starch gelatinization properties and their vermicellis have a significant correlation. These influential parameters were in turn according to the p value:peak viscosity> valley viscosity value> attenuation value>setback viscosity, final viscosity. In addition, starch gel hardness, elasticity, viscosity and chewiness have a bigger influence on the quality of starch vermicellis, according to the degree of significant size value (p) in turn is:hardness> viscosity> chewiness> elasticity. There was a significant correlation between the quality of starch vermicellis and the parameters of valley viscosity, setback, resilience, chewiness and sticky, which was considered as an important way of predicting the qualities of starch vermicellis and can be regarded as the major indexes for starch vermicelli raw material selection. This research results can provide a sensitive method for monitoring quality of starch for starch vermicellis production and explore a convenient method for evaluating the qualities of starch vermicellis, which can provide the theory basis for starch vermicellis qualities improvement.2、Comparative study the quality of sweet potato starch and its vermicelli between by heat moisture treatment and non-heat moisture treatment.In order to explore the heat moisture treatment to improve the properties of sweet potato starch, and the feasibility of using sweet potato starch vermicelli production, Sweet potato starch was modified by lactic acid bacteria fermentation, lactic acid treatment and heat-moisture treatment, respectively. Then its structural properties and vermicellis properties were explored by rapid visco-analyser (RVA), Fourier transform infrared spectrum (FTIR), scanning electron microscopy (SEM), texture profile analysis (TPA) and other test methods. The results showed that, in comparison with native starch, the three modified starch showed lower values of peak viscosity and breakdown,higher values of the setback and the ordered degree of structure. The modified starches have damaged starch granule structure surface except heat moisture modified starch. Comparative qualities of starch vermicelli showed that the heat moisture modified starch vermicelli broken rate reduced 50%, the hardness of starch vermicelli increased from the original23.91N to 29.64N, the tensile strength of starch vermicelli increased from the original0.79N to1.61N.3、Optimized conditions heat moisture treatmented sweet potato starch for applied in vermicelli production researchSweet potato starch gelatinization characteristic of setback is the key factor that influence the quality of sweet potato starch vermicelli, and the heat moisture treatment (HMT) has obvious improvement effect on the quality of sweet potato starch vermicelli. In order to obtain the optimal reaction conditions of improving sweet potato starch vermicellis quality by heat moisture treatment, the process conditions of improvement with heat moisture treatment on sweet potato starch were optimized by a Box-Behnken center-united experiment design. Taking setback as a dependent variable, the models were obtained by using a response surface analysis of the three factors of the water content of starch, heat moisture treatment temperature and heat moisture treatment time based on a single factor experiments. The resulting model can be used for analysis and prediction for its goodness of it. The experiments were designed to explore the effects of three factors including the water content of starch, heat moisture treatment temperature and heat moisture treatment time on the value of setback of modified starch products with response surface methodology. The results showed that the optimum conditions were obtained with the water content of 34%, the treatment temperature of 105.8℃,and the treatment time of 1h. The properties index of sweet potato starch vermicellis before and after heat moisture treatment were investigated in the study. Comparative qualities of starch vermicelli showed that the optimized conditions heat moisture modified starch vermicelli broken rate reduced 70%, the hardness of starch vermicelli increased from the original23.91N to 30.81N, the tensile strength of starch vermicelli increased from the original0.79N to 1.71N.These research results can provide a sensitive method for monitoring the quality of starch for starch vermicellis production and explore a convenient method for evaluating the qualities of starch vermicellis. In doing so, this can provide the theory basis for starch vermicellis’qualities improvement.4、Effect of different heat moisture treatment conditions on the properties of sweet potato starch pastesUsing rapid viscosity analyzer (RVA) and dynamic rheometer investigate the changes of sweet potato starch gelatinization and the rheological properties under different conditions by heat moisture treatment, and get the influence role of sweet potato starch properties through the statistical analysis of main parameters, which helps to reveal the mechanism of the heat moisture treatment for improving the quality of sweet potato vermicelli. The results show that sweet potato starch pasting curve have taken place large changes, and sweet potato starch RVA pasting characteristics differ significant difference (p<0.05) between under different conditions by heat moisture treatment each other. The value of heat moisture treated sweet potato starch paste viscosity, final viscosity, setback viscosity and gelatinization temperature, gelatinization time significantly higher than the original sweet potato starch, and the value of peak viscosity and breakdown viscosity relative to the original starch has dropped significantly. The rheological properties of the static test result shows that the static rheological curve fit all starch samples with Herschel -- Bulkley equation, and complex correlation coefficient is greater than 0.99, which illustrate the fitting precision is high. After heat moisture treatment, the yield stress of sweet potato starch is reduced, the consistency coefficient K value increases, the fluid index n value decreases, which declare the pseudoplastic of sweet potato starch enhance. Dynamic rheological properties testing results show that within the scope of the test frequency, the heat moisture treatment sweet potato starch G’ and G" effect is remarkable. The heat moisture treatment sweet potato starch G’ rising significantly, and the viscosity changes modulus (G") basically also showed a trend of rising, but the condition of water content 34%, treatment temperature of 105℃, treatment time of 1 h that viscosity modulus (G") is on the decline, which showed better elasticity and low viscosity than other starch.5、Influence mechanism research on sweet potato starch pastes properties by heat moisture treatmentThis chapter studies the structural differences with sweet potato starch under different conditions heat moisture treatment by analytical methods of Fourier transform infrared spectrum, X-ray diffraction and the content of amylose, which will help to further explain functional characteristics of mechanism with the change of the starch structure. Research results indicated that the heat moisture treatment starch do not produce new chemical compound through FTIR analysis, and the crystal form do not change through X-diffraction analysis too. But the absorption peak and the X-diffraction intensity change with the difference condition heat moisture treatment. The heat moisture treatment starch with the condition of water content 34%, treatment temperature of 105℃, treatment time of 1 h of orderly degree increase and the degree of crystallinity are bigger than the native starch, especially in the scope of 1650-2029 cm-1、2210-2935 cm-1、3000-3850 cm-1, which show that molecular structure have change, the long chain starch molecular break, the quantity of the carbonyl and hydroxyl increase, and maybe also add new C-H. The content of amylase increase with the heat treatment under different conditions, The heat moisture treatment starch with the condition of water content 34%, treatment temperature of 105℃, treatment time of 1 h increase significantly. The main causes of improving the quality of sweet potato starch vermicelli by heat moisture treatment is:on the one hand, due to the role of water and heat, degradation in the starch molecules, lead to increase amylose content, on the other hand, is likely to the starch degradation of macromolecular make chain length to close, and molecular chain is concentrated, which make starch structure become more orderly. |
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