| Resistant starch (RS) is that portion of the starch that is not broken down by human enzymes in the small intestine. It enters the large intestine where it is partially or wholly fermented. RS is generally considered to be one of the components that make up total dietary fiber. Recently RS has attracted much attention due to its some interesting physiological functions. In this paper, sweetpotato RS from 21 genotypes was studied by adopting near infrared reflectance spectrophotometer analysis (NIRS);rapid viscosity analysis(RVA);scanning electron microscope(SEM), x-ray diffraction and differential scanning calorimetry(DSC). The research involves RS determination, RS content genotype variation and environmental effect, RS physicochemical properties and RS content correlations with some other important storage root quality traits and starch quality traits. The main results are as follows:1. Based on spectrum properties of sweetpotato RS, a new method to determine RS content, the near infrared spectroscopy (NIRS) method, was introduced, a successful NIRS calibration models for sweetpotato RS was established, and can be used in the breeding program. The R~2(RSQ) of NIRS prediction reaches 0.893 with 0.697 of SEP(Standard error of prediction).2. The RS content genotype variation and environmental effects of sweetpotato was determined, genotypes, locations and genotype by location interaction were found to have significant effects on RS content of sweetpotato. After a comprehensive assessment, some genotypes with high RS contents, such as Zhe6025 Xu55-2, Zhe7528 and Zhe3449 were identified and can be used as parents for high RS content breeding.3. Through orthogonal experiment design, an optimum production conditions of sweetpotato RS was selected, that involves 120℃ of heating temperature, 80% of water, 5 of pH, and 60min of heating time. It is also found that the temperature, time, moisture content, pH and other factors may be more significant impact on sweetpotato RS. The pH value, lower temperature and some of the materials in starch may also have a certain impact on sweetpotato RS.4. The physicochemical analysis indicated that the starch particles between the crystal structures have no large difference. X- RD graphs of sweetpotato starch are mainly type A. In pasting and cooling treatment process, significant structure differences between forming RS crystals from different sweetpotato genotypes are found, mainly type B. There is a single peak;DSC analysis found there is a decalescence peak in over 90℃-120℃, the sweetpotato RS shows a unique peak. RVA analysis showed that it is type A pasting curves, characterized by high pasting peak and followed by a high degree of shear-shining;But the viscosity of sweetpotato RS almost completely disappeared. Results of DP analysis showed that There were obvious differences in DP between RS and common starch. The results of NIRS analysis indicated that starch and/or RS has similar NIRS spectral characteristics and features, but there are many differences between different varieties. In SEM investigations, there is only rigid and compact direct chain starch crystallization zone and not regular structure starch elements in RS. The absorbability of starch is lower than RS, but no significant differences between the varieties.5. The correlation between sweetpotato RS content and some other important quality traits was determined. The storage root RS content showed to have significant correlations with amylose content. Some other correlation between RS content and other quality indexes were also studied.
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