| Resistant starch (RS) is becoming a research hotspot in the field of food science due to its physiological functions in preventing gastrointestinal diseases, controlling blood glucose response, promoting inorganic salts absorption, improving the colon microbial environment, and promoting probiotics growth as prebiotics. In this paper, we optimized the conditions in resistant starch production with autoclaving and enzyme-autoclaving, which led to a higher yield of resistant starch. We also investigated the resistant starch from purple sweet potato in terms of granule properties, physical and chemical characteristics and its proliferation effect on Bifidobacterium. We compared these aspects of the original purple sweet potato with those of ones prepared with autoclaving (RS3) and autoclaving-enzyme combined treatment (ED-RS3). A systematic study was carried out to understand the preparation process and the structure of purple sweet potato resistant starch, which could provide a theoretical basis for future research on the biological functions and formation of resistant starch from purple sweet potato and its biological functions.1、We studied the effects of starch concentration, autoclaving temperature, autoclaving time and pH value on the yield of resistant starch from purple sweet potato. Parameters were optimized with orthogonal method. The results showed a significant impact of starch concentration and autoclaving time on the yield of purple sweet potato resistant starch. The optimal parameters were determined as:autoclaving temperature 110℃, autoclaving time 40 min, starch concentration 35%, and pH 6. Under these conditions, the yield reached the maximum value of 10.23%.2、To optimize the parameters associated with enzyme-autoclaving combined treatment, we evaluated the effects of starch concentration, pullulanase dosage, reaction time, and autoclaving time on the yield of purple sweet potato resistant starch. Pullulanase dosage and autoclaving time both had significant effects on the yield and orthogonal method was applied to maximize the yield. The maximum concentration of 17.16% was reached with the following conditions:starch concentration 30%, enzyme dosage 1u/g, reaction time 12h and reaction time 45min.3、With studies on the physical and chemical properties of original purple sweet potato starch, RS3, and ED-RS3, we observed the highest content of amylase in ED-RS3. The resistant starch of RS3 and ED-RS3 took on an irregular bulky shape with a rough surface under SEM. ED-RS3 showed a gully shape with a rough lamellar surface but smoother than the surface of RS3. The purple sweet potato resistant starch (RS3, ED-RS3) had a better solubility, transparency and tendency for gelatinization while reduced expansion degree than those of untreated one. By analyzing the results from DSC, we found both RS3 and ED-RS3 demonstrated good thermal stability and higher gelatinization temperature than that of original starch. ED-RS3 showed the highest gelatinization enthalpy. Analysis of X-ray diffraction suggested the crystal structure of resistant starch changed from C-type to B-type. Analysis with Fourier transform infrared spectra indicated no new substance was formed or changed that the resistant starch in purple sweet potato was physical modified starch.4、Taking glucose and HAMS as controls, we studied the effect of RS3 and ED-RS3 on Bifidobacterium proliferation. The results suggested the addition of purple sweet potato resistant starch should be of appropriate amount, not the higher the better. The value of OD600nm reached the highest level of 1.39 when the concentrations of RS3, ED-RS3 and HAMS was 15 g/L,1.60, and 1.13, respectively. For glucose, when its concentration was 10 g/L, the OD600nm value reached the highest level of 0.83. With Bifidobacteria increasing in number, pH value dropped, which suggests the fermentation of resistant starch by Bifidobacterium. |
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