| Resistant starch (RS) is defined as the sum of starch and products of starch degradation not absorbed in the small intestine of healthy individuals. It may be (partially) fermented in the large bowel by the microflora, producing short chain fatty acids. Common maize starch and high amylose maize starch were used as raw material in this study, respectively. RS was prepared by three different treatments, cycles of autoclaving-cooling, acid hydrolysis combined with cycles of autoclaving-cooling and enzyme hydrolysis combined with cycles of autoclaving-cooling, respectively. The main factors affected the yield of RS were studied. Then, RS was characterised by X-ray diffraction, differential scanning calorimetry and rapid viscosity analyzer. Finally, the fermented characteristics of RS in the colon were determined by simulated fermentation in vitro. The results obtained in this study were as follow:(1) Common maize starch and high amylose maize starch were used as raw material, respectively. RS was prepared by cycles of autoclaving-cooling. The effect of times of autoclaving-cooling on the yield of RS was studied. The results showed that three times of autoclaving-cooling were suitable for common maize starch, but two times of autoclaving-cooling were suitable for high amylose maize starch. And the following studies were based on these results. The effect of cycles of autoclaving-cooling on the yield of RS from common maize starch was better than that from high amylose maize starch.(2) Common maize starch and high amylose maize starch were used as raw material, respectively. RS was prepared by acid hydrolysis combined with cycles of autoclaving-cooling. The effect of the types, concentration and hydrolysis time of acids on the yield of RS was studied. The results showed that the suitable conditions for the preparation of RS were that for common maize starch, after the starch sample was treated by three times of autoclaving-cooling, acetic acid was added till the concentration of acid was 0.1 mol·L-1, or for high amylose maize starch, after the starch sample was treated by two times of autoclaving-cooling, citric acid was added till the concentration of acid was 0.1 mol·L-1, and then the starch sample was hydrolyzed for 12 h at room temperature, stored for 24 h at 4℃. The effect of this method on the yield of RS from high amylose maize starch was better than that from common maize starch.(3) Common maize starch was used as raw material. RS was prepared by enzyme hydrolysis combined with cycles of autoclaving-cooling. The results showed that the suitable conditions for the preparation of RS were that after the starch sample gelatinized once, the pullulanase was added and the starch sample was hydrolyzed for 6 h, stored for 24 h at 4℃, or that after the starch sample retrograded once, the pullulanase was added and the starch sample was hydrolyzed for 10 h, and then the starch sample was treated by two times of autoclaving-cooling. The effect of the second treatment on the yield of RS was better than the first treatment.(4) Waste liquid produced from the analysis of RS was extracted by graded deposition with water and ethanol. The product obtained was white powder, not sweet, and the DE of it was 10.7, the ratio of extraction was 34.4%.(5) X-ray diffraction graph of RS was B-type. The crystal structure between gelatinized starch and RS were significantly different. DSC analysis showed that there was a single peak for RS (about 120℃). Comparably, there were two peak for common maize starch (about 65℃and 120℃). RVA analysis showed that the pasting curve of RS was almost linearity, so its viscosity was very low. But the viscosity of common maize starch was much higher.(6) Extraction of fresh fecal of healthy human and infant were used, respectively. At the stimulated condition of the large intestines (anaerobic and 37℃), it was mixed with several content of resistant starch, and then fermented for some time. The concentration of short chain fatty acids in the fermented production was determined. The results showed that as the increase of fermented time and content of resistant starch, the concentration of short chain fatty acids in the fermented production increased gradually, especially for the concentration of butyric acid. However, the concentration of short chain fatty acids in the fermented production with infant fecal extraction, especially for the concentration of butyric acid, was much higher than that with human fecal extraction. It meant that the fermentation of resistant starch in simulated intestinal conditions to produce short chain fatty acids might be affected by the intestinal microflora.
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