| Resistant starch (RS) was defined as the starch which could not be absorbed in the small intestine, but could be fermented by coliform in healthy individuals. RS has the functions of maintaining intestinal morphology, increasing the volume of excrement and fecal moisture content, decreasing the content of free ammonia and indole, promoting intestinal peristalsis, anti-tumor activing, regulation of the immune and gene. Furthermore, RS can enhance the apparent absorption of minerals through increasing surface area and reducing the pH value of the intestine. RS has the proliferation effects on probiotics. Our previous study showed that lotus seed resistant starch (GP-LRS3) prepared by autoclaving method had the function of promoting Bifidobacterium proliferation which was associated with the layered surface structure, stable double helix structure and highly degree of crystallinity. The lotus seed starch was used as raw material to study the optimal conditions of microwave-moisture method and ultrasonic-autoclaving method in the preparation of lotus seed resistant starch, and to compare the differences of structural characteristics and physicochemical properties among lotus seed resistant starch prepared by autoclaving method (GP-LRS3), microwave-moisture method (MP-LRS3) and ultrasonic-autoclaving method (UP-LRS3). The in vitro proliferation effects on Lactobacillus and Bifidobacterium of GP-LRS3, MP-LRS3 and UP-LRS3 were investigated.Based on the preparation of lotus seed resistant starch by the microwave-moisture method, the single factor tests showed that the factors of affecting the yield of lotus seed resistant starch was:starch concentration? microwave power?microwave time. The orthogonal experiment results showed that the optimal conditions for resistant starch preparation were 15% of starch,120s microwave time and 640W microwave power. Under this condition, the lotus seed resistant starch yield was 39.53%. For preparation of lotus seed resistant starch by the ultrasonic-autoclaving method, the single factor tests showed that the factors of affecting the yield of lotus seed resistant starch was:autoclaving time ? starch concentration ?autoclaving temperature?ultrasonic times. The optimal preparation conditions were determined with 300W of ultrasonic power,45% of starch,55 min of ultrasonic time,15 min of autoclaving time and 115? of autoclaving temperature using orthogonal experiment. Under this condition, the lotus seed resistant starch yield was 56.12%.The structural characteristics of resistant starch prepared by three different methods were analyzed. The results showed that GP-LRS3, MP-LRS3 and UP-LRS3 had smaller molecular weight and degree of polymerization. The molecular weights of GP-LRS3 and UP-LRS3 were mainly distributed in the range of 1.0×104?2.0×104 g/mol, and the amount of the molecules with molecular weight located in this range accounted for 67.69% and 69.26% of the total RS molecules, respectvely; while less MP-LRS3 was observed at the same molecular weight range, accounting for 47.87% of the total RS molecules. From the results of environmental scanning electron microscope (ESEM), all of resistant starch prepared by three different mothods behaved compact granule structure; the particle size of MP-LRS3 was smaller and smoother than GP-LRS3, while UP-LRS3 had bigger particle size and rougher particle surface than GP-LRS3. Moreover, cavities were observed on the rough surfaces of UP-LRS3. X-ray diffraction (XRD) showed that the resistant starch prepared by three different mothods was all B-type of crystal structure, and the crystallinity was:GP-LRS3?UP-LRS3?MP-LRS3. Fourier transform infrared spectroscopy (FT-IR) concluded that the content of double helix structure was: UP-LRS3?GP-LRS3?MP-LRS3. The results from solid state 13C nuclear magnetic resonance spectroscopy (13C NMR) indicated that the amorphous structure scale was: MP-LRS3?GP-LRS3?UP-LRS3. The results showed that the structural characteristics of GP-LRS3, MP-LRS3 and UP-LRS3 were significantly different, which may be caused by different preparation methods.The physical and chemical properties of resistant starch prepared from three different methods were studied. MP-LRS3 showed the highest solubility and swelling capacity, and UP-LRS3 showed the strongest iodine absorption capacity and thermal stability. The different physical and chemical properties of GP-LRS3, MP-LRS3 and UP-LRS3 may be associated with the difference on their structural characteristics, and may be resulted from the combination of multiple structural factors.Taken glucose (GLU) and high amylose maize starch (HAMS) as positive control and blank control, respectively, the in vitro proliferation effect of lotus seed resistant starch prepared by three different methods on Bifidobacterium and Lactobacillus were studied. The results showed that the stimulative effect of lotus seed resistant starch prepared by three different methods on bifidobacterium proliferation were superior to GLU and HAMS:the growth lag phase of Bifidobacterium in GP-LRS3, MP-LRS3 and UP-LRS3 medium were about 10 h shorter than that in GLU medium and HAMS medium; GP-LRS3, MP-LRS3 and UP-LRS3 could promote Bifidobacterium to produce butyric acid which could improve the intestinal environment. The results also showed that the stimulative effect of lotus seed resistant starch prepared by three different methods on Lactobacillus proliferation were superior to GLU and HAMS:the growth rate of Lactobacillus in experimental group and control group were all in the logarithmic phase when the trainning time was 8h, but the growth rate of Lactobacillus in GP-LRS3, MP-LRS3 and UP-LRS3 medium were significantly higher than that in GLU medium and HAMS medium. Furthermore, lotus seed resistant starch prepared by three different methods could enhance the tolerance of Bifidobacterium and Lactobacillus to the high concentrations of bile salt and simulated pepsase and trypsase. |
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