| Fresh corn bracts are rich in dietary fiber,mainly insoluble dietary fiber(IDF),but not effectively utilized in production and processing,resulting in wasted resources.Dietary fiber has been widely concerned about the health benefits of human body,but its source is limited.It is particularly necessary to expand new sources of dietary fiber to obtain high functional dietary fiber products.In this paper,IDF was prepared by ultrasonic-assisted enzymatic method using fresh corn bracts as raw materials,and the extracted IDF was modified by dynamic high-pressure microfluidization(DHPM).The physicochemical,functional properties and modification effects of modified dietary fiber(MDF)were investigated.Its physiological activity was explored by establishing a mouse high-fat obesity model.The main results were as follows:(1)The ultrasonic assisted cellulase method was adopted to extract IDF from fresh corn bracts,and the best preparation process conditions were optimized by establishing a quadratic polynomial regression mathematical model through single-factor and response surface experiments:cellulase concentration of 1.65%,ultrasonic power of 250W,liquid-solid ratio of1:30 g/m L,and ultrasonic time of 60 min,at which the actual yield of IDF was 62.38%.The product appearance was light yellow-green,and the process was feasible.DHPM was used to modify fresh corn bract IDF,and the optimum conditions were optimized by single-factor and response surface experiments with a quadratic polynomial regression mathematical model:solid-liquid ratio of 1.5 g/100 m L,pressure of 12900 PSI,treatment of 1 time,and a particle size of 3.06μm and polydispersity index of 0.64 for the obtained MDF.(2)The structure analysis of MDF was carried out using soluble dietary fiber(SDF)and IDF as controls.Scanning electron microscopy results showed that MDF surface curled,holes and cracks appeared.The results of automatic nitrogen adsorption specific surface analyzer showed that the specific surface area of MDF(1.63 g/m~2)increased by 61.76%compared with IDF(1.02g/m~2),which was not significantly different from that of SDF(1.65 g/m~2)(P>0.05).The X-ray diffraction results revealed that the crystallinity of MDF(32.56%)decreased by 14.80%compared to IDF(38.22%)and was higher than that of SDF(21.04%),which still belonged to type I crystalline structure.The results of differential scanning calorimetry and thermogravimetric analysis showed that the properties of IDF,MDF and SDF were stable below200°C.After modification,the thermal stability of MDF decreased and the final mass residue(8.77%)was the least.The results of Fourier transform infrared spectroscopy showed no significant difference between the absorption peaks of MDF and IDF,both containing hemicellulose,cellulose,lignin,etc.,but the intensity of the peaks was changed.Under the action of DHPM,MDF underwent fragmentation,swelling and fracture,producing cracks and holes on the surface and inside,and the intermolecular arrangement might also be changed,which led to the increase of water holding capacity(3.57 g/g),oil holding capacity(4.67 g/g)and water expansion capacity(3.47 m L/g)of MDF by 99.46%,75.64%and 7.27%,respectively,and also led to a decrease in apparent viscosity.(3)DHPM treatment improved the glucose adsorption capacity(60.72 mg/g),glucose diffusion and dialysis delay index,α-amylase inhibition capacity(half inhibitor amount:0.77m/m L),sodium cholate adsorption capacity(55.85 mg/g),cholesterol adsorption capacity of MDF(5.75 mg/g,p H=2.0;14.36 mg/g,p H=7.0).However,the antioxidant capacity was decreased compared to IDF,which may be caused by the impairment of antioxidant substances due to DHPM treatment.The increase in functional activity of MDF was mainly the result of the combination of the reduction in surface accessibility and more complex internal structure of MDF due to DHMP modification.(4)After 12 weeks of dietary intervention using IDF and MDF in mice fed with high-fat diet,it was found that the mice lost weight,returned to normal fasting blood glucose levels,reduced insulin resistance index,significantly decreased blood triglyceride content,low-density lipoprotein content,alkaline phosphatase content,malondialdehyde content,liver triglyceride and cholesterol content,and glutathione content and superoxide dismutase activity increased(P<0.05).The degree of fatty liver lesions was reduced and the degree of intestinal damage was decreased.This indicates that MDF and IDF can reduce the adverse effects caused by high-fat diets,but the effect of MDF was more significant.The structure analysis of fecal microflora showed that IDF and MDF reduced the abundance and richness of fecal microflora in mice caused by high-fat diet,reduced the ratio of Firmicutes/Bacteroidetes,promoted the transformation of fecal microflora in mice to healthy species distribution,and the proliferation of short chain fatty acids-producing strains Lachnospiraceae and Alloprevotella,and decreased the proportion of harmful bacteria Oscillospiraceae.The beneficial effects of MDF were more obvious.Bifidobacteriales were the marker species of difference between MDF groups,indicating that MDF promoted the proliferation of Bifidobacteriales,and MDF facilitated the production of acetic acid,propionic acid and butyric acid,showing a probiotic effect,while IDF did not show this effect. |
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