| Okra(Abelmoschus esculentus(L.)Moench),a kind of herbaceous plant of Malvaceae family,is originated from Africa,South Asia and some other tropical or subtropical areas.Okra as a new type of vegetable is widely applauded not only for its smooth flavor and delicious taste,but also for its high nutritional value.At present,less research on extraction of soluble dietary fiber(SDF)from okra has been found,studies on physicochemical properties of okra have not got deep enough into the microstructure level.The structure-activity relationship of SDF from okra has not been reported.In this paper,the SDF from okra pods was obtained by mixed enzyme extraction method,response surface analysis was employed to investigate the optimal parameters of the extraction.Physicochemical properties and structure characterizations of the SDF extracted under optimal conditions were studied.Glucose adsorption capacity,cholesterol adsorption capacity,cation exchange capacity and antioxidant capacity of SDF from okra were studied in vitro;laxative effect of SDF from okra was studied by animal experiments.(1)Effects of material-to-water ratio,enzyme content,extraction temperature and extraction time on the extraction of SDF were investigated by one-factor-at-a-time experiments.Based on one-factor-at-a-time experiments,response surface analysis was employed to investigate the optimal parameters of the extraction.The result showed that the optimal conditions were as follows:material-to-water ratio,1:24 g/m L;enzyme content,1.8%;extraction time,54 min;extraction temperature,62?.Under these conditions,the yield of SDF achieved 10.94%,the relative error with the predicted value is 1.48%,the accuracy of prediction results were proved and can be used to forecast the extraction yield of SDF from okra pods.(2)The SDF extracted from okra with different particle sizes were obtained by classifying screen.Physicochemical properties of okra SDF,such as water holding capacity,oil holding capacity,swelling capacity and solubility,were measured.Structure characterizations of okra SDF were studied by scanning electron microscope,infrared spectrum and X-ray diffraction.Okra SDF exhibited significant water holding capacity(5.61 g/g),swelling capacity(3.35 m L/g)and oil holding capacity(4.88 g/g).The solubility of okra SDF increased significantly with the increase of temperature,while increased at first and then decreased with the increase of pH value,the solubility reached the highest level when the pH value was at 7.0.Microstructure of okra SDF showed that starch substances on its surface were removed completely.The crystal structure of okra SDF was accord with crystal form of cellulose I.Fourier transform infrared spectroscopy of SDF was accord with typical characteristics of dietary fibers.(3)Glucose adsorption capacity of okra SDF increased significantly with the increase of glucose concentration during the glucose adsorption experiment,SDF with smaller particle size showed better glucose adsorption capacity.Cholesterol adsorption capacity of okra SDF under neutral conditions was stronger than acid conditions,while increased at first and then decreased with the increase of comminution degree,with a maximum of 9.429 mg/g.Okra SDF after acidification possessed some properties similar to weak acid,which can slow down the rise of pH value,exhibited significant cation exchange capacity(0.377 mmol/g).The total phenol content of okra SDF was 23.44±1.45 mg/g,which was higher than okra powders by 10%.Okra SDF showed better antioxidant activity than okra powders,which were reflected in its ability of scavenging DPPH·free radical,ABTS~+·free radical,and capacity of ferric ion reducing.(4)Laxative effect of okra SDF was studied by animal experiments.Constipation model of mice was successfully established by receiving 10 mg/kg·bw loperamide hydrochloride with gastric perfusion for 14 days.Experimental groups were as follows:blank control group,model control group(negative control group),low dose group,middle dose group and high dose group.Each group consisted of 20 mice.During daily feeding,the average body weight of each dose groups and model control group showed no significant difference with blank control group,none of these mice showed any serious adverse reactions.Food intake,water intake and weight change of all experimental mice were within normal range.Experimental mice(middle dose group)which received 0.6 g/kg·bw okra SDF with gastric perfusion for 14 days,showed better recovery situation of defecation frequency,defecation quantity and intestinal motility than other dose groups. |
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