| The okra plant, Abelmoschus esculenlus (L.) Moench, is an annual herbal food and medicine which belongs to the malvaceae family. Okra is a nutrient-rich vegetable whose roots, stem, leaves, flower and fruits can be eaten. It has numerous medicinal properties that can be harnessed. However, little research on the flowers. The okra flower is good resources of pectin and has good utilization value. Response Surface Method (RSM) was applied to optimize the pectic polysaccharide extraction condition of okra flowers. In addition, we had analyzed the basic physicochemical properties, the rheological property and the structure of pectic polysaccharide from okra flower.Acid hydrolysis followed by ethanol precipitation was used to extract pectic polysaccharide from okra flowers in the present work. The effects of acid kinds, material-to-liquid ratio, extraction temperature, extraction time and pH of HCl soiution on the extraction yield of pectic polysaccharide were discussed. Based on the single-factor method, the optimum extraction conditions were obtained by response surface method. As a result, the optimal conditions for pectic polysaccharide extraction were determined as follows:2times of extraction, material-to-liquid ratio30:1, temperature90℃, extraction time2.76h, and pH1.60. Under these conditions, the actual pectic polysaccharide yield was32.46%.Acid hydrolysis followed by ethanol precipitation was used to extract pectic polysaccharide from okra flowers. Effects of concentration, temperature, pH, sugar concentration, different heating time on the rheological property of pectic polysaccharide were investigated. The result showed that the viscosity of pectic polysaccharide solution decreased with the increased shear rate, and the pectic polysaccharide solution was a typical non-Newtonian fluid. The degree of impact on the rheological property enhanced with the increasing of pectic polysaccharide solution concentration. The impact on the viscosities of pectic polysaccharide solutions of pH were complex. The changes of pH value would lead up to the decrease of viscosity of pectic polysaccharide solution. The viscosity decreased with the increase of temperature and the overtime of heat treatment at100℃, and increased with the addition of sucrose.The okra pectic polysaccharide was shown to be rich in galactose, rhamnose and galacturonic acid determined by HPLC. The Mw distribution of the pectic polysaccharide obtained from okra is detected by HPLC. The Mw distribution pattern of the okra pectin showed a broader Mw distribution. The content of uronieaeid was41.43%by carbazol-sulphate method. With high-performance liquid chromatography assay, degrees of methylation and acetylation were assayed to be49.86%and51.31%in okra pectic polysaecharide, respectively. Therefore, okra pectic polysaccharide ia kind of acidic heteropolysaccharide with low degree of esterifieation.AEP-1and AEP-2were sequentially obtained from okra flowers by acid hydrolysis in the first extraction and in the second extractin. DEAE Cellulose-52was used to isolate and purify AEP-1and the results showed that AEP-1was composed of a neutral polysaccharide and an acidic polysaccharide (APP-1). AEP-2was completely fractionated into one neutral fraction and an acidic fraction (APP-2) by ion-exchange chromatography. which is mainly composed by APP-2. APP-1mainly contained rhamnogalacturonan type I with longer galactose-rich side chains was part of this fraction. APP-2fractions contain rhamnogalacturonan type I next to homogalacturonan with much higher levels of methyl esterified galacturonic acid residues. These samples were subjected to NMR analysis, which indicated that, only part of the acetyl groups are located on the RG I galacturonic acid residues for APP-2. |
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