Sengkhamparn Nipaporn, Verhoef René, Schols Henk A, Sajjaanantakul Tanaboon, Voragen Alphons G J
Department of Agrotechnology and Food Sciences, Wageningen University, The Netherlands.
Carbohydr Res. 2009 Sep 28;344(14):1824-32. doi: 10.1016/j.carres.2008.10.012. Epub 2008 Oct 21.
Okra pods are commonly used in Asia as a vegetable, food ingredient, as well as a traditional medicine for many different purposes; for example, as diuretic agent, for treatment of dental diseases and to reduce/prevent gastric irritations. The healthy properties are suggested to originate from the high polysaccharide content of okra pods, resulting in a highly viscous solution with a slimy appearance when okra is extracted with water. In this study, we present a structural characterisation of all major cell wall polysaccharides originating from okra pods. The sequential extraction of okra cell wall material yielded fractions of soluble solids extractable using hot buffer (HBSS), chelating agent (CHSS), dilute alkaline (DASS) and concentrated alkaline (CASS). The HBSS fraction was shown to be rich in galactose, rhamnose and galacturonic acid in the ratio 1.3:1:1.3. The degree of acetylation is relatively high (DA=58) while the degree of methyl esterification is relatively low (DM=24). The CHSS fraction contained much higher levels of methyl esterified galacturonic acid residues (63% galacturonic acid; DM=48) in addition to minor amounts of rhamnose and galactose. The ratio of galactose to rhamnose to galacturonic acid was 1.3:1.0:1.3 and 4.5:1.0:1.2 for HBSS and CHSS, respectively. These results indicated that the HBSS and CHSS fractions contain rhamnogalacturonan type I next to homogalacturonan, while the latter is more prevailing in CHSS. Also the DASS fraction is characterised by high amounts of rhamnose, galactose, galacturonic acid and some arabinose, indicating that rhamnogalacturonan I elements with longer arabinose- and galactose-rich side chains were part of this fraction. Partial digestion of HBSS and CHSS by pectin methyl esterase and polygalacturonase resulted in a fraction with a lower Mw and lower viscosity in solution. These samples were subjected to NMR analysis, which indicated that, in contrast to known RG I structure, the acetyl groups in HBSS are not located on the galacturonic acid residues, while for CHSS only part of the acetyl groups are located on the RG I galacturonic acid residues. The CASS fraction consisted of XXXG-type xyloglucan and 4-methylglucuronoxylan as shown by their sugar (linkage) composition and enzymatic digestion.
秋葵荚在亚洲通常用作蔬菜、食品原料以及用于多种不同用途的传统药物；例如，作为利尿剂，用于治疗牙科疾病以及减轻/预防胃部刺激。秋葵荚的健康特性被认为源于其高多糖含量，用水提取秋葵时会形成具有粘性外观的高粘性溶液。在本研究中，我们对源自秋葵荚的所有主要细胞壁多糖进行了结构表征。秋葵细胞壁材料的顺序提取产生了可使用热缓冲液（HBSS）、螯合剂（CHSS）、稀碱（DASS）和浓碱（CASS）提取的可溶性固体部分。HBSS部分显示富含半乳糖、鼠李糖和半乳糖醛酸，比例为1.3:1:1.3。乙酰化程度相对较高（DA = 58），而甲酯化程度相对较低（DM = 24）。CHSS部分除了含有少量鼠李糖和半乳糖外，还含有更高水平的甲酯化半乳糖醛酸残基（63%半乳糖醛酸；DM = 48）。HBSS和CHSS中半乳糖、鼠李糖和半乳糖醛酸的比例分别为1.3:1.0:1.3和4.5:1.0:1.2。这些结果表明，HBSS和CHSS部分除了同型半乳糖醛酸外还含有I型鼠李半乳糖醛酸聚糖，而后者在CHSS中更为普遍。DASS部分的特征还在于含有大量的鼠李糖、半乳糖、半乳糖醛酸和一些阿拉伯糖，表明具有较长阿拉伯糖和半乳糖丰富侧链的I型鼠李半乳糖醛酸聚糖元素是该部分的一部分。用果胶甲酯酶和多聚半乳糖醛酸酶对HBSS和CHSS进行部分消化，得到溶液中分子量较低且粘度较低的部分。对这些样品进行了核磁共振分析，结果表明，与已知的RG I结构不同，HBSS中的乙酰基不在半乳糖醛酸残基上，而对于CHSS，只有部分乙酰基位于RG I半乳糖醛酸残基上。如糖（连接）组成和酶消化所示，CASS部分由XXXG型木葡聚糖和4 - 甲基葡糖醛酸木聚糖组成。
