全榖物膳食纖維之聚醣多樣性研究

Abstract

全榖被重視與推廣，因其有對人體健康有益處的豐富營養素，如膳食纖維、礦物質、維生素B、維生素E與植化素。而膳食纖維可分為非水溶與水溶性膳食纖維。水溶性膳食纖維可做為益生質被腸道菌相利用，本研究使用台灣產不同品種稻米、不同品種薏仁、小麥、大麥、燕麥、黑麥為原料，分析不同品種、不同穀物中水溶性膳食纖維的組成差異。單醣組成分析顯示大麥與燕麥主要由混合型鍵結β-D-葡聚醣組成；而黑麥除了β-D-葡聚醣外還有阿拉伯木聚醣；在小麥、稻米、薏仁當中單醣組成較為豐富，像是小麥富含阿拉伯木聚醣；稻米與薏仁則是富含甘露聚醣，與些許果膠多醣及阿拉伯木聚醣。糙米與糙薏仁之水溶性膳食纖維主要組成-甘露聚醣，具有免疫調節潛力，為了解其甘露聚醣結構特徵，會利用內切甘露聚醣酶將不同穀物來源甘露聚醣水解出保有主鏈、側鏈不同醣組成的寡醣，以液相層析串聯軌道阱質譜 (LC-Orbitrap-MS/MS)進行結構解析，鑑別主鏈與側鏈的鍵結與官能基修飾資訊。使用內切甘露聚醣酶水解已知結構特徵之甘露聚醣，獲得具有不同結構特徵之甘露寡醣譜型，可建立辨別樣品中甘露聚醣結構特徵之分析平台。糙米與薏仁水溶性膳食纖維當中約有40~50% 甘露聚醣，是主要的組成。糙米中甘露聚醣型態為帶有葡萄糖基取代的葡甘露聚醣及半乳糖側支修飾的半乳甘露聚醣；薏仁則是混合型的葡半乳甘露聚醣。小麥與黑麥水溶性膳食纖維當中約有4% 甘露聚醣。小麥中甘露聚醣型態為帶有葡萄糖基取代的葡甘露聚醣及半乳糖側支修飾的半乳甘露聚醣；黑麥則是混合型的葡半乳甘露聚醣。本研究有助於穀物尤其是糙米與薏仁的水溶性多醣組成有更深入的了解。

Dietary fiber is a nutrient that decreases total mortality, cardiovascular mortality, cancer mortality, and Type 2 diabetes mellitus incidence in whole grains. The soluble dietary fibers (SDF) have higher fermentability compared to insoluble dietary fibers (IDF). The fermentability and prebiotic efficiency have been reported to be related to the molecular characteristics, including solubility, monosaccharide composition, linkage pattern, and the content and position of substituent groups of polysaccharides, the major components of SDF. To understand the profile difference of SDFs from different cereals, including barley, oat, rye, wheat, rice, and adlay. Our results indicated that barley and oat are rich in mixed-linked β-D-glucans that contain glucose 81~85% in SDF. In addition to β-D-glucans, rye also contained a substantial amount of arabinoxylans. The polysaccharide compositions in SDFs of wheat, rice, and adlay were found to be more diverse. SDF of wheat was rich in arabinoxylans, and SDF from rice and adlay are rich in mannans and pectins in addition to arabinoxylans. The mannans from cereals have been less studied. Therefore, we have developed an endo-mannanase-assisted HPLC-MS/MS method to reveal the characteristics of the molecules. The methodology of the developed approach was the conversion of mannans into mannooligosaccharides (MOS) and analyzing glycosidic linkage patterns of MOS by using an HPLC-MS/MS. Brown rice and adlay contain water-soluble dietary fiber in which mannans are the major component, comprising 40–50%. In brown rice, the mannans are primarily glucomannans substituted with glucose residues and galactomannans with galactose side chains, while adlay contains predominantly mixed-type galactoglucomannans. In contrast, wheat and rye contain about 4% mannans within their water-soluble dietary fiber. Wheat mannans are mainly glucomannans with glucose substitutions and galactomannans with galactose side chains, whereas those in rye are chiefly mixed-type galactoglucomannans. The results of the study facilitate our understanding of the composition profile of Taiwanese rice and adlay cultivars.