Asp N G
Scand J Gastroenterol Suppl. 1987;129:16-20. doi: 10.3109/00365528709095845.
The definition of dietary fibre as "non-starch polysaccharides plus lignin", that has now been widely accepted, is chemically more distinct than earlier definitions, but still implies some difficulties in its demarcation. In practice, analytical problems and limitations are important, since definition and analysis of dietary fibre are closely related. The delimitation towards more or less undigestible starch fractions, highly soluble polysaccharides, oligosaccharides, and undigestible protein is discussed, as well as phytate, tannins and some other components. Methods for analysis of dietary fibre are based on one or more of three different principles: 1) Weighing after removal of non-fibre components, 2) Colorimetric carbohydrate determinations 3) Specific determination of monomeric constituents by gas-liquid chromatography (GLC) or high performance liquid chromatography (HPLC). Gravimetric methods, using enzymatic degradation of protein and starch, are generally preferred for assay of total dietary fibre, or soluble and insoluble fibre separately. Colorimetric methods are used mainly for determining uronic acids as a measure of pectins. Detailed methods usually employ GLC determination of monomers after acid hydrolysis, but HPLC appear to develop as a convenient alternative. Uronic acids are determined separately by colorimetry or decarboxylation, and lignin usually as Klason lignin, i.e. acid insoluble material.
膳食纤维的定义为“非淀粉多糖加木质素”，这一定义现已被广泛接受，在化学上比早期的定义更为明确，但在其界定方面仍存在一些困难。实际上，分析问题和局限性很重要，因为膳食纤维的定义和分析密切相关。本文讨论了膳食纤维与或多或少难以消化的淀粉组分、高溶解性多糖、寡糖及难以消化的蛋白质的界限，以及植酸盐、单宁和其他一些成分。膳食纤维的分析方法基于三种不同原理中的一种或多种：1）去除非纤维成分后称重；2）比色法测定碳水化合物；3）通过气液色谱法（GLC）或高效液相色谱法（HPLC）对单体成分进行特异性测定。重量法利用蛋白质和淀粉的酶促降解，通常优先用于分别测定总膳食纤维或可溶性和不溶性膳食纤维。比色法主要用于测定糖醛酸以衡量果胶含量。详细方法通常采用酸水解后通过GLC测定单体，但HPLC似乎正在发展成为一种方便的替代方法。糖醛酸通过比色法或脱羧法单独测定，木质素通常按克拉森木质素测定，即酸不溶性物质。
