Indigestible fraction of edible marine seaweeds

As dietary fibre constitutes only part of the non‐digestible components of plant foods, there is a general trend to extend the fibre concept to include all the main food constituents that reach the colon undegraded. In this study the major non‐digestible components of five edible brown and red Spanish marine seaweeds—Fucus vesiculosus. Laminaria digitata (Kombu), Undaria pinnatifida (Wakame), Chondrus crispus (Irish moss) and Porphyra tenera (Nori)—were determined under simulated physiological conditions by an in vitro enzymatic method (Sauro‐Calixto F et al, J Agric Food Chem 48: 3342–3347 (2000)) developed as an alternative to dietary fibre analysis. Two indigestible fractions, soluble (SIF) and insoluble (IIF), were obtained after enzymatic treatments of seaweeds. SIF amounted to 40–170 g kg−1 algal dry weight. Gravimetric values of IIF were 246–599 g kg−1 and its major components were resistant protein (37–133 g kg−1), minerals (13–78 g kg−1) and non‐starch polysaccharides plus klason lignin (196–415 g kg−1). The total indigestible fraction determined by colorimetry (335–516 g kg−1) was similar to the total dietary fibre content of seaweeds determined previously by the AOAC method. However, the distribution of the soluble and insoluble fractions differed between the two procedures. Estimation of the indigestible fraction of edible seaweeds could be useful from both nutritional and commercial points of view. Copyright © 2003 Society of Chemical Industry