Fig. 3.

Digestibility of barley straw plant cell wall linkages. (A) Glycans were sampled from barley straw (BS) and total tract indigestible residue (TTIR) plant whole cell wall (de-starched alcohol insoluble residue, AIR) and isolated non-starch polysaccharides fractions (EDTA + Na₂CO₃, 4 M KOH, and cellulosic-residue). The relative abundance (molar %) of glycosidic linkages was determined by gas chromatography – mass spectrometry/flame ionization detection (GC–MS/FID) of partially methylated acetylated alditol (PMAA) derivatives. Heat maps were generated based on the calculated ratio of linkage abundance in the BS control over the digested TTIR (black = indigestible, bright green = most digestible). (B) Bar graphs were generated for the top 10 indigestible linkages within each plant cell wall fraction, representing the ratio of the highest average abundance calculated in TTIR over that of BS control. Linkages with standard deviations of greater than 50% were excluded as they were considered unreliable. (C) Linkage composition data for BS and TTIR were assigned to classes of polysaccharides according to Pettolino, et al. [13]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)