Feruloyl and p-coumaroyl groups in spinach cell walls (CW) were labelled using [14C]cinnamic acid and fed to rats. In the caecum and colon, ferulic acid (FA) and p-coumaric acid (PCA) were released from the CW. Few feruloyl or coumaroyl groups remained in the CW to be excreted in faeces, and thus the presence of simple phenol-sugar esters provided little protection of the polysaccharides to enzymic attack. Some oxidatively coupled phenols were also released but a portion remained in the CW. The oxidatively coupled phenols accumulated in the gut whereas the FA and PCA were absorbed by the rat. Thus enzyme-resistant fragments, containing oxidatively coupled phenols (and possibly sugar residues), may survive microbial attack by rat intestinal bacteria.

Extracts prepared from cultures of Bacillus subtilis, grown on maltose as the sole carbon source, lacked maltose phosphotransferase system activity. There was, however, evidence for a maltose phosphorylase activity, and such extracts also possessed both glucokinase and glucose phosphotransferase system activities. Maltose was accumulated by whole cells of B. subtilis by an energy-dependent mechanism. This uptake was sensitive to the effects of uncouplers, suggesting a role for the proton-motive force in maltose transport. Accumulation of maltose was inhibited in the presence of glucose, and there was no accumulation of maltose by a strain carrying the ptsI6 null-mutation. A strain carrying the temperature-sensitive ptsI1 mutation accumulated maltose normally at 37 degrees C but, in contrast to the wild-type, was devoid of maltose transport activity at 47 degrees C. The results indicate a role for the phosphotransferase system in the regulation of maltose transport activity in this organism.

Abstract:The aim of this work was to investigate the fate, in the upper gut of a monogastric animal, of polymers bound within plant cell walls. Uniformly and specifically 14C-labelled spinach cell walls were incubated in artificial body fluids with and without pepsin or pancreatin. In the absence of enzymes, artificial pancreatic juice (pH 8.8) at 37°C hydrolysed the methyl ester groups of wall-bound pectins [half-life (t1,2) 25 h]; the O-acetyl ester groups of cell wall polysaccharides were much more stable (tliz 84 h). In contrast, artificial gastric juice (pH 1.85) hydrolysed wall-bound acetyl groups more rapidly (t,,2 -24 h) than methyl ester groups ( t , / 2 -350 h). Thus, a proportion of the methyl and acetyl groups of plant cell wall polymers will be released in the upper gut as methanol and acetic acid, raising the question of whether these groups should be included within the definition of dietary fibre. The artificial body fluids also caused limited solubilisation of wall polymers but no hydrolysis to mono-or oligosaccharides. Neither pepsin nor pancreatin promoted the hydrolysis of methyl ester or acetyl groups. The small amounts of [14C]protein present in the cell wall preparations were hydrolysed by pepsin or pancreatin to yield amino acids and oligopeptides; however, the major polysaccharides of spinach cell walls were neither degraded to low-molecular-weight products nor solubilised by these enzymes.

Using uniformly '4C-labelled spinach (Spinacia oleracea L) plant cell walls (PCW) the metabolism of PCW can be followed in a defined manner in the rat. Only 10% of the I4C was recoverable in the gut contents and faeces 18 h post-gavage. Two percent of the I4C was excreted in urine and 25% excreted as CO, . I4C was found in all tissues of the body but was most concentrated in the adrenal glands, colon and caecum. The I4C was also present at moderately high concentration in the liver pelt, and owing to their larger size, these tissues accounted for a high percentage of the total I4C. In the liver the I4C was predominantly associated with phospholipid, whereas in the pelt it was present in protein and in Fatty acid residues esterified to cholesterol. Dietary PCW material is extensively fermented in the caecum and colon. Also, the products of fermentation are a source of energy and important structural precursors of lipids and proteins for the animal.