The solubilisation and hydrolysis of spinach cell wall polysaccharides in gastric and pancreatic fluids

Abstract

AbstractThe 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 (t 1/2 84 h). In contrast, artificial gastric juice (pH 1.85) hydrolysed wall‐bound acetyl groups more rapidly (t 1/2 ∼ 24 h) than methyl ester groups (t 1/2 ∼ 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.