Measuring lignin in human and rat faeces

The two objectives of these experiments were to evaluate solvent systems for removal of artefact lignin from crude faecal lignin and to determine the effect of the solvents on the neutral sugar content of faeces. Four human and three rat faecal samples collected during different dietary intakes were extracted with a 1:1 (v) mixture of ethyl acetate and acetic acid (EAc) or with water followed by EAc. Crude lignin (CL), determined as the insoluble material after a Saeman acid hydrolysis, was measured in the faeces and its various fractions, and compared with Klason lignin, the residue after sulphuric acid treatment of acid detergent fibre, and with permanganate lignin. EAc extraction significantly reduced the CL content of all samples. Water extraction alone generally did not lower faecal CL contents as much as did EAc extraction. EAc extraction alone, or in combination with water, of two rat faecal samples indicated zero CL, consistent with the zero CL content of dietary cellulose; in all other samples, human cellulose and wheat bran and rat wheat bran faeces, Klason lignin and permanganate lignin were lower than CL. The two‐step extraction did remove more nitrogen than EAc alone. EAc extracted 1 to 2% of the faecal total neutral sugars and water extracted 2–5% total neutral sugars from six of the samples; 11 and 35% respectively of total neutral sugars were extracted from fibre‐free human faeces. Analysis of cellulose‐containing rat faeces with and without cholesterol and cholic acid suggested that sterols or their microbial metabolic products, as well as nitrogenous compounds, were part of the artefact lignin.