Detailed faecal fat analysis using Fourier transform infrared spectroscopy: Exploring the possibilities

Fourier transform infrared (FTIR) spectroscopic determination of faecal fat is a simple and elegant alternative for the classical Van De Kamer approach. Besides quantification of the total amount of fat, analysis of the lipase hydrolysis efficiency (fatty acid/triglyceride ratio), fatty acid chain length and trans-unsaturated fatty acids could provide a better monitoring of dietary treatment.

Stool samples (26 routine samples and 36 cystic fibrosis patients) were analysed with the Perkin Elmer Spectrum Two® spectrometer (3500-450cm^-1). Fatty acid/triglyceride ratio was calculated using the absorbance ratio at 2855:1746cm^-1. To estimate lipase hydrolysis efficiency, sample ratios were compared with the ratio of butter and pure free fatty acids. Mean fatty acid chain length was calculated using the absorbance ratio at 2855:1709cm^-1. The absorbance at 966cm^-1 was used to trace the presence of trans-type unsaturated fatty acids.

Butter showed a low fatty acid/triglyceride ratio (1.21) and pure free fatty acids a high fatty acid/triglyceride ratio (6.76). Mean fatty acid/triglyceride ratio of routine stool samples was 4.16±1.01. The applicability of fatty acid/triglyceride ratios was also tested in cystic fibrosis patients under treatment with a mean of 4.92±0.98. Relative absorbance contribution per carbon atom was 0.06 (ratio 1.06 for C18 standard, 0.91 for C16 standard). The mean ratio of the stool samples was 1.12 (mean acyl chain length of C19), with values ranging from 0.73 (C12) to 1.68 (C28). The presence of traceable amounts of trans-unsaturated fatty acids was also demonstrated.

For the analysis of faecal material, FTIR provides unique information, difficult to obtain using other techniques. These findings offer perspectives for diet monitoring in patients with (non-)pancreatic malabsorption.