2.4.2. Acquisition and Processing of 1H NMR Data

¹H NMR spectra of the feces were measured by a Bruker Avance 500 MHz NMR spectrometer (Bruker, Karlsruhe, Germany) at a ¹H frequency of 500.13 MHz and a temperature of 298 K. Fecal extract samples were recorded using the water pre-saturated standard one-dimensional NOESYPR1D pulse sequence (recycle delay − 90° − t₁ − 90° − t_m − 90° − acquisition) with water suppression to obtain the representative total metabolite compositions. The acquisition parameters were as follows: relaxation delay, 2.0 s; mixing time, 0.1 s; number of scans, 64; spectral size, 65,536 points; spectral width, 10,000 Hz. MestReNova (version 14.0, Mestrelab Research, Santiago de Compostela, Spain) was used to obtain the NMR spectra. All free induction decays (FIDs) from 1D ¹H NMR were multiplied by a 0.5 Hz exponential line broadening before Fourier transformation. After corrections for phase and baseline distortion, ¹H NMR spectra were referenced to the TSP signal (δ 0.0), and the spectral regions of 0.00–9.00 ppm were integrated into regions with equal widths of 0.001 ppm. The water signal, dominating the spectrum between 4.70 ppm and 5.10 ppm, was excluded to eliminate the spurious effect of water suppression, and the integration data were normalized for further analysis.