FTIR spectra will be sharper if the sample is dried. Water will hydrogen bond with flour (starches) and broaden polar group absorptions, such as C-O-H, C-O-C and create a broad high absorption background that will obscure otherwise sharp fingerprint peaks. The sample (flour) will tend to rapidly absorb moisture from air during sample preparation and/or introduction into the instrument. A spectrometer with sample compartment purged with dry nitrogen will be desirable, and leave the sample for maybe 15 min to equilibrate before starting a scan.

FTIR spectra will be sharper if the sample is dried. Water will hydrogen bond with flour (starches) and broaden polar group absorptions, such as C-O-H, C-O-C and create a broad high absorption background that will obscure otherwise sharp fingerprint peaks. The sample (flour) will tend to rapidly absorb moisture from air during sample preparation and/or introduction into the instrument. A spectrometer with sample compartment purged with dry nitrogen will be desirable, and leave the sample for maybe 15 min to equilibrate before starting a scan.

Supposed to have a broader peaks at those wavenumber, is there any effect on other functional groups?

Hydrogen bonded atoms broaden the associated vibrational peaks, such as -O-H…H- and -COOH…H- or C-O-C with HO-. The OH peak at 3500 /cm and C-O peak at ~1100 /cm are broadened and they can then obscure other peaks in their vicinity that may arise from non-polar groups. This is a simplification because it assumes vibrational and deformational modes are isolated. Vibratioaln and deformational modes are typically coupled so that more than the functional group being considered move. This is why peaks due to the same functional group have band shifts in different environments (molecules). So hydrogen bonding of polar groups may cause shifts of other coupled groups in the same molecule. A way to observe this is to view animations of vibrational or deformational modes of molecules, and it will be seen that for instance a bond vibration actually moves other nearby atoms/bonds.