1H NMR Analysis of Peanut-Soaked Solutions
Under various processing conditions, the molecular composition of the
peanut is expected to change due to chemical reactions such as the
Maillard reaction, macromolecule hydrolysis, protein denaturation and
the generation of small molecules such as monosaccharides and free amino
acids. Thus, we sought to monitor differences between solutions derived
from soaking the peanut under different conditions. In order to track
these modifications, we chose 1H Nuclear Magnetic
Resonance (NMR) spectroscopy as the most suitable method.1H NMR spectroscopy provides a characteristic spectrum
dependent on the chemical environments of individual hydrogen nuclei in
the sample. We used this technique to obtain molecular profiles and to
identify the chemical changes across different processing conditions.
Raw, roasted and autoclaved peanuts were each soaked in distilled water
for 48 hours and the resulting solution was analyzed by1H NMR spectroscopy (Figure 1).
The spectra of the raw and roasted peanut-soaked solutions did not
differ greatly in peak distribution or intensity (Figure 1A & 1B).
However, that of the autoclaved peanut-soaked solution was strikingly
different (Figure 1C). Particularly, in the regions between 0.5 ppm and
2.0 ppm as well as between 6.5 ppm and 8.5 ppm, the autoclaved
peanut-soaked spectrum had a different peak distribution with a series
of broad peaks, indicating the presence of more soluble molecules,
likely amino acids and peptides leaching out into solution. The
higher-field region in the spectrum (0.5 ppm – 2.0 ppm) corresponds to1H atoms of alkyl groups, while the lower-field region
(6.5 ppm – 8.5 ppm) corresponds to 1H atoms of amide
bonds and aromatic groups, which likely represent free amino acids and
peptide side chains.