Molecular Profiling of Peanut under Raw, Roasting, and Autoclaving Conditions Using High-Resolution Magic Angle Spinning and Solution 1H NMR Spectroscopy

Abstract

Higher rates of peanut allergy have been observed in countries that commonly roast peanuts prior to consumption. Despite the importance of understanding the role of thermal processing in allergy and on peanut composition, studies toward generating signatures that identify molecular contents following processing are scant. Here, we identified spectral signatures to track changes and differences in the molecular composition of peanuts under raw, roasted, and high-pressure and high-temperature autoclaved conditions. We analyzed both the solid flesh of the seed and solutions derived from soaking peanuts using High-Resolution Magic Angle Spinning (HR-MAS) and solution ¹H Nuclear Magnetic Resonance (NMR) spectroscopy, respectively. The NMR spectra of intact peanuts revealed triglycerides as the dominant species, assigned on the basis of multiplets at 4.1 and 4.3 ppm, and corresponding defatted flours revealed the presence of sugars. Sucrose assigned based on a doublet at 5.4 ppm (anomeric proton), and triglycerides were the most abundant small molecules observed, with little variation between conditions. Soaked peanut solutions were devoid of lipids, and their resulting spectra matched the profiles of defatted peanuts. Spectral signatures resulting from autoclaving differed strikingly between those from raw and roasted peanuts, with considerable line-broadening in regions corresponding to proteins and amino-acid side chains, from 0.5 to 2.0 ppm and 6.5 to 8.5 ppm. Taken together, by using complementary NMR methods to obtain a fingerprint of the molecular components in peanuts, we demonstrated that autoclaving led to a distinct composition, likely resulting from the hydrolytic cleavage of proteins, the most important molecule of the allergic reaction.

Keywords: autoclaving; food processing; molecular profiling; nuclear magnetic resonance; peanut.

Figure A1

2D HSQC ¹H–¹³C solution NMR analyses of soaked solutions derived from raw peanuts soaked in water for 24 h. Lowercase letter assignments highlight protons on the corresponding carbons of sucrose. CH peaks are in blue and CH₂ peaks are in red.

Figure A2

2D HSQC ¹H–¹³C solution NMR analyses of soaked solutions derived from roasted peanuts soaked in water for 24 h. Lowercase letter assignments highlight protons on the corresponding carbons of sucrose. CH peaks are in blue and CH₂ peaks are in red.

Figure A3

2D HSQC ¹H–¹³C solution NMR analyses of soaked solutions derived from autoclaved peanuts soaked in water for 24 h. Lowercase letter assignments highlight protons on the corresponding carbons of sucrose. CH peaks are in blue and CH₂ peaks are in red.

Figure 1

HR-MAS ¹H NMR spectra of raw and roasted intact peanut. Shaded boxes highlight peaks corresponding to triglyceride protons, which dominate the spectra. In the general structure of the triglyceride molecule shown, R, R′, and R″ represent aliphatic or olefinic side chains.

Figure 2

HR-MAS ¹H NMR spectra of autoclaved peanut flour, raw peanut flour, and whole, intact raw peanut. Peanut flour was defatted with hexane. Shaded boxes highlight sugar-corresponding peaks, revealed through defatting.

Figure 3

HR-MAS ¹H NMR spectrum of defatted raw peanut flour and solution. ¹H NMR spectrum of a peanut-soaked solution of six raw peanuts in distilled water for 24 h. Shaded boxes highlight: (A,D) regions containing protons of peptide and amino-acid side chains of proteins, uncovered via soaking the peanuts in water and (B,C) peaks corresponding to the anomeric protons of sucrose and glucose. Lowercase letters highlight select peaks corresponding to protons in the structure of sucrose.

Figure 4

(A) Solution ¹H NMR spectra of peanut-soaked solutions of six whole raw, roasted, or autoclaved peanuts in distilled water for 24 h. Shaded boxes highlight peaks corresponding to H atoms in peptide and amino-acid side chains. (B) Coomassie stain of proteins following SDS PAGE of the peanut-soaked solutions of each condition showing protein band distributions.