Polyphenol-based nuclear magnetic resonance non-targeted metabolomics of temperature- and time-controlled blue and red maize sprouting

Abstract

Zea mays L corps apport to human consumption, complex matrices of compounds such as free and bounded phenolics, flavonoids and anthocyanins with high nutritional values and proved health benefits, which are dynamically synthesized since sprouting of grains. This study presents for the first time a Nuclear Magnetic Resonance (NMR) non-targeted metabolomics study of aqueous methanolic extracts of Mexican native blue and red Zea mays L. sprouts, produced with a specific germination scheme, at three different controlled temperatures. The proposed model comprises the rationalization of (poly)-phenolics metabolism dynamics as a function of sprouting time and temperature, which can be identified by more than thirty 1H NMR discriminant resonances at a chemical shift range between 7.7 and 6.3 ppm -mostly comprising typical hydroxyphenyl polyphenolic 1H frequencies- obtained with multivariate statistical analysis. Both principal component (PCA) and orthogonal projections to latent structures discriminant analysis (OPLS-DA) reveal a unique maize strain-, temperature- and time-dependent mapping of polyphenolic machinery during sprouting that might serve for optimizing germination schemes. Strengths and limitations of PCA and OPLS-DA analysis of non-targeted (poly)-phenolics NMR data matrix obtained from different blue and red maize sprouts’ methanolic extracts are discussed. Furthermore, a clear inverse correlation between temperature- and time-dependent signal intensity modulation of phenolic resonances and water line widths at half height is observed, suggesting a mechanism of how solvent could participate within the complex metabolomic matrix formation during germination. Finally, non-targeted NMR metabolomics data from sprouts’ methanolic extracts are contrasted with temperature- and time-dependent total phenolic contents obtained with standard quantitative methods.