Dynamic Metabolomics Elucidates Phenolic Profiles in Sorghum Grain: a Study From Flowering to Final Product
Year: 2024
Type: conference-paper
Abstract: Sorghum grains (Sorghum bicolor L.) is increasingly used into human diets, due to its agronomic advantages and the potential health benefits associated with its phenolic compound (PC) content. Despite substantial advancements in metabolomics field for elucidating the complex and dynamic of cereals PC, significant gaps regarding nonconventional cereals, such as sorghum grains, remain to be clarify. This work aims to provide deep information about PC accumulation throughout sorghum grain maturation; and their changes after biological, physical and thermal processing. Sorghum genotypes, contrasting in pericarp colors and tannin levels, were harvested at five different days after flowering (10 to 40 DAF; from cellular division, grain filling, physiological maturity to mature stage; total of 10 samples). Mature grains were subjected to three technological processes: germination (16 °C for 72 and 144 hours, 60% relative humidity; total of 9 samples), dehulling (approximately 15% removal: whole grain, decorticated grain, and bran; total of 12 samples), and cooking (1:6 sample-to-water ratio; 30 minutes; total of 24 samples). Phenolic compounds (PC) were sequentially extracted and analyzed using high-resolution untargeted metabolomics (UPLC-ESI-QTOF/MS). Commercial standards and quality control were also injected. The raw data was normalized by using Progenesis QI to enable annotation/identification and quantitative comparisons of detected features. Tentative annotation was conducted according to Metabolomics Standards Initiative levels, with customized database built from PubChem and Phenol-Explorer. The software XLSTAT and Metaboanalyst 6.0 were applied to statistical and multivariate analysis. Globally, 318 phenolic compounds were tentatively identified in all samples. Sorghum PC are synthesized during grain growth (40DAF PC content was nine-fold higher than 10DAF). The phenolic profile also changes throughout maturation: in the early stages (10-17 DAF), phenolic acids were predominant (50%); however, from 25 DAF onwards, the flavonoids biosynthesis pathway seems to be prioritized. Dimer/trimer procyanidins (eight isomers) were identified at all stages, indicating the presence of tannins even in immature grains (10 DAF). For mature sorghum, principal component analysis (PCA) was conducted to provide an overview of phenolic changes post-processing. Mechanical process had a significant impact on sorghum phenolic content (-45%) and profile, i.e., dehulled grains and bran showed distinct separation in the PCA biplot. Twenty-five PC were differentially abundant after germination: 4-hydroxybelzaldehyde increased (+64% and +4-times higher) after 72h and 144h; while important sorghum PC (daidzin, caffeic acid, isoferulic acid and p-coumaric acid) decreased during germination. Both germination and dehulling proved to be effective processes for procyanidins depolymerization. Cooking had a minimal impact on the phenolic profile of mature sorghum grains, resulting in a modest increase in phenolic levels (+24%). Such variation may be due to heat-induced disruption of the grain's cellular structure, which facilitates the release of bound phenolic compounds. The only common outcome among the three processing methods was a reduction in flavonoid levels. In conclusion, our findings elucidate the robust phenolic profile of sorghum grains and suggest processing techniques or optimal maturity stages to enhance its consumption and geographical distribution.
Source: HAL
Language: English
Subfield: Biochemistry (medical)
Field: Medicine
Domain: Health Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W7204361930