Effects of Cooking Treatment on the Changes of Polyphenol and Antioxidant Activity in Sorghum and its Exploration on the Flavor Enhancement Based on the Multi-omics Technique

To explore the effects of cooking treatment on the nutrient composition, polyphenol content, antioxidant capacity and flavor compound of sorghum, ultrasonic-assisted extraction of polyphenols was performed and their antioxidant capacity was evaluated, and non-targeted metabolomics and plant-wide polyphenol metabolomics were combined to analyze the metabolic differences between sorghum grain (SR) and cooked sorghum rice (SRC). Results showed that the protein, total starch, and fat contents in SRC were significantly decreased (P<0.05) in comparison with those in SR. Polyphenol content, hydroxyl radical scavenging capacity, T-AOC, and ABTS⁺· scavenging capacity in SRC were significantly decreased by 35%, 17%, 12%, and 10%, respectively (P<0.05). LC-MS analysis showed that a total of 341 metabolites were detected in both SR and SRC, among which 223 were differentially expressed. L-tyrosine, L-isoleucine, and guaiacol in SRC may be related to its flavor formation. KEGG metabolic pathway analysis showed that the up-regulated compound serotonin in SRC may be related to its aroma-enhancing effect. Through plant-wide polyphenol metabolomics analysis, 67 phenolic compounds were identified in SRC, among which 11 compounds, including quercetin and catechin, were significantly up-regulated, and 21 compounds, including 7,4'-dihydroxyflavone and 2,5-diisopropylphenol, were significantly down-regulated (P<0.05). This study provides a theoretical basis for the further research and application of the functionality of sorghum food.