Heat-induced regulation on metabolite biosynthesis improves antioxidant capacity and nutritional quality of black highland barley (Hordeum vulgare L.).

Abstract

Appropriate heat treatment is an effective approach to enhance the overall quality of grains by increasing the content of specific nutritional components. In this study, highland barley grains were treated with heat acclimation (HA, 37 °C for 72 h) and intensive heat stress (HS, 70 °C for 108 h), after which the biochemical and metabolomic regulations were investigated. The results showed that the 1,1-diphenyl-2-trinitrophenylhydrazine radical scavenging activity and ferric reducing antioxidant power of HA + HS-treated grains increased by 19.9% and 5.7%, respectively, greatly enhancing the overall antioxidant capacity, while the original aroma and texture attributes remained largely preserved. From a plant physiological perspective, the HA treatment improved seed vigor by 32.2%, whereas HS reduced it by 81.4% compared to untreated grains. Additionally, this heat treatment (HA + HS) increased the total amino acid index, total phenolic acid index, and total flavonoid index by 13.3%, 23.5%, and 14.4%, respectively. Further, metabolomic and quantitative analysis revealed a remarkable metabolic reprogramming of amino acids and polyphenolics. Specifically, HA + HS treatment upregulated flavonoid and flavonol biosynthesis, as well as tyrosine metabolism, in grains, significantly increasing the levels of proline, tyrosine, flavonols, and their derivatives (such as naringin, quercetin, and kaempferol). Correlation analysis revealed a strong positive correlation between flavonoid compounds, especially flavonols and their derivatives, and antioxidant activity. Overall, our results, both technical and theoretical, support the use of heat treatment to improve the nutritional value and antioxidant capacity of highland barley grains, with potential implications for grain fortification.