Metabolite identification in fresh wheat grains of different colors and the influence of heat processing on metabolites via targeted and non-targeted metabolomics.

Phenolic antioxidants are phytochemical components in wheat grains that provide a variety of potential health benefits. The metabolites and antioxidant activity of fresh, mature, and heat-treated, wheat grains with black, blue, purple, and white grain coats were identified by targeted and non-targeted metabolomics. The total phenolic (TPC) and flavonoid contents (TFC) and antioxidant activity (AOA) increased with the darkening of grain color, the general trend being black > purple > blue > white. Purple and black wheat are rich in rutin (3916 µg/kg and 3066 µg/kg, respectively) and peonidin-3-O-glucoside chloride (2595 µg/kg and 1740 µg/kg, respectively), while blue wheat is rich in luteolin (2076 µg/kg). In most cases, TPC, TFC, and AOA had the greatest values in fresh grains and the lowest values in mature grains. Using non-targeted metabolomics, a total of 866 metabolites were identified in the tested fresh wheat grains, 106 flavonoids and 39 phenolic acids. In total, the relative abundance of flavonoids in purple and black wheat was higher than in blue wheat, indicating a higher nutritional value of fresh black and purple grains. After heat processing, the content of most metabolites decreased in heat-treated purple grain, whereas heat treatment significantly increased the content of peonidin-3-O-glucoside chloride (2.27-fold) and cynaroside (12.01-fold). This study clarifies that seed coat color and processing treatments impact the metabolite contents and antioxidant activity of wheat grains, providing valuable information for improving the nutritional quality of food during processing.