Comparison of Nutritional and Functional Components and Antioxidant Activity of Different Foxtail Millet Varieties Grown in the Same Conditions

The proximate and phytochemical compounds, antioxidant capacity, and color characteristics of 22 foxtail millet varieties grown in the same location with the same planting conditions and consistent dehulling procedures were compared. The total protein, fat, starch, and resistant starch levels varied significantly (p < 0.05) from 8.17 to 11.23 g/100 g, 1.76 to 4.20 g/100 g, 57.69 to 79.64 g/100 g, and 3.15 to 6.53 g/100 g, respectively. The variety JS1 presented the highest total carotenoid content (TCC) of 43.67 mg/kg, together with the highest b* value (b* represents yellowness–blueness). The highest total flavonoid content (TFC) was observed in Yugu 36 (YG36), while Yugu 47 (YG47) displayed the highest total phenolic content (TPC) of 889.57 mg FAE/kg DW. Trans-ferulic acid and N′, N″-diferuloylspermidine were detected as the main phenolics in the free phenolic fraction, while the predominate bound phenolic compounds were trans-ferulic acid and trans-p-coumaric acid, ranging from 64.97 to 266.89 mg/kg and 11.76 to 190.74 mg/kg, respectively. The Pearson correlation analysis revealed that b* value was significantly positively correlated with TCC and TPC (p < 0.05) while significantly negatively correlated with total starch content (p < 0.05). The antioxidant activities were significantly correlated positively with TFC and TPC. The 22 foxtail millets could be classified into three categories by hierarchical clustering analysis (HCA), which exhibited higher TCC and b* value, higher total protein and fat contents, and higher TPC and antioxidant activity, respectively. The heatmap visualization revealed similarities and variations in the color characteristics and phytochemical profiles of the different foxtail millet varieties, and the difference was suggested to be attributed to a gene factor.