Analysis of dynamic flavor changes of volatile and non-volatile fractions analysis of black qingke (Hordeum vulgare L. var. nudum Hook. f.) during steaming process

Qingke (Hordeum vulgare L. var. nudum Hook. f.) is a cereal of Gramineae, and it is an indispensable food crop for people in the Qinghai—Tibetan Plateau of China. This work focused on the dynamic changes of volatile and non-volatile fractions of qingke (Heilaoya), that is, black qingke, during steaming, and the flavor variations were discussed combined with their correlation. According to the results of sensory analysis, it revealed that the rice and sweet aroma of black qingke increased with the extension of steaming time and reached the maximum at 60 min, whereas the grassy aroma decreased. Besides, a total of 43 aroma fractions were identified by gas chromatography–olfactometry–mass spectrometry, with the largest quantity showing up at 60 min. In addition, the overall flavor of black qingke became more abundant after steaming for 40–60 min. Furthermore, combined with the changes of the non-volatile substances, it was inferred that Maillard and Strecker reactions occurred between reducing sugars and amino acids, and the fractions, such as 2-acetylthiazole, 2-methylpyrazine, 2-pentylfuran, and furfural, were generated. These components mainly presented notes of baked, rice, and grain. In addition, the fatty acids undergo oxidative degradation to generate hexanal and (E,E)-2,4-decadienal. These results can provide a theoretical basis for the flavor quality control and industrial production of qingke.