The effect of germination time on soymilk odor: Key odor compounds and formation mechanisms

Germination, as a distinctive natural processing technique for grains, can regulate their odor and nutritional quality by eliciting intricate biometabolic processes within the grains. However, the odor metabolic pathways that occur during germination remain unclear. This study aims to investigate the succession patterns and underlying molecular mechanisms of odor precursors, endogenous enzymes, and pivotal odor substances in soybean milk prepared following various germination durations (0 h, 24 h, 48 h, and 72 h) using gas chromatography-olfactory-mass spectrometry (GC-O-MS) and other techniques. Soybean germination significantly induced the expression of endogenous enzymes and altered the contents of odor precursors, such as lipids and proteins. Notably, the sweetness sensory score of soymilk prepared after 24 h of germination increased from 1.7 to 8.0, while the concentration of hexanal—a key odor marker—decreased from 74 to 43 μg/kg. Further analyses revealed that 22 key odor substances, including hexanal, 2-heptanone, and methyl isovalerate, were critical for differentiating germinated and raw soymilk. Moreover, pathways involving lipoxygenase, glycolysis, and amino acid transamination contributed to the rise in ketones, aldehydes, and esters. This study offers theoretical and experimental data to enhance sprouted soybean milk odor and supports using sprouted soybeans as an innovative food ingredient. • Soybeans' different germination (0-72h) affects soymilk's nutrition and flavor. • Soybean germination activates enzymes and produce key flavorants (methyl octanoate). • Soybean germination reduced beany compounds, such as heptanal. • Soymilk from germinated 24 h soybean enhanced fruity aroma, reduced beany flavor.