Integrating lipidomics with untargeted and pseudo-targeted flavoromics to unlock the dynamic response of volatile development of specialty barley malt: A time-course study

Roasting is an efficient way to enhance the aroma of malts. However, the dynamic response of volatile development throughout roasting has been rarely explored. In this study, multiple omics approaches were applied to systematically investigate underlying mechanisms of volatile development at a time-course manner during roasting. Roasted malts (RMs) with color ranging from 2° to 243°L were sampled at six roasting stages (RT0-5). Initially, malt color was assessed, showing progressive darkening as roasting advanced. Subsequently, the primary Maillard reaction precursors including free amino acids and free reducing sugars were detected and quantitated. The free fatty acids (FAs) were also determined via untargeted and targeted lipidomics, demonstrating 9 FAs that were differentiated among the six RTs. The behavior of three precursors all exhibited fluctuating decreases across the roasting regime. This non-linear consumption trend was first observed and reported in RM production. Lastly, in terms of the dynamic response of volatile generation and development, a comprehensive hierarchical flavoromics approach was employed, consisting of three steps: untargeted, pseudo-targeted, and targeted analysis. Untargeted flavoromics was initially performed to narrow down the detected volatiles for the subsequent pseudo-targeted analysis, which focused on identifying significant volatiles and providing semi-quantitative data. Finally, targeted quantification of 14 key aromas was carried out to calculate odor activity values (OAVs) and monitor aroma balance at each RT. Throughout the roasting process, the concentration of volatiles also followed a non-linear pattern, which was consistent across all other analyses. This research is the first to systematically unveil the non-linear behavior of malt coloration, precursor consumption, and dynamic response of volatile development during roasting. These findings provide valuable insights for researchers and maltsters in the production and application of RMs.