Flavor compounds of traditional fermented bean condiments: Classes, synthesis, and factors involved in flavor formation

Traditional fermented bean condiments (TFBCs) are widely spread in East Asian due to their special flavor and have a history of thousands of years. Currently, identification of volatile flavor compounds and key aroma compounds, correlation analysis between microbial community structure and flavor substances, taste characteristics of flavoring peptides, and mechanisms of aroma production have gradually become the focus of research. According to existing literature knowledge, the types, the flavor components of TFBCs and their synthesis pathways were summarized. The flavor components of different condiments and their concentrations displayed a large difference, thus, the potential factors affecting flavor formation were elucidated. Additionally, potential problems need to be further revealed including future research point of flavor components detection and possible synthesis pathways were also reviewed. The flavor compounds in TFBCs mainly include esters, alcohols, aldehydes, ketones, free amino acids, taste peptides, organic acids. Besides, the possible synthesis pathways of flavor components in TFBCs were also predicted, especially the synthesis pathways of esters. Generally, raw materials, microbial composition, fermentation processing, environment and climate, fermentation period and salinity are all closely related to the flavor formation, and are possible reasons for those huge difference in flavor components. In addition, future studies need to be conducted to elucidate the biosynthetic pathway and metabolism of flavor compounds in TFBCs, to establish an efficient method for the separation, identification and quantification of flavor components, and to regulate the synthesis of flavor compounds effectively.