Flavor optimization in dairy fermentation: From strain screening and metabolic diversity to aroma regulation

Currently, fermented dairy products whose flavor enhancement directly arises from biochemical reactions by microorganisms are becoming more meaningful and popular among consumers, further providing more challenges in fermented dairy products. Importantly, this clean method allows an endogenous approach to aroma compound generation. However, distinctive metabolic features exhibited by bacterial strains, and aroma profiles are very strain dependent, which is very noteworthy for fully understanding the role of microorganisms in generating aroma compounds to enhance fermented dairy flavor. This review summarizes recent findings regarding microflora-mediated enhancement of flavor in various fermented dairy products, with a focus on identification of aroma compound profiles, screening of aroma-enhancing strains, metabolic diversity with key “flavor genes”, and regulation of aroma compounds by key driving factors, namely fermentation conditions, microbial interactions, enzymatic reactions and genetic modifications. Comprehensive links between flavor formation and microflora have been confirmed, marking their industrial usefulness in dairy fermentation, predominantly resulting from microbiota diversity. The functional genomics affecting key aroma compounds can be identified, which provides a reference for rapid screening of aroma-enhanced strains as well as target formation of aroma by modifying relative genes. Meanwhile, microflora-mediated volatile evolution can be controlled by key driving factors to protect and enhance strain flavor-generating characteristics. Further works on the preparation of aroma-enhanced industrial adjunct cultures, construction of genome-scale metabolic model, realization of computer network monitoring, and automation control in fermentation process should be evaluated to provide significant advances toward flavor improvement of fermented dairy products.