Metabolomic and Transcriptomic Integration Reveals the Mechanism of Aroma Formation as Strawberries Naturally Turn Colors While Ripening

Aroma is an important indicator of the quality of fruit flavor, but the mechanism of aroma formation in strawberries (Fragaria spp.) during natural ripening merit further research. In this study, the aroma compounds in strawberry cultivars of varying types of aromas in different developmental stages were analyzed using gas chromatography-mass spectrometry. Richly creamy strawberry cultivars in particular expressed high levels of volatile phenol esters (mainly vanillin acetate and coumarin), while the aroma-free cultivars were dominated by differential changes in terpenes. Further research using liquid chromatography-mass spectrometry and RNA-Seq indicated that the activation of the phenylpropanoid biosynthesis and α-linolenic acid metabolic pathways, which used phenylalanine and α-linolenic acid as precursors and phenylalanine ammonia lyase and lipoxygenase as reactive enzymes, constituted the key to formation of aroma compounds in creamy strawberry cultivars. This study provides a new technical basis to understand the types and mechanisms of formation of aroma compounds in strawberries.