Identification of Key Flavor Compounds in Citrus Fruits: A Flavoromics Approach

In the Huanglongbing (HLB) era, the flavor quality of orange juice has been largely affected by the sensitivity of commercial sweet orange varieties to HLB. Therefore, great interest has been raised to explore the utilization of juice from HLB-tolerant mandarin hybrids, especially those with sweet-orange-like flavor notes, in orange juice. A better understanding of the flavor of sweet orange, mandarin, as well as their related hybrids, will facilitate the blending of HLB-tolerant fruits with sweet orange. In this study, flavoromics was applied to investigate the citrus fruit flavor and identify key flavor compounds in diverse groups of citrus fruits through multivariate statistical analysis. Volatile and nonvolatile chemicals were determined by mass spectrometry (MS) techniques while the rating of sensory attributes was collected from a trained sensory panel. By using principle component analysis (PCA), sensory profiles of different citrus fruits were discriminated. The results of Pearson correlations showed the extent of positive/negative correlation between the sweet attribute and other sensory attributes in citrus fruits. On the basis of the correlation between chemicals and sensory attributes showed in PCA, sugars were highly correlated with the sweet attribute while flavonoids and limonoids were highly correlated with the bitter attribute. Organic acids showed a strong correlation with the sour attribute and a contribution to the citrusy attribute. Terpenes were highly associated with the terpene-like attribute, while octanal, decanal, ethyl hexanoate, and ethyl octanoate were found to be highly correlated with the citrusy attribute. The correlations between compounds of linalool, citronellol, and 1-octanol and the fruity/floral attribute were also observed. In addition, pathway enrichment analysis demonstrated a close correlation between the biosynthesis of terpenoids and steroids pathway and the identified key flavor compounds in sweet-orange-like mandarin hybrids.