Tree Genetics and Molecular Breeding 2025, Vol.15, No.5, 185-191 http://genbreedpublisher.com/index.php/tgmb 186 main source of floral fragrance (Song et al., 2009; Kuwahara et al., 2014; Kuwahara and Asano, 2018). In addition, some terpenoids (such as triterpenoids and sesquiterpenoids) have also been detected in leaves, flowers and roots, many of which have biological activity (Wang, 2021). Alcohols, such as benzyl alcohol and 2-phenylethanol, have also been identified as important aroma components of loquat flowers (Song et al., 2009; Kuwahara and Asano, 2018). 2.2 Biosynthetic pathways underlying aroma compound formation The biosynthesis of loquat aroma mainly relies on the phenylpropane pathway and the terpene synthesis pathway. Benzoic acids and related phenethyl compounds, with L-phenylalanine as the precursor, are metabolized through the phenylpropane pathway to generate benzaldehyde, benzyl alcohol and 2-phenylethanol, etc. Some compounds, such as (2-nitroethyl) benzene, can be directly derived from Z- and E-2-phenylacetaldehyde oxime (Kuwahara and Asano, 2018). The synthesis of terpene compounds involves the generation of terpene skeletons, monoterpenes and triterpenes. The related terpene synthases are expressed in different tissues of loquat (Wang, 2021). In addition, the formation of esters and aldehydes is closely related to fatty acid metabolism and the activities of related enzymes (Song et al., 2009; Wang, 2021). 2.3 Genetic and developmental regulation of aroma traits Aroma traits are regulated by multiple genes, involving the combined effects of structural genes and transcription factors. Transcriptome and genomic studies have shown that structural genes related to phenylpropane metabolism (such as F5H, BGH3B) are regulated by transcription factors such as MYB, bHLH and NAC, which affect the accumulation of aroma precursors and secondary metabolites by regulating enzyme expression (Wang, 2021; Zhang et al., 2024). In addition, the family amplification of terpene synthesis-related genes contributes to the massive accumulation of aroma substances in loquats (Wang, 2021). During the fruit development process, the accumulation of aroma metabolites is closely related to fruit ripening and tissue differentiation. The aroma components and contents vary significantly among different varieties and development stages (Wang, 2021; Zhang et al., 2024). 3 Metabolomic Approaches for Aroma Profiling 3.1 Analytical platforms: GC - MS, LC - MS, and NMR-based metabolomics In the study of aroma metabolism of loquat and related plants, commonly used analytical platforms include gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and nuclear magnetic resonance (NMR). GC-MS is suitable for detecting volatile and semi-volatile aroma components and can efficiently separate and identify complex organic compounds (Ye et al., 2025). LC-MS is more suitable for detecting non-volatile metabolites with high polarity and thermal instability, and is often used for metabolite profile analysis of tissues such as loquat leaves, flowers and roots (Wang, 2021; Ali et al., 2022). NMR is less applied in aroma analysis, but it has the advantages of being non-destructive, quantitative and structurally analytical, and can serve as a supplement (Wang, 2021). 3.2 Data processing, annotation, and compound identification workflows The data processing flow of metabolomics generally includes the preprocessing of raw data (peak extraction, denoising, alignment), multivariate statistical analysis (such as principal component analysis, OPLS-DA), and compound annotation identification. Researchers often compare the detected metabolites with databases (such as KEGG) and conduct structural identification in combination with reference standards or fragment information (Wang, 2021; Ali et al., 2022). In loquat research, by using LC-MS/MS in combination with the KEGG database, hundreds of metabolites can be annotated and some of them can be classified into specific biosynthetic pathways (Wang, 2021). In addition, chemometrics methods (such as OAV, OPLS-DA) are also often used to screen key aroma components, helping to distinguish samples and conduct traceability (Ye et al., 2025). 3.3 Targeted vs. untargeted metabolomic strategies Targeted metabolomics is mainly used for quantitative analysis of known aroma compounds and is often used to verify changes in specific metabolic pathways or key components (Ho et al., 2020; Ali et al., 2022). Non-targeted metabolomics focuses more on the comprehensive detection of all metabolites in the sample, which is suitable for
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