Comprehensive Profiling of Free Amino Acids in Litchi (Litchi chinensis Sonn.) Germplasm and Their Implications for Flavor Quality

<i>Litchi chinensis</i> Sonn. is an economically and culturally significant fruit crop in China, valued for its distinctive flavor, which arises from the combined contributions of taste and aroma metabolites. While the accumulation of sugars, organic acids, and volatile terpenes in litchi has been extensively studied, the role of nitrogenous flavor compounds, particularly free amino acids (FAAs), remains poorly characterized across diverse germplasm. To address this gap, high-performance liquid chromatography (HPLC) was employed to quantify 20 free amino acids in the pulp of 148 distinct litchi germplasm accessions. Comprehensive statistical analyses, including non-parametric tests, correlation analysis, and hierarchical clustering, were performed to elucidate compositional variations. Alanine (Ala), glutamate (Glu), and γ-aminobutyric acid (GABA) were the most abundant FAAs, contributing strongly to sweetness and umami. FAA profiles differed significantly among genomic groups, and clustering analysis identified three major chemotypes: Glu-accumulating, GABA-accumulating, and Ala-accumulating types. This study provides the first large-scale survey of FAA diversity in litchi germplasm and establishes a foundation for selecting cultivars with desirable flavor attributes and for future genomic dissection of amino acid metabolism.