Differences and characteristics in amino acids, catechins, and flavonoids among alfalfa (Medicago sativa L.) germplasms and tissues according to UHPLC-Q Exactive-MS technology.

内容摘要

Alfalfa (Medicago sativa L.) is one of the most widely planted forages worldwide. It is rich in anthocyanins, polyphenols, amino acids, and other functional flavor non-volatile metabolites (NVMs). Its various germplasms and plant parts differ markedly with regard to quality components; however, a rigorous assessment of these differences is lacking, which hampers the optimization and diversified use of alfalfa. Using a targeted metabolomics approach based on UHPLC-Q Exactive-MS, we absolutely quantified 60 non-volatile metabolites (including catechins, flavonoids, amino acids, alkaloids, theaflavins, and phenolic acids) in the stem, leaf, and flower tissues of eight alfalfa germplasms, among which 43 were identified as alfalfa-associated quality NVMs. Six catechin components (epigallocatechin gallate [EGCG], catechin [C], epicatechin [EC], epigallocatechin [EGC], gallocatechin gallate [GCG], and epicatechin gallate [ECG]) were first identified, of which EGCG showed the highest content (0.241 mg/g). Overall, stem tissue was rich in catechins and phenolic acids, flower tissue was rich in flavonoids, SAAs, BAAs, and OAAs, and leaf tissue was rich in UAAs and (UAAs+SAAs)/BAAs. Meanwhile, 35zg germplasm stem was rich in catechins, 207kc flower was rich in flavonoids, phenolic acids, and BAAs, 260dy flower was rich in SAAs and OAAs, and 207kc leaf was rich in UAAs. A total of 18 differential NVMs, including 10 amino acids, 4 catechins, and 4 flavonoids, were screened according to the significant difference values, variable importance in projection, heatmapping, and classification analyses. Tissue classification analysis showed that alfalfa stems and leaves were rich in glutamic acid (producing an umami taste), EGCG, catechin (C), epicatechin (EC), and epigallocatechin (EGC) (with an intense taste). Meanwhile, flowers were rich in prunin, myricetin, and quercetin 3-O-D-glucose-7-O-D-gentiobioside (producing an astringent taste), whereas valine, leucine, isoleucine, methionine, citrulline, and histidine resulted in a bitter taste. Germplasm classification analysis showed that 35zg was confirmed to be rich in EGCG, C, EC, and EGC (with an intense taste), and the L-tyrosine, valine, leucine, and citrulline contents (which result in a bitter and astringent taste) were low. Our results provide theoretical and technical support for the characteristic analysis and diversified utilization of alfalfa materials and the development of characteristic herbal tea products.