Metabolite profiling of buckwheat – a treasure hunt

Common buckwheat (Fagopyrum esculentum Moench) belongs, like rhubarb, to the knotweed family (Polygonaceae). These annual plants grow up to 1.5 meters tall and have heart-shaped leaves that grow alternately along the stem. They grow rapidly and bloom after just four to five weeks. Their white to pink flowers produce brown, black, or mottled, triangular achenes that are four to six millimeters long. With a growing season of about 100 days, buckwheat is ideally suited as a cover crop or second crop due to its short growing period. It has been cultivated in Europe since the Middle Ages; however, with the introduction of the potato and increased grain production, its cultivation in Germany declined sharply. Today, the leading buckwheat producers are China, Russia, and Kazakhstan (FAOSTAT 2024).

Buckwheat is not related to beech trees or wheat. Its name comes from the resemblance of its fruit's shape and color to beech nuts and the resemblance of its endosperm to wheat flour. Like amaranth and quinoa, buckwheat is classified as a pseudocereal. Its seeds are high in starch, minerals, vitamins, and dietary fiber. Buckwheat starch is gluten-free, making it well-suited for people with gluten sensitivity or celiac disease. Unlike wheat, rye, or barley, buckwheat contains no gluten proteins and is frequently used in gluten-free baked goods and pasta. Overall, buckwheat products are considered particularly valuable from a nutritional standpoint and are becoming increasingly important in functional foods and nutraceuticals. Demand is also growing in Germany.

The BIMOTEC initiative, funded by the Federal Ministry of Research, Technology, and Space (BMFTR), aims to strengthen buckwheat cultivation in Germany. To this end, the initiative seeks to create optimal conditions for breeding local varieties that are suitable for second-crop cultivation. This not only increases yields for farmers but also promotes agrobiodiversity.

In addition to using the grains for food, the project investigates extracting valuable plant compounds from the leaves, stems, and husks of residual biomass. The BIMOTEC partners are addressing various aspects to advance buckwheat production and processing in Germany using an interdisciplinary approach.

The Fraunhofer IME in Münster plays a crucial role in this effort, conducting comprehensive metabolite analyses of leaf material from fifty buckwheat varieties from twenty different countries, among other things. Metabolite profiling and searching for valuable secondary metabolites are essential steps toward identifying significant industrial compounds. By discovering and utilizing these metabolites, the project aims to improve the economic viability of buckwheat cultivation. This will support efforts to reestablish the crop in Germany and maximize its potential in accordance with bioeconomic strategies.

First results

Buckwheat has a unique metabolite profile, containing high levels of flavonoids, phenolic acids, amino acids, and other valuable phytochemicals in both its grains and its remaining biomass, including leaves, stems, and husks.

First, the researchers established a robust procedure for sampling and sample preparation, including conversation, homogenization, and extraction. This procedure serves as an “all-in-one” protocol for multiple mass spectrometry platforms. Lipophilic metabolite analysis, such as that of sterols or triterpenoids, is performed using gas chromatography coupled with mass spectrometry (GC-MS). Polar mixtures containing metabolites such as phenolic acids or flavonoids are separated using high-performance liquid chromatography (HPLC) and detected by mass spectrometry (MS). The “all-in-one” protocol was used with leaf material from 28 genotypes for non-targeted metabolite profiling. Approximately 75,000 masses from 9,000 compounds/substances were detected in the process. The resulting MS spectra were compared using mass spectrometry compound libraries. In total, the researchers identified 3,275 substances in the curated databases. Figure 1 shows the initial LC-MS analysis results for the flavonoid metabolites kaempferol, quercetin, and rutin. Rutin is one of the best-known flavonoids, consisting of the flavonol quercetin glycosidically bound via the disaccharide rutinose, composed of rhamnose and glucose. In its purified form, rutin appears as a pale yellow, odorless powder. Rutin protects plants from UV radiation, and in pharmacological applications, its antioxidant effect and stabilization of blood vessels in diseases of the leg veins are often the primary focus. There is high variability among genotypes in rutin and its biosynthetic precursors' (kaempferol and quercetin) concentrations. Additionally, rutin was extracted from buckwheat plant material and transferred to a project partner for microbial bioconversion.