Abstract

Legumes are known on our planet as sources of such important food ingredients as high-quality proteins, carbohydrates and fats. In addition, they carry in their seeds a significant amount of functional biologically active substances of non-food type, but extremely important for ensuring a balanced diet. 
Soybean is the main source of complete protein for the needs of feed production and human nutrition on our planet. In this regard, its area and gross yields are growing rapidly and now amount to 137 million hectares and more than 370 million tons, respectively. The intensive spread of soybeans in the world is due not only to the high content of protein and oil in the seeds, but also to the presence of a complex of functional compounds that have a significant beneficial effect on human health. 
In the period 2015–2019, the amount of flavonoids in 17 soybean varieties of Ukrainian selection was studied. Their average composition varied within 77.4–375.3 μg/g. The Smolyanka variety, which has black seeds, was characterized by a very high concentration of these compounds (375.3 μg/g). In other yellow-seeded varieties, their content was 77.4–175.6 μg/g. In this study, the Smolyanka variety, which was distinguished by the black color of its seeds, clearly stood out in terms of flavonoid content. During this period, the amount of flavonoids was also assessed in a set of 12 breeding lines with different seed colors obtained by crossing the Kobra collection variety, which has black seeds, with the Yug 30 variety of Ukrainian origin and the K-4937 collection sample. The recombinant lines were characterized by different levels of color intensity, from light brown to completely black. This made it possible to differentiate the amount of flavonoids depending on the color of the seed coat. In black-seeded lines (5 pcs.), the total amount of these compounds varied within 257–291 μg/g, in light-brown (2 pcs.) – 180.8–227.7, in red-brown (2 pcs.) – 212.3–219.7, and in brown (1 pc.) – 165.1 μg/g. In the yellow-seeded line of this hybrid combination, the amount of flavonoids was only 84.4 μg/g. The obtained results clearly indicate that the presence of pigments in the seed coat contributes to an increased amount of flavonoids. It is known that the color of soybean seeds is influenced by three independent genetic loci (I, R and T). Genes R and T determine the synthesis of anthocyanin and proanthocyanidin in the seed coat. The combination of genes RT leads to black color, Rt - partially black, rT - brown and rt - dark yellow. The presence of gene I in the soybean genotype inhibits the biosynthesis and accumulation of pigments, resulting in the formation of yellow seeds, and its recessive allele leads to a uniform distribution of pigment in the seed coat. Thus, by combining individual gene loci, it is possible to regulate the biosynthesis of flavonoids in individual soybean genotypes. For specific purposes, through targeted selection of parental lines and repeated selection in early hybrid generations, it is possible to create recombinant lines with an increased amount of these compounds.
It is also necessary to note the significant variability of flavonoids over the years. For example, the new Taverna variety had the amount of these compounds in 2015 at 35.5 μg/g, in 2017 at 81.3, in 2018 at 130, and in 2019 at 111.4 μg/g. The Smolyanka variety, which stands out for its high amount of flavonoids, had the following variability over the years: 2017 at 380 μg/g, 2018 at 367, 2019 at 354.4, 2020 at 144, 2021 at 96, 2022 at 370 μg/g.