Determination of allomelanins in sunflower husk by the gravimetric method

Background. Melanins are a group of pigments with a complex crystalline structure and high molecular weight, which are widely used in modern medical, perfume, food, and polymer production. They have pronounced antiviral, antibacterial, antifungal, antiradiation effects, and antioxidant activity. Melanins of animal (melanin), microbial (mycomelanin), and plant (phytomelanin) origin are distinguished. At present, the search for new sources of plant melanins and simple methods for their determination is relevant, allowing for the further identification of accessions with a higher content of these substances for various uses. An important role of melanin, which accumulates in the sunflower seed coat, is its role in ensuring the resistance of this crop to the sunflower moth ( Homoeosoma nebulella Hb.). The present study was aimed at developing a method and demonstrating its capabilities using accessions from the VIR sunflower collection. Materials and methods. The paper presents a modified method for determining allomelanins (phytomelanins) in husk and seed of sunflower accessions from the VIR collection. Optimal modes of allomelanin extraction, filtration, precipitation and washing from impurities have been developed. Results. The allomelanin content in sunflower husk averaged 5.7% with a minimum of 1.5% and a maximum of 8.7%. The fraction of pigment in the studied sunflower seeds ranged from 0.4% to 2.7% and averaged 1.7%. The accessions with a higher pigment content in husk are k-2776, k-3511, k-3892, k-3901, and k-641884, and those with a lower pigment content are k-3568, k-3647, k-3649, k-3760, and k-3762. A high positive correlation was found between the allomelanin content in husk and seed (r=0.83). Conclusion. A simple method for isolating allomelanins has been developed. It yields highly reproducible results and can be used to screen a collection of plant genetic resources to identify accessions with high melanin content. This method allows the identification of the most promising accessions which can be involved in breeding for resistance to the damaging effects of sunflower moth caterpillars.