Soybeans are generally differentiated based on the color of their seed coats. Soybeans ( Glycine max (L.) Merr.) are one of the top five largely produced crops in the world, and their demand in food, pharmaceutical, cosmetic, and biofuel industries is increasing 1, 2. Besides, the dominant anthocyanins and isoflavones were the principal contributors to the variations observed in the black soybean varieties, and hence, these components could be selectively targeted to discriminate a large population of black soybean genetic resources. Overall, our findings demonstrated the influence of seed weight on anthocyanin, isoflavone, and phenolic contents and antioxidant activities in black soybeans.
On the other hand, ABTS and DPPH activities were positively correlated to TPC, the later association being significant. FRAP activity was positively associated with TIC and TAC, the former association being significant. Besides, large seeds showed the maximum 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) scavenging activity, whereas small seeds showed the maximum ferric reducing antioxidant power (FRAP) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical (ABTS) scavenging activities. By comparison, the average TAC and TIC were the highest in large seeds than in small and medium seeds while the total phenolic content (TPC) was in the order of small seeds > large seeds > medium seeds. The total anthocyanin (TAC) and total isoflavone (TIC) contents were in the ranges of 189.461–2633.454 mg/100 g and 2.110–5.777 mg/g, respectively and were significantly different among the black soybean varieties.
The contents of six anthocyanins, twelve isoflavones, and total phenolic, and the antioxidant activities were determined, and the association of each with seed weight was analyzed. In this study, seeds of 24 black soybean varieties and a reference genotype were grown in Korea, and grouped as small ( 24 g) seeds based on their seed weight. Due to these, seed weight is receiving much attention in soybean breeding. Seed weight is regulated by several genes which in turn could affect the metabolite contents, yield, and quality of soybean seeds.