Abstract
Different physiological and genetic studies show that the variations in the accumulation of pigment-stimulating metabolites result in color differences in soybean seed coats. The objective of this study was to analyze the nutrient contents and antioxidant potential in black, brown, and green seed-coated soybeans. Significant variations in protein (38.9–43.3%), oil (13.9–20.4%), total sugar (63.5–97.0 mg/g seed), total anthocyanin (3826.0–21,856.0 μg/g seed coat), total isoflavone (709.5–3394.3 μg/g seed), lutein (1.9–14.8 μg/g), total polyphenol (123.0–385.8 mg gallic acid/100 g seed), total flavonoid (22.1–208.5 mg catechin/100 g seed), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid (ABTS; 275.0–818.8 mg Trolox/100 g seed), and 2,2-diphenyl-1-picrylhydrazyl (DPPH; 96.3–579.7 mg Trolox/100 g seed) were found among the soybean genotypes. Ilpumgeomjeong2 contained the lowest protein but the highest oil and total sugar. The lowest oil-containing Wonheug had the highest protein content. Socheong2 was rich in all four variables of antioxidants. Anthocyanins were detected only in black soybeans but not in brown and green soybeans. The variation in isoflavone content was up to 5-fold among the soybean genotypes. This study could be a valuable resource for the selection and improvement of soybean because an understanding of the nutrient content and antioxidant potentials is useful to develop effective strategies for improving the economic traits; for example, the major emphasis of soybean breeding for fatty acids is to enhance the oleic and linoleic acid contents and to decrease linolenic acid content.
Highlights
The demand for soybean (Glycine max (L.) Merr.), one of the top five largely produced crops globally, is increasing in the food, pharmaceutical, cosmetic, and biofuel industries [1,2] owing to their abundant protein, lipids, and several phytochemicals, including availability of isoflavones, anthocyanins, phenolics, and saponins [3–6]
The soybean genotypes included in this study varied in seed coat color, cotyledon color, 100-seed weight, and maturity duration
Dhungana et al [36] found the seed protein content in the range of 39.4−45.7% in the black soybeans grown in Korea
Summary
The demand for soybean (Glycine max (L.) Merr.), one of the top five largely produced crops globally, is increasing in the food, pharmaceutical, cosmetic, and biofuel industries [1,2] owing to their abundant protein, lipids, and several phytochemicals, including availability of isoflavones, anthocyanins, phenolics, and saponins [3–6]. Soybeans are available in a range of colors from yellow, green, brown, and black, to mottled [7]. Physiological and genetic studies indicate that the color variation is due to the difference in the accumulation of pigment-stimulating metabolites [8–11]. Black soybeans have been widely used in Asian countries, as a folk medicine in China, Japan, and Korea for hundreds of years [12,13]. Studies have shown that anthocyanins are highly concentrated in black soybeans than in other soybeans [12,14,15]. The high level of anthocyanin content imparts to the better pharmacological capacities of black soybeans than other colored soybeans [16,17]
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