Differences in Cotyledon Color and Harvest Period Affect the Contents of Major Isoflavones and Anthocyanins in Black Soybeans

Several environmental and genetic factors affect the isoflavone and anthocyanin contents in soybeans. This study aimed to assess the influences of cotyledon color and harvest period on the contents of five major isoflavones and three major anthocyanins in 323 black soybean landraces grown in Korea. In all the soybeans, malonylgenistin, malonyldaidzin and cyanidin-3-O-glucoside were the foremost components. The total isoflavone (TIC) and total anthocyanin (TAC) contents were in the ranges of 491.29-1998.39 μg/g and 452.60-2789.37 mg/100 g on dry weight basis, respectively. Both the average TIC and TAC were higher in green cotyledon soybeans (1493.93 μg/g and 1656.05 mg/100 g, respectively) than in yellow cotyledon soybeans (1423.09 μg/g and 1489.30 mg/100 g, respectively). With respect to the harvest period, the average TIC was in the order of Late-October (1517.31 μg/g) > Mid-October (1454.54 μg/g) > Early-October (1340.95 μg/g). Moreover, the average TAC decreased in the order of Late-October (1765.76 mg/100 g) > Mid-October (1503.93 mg/100 g) > Early-October (1350.91 mg/100 g). In general, cotyledon color appeared to cause a significant variation on TAC (P < 0.05) but not on TIC, whereas the harvest period appeared to cause significant variations on both the TAC and TIC. Among the 323 landraces, 20 were identified to contain high TIC (> 1800 μg/g) and TAC (> 2000 mg/100 g) in their seeds and hence, could be considered as important sources of dietary isoflavones and anthocyanins. Besides, they possibly provide a wide spectrum of options if considered during the development of improved soybean genotypes.