Efforts to increase soybean production in Indonesia have been intensively performed through extending the harvested area to outside of Java. However, the agro ecological conditions were marginal, primarily due to acid soil that accounts for 69.4% of the total dry land area in Indonesia. Spesific characteristics of acid soil, such as low pH (< 5,5), high Al and P fixation, low organic nutrients and ion exchange capacity as well as low population of beneficial micro-organisms (Rhizobium spp.) may limit the soybean productivity. Therefore, soybean varieties tolerant to acid soil are essential as improvement of soil acidity by the addition of lime (amelioration) is yet costly for marginal farmers.
A number of soybean promising lines tolerant to acid soil are currently available. Supportive data on the nutritional value, particularly protein is needed as soybeans play an important role in the Indonesian diet as a protein source, primarily as tempe and tofu. Soybeans also contain approximately 20% of fat (dw), which consist of 85% unsaturated fatty acids (UFA), namely oleic, linoleic, and linolenic and 15% saturated fatty acids, such as palmitic and stearic acids. Linoleic (ω-6) and linolenic (ω-3) belong to essential fatty acids and a diet containing fat high in UFA may lower the risks for high blood cholesterol and coronary heart disease. However, they are susceptible to oxidation, thus more amounts of oleic acid (ω-9) is preferred in soybean oil.
Isoflavones, the bioactive components in soybeans are beneficial to health due to their biological activities as phytoestrogens and antioxidant capacities that protect cells from oxidative damage (premature aging), prevent osteoporosis, coronary heart disease, cancer, and health problems associated with menopause. About 12 isoflavones have been identified in soybeans, which the majority belong to genistin, daidzin, and glycitin glycones and genistein, daidzein, and glycitein aglycones. The total isoflavones and their profiles are highly dependent on soybean cultivar, planting season, cultivation practices, environmental conditions and stresses, postharvest handling.
Twenty soybean promising lines tolerant to acid soil that were grown at Tegineneng Experimental Field in Lampung, Indonesia contained protein from 39.64% up to 46,76% dw (using a Dumas method) as seen in Table 1. Three lines had considerably high protein (≥ 45% dw), namely Tgm/Anj-888, Tgm/Anj-862 and Tgm/Anj-858, which were slightly higher than that of Tanggamus, a released variety tolerant to acid soil (44.5% dw). The fat contents ranged from 16.85 to 21.20% dw and showed a negative correlation with the protein content (r = -0.64). Tgm/Anj-847, Tgm/Anj-857, and Tgm/Anj-832 lines contained fairly high fat (≥ 20% dw), approaching the fat content of imported soybean c.a. 21.4-21.7% dw, thus tailored for oil extraction purposes.
|Table 1. Protein, Fat, and fatty acid contents of 20 soybean lines toleran to acid soil|
Oleic / Linoleic
|dw = dry weight, a=percentage of the total fat|
On average, soybean fat consisted of 9.42% palmitic acid (C16:0), 2.77% stearic acid (C18:0), 43.93% oleic acid (C18:1), 38.53% linoleic acid (C18:2), and 5.35% linolenic acid (C18:3) (Fig. 1). The oleic/linoleic ratio varied from 0.45 to 2.52 (Table 1) and negatively correlated (r = -0.98). Another study reported that Anjasmoro and Burangrang varieties contained more linoleic acid (48.1% and 52.5%, respectively) than oleic acid (32.3% and 24.7%). This suggests that environmental growing conditions such as acid soil may also contribute to higher oleic acid obtained at present study. Two lines, namely Tgm/Anj-889 and Tgm/Anj-857 could achieve 55.54-60.35% of oleic acid (Table 1), thus suitable as ingredients for oil-based food industries, such as margarine and shortening.
Ten isoflavones were identified in 20 soybean lines with malonylgenistin as the major component (29.49%), followed by malonyldaidzin (19.04%) and glycitin (16.70%) (Fig. 2). Tgm/Anj-995 line showed the highest total of isoflavones (2,130.2 µg/g dw), followed by Tgm/Anj-784 and Tgm/Anj-832 (1,719.9 µg and 1,710.0 µg/g dw, respectively). The isoflavone content of Tgm/Anj-995 line was slightly lower than that of Devon 1, a high-isoflavone variety released in 2016 with total isoflavones of 2,219.7 µg/g. This nutritional information would be useful for the breeder to release new soybean varieties tolerant to acid soil as supportive data to their agronomic characters.
E. Ginting, R. Yulifianti, H. Kuswantoro, B. Won Lee, I. Youl Baek.