The national demand of soybean is about 2.4 million ton per year and predominantly used for tempe and tofu (83.7%.). However, the domestic production can only meet 34% of the national demand and the rest is imported. Therefore, improved varieties with high potential yield (≥ 2 ton/ha) and tolerant to particular biotic and abiotic stresses are crucial in order to increase national soybean production. Yellow and large-seeded soybean (> 13 g/100 grains) are tailored for tempe ingredient as it would give good colour and high recovery of tempe. Tempe processors therefore prefer to use imported soybeans with large seed sizes (14−16 g/100 grains). In fact, selected improved cultivars, such as Bromo, Argomulyo, Anjasmoro, Burangrang, Panderman, and Grobogan are similar, even larger than those of imported soybeans (14−19 g/100 grains). However, imported soybean is more continuously available in the market, thereby frequently used by tempe processors rather than such cultivars. Therefore, it is essential to study the suitability of soybean promising lines for tempe ingredient prior to be released as improved cultivars. This would enhance their adoption by farmers and utilization by tempe processors. N-10 and N-12 genotypes are soybean promising lines that are tolerant to ≤ 50% shading cultivation, thus they can be intercropped with young high state crops, such as teak, palm, rubber, etc. In rubber plantation, about 70% of the area can be grown with soybean for the first year and 50% for the third year. Soybean can be also intercropped with other food crops, such as maize, cassava, citrus, etc. Meanwhile, K-12 and K-13 genotypes are promising lines tolerant to soybean rust, the predominant disease caused by Phakopsora pachyrhizi that may cause yield loss of 40% up to 80%. These four lines belonged to large-seeded (Table 1), that are suitable for tempe ingredient. The yield recovery of tempe positively correlated with the soybean seed size (r = 0.76) and Grobogan cultivar showed the highest value (Table 1). Their protein contents as well as Anjasmoro and Grobogan as check cultivars (36.35−38.54% db) were higher than those of imported soybeans (32.76−33.44% db), thus giving higher protein content of the tempe produced relative to imported soybeans (Table 1). The lightness (L*) values of fresh tempe derived from K-12, K-13, and N-10 lines were similar to those of imported soybeans, while N-12 had slightly a lower value. The fresh tempe prepared from N-12, Anjasmoro, and Grobogan cultivars had similar scores of colour, aroma, compactness, and texture acceptances to that of USA Merah (first quality imported soybean), while the rest were similar to that of Pelangi (second quality of imported soybean) (Fig. 1 and Fig 2.). This study suggests that N-12 line was considerably suitable for tempe preparation, followed by K-12, K-13, and N-10. This N-12 line has been released as a new improved soybean cultivar in 2014, namely Dena 1 (tolerant to shading).
Fig. 1. Soybean seed and tempe prepared from N-12 breeding line (Dena 1 cultivar) (a), Anjasmoro cultivar (b), and imported soybean (c).