Seed Protein and its Relationship to Soluble Sugars in Soybean
- Edgar E. Hartwig,
- Tsung Min Kuo and
- Michael M. Kenty
Protein meal from soybean [Glycine max (L.) Merr.] contains the soluble sugars raffinose and stachyose. Because of these sugars, the quantity of soybean meal must be limited in rations to avoid flatulence in dogs (Canis familiaris) and digestive disturbances in baby pigs (Sus scrofa) and chicks (Gallus domesticus). Identifying soybean with a lower level of these sugars could lead to an increase in the quantity of soybean meal used in specific rations. As protein content of soybean seed is increased and oil is reduced, the total protein + oil + seed coat is greater than in standard type soybean. The residual portion is therefore reduced, and soluble sugars could account for a part of this reduction. Twenty standard type (high-oil) soybean cultivars and breeding lines and 20 high-protein breeding lines were grown in replicated trials on Sharkey clay (very-fine, montmorillonitic, nonacid, thermic Vertic Haplaquept) at Stoneville in 1991 and 1992. Seed was analyzed for protein, oil, raffinose, stachyose, and sucrose. Range in protein content was from 387 to 537 g kg−1 dry seed and oil was from 145 to 216 g kg−1 dry seed. Range in g stachyose + raffinose kg−1 protein was 78.3 to 133.7. The correlation between protein and stachyose + raffinose was negative but nonsignificant. The g stachyose + raffinose kg−1 protein for the cultivar Forrest was used as a basis for comparison with the other genotypes evaluated. On this basis, the quantity of protein that might be used in a ration without changing the raffinose + stachyose level from that in Forrest ranged from 89 to 153%.
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