Amino Acid Patterns of Kidney Beans Grown Under Different S and K Regimes1
- S. M. Hojjati2
The protein of kidney beans (Phaseolus vulgaris L.), an important food crop, is poor in S-containing amino acids and needs improvement. Solution and sand-culture studies have shown that S fertilization increases the concentration of S-containing amino acids in several crops. K application affects protein composition of some crops. The objective of this research was, therefore, to determine the amino-acid concentrations of ‘Naze’ kidney beans and to study the effects of soil-SO42- levels and K2SO4 application on grain yield and amino-acid composition, especially the concentration of methionine.
An area of Xerollic Calciorthid, fine, vermiculitic, chermic soil which had been used previously for a S- fertility study with wheat (Triticum aestivum L. em. Thell.) was used for this trial at Pahlavi University, Shiraz, Iran. The design of the experiment was a split plot with K2SO4, levels as main-plot treatments and the prior S levels constituting the split-plot treatments. (NH4)2HPO4 was applied uniformly at 200 kg/ha. Kidney beans were seeded at the rate of 75 kg/ha.
Proximate protein analyses were made by determining total N content and multiplying by a factor of 6.25. Tryptophan was analyzed colorimetrically and the other amino acids were determined in a Beckman Spinco amino-acid analyzer. Chemical scores reflecting protein quality were calculated by FAO instructions.
Neither K2SO4 fertilization nor the prior S treatments had any effect on yield of dry matter or grain, ratio of grain to total dry matter, or grain-protein concentration. Methionine concentration was positively correlated with soil-SO42- level (r : 0.75; significant at the 1% level.). The first limiting amino acid was methionine, followed by valine and/or isoleucine. Tryptophan was not limiting Regression equations for predicting methionine from soil-SO42- levels and valine and tryptophan from total-protein concentrations are presented.
Sulfur application may increase the methionine concentration of bean protein, but the large amounts of S required and the high costs involved appear to limit the usefulness of this approach for improving protein quality.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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