TOTAL SULFUR AS A SCREENING CRITERION FOR SULFUR AMINO ACIDS IN LEGUMES

Abstract

The relationship between total sulfur, determined by two methods, and sulfur-containing amino acids methionine and cystine was investigated in 33 genotypes of beans (Phaseolus vulgaris L.), faba beans (Vicia faba L.), peas (Pisum sativum L.), and lentils (Lens culinaris Medik.). The Leco Sulfur Analyzer (method 1) gave values for total sulfur in the legumes 29.2–47.6% lower than the gravimetric procedure (method 2). The mean coefficient of variability of method 1 was 36% higher than for method 2. The correlation coefficient between the two methods for the 33 genotypes was +0.42*. The correlation between percent meal protein and percent total sulfur in the legumes was +0.56**. The correlation between percent meal protein and total sulfur expressed as percent of meal protein or g/16 g N was negative (−0.75**). Faba beans, peas and lentils contained, on the average, 48% more cystine than methionine. Except for lentils, the mean total sulfur amino acid content of the legumes was generally similar. The correlation between percent total sulfur and total sulfur amino acid (mmoles/g meal) content of the legumes was +0.69** for peas and +0.46** for all the legumes. There was little or no change in the correlation when total sulfur and total sulfur amino acid data were expressed as percentages of the meal protein. The sulfur in the sulfur amino acids formed between 44.8 and 66.5% of the total meal sulfur. The rest of the sulfur was present in the meal as non-methionine and non-cystine sulfur. Total sulfur determination in the legume species used in the study is a poor indicator of methionine and cystine contents.