Comparisons of amino acid and protein levels in oil-extracted seeds of Brassica and Sinapis species, with observations on environmental effects

Seeds from 21 selections of Brassica and Sinapis were analyzed for crude protein (CP; N x 6.25) and amino acid content following oil extraction and grinding. In exp. 1 three cultivars of B. napus, B. rapa and B. juncea were grown in four locations in 4 successive years, with duplicate samples taken from each plot. Brassica juncea contained more CP (P < 0.001) than B. napus or B. rapa (44.6 > 40.1 > 38.8%, respectively). Location affected CP level but not the ranking among cultivars. Year-to-year effects on CP levels (P < 0.001) were of lower magnitude than location effects. Treatments (cultivar, location, year) affected CP and amino acid levels differently. Amino acid levels expressed as percent of CP differed among many cultivars (P < 0.01). Threonine, valine, histidine, lysine and arginine were strongly influenced by location (P < 0.001), as were the dispensable amino acids serine, glutamine and tyrosine. In exp. 2, 10 cultivars and strains grown in one location and in three replicates resulted in greater CP levels in two B. juncea cultivars than in B. napus and B. rapa (42.9 and 43.2 vs. 39.7 and 38.8%), respectively, but lower levels of lysine and threonine in the CP (lysine: 5.4 vs. 6.3; threonine: 3.5 and 3.7 vs. 3.8 and 4.0%). Brassica napus and B. rapa ranked among the lowest in percent CP. In exp. 3, comparisons of eight samples from B. napus, B. rapa and Sinapis alba plots revealed a CP range of 38.1 to 45.0% but differences in amino acid content of the CP were relatively small.