Relations between the crude protein content and the amino acid profile of organically produced field beans (Vicia faba L.) and field peas (Pisum sativum L.)

Summary

In Organic Farming, grain legumes are important protein feedstuffs. There are hints indicating that the amino acid (AA) profile is affected by factors associated with varying crude protein (CP) contents of crops. The knowledge on this relationship between CP and AA profile needs to be extended to optimize feeding strategies for monogastrics as well as the selection of cultivars and varieties in fodder crop cultivation. Therefore, samples of 67 field beans (Vicia faba L.) and 86 field peas (Pisum sativum L.) were collected from field trials of various organically managed experimental locations in Germany in the years 2011, 2012 and 2013 and analyzed for their contents of CP and AA. Compared to tabular values derived from conventional samples organically produced field beans contained similar amounts of CP, whereas the CP content of field peas was lower. The protein of field peas contained significantly (p < 0.05) larger amounts of the essential and semi-essential AAs except threonine, histidine and arginine. Thus, the relations between CP and AA differed between field beans and field peas. In field beans, the limiting AAs (for swine and poultry) lysine, methionine, and cysteine were negatively correlated with the CP content. However, the field pea sample revealed negative correlations between the amount of CP and the contents of methionine, threonine, isoleucine, and valine. The content of arginine increased with decreasing amounts of CP in both grain legume cultivars. Furthermore, the contents of proline and glycine were negatively correlated with the CP content of field peas (p < 0.01). No notable correlations between the non-essential AAs and CP were found in field beans.
The results demonstrate that high CP contents in grain legumes are not the only factor to be considered, when protein feedstuffs for monogastrics in Organic Farming are needed. Although significant negative correlations between essential AA and CP contents are repeatedly found, it is not observed that non-essential AAs mainly account for these changes. Nevertheless, a decline of the amounts of lysine and sulfur-containing AAs negatively affects the quality of crude protein. Further studies with large samples are needed to detect the influence of environmental and genetic factors.