Vicine and convicine - the main anti-nutritional factors restriciting faba bean usage

In spite of the vast nutritional and environmental benefits provided by faba bean cultivation, its use as a food crop has been restricted, primarily due to the presence of the pyrimidine glycosides vicine and convicine. The pyrimidine glycosides are precursors of the aglycones divicine and isouramil, which are the main factors of favism - a genetic condition which may lead to severe hemolysis after faba bean ingestion.
Faba bean (Vicia faba L.) is a leguminous plant belonging to the Fabaceae family, able to grow in different climates. It is an important plant for human consumption, having a valuable nutritional composition, particularly rich in plant-based protein. Faba bean provides symbiotically fixed nitrogen, thus improving soil fertility for itself and successive crops. Cultivation of faba bean as a legume crop delivers generous economic and environmental benefits, stemming from its low reliance on nitrogen inputs and consequent reduced greenhouse gas emissions. Production of plant-based protein has a much lower environmental cost than that of animal-based protein.

Figure 1. Faba bean, flower (left) and seeds (right).

In spite of the many benefits of faba bean, its cultivation and consumption has been historically restricted due to the presence of pyrimidine glycosides vicine and convicine (v-c), which upon hydrolysis generate the aglycones divicine (2,6-diamino-4,5-dihydroxypyrimidine) and isouramil (6-amino-2,4,5-trihydroxypyrimidine), respectively (Figure 2). Divicine and isouramil have been identified as the main factors of favism, a life-threatening hemolytic crisis that can result from the ingestion of faba beans. Favism is induced in humans that carry G6PD deficiency which is common in the Mediterranean basin, Middle East, North Africa, and other areas in which malaria is or has been endemic. However, low v-c faba bean lines are safe for G6PD-deficient individuals.

Vicine and convicine are mostly found in the seeds, where they reach concentrations up to 5 mg and 2 mg/g of dry weight, respectively. Despite there are some studies available v-c degradation, very little is still known about the fate and, in particular, about the abundance and the toxicity of the favism-inducing derivatives, divicine and isouramil. Nowadays, the elimination of these glucosides is a goal of most faba bean breeding programs worldwide.

Figure 2. Moelcular structures of vicine, convicine and their respective aglycones, divicine and isouramil.

SMILE:  O=C2\N=C(\N)NC(=C2/O[C@@H]1O[C@@H]([C@@H](O)[C@H](O)[C@H]1O)CO)/N
C([C@@H]1[C@H]([C@@H]([C@H]([C@@H](O1)OC2=C(N=C(NC2=O)N)N)O)O)O)O

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• https://commons.wikimedia.org/wiki/File:Vicia_faba_L._Flower.jpg
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