Occurrence of vicine and convicine in faba bean and their removal by hydrolysis

Legumes are a sustainable source of plant protein, and their production could be increased in Europe. The use of faba bean (Vicia faba L.) is limited in part due to the presence of the pyrimidine glycosides vicine and convicine. Vicine and convicine, and particularly their aglycones, can cause a form of haemolytic anaemia called favism in individuals who have genetic deficiency in the glucose-6-phosphate dehydrogenase (G6PD) enzyme. Different processing methods have reduced the vicine and convicine contents to varying levels, but the formation of the aglycones have not been studied. Practical processing methods for removal of vicine, convicine and their aglycones are still required. The main aim of this study was to implement methods for the total elimination of vicine and convicine, with a focus on the aglycones. The compounds of interest were quantified using reversed phase high performance liquid chromatography (RP-HPLC) with ultraviolet (UV) detection against an internal standard uridine. The contents of vicine and convicine were determined in cultivars grown in Finland, and the contents were compared within a selected growing year and among three growing years. Vicine and convicine were hydrolysed in faba bean extracts, in vicine and convicine fractions and in faba bean suspensions by using glucosidase to study the formation and stability of the aglycones. Finally, the formation and stability reactions were studied under selected model conditions and in sourdoughs and breads. The performance of the HPLC method was suitable for the analysis of vicine and convicine. The levels in the studied cultivars varied from 5.2–7.6 mg/g dry matter (DM) and 2.1–3.6 mg/g DM within one growing year for vicine and convicine, respectively. Cultivar comparison showed that the cultivar ‘Kontu’, the commonly grown cultivar in Finland, contained high amounts of vicine and convicine. No extensive variation was noted among three studied growing years, even though the weather conditions varied markedly. The aglycones were detected and monitored with the HPLC method used for vicine and convicine analysis. The aglycones formed in the vicine and convicine fractions decreased in amount and finally lost their UV absorptivity after 2 h at pH 5 at 37 °C. The need for an external enzyme source was confirmed, as losses of vicine and convicine were rather small in faba bean suspensions. Selected lactic acid bacteria (LAB) strains were able to hydrolyse vicine and convicine in faba bean sourdoughs at 25 °C, 24 h; the hydrolysis depended on the fermentation temperature. Sourdoughs lost up to 82–85% of the vicine and up to 34– 47% of the convicine. The amounts of vicine and convicine in wheat breads, containing 30% faba bean, were comparable to the amounts that were in sourdoughs after 24 h of fermentation. The aglycones were measured from sourdoughs fermented at 25 °C and from the corresponding doughs, but not from the breads. This study showed that vicine and convicine can be analysed simultaneously with their aglycones with an RP-HPLC-UV method, which provides the benefit of estimation of the total elimination of these compounds. The aglycones were found to disappear in all the studied matrices. Fermentation can induce losses of vicine and convicine, but the efficiency of hydrolysis depends on the selection of strains and the fermentation conditions. Furthermore, controlled acidification is necessary for maintain acceptable sensory quality.