Enhancing the digestibility of cowpea (Vigna unguiculata) by traditional processing and fermentation

- Hulls are not the main fraction of cowpeas causing flatus formation.
- Traditional cooking and dehulling reduce flatus formation only slightly.
- Fermentations with Weissella, Bacillus and Rhizopus strongly reduce flatus formation.
- Chemical, in-vitro and in-vivo analyses reflect different flatulence mechanisms.

Flatulence is an important drawback for the consumption of legumes. Therefore, the ability of traditional processing (dehulling, boiling, soaking) and fermentation (bacterial, fungal or yeast) of cowpeas to reduce flatulence was investigated. Raw and processed cowpeas were assessed for their galactose-oligosaccharide content, the amount of gas produced by Clostridium perfringens using in-vitro cowpea digests as main carbohydrate substrate (in-vitro fermentability index) and the alveolar hydrogen concentration of the breath of 18 healthy adults after the consumption of a cowpea porridge breakfast (in-vivo fermentability index). Galactose-oligosaccharides could not be detected in cowpea hulls which yielded low in-vitro fermentability index as compared with other treatments. Traditional processing induced a limited reduction of raffinose and verbascose content contrary to fermentations. The in-vitro fermentability index appeared similarly high for all processed cowpea except after Rhizopus and Bacillus fermentation. The in-vivo fermentability index of fermented cowpeas was significantly lower than that of traditionally processed cowpeas. Consequently, soaking and fermentation in cowpea processing deserve further investigation and promotion.