Nutritional improvement of beans (Phaseolus vulgaris) by natural fermentation

The effect of natural fermentation of flour and whole bean seeds (Phaseolus vulgaris) on the content of nutrients (protein, fat, starch, dietary fiber, vitamins B₁ and B₂) and antinutritional factors (α-galactosides, trypsin inhibitor activity and inositol phosphates) has been studied. After fermentation, total protein content decreased (2–15%) but the in vitro protein digestibility increased (4–8%) and the fat content did not change. In fermented bean flours, fructose and sucrose decreased (67–83% and 99–100% respectively), glucose increased (175–750%) and galactose was present at the concentration 1:4 g/ml (flour:water), but when whole beans were fermented none of these soluble sugars were detected. Total starch, available starch, insoluble fiber content decreased after fermentation (5–13%, 10–24%, and 5–26%, respectively), which was less pronounced in whole fermented beans. The soluble dietary fiber decreased (61–71%). The vitamin B₁ content decreased (17–38%) and the vitamin B₂ content increased (16–35%) after fermentation. Fe, P, Mg, Ca, and K decreased and Zn content did not change after natural fermentation. In either fermented flour or whole beans, the alpha-galactosides and IP₆ decreased (99–100%, 7–39% respectively); however in fermented flour beans IP₅ content did not modify or decrease and IP₄ content could also increase. When whole bean grains were fermented no IP₅ and IP₄ was detected. TIA levels and tannins content decreased (58–71% and 61–70%) after fermentation. Natural fermentation of beans has been a very effective process for increasing functionality of Phaseolus vulgaris and the whole bean fermentation is very promising due to the lower cost.