Lactic-fermented cereal gruels with improved in vitro protein digestibility

Abstract

The effect of different lactic fermentation techniques was studied on the in vitro protein digestibility of non-tannin and high-tannin varieties of maize, sorghum, finger millet and bulrush millet, respectively. Lactic fermentation was achieved in gruels or water slurries of the cereal flours by addition of different starter cultures. In vitro protein digestibility was measured with a pepsin/pancreatin enzymatic digestion procedure that simulates digestion in humans and that shows results corresponding to human studies. Lactic fermentation significantly (P < 0.01) improved the in vitro protein digestibility of the gruels, except for the non-tannin maize variety. There was no difference in protein digestibility between gruels fermented before or after cooking. Unfermented, non-tannin cereal gruels had significantly (P < 0.05) higher in vitro protein digestibility values, range 61–79%, compared with unfermented high-tannin cereal gruels of sorghum and finger millet, range 33–40%, and lactic-fermented samples of these varieties, range of average values 41–55%, respectively. A high-tannin variety of bulrush millet, however, had an average protein digestibility value of 79% after lactic fermentation, equal to the value for unfermented maize. The protein digestibility increased significantly (P < 0.01) more by fermenting with a natural lactic fermentation starter culture with dominance of strains from Lactobacillus, Streptococcus and Candida compared with the use of a pure culture of L. plantarum.