Natural Fermentation of Cowpea (Vigna unguiculata) Flour Improves the Nutritive Utilization of Indispensable Amino Acids and Phosphorus by Growing Rats

Abstract

Cowpea (Vigna unguiculata) is among the most cultivated legumes, with interesting agronomic and environmental properties, and great potential as a nutritious food. The nutritional value of cowpea can be improved by technological processing. In this study, we showed that natural fermentation improved bioavailability of protein, amino acids, and dietary essential minerals from cowpea in growing rats, thus strengthening its potential value as functional food or food supplement. Forty Wistar albino rats (48 ± 1.8 g), were fed one of four experimental diets (n = 10 rats per diet): casein, raw cowpea, fermented cowpea or fermented and autoclaved cowpea. Despite lower growth indices of raw and fermented cowpea protein (PER, FTI) than casein, fermentation enhanced apparent digestibility of arginine, leucine, lysine, methionine, phenylalanine, tyrosine, and valine, and true digestibility of essential amino acids, except for tyrosine and valine, compared to raw cowpea. On the other hand, autoclaving of fermented cowpea flour decreased apparent, as did true digestibility of sulfur amino acids. Regarding the nutritive utilization of dietary essential minerals, Vigna unguiculata was a good source of available P, Mg, and K, while fermentation significantly improved the availability of P. Overall, cowpea was a good source of digestible essential amino acids and minerals and fermentation significantly improved its nutritional value that was not further enhanced by autoclaving.

Keywords: Vigna unguiculata; amino acids; digestibility; fermentation; mineral bioavailability; rat.

Figure A1

Fecal and urinary endogenous Nitrogen excretion calculated by a regression methodology using different dietary protein levels. (A) Endogenous fecal N excretion expressed as mg N per gram of dry matter intake. (B) Endogenous urinary excretion expressed as mg N per 100 g of body weight.

Figure 1

Experimental design of the study. D1–D16, correspond to day 1 to day 16 of the experiment; AdapP: Adaptation Period; ExperP: Experimental Period.

Figure 2

Effects of raw and fermented Vigna unguiculata on food intake and growth parameters of rats. (A) Food intake and body weight in the different experimental diets. Control: casein diet, RV: raw cowpea diet; FV: fermented cowpea diet; FAV: fermented and autoclaved cowpea diet. Different letters above columns indicate significant differences (p < 0.05). (B) Growth parameters in the different experimental diets. Control: casein diet; RV: raw cowpea diet; FV: fermented cowpea diet; FAV: fermented and autoclaved cowpea diet. PER: Protein Efficiency Ratio (weight gain, grams per day/protein intake, grams per day); FTI: Food Transformation Index (total intake, grams dry matter per day/increase in body weight). Different letters above columns indicate significant differences (p < 0.05).