Comparative profiling of lactic acid bacteria isolates in optimized and spontaneous fermentation of cowpea leaves

Abstract

In as much as spontaneous fermentation of cowpea leaves enhances product diversification, the process is rather slow with poor product quality. Limited work has been undertaken to provide input toward standardization of the process and enhancing of product quality. The current study sought to evaluate the in-process fermentative bacteria profile changes due to the effect of optimization of fermentation process of cowpea leaves. Lactic acid bacteria (LAB) isolates from spontaneous and optimized fermentation were characterized using biochemical tests, whereby optimization was done using the Response Surface Methodology model of the central composite design in the Design Expert Software. The RSM models accounted for 89% and 60% variability in the response variables of pH and titratable acidity, respectively (p < .001). Increasing the sugar concentration and period of fermentation significantly (p < .05) increased the titratable acidity, while reducing the pH. The optimal fermentation parameters were established as sugar and salt concentrations of 5% and 2%, respectively, 16 days of fermentation, pH of 3.8 and titratable acidity of 1.22% with a desirability of 0.859. Of the 13 identified LAB isolates, Lactobacillus brevis and Lactococcus lactis dominated the onset stage of spontaneous fermentation whereas only Lactobacillus brevis dominated the onset stage of optimized fermentation. Additionally, the final stage with the dominant isolates of L. plantarum was longer in the spontaneous fermentation process than in the optimized process. Evidently, optimizing the fermentation process resulted in increasing dominance by heterofermenters in the production of soured cowpea leaves, with the yielded product having enhanced acidity.

Keywords: biochemical; cowpea leaves; fermented; pH; response surface methodology; titratable acidity.

FIGURE 1

Studentized residuals and percent normality probability for pH

FIGURE 2

Studentized residuals and percent normality probability for titratable acidity

FIGURE 3

Actual and predicted values of pH of the fermented cowpea leaves

FIGURE 4

Actual and predicted values of titratable acidity of the fermented cowpea leaves

FIGURE 5

Effect of individual factors of concentrations of sugar and salt and period of fermentation on pH of fermented cowpea leaves

FIGURE 6

Effect of individual factors of concentrations of sugar and salt and period of fermentation on titatable acidity fermented cowpea leaves

FIGURE 7

Three dimensional response surface plots showing the interactive effect of the concentrations of sugar and period of fermentation at 3.5% salt concentration

FIGURE 8

Three dimensional response surface plots showing the interactive effect of the concentrations of salt and period of fermentation at 3.5% sugar concentration

FIGURE 9

Optimized fermentation parameters for production of soured cowpea leaves

FIGURE 10

Relative eigen values explaining variation in the biochemical traits of lactic acid bacteria isolates from fermentation of cowpea leaves

FIGURE 11

Principal coordinate analysis of biochemical traits of lactic acid bacteria isolates from spontaneous fermentation of cowpea leaves. PCoA 1‐First principal coordinate, PCoA 2‐Second principal coordinate

FIGURE 12

Dominant lactic acid bacteria involved in optimized fermentation of cowpea leaves

FIGURE 13

Dominant lactic acid bacteria involved in spontaneous fermentation of cowpea leaves