Naturally Fermented Milk From Northern Senegal: Bacterial Community Composition and Probiotic Enrichment With Lactobacillus rhamnosus

Abstract

A variety of foods fermented with lactic acid bacteria serve as dietary staples in many African communities; yet, their bacterial profiles are poorly characterized. The integration of health-promoting probiotics into naturally fermented milk products could make a profound impact on human health. Here, we characterize the bacterial community composition of a naturally fermented milk product (<i>lait caillé</i>) from northern Senegal, prepared in wooden bowls (lahals) with a bacterial biofilm to steer the fermentation process. We incorporated a probiotic starter culture containing the most documented probiotic strain <i>Lactobacillus rhamnosus</i> GG (generic strain name yoba 2012) into the local fermentation process. Bar-coded 16S rRNA amplicon sequencing of <i>lait caillé</i> samples indicated that the bacterial community of <i>lait caillé</i> has high species richness with over 100 bacterial genera; however, few have high abundance. In contrast to the diverse bacterial compositions of other characterized naturally fermented milk products, the composition of <i>lait caillé</i> predominantly consists of the lactic acid bacteria <i>Streptococcus</i> and <i>Lactobacillus</i>, resembling the bacterial composition in regular yogurt. The bacterial community composition of <i>lait caillé</i> varies geographically based on the presence of some genera, including <i>Lactoccoccus, Enterococcus, Bifidobacterium</i>, and <i>Bacillus</i>, but this trend is not consistent within production communities. The diversity of bacterial communities is much higher in the <i>lahal</i> biofilm than in the naturally fermented milk products, which is in turn greater than in commercial yogurts. Addition of a starter culture with <i>L. rhamnosus</i> yoba 2012 to milk in <i>lahals</i> led to substantial growth of this probiotic bacterium during the fermentation process. Two independent quantitative PCR-analyses specific for <i>L. rhamnosus</i> yoba 2012 indicated a 20- to 60-fold increase in the total number of probiotic bacteria in the first batch after inoculation. A similar increase of the probiotic was observed in a variation of <i>lait caillé</i> prepared with carbohydrate-rich millet granules (<i>thiakry</i>) added prior to fermentation. This study shows the feasibility of integrating health-promoting probiotic strains into naturally fermented foods produced in regions with a high prevalence of malnutrition.