Abstract
Nono, an important traditional fermented dairy food produced from cow’s milk in Nigeria, was studied for microbial diversity and for starter culture development for industrial production. On the basis of a polyphasic approach, including phenotypic and genotypic methods such as 16S rRNA gene sequencing, repetitive element PCR (rep-PCR) fingerprinting metagenomics, and whole genome sequencing, we identified Lactobacillus (Lb.) helveticus, Limosilactobacillus (L.) fermentum, Lb. delbrueckii, and Streptococcus (S.) thermophilus as predominant bacterial species involved with milk fermentation during traditional nono production in Nigeria, while the predominant yeast species in nono was identified as Saccharomyces cerevisiae. Using metagenomics, Shigella and potential pathogens such as enterobacteria were detected at low levels of abundance. Strains of the predominant lactic acid bacteria (LAB) were selected for starter cultures combination on the basis of their capacities for rapid growth in milk and reduction of pH below 4.5 and their gelling characteristic, which was demonstrated noticeably only by the S. thermophilus strains. Whole genome sequence analysis of selected bacterial strains showed the largest assembled genome size to be 2,169,635 bp in Lb. helveticus 314, while the smallest genome size was 1,785,639 bp in Lb. delbrueckii 328M. Genes encoding bacteriocins were not detected in all the strains, but all the LAB possessed genes potentially involved in diacetyl production and citrate metabolism. These bacteria isolated from nono can thus be used to improve the microbial safety quality of nono in Nigeria, in addition to improving technological parameters such as gelling viscosity, palatability, and product consistency.
Highlights
Nono samples obtained from various Nigerian markets showed a large variation in bacterial counts (Figure 1)
1,814,605 bp Generally, the bacterial counts determined on M17 medium incubated at 45 ◦ C in this study were similar to those determined on the same M17 incubated at 30 ◦ C, in some samples the counts were higher on the latter medium by up to 1 cfu/mL
Okonkwo [2] reported highly variable counts of different bacterial groups in nono samples from Nigerian markets, and in that study, the mesophilic, aerobic plate counts ranged from log 2.53 to log 4.89 per mL, while enterobacterial counts ranged from log 1.37 to log 3.29 per mL
Summary
Nono is a spontaneously lactic acid fermented milk that originates from the northern parts of Nigeria. It is predominantly prepared and sold in local markets by the. Nono is prepared in homes from unpasteurised cow’s milk collected in a calabash and allowed to ferment naturally for 24 h [3,4,5]. Depending on uncontrolled production processes and too poor hygiene during preparation, bacteria other than lactic acid bacteria (LAB), including foodborne pathogenic bacteria such as Escherichia coli, Salmonella, Shigella, Staphylococcus aureus, and Bacillus cereus can occur in these products [2,5,6,7,8]. The presence of foodborne pathogens in such products suggests that the nono products are
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