Isolation and identification of the microbial consortium present in fermented milks from Sub-Saharan Africa
Year: 2013
Type: dissertation
Abstract: A wide variety of traditionally and commercially fermented milks are commonly consumed in various countries of Sub-Saharan Africa.Commercially fermented milk is produced on an industrial scale according to well-managed, standardised production processes and starters are used to initiate fermentation.Traditionally fermented milk is prepared domestically and fermentation occurs spontaneously at ambient temperatures.Lactic acid bacteria (LAB) are responsible for milk fermentation during which they convert the milk carbohydrates to lactic acid, carbon dioxide, alcohol and other organic metabolites.Acetic acid bacteria (AAB), yeasts and mycelial fungi have also been isolated from fermented milks.In this study the microbial consortium present in three traditionally fermented milks, namely omashikwa from Namibia, masse from Mozambique and chekapmkaika from Uganda and two commercially fermented milks, namely chambiko from Malawi and omaere from Namibia, were isolated and enumerated on six different selective media that included MSR + C (specific for lactobacilli), KCA + TTC (specific for lactococci), KCA + V (specific for leuconostocs), MRS + E (specific for AAB), MEA (specific for mycelial fungi) and YPD (specific for yeasts).No significant differences were found between the enumeration values obtained for the three chambiko samples, as well as for enumeration values obtained for the two omaere samples on each of the selective media, indicating low sample variance.Significant differences between enumeration values obtained for the three omashikwa samples were found on all six selective media.Significant differences between enumeration values of the three masse samples and both the chekapmkaika samples were also observed on the selective media.In addition to this, significant differences were observed between average enumeration values obtained for each media between the masse and chekapmkaika, the chambiko and omaere, as well as when the traditional and commercial milks were compared.According to the average enumeration values obtained on each media selective for LAB, the highest bacterial counts were detected on KCA + TTC medium for omaere (2.3 x 10 6 cfu.ml -1 ), KCA + V for chambiko (1.8 x 10 5 cfu.ml -1 ), KCA + TTC for omashikwa and MRS + C for masse and chekapmkaika (6.2 x 10 6 and 2.0 x 10 3 cfu.ml-1 , respectively).After isolation and enumeration of the microbes present in each milk, bacterial isolates on the media selective for LAB and AAB were obtained according to the Harrison Disk method.These isolates were identified by amplifying a 1.5 kilobase (kb)Stellenbosch University http://scholar.sun.ac.za part of the 16S ribosomal RNA (rRNA) gene using the polymerase chain reaction (PCR), followed by DNA sequencing.The isolates were identified by comparing the sequences obtained to sequences listed in the NCBI database using the BLAST algorithm and searching for the closest relative.The main LAB group present in the omaere was lactococci (94%), in chambiko and chekapmkaika it was lactobacilli (30% and 45%, respectively), in omashikwa it was enterococci (43%) and in masse it was leuconostocs (68%).The same microbial species were present on a number of the selective media used in this study.Lactococcus spp., Enterococcus spp.and Lactobacillus spp.were isolated from MRS + C, KCA + TTC, KCA + V and MRS + E and Leuconostoc spp.were isolated from MRS + C, MRS + E and KCA + V. Hygienic standards during traditional milk fermentation is often poor and, therefore, microbial contaminants were isolated from the traditional milk and these included Acinetobacter johnsonii and Klebsiella pneumoniae from KCA + V, Mesorhizobium loti, Acinetobacter radioresistens, Escherichia coli, Staphylococcus spp., Kluyvera georgiana, Enterobacter spp.and Klebsiella oxytoca from KCA + TTC, Staphylococcus spp.from MRS + C and Bacillus spp.from MRS + E. Since the media used for the isolation of the LAB and AAB in this study were not selective further identification of the enumerated microbes is of importance for the identification of the microbial groups present in each fermented milk.The data obtained in this study clearly shows that fermented milks from Sub-Saharan Africa vary significantly from each other in terms of microbial numbers, microbial diversity and the dominant microbial groups present.The microbial diversity of the traditionally fermented milks was more diverse than the microbial diversity of the commercially fermented milks.LAB strains isolated from these traditionally fermented milks can be used to develop novel starters and as a result new commercially fermented dairy products with unique aromas, tastes and characteristics can be produced.
Author: Lionie Marie Schutte
Language: English
Subfield: Food Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2112061819