Microbial content and anti-microbial activity of Namibian traditionally fermented milk

Kutaa, Georgina (2017-12)

Thesis (MScFoodSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The incorporation of bacteriocins as biopreservatives into model food systems has been studied extensively and has been shown to be effective in the control of pathogenic and spoilage microorganisms. However, a more practical and economic option of incorporating bacteriocins into foods can be by direct addition of bacteriocin-producing cultures into food. In this study five samples of traditionally fermented Omaere was sourced from households in Namibia. The microbial consortium present was isolated and enumerated on six different selective media that included deMan, Rogosa and Sharpe Medium (MRS) supplemented with cycloheximide for lactobacilli (MRS+C), MRS supplemented with vancomycin for leuconostocs (MRS+V), MRS supplemented with ethanol for acetic acid bacteria, M17 agar for lactococci, and Chloramphenicol Glucose Agar (CGA) and Potato Dextrose Agar (PDA) for yeasts. The highest enumeration values obtained for Omaere samples 2 and 3 were from MRS+V used for the growth of Leuconostoc spp. However, for samples 1, 4 and 5 the highest values were obtained from MRS+C used for the growth of lactobacilli. This variance among samples can be attributed to the inconsistency in the preparation methods of traditionally fermented milks. After isolation and enumeration of the microbes present in each milk sample, the Harrison Disc method was used to select bacteria and yeast colonies for further testing. The primers 27F and R1492 were used to amplify a 1.5 kilobase (kb) fragment of the 16S ribosomal RNA (rRNA) gene of the selected bacteria colonies using the polymerase chain reaction (PCR). The primers ITS4 and ITS5 were used to amplify a 600 base pair fragment of the internal transcribed spacer (ITS) regions of the fungal rRNA gene and NL1 and NL4 was used to amplify the D1/D2 domain of the 26S rRNA gene of the selected yeast isolates. The resulting PCR products were sequenced and compared to sequences listed in NCBI database using the BLAST algorithm and identified according to the closest relative. The LAB found in Namibian fermented milk Omaere belonged to the genus Lactobacillus, with the predominant species Lactobacillus plantarum (52%) and in lesser numbers Lactobacillus paracasei subsp. paracasei (12%), Lactobacillus paraplantarum (8%), Lactobacillus kefiri (8%), and Lactobacillus casei (2%). The yeasts isolated were Kazachstonia unispora formerly known as Sacchromyces unisporus (9%), Saccharomyces cerevisiae (8%) and Candida pararugosa (2%). Pure cultures of the Lactobacillus spp. isolated were used to ferment milk that was inoculated with Listeria monocytogenes and Escherichia coli and their interaction was monitored over time. After 48 h of fermentation, L. monocytogenes was not detected in milk samples inoculated with Lactobacillus plantarum, Lactobacillus paraplantarum and Lactobacillus casei subsp. paracasei. In contrast, when Lactobacillus kefiri was inoculated with the two foodborne pathogens, after 48 h of fermentation the concentration of L. monocytogenes was reduced by 4 log and was not detected after 72 h. In milk fermented without the addition of starters, the concentration of L. monocytogenes was only reduced by 2.8 log after 72 h of fermentation. In the milk with Lactobacillus plantarum, Lactobacillus paraplantarum and Lactobacillus casei subsp. paracasei after 48 h of fermentation the E. coli concentration was reduced by 4 log and after 72 h of fermentation no E. coli was detected. In contrast, fermentation with Lactobacillus kefiri after 48 h resulted in a decreased concentration of 1 log and at the end of the 72 h the E. coli concentration was only reduced by 1.7 log. In milk fermented without the addition of starter the concentration of E. coli was only reduced by 1.6 log after 72 h of fermentation. The results obtained in this study show that three of the four LAB strains isolated from the Namibian fermented milk, Omaere namely, L. plantarum, L. paraplantarum, L. parcasaei subsp. paracasei had inhibitory effect against the studied foodborne pathogens. Therefore, after further characterization of the types of antibacterial agents that are produced by these LAB, they could be considered as potential candidates for development of starter cultures that can be used for the production of microbiologically safe commercial fermented milk products. However, the L. kefiri strain used in this study is likely not to be used as starter culture as it took longer to eliminate or failed to eliminate the foodborne pathogens used in the study.

AFRIKAANSE OPSOMMING: Die gebruik van bakteriosiene as bio-preserveermiddels in voedselsisteme is omvattend bestudeer en is bewys om doeltreffend te wees in die beheer van patogene en mikroörganismes. Daar kan egter 'n meer praktiese en ekonomiese opsie wees vir die integrasie van bakteriosiene in voedsel deur direkte toevoeging van bakteriosien-vervaardigende suurselkulture tot kosse. Hierdie studie beskryf vyf monsters van tradisioneel gefermenteerde Omaere, afkomstig van huishoudings in Namibië. Die mikrobiese konsortium teenwoordig is geïsoleer op ses verskillende selektiewe media, insluitend deMan, Rogosa and Sharpe Medium (MRS) aangevul met cycloheximied vir lactobacilli, MRS aangevul met vancomycin vir leuconostocs (MRS+V), MRS aangevul met etanol vir asynsuur bakterieë, M17 agar vir lactococci, asook Chlooramfenikol Glukose Agar (CGA) en aartappel Dekstrose Agar (PDA) vir gis. Die hoogste tellings verkry vir Omaere monsters 2 en 3, was met MRS+V wat gebruik word vir die groei van Leuconostoc spp. Vir die monsters 1, 4 en 5 is die hoogste waardes verkry op MRS+C wat gebruik word vir die groei van lactobacilli. Hierdie verskille tussen die monsters kan toegeskryf word aan die verskille in voorbereidingsmetodes van tradisionele suurmelkdranke. Na die isolasie en tel van die mikrobes in elke melkmonster, is die Harrison Skyfmetode gebruik om bakterieë en gis kolonies vir verdere toetse te kies. Die priemstukke 27f en R1492 is gebruik om 'n 1.5 kilobasis (kb) fragment van die 16S ribosomale RNA (rRNA) geen te amplifiseer van die gekose bakteriële kolonies met behulp van die polymerase-kettingreaksie (PKR). Die priemstukke ITS4 en ITS5 is gebruik om 'n 600 basispaar fragment van die interne getranskribeerde spasie van fungi ribosomale DNA (rDNA) te amplifiseer en NL1 en NL4 is gebruik om die D1 en D2 area te amplifiseer. Die gevolglike PKR produkte se basispaaropeenvolging is bepaal en in die NCBI databasis met behulp van die BLAST algoritme geïdentifiseer volgens die naaste familielid. Die melksuurbakterieë in Namibiese gefermenteerde melk, Omaere behoort aan die genus Lactobacillus, met die oorheersende spesie Lactobacillus plantarum (52%) en in mindere getalle Lactobacillus paracasei subsp. paracasei (12%), Lactobacillus paraplantarum (8%), Lactobacillus kefiri (8%), en Lactobacillus casei (2%). Die gis geïsoleer was Kazachstonia unispora voorheen bekend as Sacchromyces unisporus (9%), Saccharomyces cerevisiae (8%) en Candida pararugosa (2%). Suiwer kulture van die Lactobacillus spp. is gebruik om melk wat ingeënt is met Listeria monocytogenes en Escherichia coli te fermenteer. Hul interaksie is gemonitor met verloop van tyd en na 48 uur van fermentasie, is L. monocytogenes nie bespeur in melkmonsters wat gefermenteer is met Lactobacillus plantarum, Lactobacillus paraplantarum en Lactobacillus casei subsp. paracasei nie. In teenstelling, wanneer Lactobacillus kefiri ingeënt is saam met die twee voedselverwante patogene is die konsentrasie van die L. monocytogenes verminder met 4 log na 48 uur en die patogeen is nie opgespoor na 72 uur nie. In melk gefermenteer sonder die byvoeging van kulture, is die konsentrasie van L. monocytogenes net verminder met 2,8 log na 72 h van fermentasie. In die melk met Lactobacillus plantarum, Lactobacillus paraplantarum en Lactobacillus casei subsp. paracasei na 48 h van fermentasie, is die E. coli konsentrasie verminder met 4 log en na 72 h is geen E. coli bespeur nie. In teenstelling, fermentasie met Lactobacillus kefiri het na 48 h gelei tot 'n afname in die konsentrasie van 1 log en aan die einde van die 72 uur is die E. coli konsentrasie verminder met 1,7 log. In melk gefermenteer sonder die byvoeging van die suurselkulture, is die konsentrasie van E. coli slegs verminder met 1,6 log na 72 h van fermentasie. Die resultate wat verkry is in hierdie studie toon dat drie van die vier melksuurbakterieë-stamme wat geïsoleer is uit die Namibiese gefermenteeerde melk, Omaere, naamlik L. plantarum, L. paraplantarum, L. parcasaei subsp. paracasei, ‘n inhiberende effek teen die spesifieke voedselverwante patogene gehad het. Dus, na verdere karakterisering van die tipe antibakteriese middels wat geproduseer word deur hierdie melksuurbakterieë kan hulle oorweeg word as potensiële kandidate vir die ontwikkeling van suurselkulture wat gebruik kan word vir die produksie van mikrobiologiese veilige, kommersieël gefermenteerde melkprodukte. Maar die L. kefiri stam wat in hierdie studie geisoleer is, kan waarskynlik nie gebruik word as 'n suurselkultuur nie, aangesien dit langer neem om die voedselverwante patogene uit te skakel.

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