In Namibia, Omashikwa traditional fermented buttermilk made with the root of Omunkunzi (Boscia albitrunca) tree by local farmers is one of the most important rural food products. It provides nutrition, jobs and generates income for food security for the community. As a traditional fermented product, it is unusual as it has a viscous consistency and low syneresis. However, the quality of Omashikwa is inconsistent and is characterized by high acid taste, low pH, rancid flavour, root taste and smell and contains filth. In this research, the production process of Omashikwa, physico-chemical properties of the traditional and laboratory prepared Omashikwa and the role of the root of B. albitrunca tree in Omashikwa, viscosity, syneresis, microbiology and sensory properties were studied and compared in order to improve the quality of Omashikwa for wider community use and for poverty alleviation. Omashikwa was found to have a protein content of about 3.3%, fat 1.6%, moisture 90%, lactose 4.6%, ash 0.7%, total solids 8.7%, lactic acid 0.9% and a pH of 3.3 The quality of traditionally processed Omashikwa (TO) was compared with the laboratory processed Omashikwa (LO), which was made without the root. Traditional fermentation was carried out with raw milk and under rural conditions. After fermentation the milk was agitated vigorously to churn into butter, whereas LO was made with pasteurized (65ºC/30 min) and filtered milk, and cream was scooped off after fermentation instead of churning. LO had a significantly (p < 0.05) higher pH (4.44) compared to traditional Omashikwa (pH 3.25), lower acidity (0.68%) compared to 0.92% of TO. Fat content was higher in LO (2.44% fat) compared to 1.56% fat in TO. LO was free from filth and had higher viscosity (2.98 Pa.s) compared to 2.54 Pa.s and lower syneresis (14.4ml/24 ml) compared to 19.6ml/24ml of TO. It was found that extract from B. albitrunca root showed a low pH of 4.7 and exhibited bacterial inhibition properties on Total Plate Count Agar ring test. The root appear to specifically inhibit Escherichi coli, Staphylococcus aureus and Clostridium species. It also had a high content of soluble carbohydrates (hydrocolloids or gum) (19.4%). Significant difference (p < 0.05) in total aerobic counts was observed in TO of 6.62 log cfu/g compared to 8.62 log cfu/g of LO and lower lactic acid bacterial counts, 6.58 log cfu/g compared to 7.87 log cfu/g of LO. Probably the most affected microorganisms in TO were the non acid formers, as lower pH of TO and inhibitory compounds in Omunkunzi root could have reduced them. Coliforms, yeasts and moulds counts were not significantly different (p<0.05). No pathogenic bacteria were found in either product. The lactic acid bacteria identified belonged to the genera Lactobacillus (Lb.) (Weissella), Leuconostoc (Leuc.), Lactococus (Lact.) and Streptococcus (Str.) Twenty representative strains of LAB isolates were identified to species level; three belonged to the species Lb. delbrueckii subsp. lactis and two belonged to Lb. plantarum and two to Weissella confusa (former Lb. confuses). Three belonged to Str. salivarius thermophilus, three to Leuc. lactis, and two to Leuc. mesenteroides subsp. mesenteroides. Three belonged to Lact. lactis subsp. lactis and two belonged to Lact. lactis subsp. cremoris. Significant differences (p < 0.05) in descriptive and consumer sensory attributes scores were observed between traditional and laboratory Omashikwa. Sensory attributes scores of TO on the levels of syneresis was 3.4 compared to 2.9 for LO, filth 3.0 compared to 1.8 in LO, rancidity scores were 3.4 in TO compared to 1.8 in LO, and bitterness 4.2 in TO compared to 2.5 in LO. Aroma scores were 2.6 for TO and 4.2 for LO, viscosity 2.5 (TO) and 3.8 (LO) and texture 2.7 for TO compared to 4.2 for LO. There was an 80% preference score given to the laboratory Omashikwa by the young consumer panelists. The results of this study indicate justification of using B. albitrunca root in the processing of Omashiwa by the rural community to improve the quality of Omashikwa in terms of flavour, smell and consistency compared to other traditional fermented milk products and in the absence of modern technology. However, application of good manufacturing practices on unit operations, particularly heat treatment of milk prior to fermentation, use of lactic acid starter cultures, maintenance of good hygiene and sanitation including packaging, seem to be the effective methods to improve and sustain the quality and safety of traditional fermented buttermilk (Omashikwa) for a wider market and better price. Namibia Dairies Ltd, just like any other dairies in the region and elsewhere, manufactures buttermilk, a byproduct of butter that is fermented with mesophilic lactic acid cultures and branded as Omashikwa for the purpose of marketing. It has nothing to do with traditional Omashikwa as such; B. albitrunca root is not added and is processed by using modern industrial method. In addition, additives such as preservatives (potassium sorbate), stabilizers (pectin) and sugar are added and packed for distribution. This research project therefore investigated the processing technology, physico-chemical, microbiological, viscosity and sensory quality of traditional Omashikwa. The remedial measures to curb inconsistency and poor quality experienced in Omashikwa processed in Namibia were also investigated and scientific measures were proposed for production of quality Omashikwa for marketing to a wider community. Since laboratory processing method of Omashikwa gave a better quality product compared to traditional method in terms of microbiological quality, sensory attributes, viscosity, filth content, syneresis and general appearance, laboratory processing technique of processing Omashikwa is therefore recommended as an alternative and appropriate processing method for small scale production in the rural set up to improve the quality of Omashikwa. / Thesis (PhD)--University of Pretoria, 2010. / Food Science / unrestricted

Thesis (MSc Food Sc)--Stellenbosch University, 2013. / ENGLISH 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 106 cfu.ml-1), KCA + V for chambiko (1.8 x 105 cfu.ml-1), KCA + TTC for omashikwa and MRS + C for masse and chekapmkaika (6.2 x 106 and 2.0 x 103 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) 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. / AFRIKAANSE OPSOMMING: 'n Wye verskeidenheid tradisioneel en kommersieel gefermenteerde melk produkte word algeneem verbruik in verskeie lande van Sub-Sahara Afrika. Kommersieel gefermenteerde melk word geproduseer op groot skaal, deur deeglik bestuurde gestandardiseerde produksieprosesse en 'n beginkultuur word gebruik om fermentasie te inisieer. Tradisioneel gefermenteerde melk word tuis gemaak en fermentasie gebeur spontaan by kamertemperatuur. Melksuurbakterieë (MSB) is verantwoordelik vir melkfermentasie waartydens die bakterieë koolhidrate omskakel na melksuur, koolstofdioksied, alkohol en ander organiese sure. Asetaatsuurbakterieë (ASB), giste en miseliale fungi is ook al van gefermenteerde melk geïsoleer. In hierdie studie is die mikrobiese konsortium teenwoordig in drie soorte tradisioneel gefermenteerde melk, naamlik omashikwa van Namibië, masse van Mosambiek en chekapmkaika van Uganda en twee soorte kommersieel gefermenteerde melk, naamlik chambiko van Malawi en omaere van Namibië, geïsoleer en getel op ses verskillende selektiewe groeimedia insluitend MRS + C (spesifiek vir lactobacilli), KCA + TTC (spesifiek vir lactococci), KCA + V (spesifiek vir leuconostocs), MRS + E (spesifiek vir ASB), MEA (spesifiek vir miseliale fungi) en YPD (spesifiek vir giste). Geen betekenisvolle verskille is gevind tussen die mikrobiese tellings verkry vir die drie chambiko monsters nie, sowel as tussen die mikrobiese tellings verkry vir die twee omaere monsters, op elk van die selektiewe groeimedia, wat dui op lae monster variansie. Betekenisvolle verskille is gevind tussen die mikrobiese tellings verkry vir die drie omashikwa monsters op al ses selektiewe groeimedia. Betekenisvolle verskille is ook waargeneem tussen die mikrobiese tellings van die drie masse monsters en beide die chekapmkaika monsters op die selektiewe groeimedia. Daarbenewens is betekenisvolle verskille waargeneem tussen gemiddelde mikrobiese tellings verkry vir elke groeimedium tussen die masse en chekapmkaika, die chambiko en omaere asook toe die tradisionele en kommersiële melk produkte met mekaar vergelyk is. Volgens die gemiddelde mikrobiese tellings verkry op elk van die groeimedia selektief vir MSB, is die hoogste mikrobiese telling waargeneem op KCA + TTC medium vir omaere (2.3 x 106 kve.ml-1), KCA + V vir chambiko (1.8 x 105 kve.ml-1), KCA + TTC vir omashikwa en MRS + C vir masse en chekapmkaika (6.2 x 106 en 2.0 x 103 kve.ml-1, respektiewelik). Na die isolasie en tel van die mikrobes teenwoordig in elke melk is bakteriese isolate op die media selektief vir MSB en ASB verkry volgends die Harrison Disk metode. Hierdie isolate is geïdentifiseer deur amplifikasie van „n 1.5 kilobasis (kb) gedeelte van die 16S ribosomale RNS (rRNS) geen deur gebruik te maak van die polimerase kettingreaksie gevolg deur DNS klonering. Die isolate is geïdentifiseer deur die gekloneerde insetsels se volgordes te vergelyk met volgordes beskikbaar op die NCBI webwerf deur van die BLAST algoritme gebruik te maak en die naas verwante insetsel op te spoor. Die hoof MSB groep teenwoordig in die omaere was lactococci (94%), in chambiko en chekapmkaika was dit lactobacilli (30% en 45%, respektiewelik), in die omashikwa was dit enterococci (43%) en in die masse was dit leuconostocs (68%). Dieselfde mikrobiese spesies was teenwoordig op verskeie van die selektiewe groeimedia gebruik in hierdie studie. Lactococcus spp., Enterococcus spp. en Lactobacillus spp. is geïsoleer van MRS + C, KCA + TTC, KCA + V en MRS + E en Leuconostoc spp. is geïsoleer van MRS + C, MRS + E en KCA + V. Higiëniese standaarde tydens tradisionele melkfermentasie is dikwels swak en dus is mikrobiese kontaminante geïsoleer van die tradisionele melk produkte insluitend Acinetobacter johnsonii en Klebsiella pneumoniae van KCA + V, Mesorhizobium loti, Acinetobacter radioresistens, Escherichia coli, Staphylococcus spp., Kluyvera georgiana, Enterobacter spp. en Klebsiella oxytoca van KCA + TTC, Staphylococcus spp. van MRS + C en Bacillus spp. van MRS + E. Aangesien die media wat gebruik is vir die isolasie van die MSB en ASB in hierdie studie nie selektief was nie, is verdere identifikasie van die getelde mikrobes belangrik vir die identifikasie van die mikrobiese groepe teenwoordig in elke melk. Die data verkry in hierdie studie dui aan dat gefermenteerde melk produkte van Sub-Sahara Afrika betekenisvol van mekaar verskil in terme van mikrobiese getalle, mikrobiese diversiteit en die dominante mikrobiese groepe teenwoordig. Die mikrobiese diversiteit van die tradisioneel gefermenteerde melk produkte was meer divers as die mikrobiese diversiteit van die kommersieel gefermenteerde melk produkte. MSB spesies geïsoleer van hierdie tradisioneel gefermenteerde melk produkte kan gebruik word om nuwe beginkulture te ontwikkel en gevolglik kan nuwe kommersieel gefermenteerde suiwelprodukte met unieke aromas, smake en eienskappe geproduseer word.