Thesis (MSc Food Sc )--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Kepi is a refreshing, fermented dairy beverage that differs from other fermented milk products
in that it is produced with a mixed microbial community which is confined to discrete grains.
These grains can be recovered as a solid matrix at the end of the fermentation and then be reutilised
as a starter to ferment the next batch of milk. The grain microbial community
consists of a symbiotic association of yeasts and lactic acid bacteria, but the overall
composition of the grains has not been completely elucidated. The microbes in the grains are
embedded in a protein-polysaccharide Kefiran matrix, which appears essential for grain
formation. The mechanism of grain formation is still not fully understood and it thus remains
undecided which organism is really responsible for the production of this proteinpolysaccharide
matrix. The aim of this study was to isolate, characterise and identify the
microbes present in Kefiran from mass cultured South African grains and then to evaluate
grain formation with these purified cultures isolated from Kefiran strings using a mass
cultivation process.
Sixteen strains of lactic acid bacteria and one yeast strain were isolated from Kefiran
strings produced during the mass cultivation of South African Kepi grains. API technology,
numerical clustering and DNA sequence comparisons were used to identify the purified
isolates. The isolates were grouped into seven clusters by numerical clustering and clustering
distance from selected reference and marker strains. The heterofermentative lactobacilli were
identified as Lactobacillus parakefiri and Lb. kefiri and the homofermentative strains as Lb.
delbrueckii ssp. bulgaricus, Lb. gallina rum, Lb. acidophilus and Lb. bavaricus. One isolate
was found to be a member of the genus Lactobacillus, but was not positively identified to
species level.
Cultures isolated from Kefiran were evaluated for ability to grain formation by
adding 1 x 109 cfu.ml:' bacteria and 1 x 108 cfu.ml' yeast to double pasteurised, full cream
milk during the mass cultivation process. It was found that the control and all the cultures in
double pasteurised milk showed grain accumulation indicating that other microbes were
present in pasteurised and double pasteurised milk which had an influence on the grain
forming ability. The cultures isolated from pasteurised and double pasteurised milk included
members of the species Pediococcus, Acinetobacter, Lactococcus laetis ssp. lactis, Candida
lipolytica, C. guilliermondii, Chryseobacterium meningosepticum, Pseudomonas putida and
four isolates of the Bacillus cereus group. It was found that these rod-shaped "milk isolates"
resulted in grain accumulation when inoculated into UHT milk and it was concluded that the
"milk isolates" did contribute to grain formation. These isolates were then combined with the Kefiran cultures and this resulted in grains very similar to the traditional Kepi grains. These
grains were made from Lb. gallinarum in double pasteurised milk as well with a combination
of Lb. gallinarum, Lb. acidophilus, Lb. kefiri, Lb. delbrueckii ssp. bulgaricus, Candida
lambica and Pseudomonas putida in URT milk. The grains were firm, elastic and did not
dissolve in water but kept their structure and were retained when sieved. An acceptable Kepi
beverage was produced from these grains.
From these typically traditional grain characteristics it was concluded that, even
though the microbial compositions were probably not the same, the general appearance was
similar to traditional grains and that it is thus possible to produce grains from pure single
strain Kefiran cultures and "milk isolates". Furthermore, it was possible to produce a Kepilike
beverage from these grains, which included similar characteristics as the traditional Kepi
beverage. / AFRIKAANSE OPSOMMING: Kepi is "n verfrissende, gefermenteerde suiweldrankie wat van ander gefermenteerde produkte
verskil in die opsig dat dit vervaardig word deur Kepi korrels in melk te inkubeer. Die Kepi
korrels kan aan die einde van die fermentasie herwin word en weer gebruik word om die
volgende lot melk te fermenteer. Die korrels bestaan uit "n simbiotiese samestelling van giste
en melksuurbakterieë, maar die presiese samestelling van die korrels is steeds onbekend. Die
mikro-organismes is vasgevang in "n proteïen-polisakkaried Kefiran matriks en die Kefiran
word as essensieel beskou vir korrelvorming. Die meganisme van korrelvorming bly steeds
onbekend en daar is nog nie tot "n gevolgtrekking gekom oor watter organisme die Kefiran
produseerder is nie. Die doel van die studie was om die mikro-organismes in Kefiran te
isoleer en te identifiseer deur Suid-Afrikaanse Kepi korrels te massa kweek. Hierdie mikroorganismes
was dan verder geëvalueer ten opsigte van korrel vorming.
Sestien melksuurbakterieë isolate en een gis isolaat is geïsoleer vanuit die Kefiran.
API tegnologie, numeriese groepering en DNA volgorde vergelykings was gebruik om die
isolate te identifiseer. Die isolate is in sewe groepe verdeel volgens numeriese groepering.
Die afstand van verwysings en merker organismes is ook in ag geneem. Die
heterofermentatiewe organismes is geïdentifiseer as Lactobacillus parakefiri en Lb. kefiri en
die heterofermentatiewe organismes as Lb. delbrueckii ssp. bulgaricus, Lb. gallina rum, Lb.
acidophilus en Lb. bavaricus. Een isolaat kon nie geïdentifiseer word tot op spesie vlak nie,
maar is verwant aan die genus Lactobacillus.
Hierdie geïsoleerde Kefiran kulture is geëvalueer ten op sigte van korrelvorming,
deur 1 x 109 kve.ml' van die bakterieë en 1 x 108 kve.ml' van die gis by dubbel
gepasteuriseerde volroom melk te voeg tydens die massakwekings proses. Die kontrole wat
geen bygevoegde kulture bevat nie, sowel as die wat wel bygevoegde kulture bevat, het korrel
vorming getoon. Laasgenoemde toon dat daar organismes teenwoordig is in gepasteuriseerde
en dubbel gepasteuriseerde melk wat "n rol kan speel tydens korrelvorming. Die kulture wat
geïsoleer is vanuit gepasteuriseerde en dubbel gepasteuriseerde melk, sluit in: Pediococcus,
Acinetobacter, Lactococcus laetis ssp. lactis, Candida lipolytica, C. guilliennondii,
Chryseobacterium menigosepticum, Pseudomonas putida en vier isolate van die Bacillus
cereus groep. Hierdie organismes wat uit melk geïsoleer is, het korrelvorming getoon in UHT
melk en die gevolgtrekking kan gemaak word dat die "melk organismes" wel "n rol speel
tydens korrel vorming. Hierdie "melk isolate" in kombinasie met die Kefiran kulture het
korrels tot gevolg gehad wat baie dieselfde was as tradisionele Kepi korrels. Laasgenoemde
korrels is gemaak deur Lb. gallina rum in dubbel gepasteuriseerde melk, sowel as deur "n kombinasie van Lb. gallina rum, Lb. acidophilus, Lb. kefiri, Lb. delbrueckii ssp. bulgaricus,
Candida lambica en Pseudomonas putida in UHT melk. Die korrels was stewig, elasties, het
nie opgelos in water nie en het hulle struktuur behou wanneer gesif.
Wanneer hierdie tipiese tradisionele korrels se eienskappe in ag geneem word, kan
die gevolgtrekking gemaak word dat alhoewel die mikrobiese samestelling van die korrels nie
dieselfde is as die tradisionele korrel nie, is die algemene voorkoms en eienskappe dieselfde
en dat dit wel moontlik is om korrels te produseer deur isolate geïsoleer vanuit Kefiran en
melk. Verder was dit moontlik om "n drankie te vervaardig met die korrels wat baie dieselfde
is as tradisionele Kepi.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53561 |
| Date | 03 1900 |
| Creators | Cronje, Marise Christine |
| Contributors | Britz, T. J., Witthuhn, R. C., Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science . |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 103 p. : ill. |
| Rights | Stellenbosch University |
Page generated in 0.0032 seconds