Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Kepi is a refreshing, fermented dairy beverage that has been consumed for
centuries and is traditionally made by incubating Kepi grains in milk. The Kepi
grain is a complex starter culture consisting of a variety of lactic acid bacteria and
yeasts. The successful marketing of the grains requires the effective preservation
of the microbes present in the grains as well as an appropriate packaging that will
retain the acidification activity of the preserved grains over an extended period of
time. The aim of this study was to evaluate different preservation techniques and
packaging materials in terms of their respective abilities to retain grain viability and
activity over an extended storage period. Four different preservation techniques
(freezing at -18°C, refrigeration at 4°C, air-drying and Iyophilisation) and three
packaging materials including a low density polyethylene film (LOPE), an oriented
polyester film (OPET) and a metallised oriented polyester film (MOPET), were
evaluated.
Activity tests were used to evaluate the impact of the preservation
techniques in terms of the retainment of the acidification activity of the preserved
grains, and the storage potential of the preserved and packaged grains. The
activity tests included changes in pH, %TA, lactic acid production and lactose and
volatile compound content over an 18 h fermentation period. In addition, the
microbial viability of the packaged Iyophilised grains after two months of storage,
was also investigated. Frozen and refrigerated grains showed the best retainment
of the acidification activity over a 10-month storage period. Air-drying and
Iyophilisation showed a good retention of the activity up to three months of
storage, but the application of these techniques both resulted in a retarded initial
acidification activity. After 10 months of storage, the air-dried and Iyophilised
grains showed only a low acidification activity. No volatile compounds could be
detected during the course of the fermentation period, due to the relative short
fermentation period of 18 h.
Overall, the best retainment of the fermentation activity was given by the
LOPE and the OPET packaging films. However, the storage period had a
considerable influence on the retention of the activity of the packaged Iyophilised grains. The viability study of the Iyophilised packaged Kepi grains after two
months of storage showed leuconostocs and lactobacilli to be the prevalent
microbes in the grains. Low microbial counts were obtained from the lactococciselecting
medium for all three of the differently packaged Kepi grains, whereas no
growth was observed on the media that selected for the propionibacteria and
yeasts. The OPET packaging film provided the best preservation of the microbial
composition.
It was, therefore, concluded that all four preservation techniques would be
suitable for the preservation of Kepi grains and the subsequent storage at room
temperature for three months. However, for storage periods of 10 months or
longer the use of freezing and refrigeration are recommended as most suitable
preservation techniques. All three of the packaging materials proved to be
suitable for the packaging and storage of the Iyophilised Kepi grains for periods of
up to one month. However, for storage periods of two months or longer, the use of
the OPET film for the packaging and retainment of the acidification activity of the
Iyophilised grains, can be recommended. / AFRIKAANSE OPSOMMING: Kepi is 'n eeu-oue verfrissende, gefermenteerde suiweldrankie wat tradisioneel
vervaardig word deur Kepikorrels in melk te inkubeer. Hierdie Kepikorrels bestaan
uit 'n komplekse samestelling van hoofsaaklik melksuurbakteriee en giste. Die
effektiewe preservering en verpakking van die korrels is belangrike voorvereistes
vir die suksesvolle bemarking daarvan. Dis belangrik dat die preserverinq en die
verpakking van die korrels 'n positiewe bydrae sal lewer tot die behoud van die
fermentasie-aktiwiteit van die mikrobes in die korrels oar 'n verlengde
opbergingsperiode. Die doel van hierdie studie was om die opbergingspotensiaal
van verskillend gepreserveerde en -verpakte Kepikorrels te evalueer in terme van
die behoud van die lewensvatbaarheid en fermentasie-aktiwiteit van die
samestellende mikrobes. Vier verskillende preserveringstegnieke (bevriesing by
-18°C, verkoeling by 4°C, lugdroging en vriesdroging) en drie verskillende tipes
verpakkingsmateriale, nl. 'n "low density polyethylene film" (LOPE), 'n "oriented
polyester film" (OPET) en 'n "metallised oriented polyester film" (MOPET) was
qeevalueer.
Aktiwiteitstoetsing was gebruik om die impak van die verskillende
preserveringstegnieke en die verpakkingsmateriale op die behoud van die
fermentasie-aktiwiteit van die Kepikorrels te ondersoek. Die verskillende
aktiwitieitstoetse wat gedoen is, het die meting van die verandering in pH, %TA,
melksuur- en laktosekonsentrasie oor 'n fermentasieperiode van 18 h ingesluit.
Tesame met die aktiwitietstoetsing IS die lewensvatbaarheid van die
gevriesdroogde, verpakte Kepikorrels na twee maande van opberging ook
ondersoek. Die bevrore en verkoelde Kepikorrels het die beste behoud van
aktiwitiet na 'n 10-maande opbergingsperiode getoon. Die gelugdroogde en
gevriesdroogde korrels het 'n goeie behoud van aktiwiteit getoon vir 'n
opbergingstydperk van tot drie maande, maar beide die lugdroging- en
vriesdrogingstegnieke het 'n aanvanklik vertraagde fermentasie-aktiwitieit getoon.
Na 'n : opbergingsperiode van 10 maande het beide die gelugdroogde en
gevriesdroogde korrels egter 'n lae fermentasie-aktiwiteit getoon. As gevolg van 'n relatiewe kort fermentasieperiode van 18 h kon geen vlugtige komponente in die
Kepimonsters gevind word nie.
Die LDPE- en OPET-verpakkingsmateriale het die beste behoud van die
fermentasie-aktiwiteit van die gevriesdroogde korrels getoon. Die
opbergingsperiode het egter 'n aansienlike impak op die aktiwitietsbehoud van die
korrels gehad. Die lewensvatbaarheidstudie het aangetoon dat Leuconostoc- en
Lactobacillus-spesies die oorheersende mikrobes in die verpakte, gevriesdroogde
Kepikorrels na 'n opbergingsperiode van twee maande was. Lae mikrobiese
tellings vir al drie van die verpakkingsmateriale was gevind op die Lactococcusselekterende
medium, en geen mikrobegroei kon op die giste- en
propionibakteriee-selekteringsmedium waargeneem word nie. Die beste behoud
van die mikrobiese samestelling in die verpakte, gevriesdroogde Kepikorrels was
gevind vir die OPET-verpakkingsmateriaal.
Die gevolgtrekking kan gemaak word dat al vier die preserveringstegnieke
geskik is vir die preservering van die Kepikorrels en die daaropvolgende opberging
van drie maande by kamertemperatuur. Vir opbergingsperiodes van 10 maande
en langer word die gebruik van bevriesing en verkoeling aanbeveel as die mees
geskikte preserveringstegnieke. AI drie verpakkingsmateriale kan gebruik word vir
die verpakking en opberging van gevriesdroogde Kepikorrels vir 'n tydperk van
een maand. Indien 'n opbergingsperiode van twee maande of langer verlang
word, word die OPET-verpakkingsmateriaal aanbeveel vir die suksesvolle behoud
van die fermentasie-aktiwiteit van die Kepikorrels.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52306 |
| Date | 12 1900 |
| Creators | Cilliers, Annamie |
| 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 | Unknown |
| Type | Thesis |
| Format | 105 p. |
| Rights | Stellenbosch University |
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