Thesis (MSc Food Sc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Kefir is a fermented dairy beverage resulting from the fermentation of milk with
reusable Kefir grains. The grains consist of a complex combination of lactic acid
bacteria and yeasts in a symbiotic relationship, embedded in a polysaccharide
matrix called kefiran. Various problems are experienced during the
commercialisation of the ready-made Kefir beverage and, therefore, it is more
advantageous to market the grains, enabling the consumer to produce the
beverage at home. Kefir grains could be mass-cultured and then preserved by
Iyohilisation for successful long-term storage and easy distribution, during
commercialisation. The microbial balance of the Kefir grains changes during both
mass-culturing and freeze-drying, which will have an influence on the sensory
properties of the Kefir beverage produced. The aim of this study was the
optimisation of the production of Kefir from mass-cultured grains and from freezedried
mass-cultured grains respectively. The sensory characteristics of the
fermented beverages produced from these mass-cultured and preserved grains
were determined.
Mass-cultured Kefir grains were activated and Kefir produced using nine
methods with different activation times and temperatures, different grain:milk ratios
(36, 72 and 108 g grains.l⁻¹) and with different heat-treated milks (pasteurised,
double pasteerised and UHT). The best Kefir beverage was produced by
activation of the grains at 22°C for two successive 24 h incubation periods,
followed by Kefir production at 22°C for 18 h and a maturation period at 18°C for 6
h. The milk was replaced before every incubation period, excluding the maturation
period, and the fermentation vessel was swirled five times at the start of
fermentation and after 18 h. This method resulted in a sour beverage with a thick
consistency and the characteristic effervescence and flavour of Kefir. The optimal
grain:milk ratio was identified as 36 g grains.l⁻¹ and the best heat-treated milks for
the production of Kefir beverage were UHT and double pasteurised milk.
Mass-cultured Kefir grains were freeze-dried for 1, 2, 3 and 6 d and the
moisture loss determined. Freeze-dried grains were rehydrated for 1, 2, 6, 12 and
18 h to determine the optimal rehydration time. A sensory analysis was performed
to compare the properties of Kefir produced from mass-cultured grains (Me),
freeze-dried mass-cultured grains that were rehydrated and activated (FDRA) and activated mass-cultured grains that were freeze-dried and rehydrated (AFDR).
The chemical compositions of mass-cultured grains (MC), mass-cultured, freezedried
grains (MCFD), mass-cultured, freeze-dried grains that were rehydrated and
activated (FDRA) and activated mass-cultured grains that were freeze-dried and
rehydrated (AFDR), were also investigated. The optimum time to freeze-dry grains
was 2 d and to rehydrate freeze-dried gtains was 1 h. The sensory analysis
indicated that Kefir beverages prepared from FDRA and AFDR grains did not differ
significantly and were less fermented than Kefir produced from MC grains.
It was concluded that Kefir with excellent sensory characteristics can be
produced from mass-cultured grains. Freeze-drying is a better method to preserve
Kefir grains than freezing due to mass loss during freezing and easier distribution
and storage of freeze-dried grains. The supplementation of freeze-dried grains
with additional lactic acid bacteria and yeast isolates should be investigated. / AFRIKAANSE OPSOMMING: Kefir is 'n gefermenteerde suiwelproduk wat geproduseer word deur die
fermentasie van melk met herbruikbare Kefirkorrels. Die korrels bestaan uit 'n
komplekse kombinasie van melksuurbakterië en giste en is ingebed in 'n
polisakkaried matriks genaamd kefiran. Verskeie probleme word ondervind met
die kommersialisering van die klaar voorbereide Kefirdrankie en dit is meer
voordelig om die korrels te bemark. Dit sal die verbruiker daartoe in staat stel om
self Kefir tuis te produseer. Kefirkorrels kan in massa gekweek word en dan
gevriesdroog word om langtermyn storing en verspreiding te vergemaklik tydens
kommersialisering. Die spesifieke mikrobiese balans van die Kefirkorrels word
tydens massakweking en vriesdroging versteur. Dus sal hierdie twee prosesse 'n
invloed hê op die sensoriese eienskappe van die Kefir drankie geproduseer. Die
doel van hierdie studie was die optimisering van die produksie van Kefir vanaf
massagekweekte korrels en gevriesdroogde massagekweekte korrels. Die
sensoriese karakteristieke van die Kefir geproduseer met hierdie korrels is
ondersoek.
Massagekweekte Kefirkorrels is geaktifeer en Kefir is geproduseer met
nege verskillende metodes met variasies in die tyd en temperatuur kombinasies,
verskillende korrel:melk verhoudings (36, 72 en 108g korrels.l⁻¹) en verskillende
hittebehandelde melke (gepasteuriseerd, dubbel gepasteuriseer en UHT). Die
beste Kefirdrankie is geproduseer deur die aktivering van die korrels by 22°C vir
twee 24 h inkubasieperiodes, gevolg deur Kefir produksie by 22°C vir 18 uur en 'n
verouderingsperiode by 18°C vir 6 h. Die melk was voor elke inkubasieperiode
vervang, uitsluitende die verouderingsperiode. Die fermentasie houer is vyf maal
gedraai aan die begin van fermentasie en na 12 h. Hierdie metode het gelei tot 'n
drankie wat suur was met 'n dik konsistensie en die karakteristieke vonkeling en
geur van Kefir. Die optimale korrel:melk ratio is geidentifiseer as 36 9 korrels.l⁻¹ en
die verkieslike hittebehandelde melke is dubbel gepasteuriseerde en UHT melk.
Massagekweekte Kefirkorrels was vir 1, 2, 3 en 6 dae gévriesdroog en die
massaverlies is bepaal. Gevriesdroog korrels is gerehidreer vir 1, 2, 6, 12 en 18 h
om die optimale rehidrasietyd te bepaal. 'n Sensoriese analise is uitgevoer om die
eienskappe te vergelyk van Kefir geproduseer van massagekweekte korrels (MC),
gevriesdroogde massagekweekte korrels wat gerehidreer en geaktiveer is (FDRA)
en geaktiveerde massagekweekte korrels wat gevriesdroog en gerehidreed is (AFDR). Die chemiese samestelling van massagekweekte korrels (MC),
massagekweekte, gevriesdroogde korrels (MCFD), massagekweekte,
gevriesdroogde korrels wat gerehidreer en geaktiveer is (FDRA) en geaktiveerde
massagekweekte korrels wat gevriesdroog en gerehidreer is (AFDR), is bepaal.
Die optimum tydperk vir vriesdroging van korrels was 2 d en vir rehidrasie van
gevriesdroogde korrels was 1 h. Die sensoriese analise het aangedui dat Kefir
wat van FDRA en AFDR korrels geproduseer is, nie betekenisvol van mekaar
verskil het nie, maar minder gefennenteerd was as Kefir wat van Me korrels
geproduseer is.
Die gevolgtrekking is gemaak dat 'n Kefirdrankie met uitstekende
eienskappe geproduseer kan word met massagekweekte korrels. Vriesdroging is
'n beter metode as bevriesing om Kefirkorrels te preserveer a.g.v die ver1iesvan
massa tydens bevriesing en die vergemakliking van vervoer en verspreiding van
gevriesdroogde korrels. Die aanvulling van gevriesdroogde korrels met
addisionele melksuurbakterieêen giste moet nog ondersoek word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50004 |
| Date | 12 1900 |
| Creators | Latsky, Anneline |
| Contributors | Witthuhn, R. C., Britz, T. J., 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 | 93 pages : illustrations |
| Rights | Stellenbosch University |
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