Thesis (MSc Food Sc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Maas is a traditional fermented milk drink of the indigenous people of Southern
Africa and can thus be used to uplift the nutritional status of the South African
population, especially for the lower income groups. Furthermore, the problem of
lactose intolerance among the Black population can also be addressed by the
consumption of Maas. The objective of this study was to screen mesophylic lactic
acid bacterial strains (25 in total) from the University of Stellenbosch Food Science
Culture Collection for suitable metabolite production and then to produce traditional
Maas with a starter culture combination that produces a distinctive acid and
traditional flavour.
The representative 25 single lactic acid starter strains were identified as
Lactococcus lactis subsp. leetis biovar diacetylactis (12 strains), L. leetis subsp.
leetis (four strains) and L. leetis subsp. cremoris (nine strains). These strains were
inoculated into pasteurised full cream milk and activated for 8 h at 22°C.
Pasteurised full cream milk was then inoculated with each of the activated starter
strains, incubated at 22°C for 16 h and assessed for acid production abilities (pH =
4.6) under controlled time-temperature conditions. The results of this study showed
that nine of the single strains, L. lactis subsp. leetis biovar diacetylactis (S1, S2, S3
and S5), L. teetis subsp. lactis (S13, S15 and S16) and two L. leetis subsp. cremoris
strains (S17 and S22), produced sufficient acid, rendering them suitable for the use
as starters in the production of traditional Maas. A pH range of 4.3 - 5.1 was
reached by the nine single strains after 16 h at 22°C.
Two-strain starter combinations were then formed by combining the most
suitable single L. leetis subsp. leetis biovar diacetylactis, L. lactis subsp. lactis and L.
lactis subsp. cremoris strains, respectively. From the data, it was concluded that
acceptable Maas could be produced with four two-strain combinations (S3S 17,
S3S22, S5S17 and S5S22). This selection was again based on suitable acid and
metabolite production, as well as on sensory evaluation of the final product. These
four two-strain combinations produced sufficient acid to reach a pH in the 4.6 - 4.8
range, and showed a high metabolite concentration for the most suitable compounds
and formed a thick, smooth and creamy body texture after 16 h at 22°C.
Three-strain combinations formed between the two-strain starter combinations
and L. leetis subsp. teetis strains (813, 815 and 816), were also evaluated. With
these combinations a lack of a pronounced Maas flavour was found. Thus, it was
decided to add aroma producing strains of the species Leuconostoc mesenteroides
subsp. dextranicum (strain L1) and L. mesenteroides subsp. citrovorum (strain L2) to
the three-strain combinations. Four culture combinations (A, B, C and D) were then
formed by combining the selected Leuconostoc strains (L1 and L2) with the most
suitable Lactococcus strains (83,817,813 and 822). These combinations produced
sufficient acid to reach the pH 4.5 - 4.6 range after 14 h at 22°C. Acetaldehyde was
the major flavour metabolite formed in the Maas made with these four combinations,
with concentrations ranging between 26.6 - 89.3 mg.l ̄ ¹, while other flavour
metabolites (ethanol, acetone, diacetyl and 2-butanone) were present at lower
concentrations. It was found that three of the four culture combinations (A, C and D)
were characterised by a superior, but delicate flavour and a typical characteristic
Maas body texture.
Fruit flavoured Maas was subsequently prepared with the three most suitable
culture combinations (A, C and D) using 11 flavours and a sensory evaluation
performed. The statistically evaluated data showed that the appearance,
smoothness, flavour intensity, sweetness and overall acceptability were influenced
by the type of fruit flavour and the culture combination. Fruit flavour 4 (banana) was
the most preferred flavour. The sensory panellists also indicated that the culture
combination C gave the best overall acceptability over a three week study period.
Data on the shelf-life study of natural unflavoured Maas, prepared with the
three culture combinations (A, C and D), showed that the Maas still had an
acceptable appearance, taste and good microbiological quality after 15 d at
refrigerated temperatures. / AFRIKAANSE OPSOMMING: Maas is 'n tradisionele gefermenteerde melkdrankie onder die inheemse bevolking
van Suid-Afrika en kan gebruik word om die voedingstatus van die Suid-Afrikaanse
bevolking te verhoog, veral vir die laer inkomste groepe. Bowendien, kan die
probleem van laktose intoleransie onder die Swart gemeenskap ook aangespreek
word deur die verbruik van Maas.
Die doel van hierdie studie was om enkelstam mesofiliese melksuur bakterieë
(25 in totaal) van die Universiteit van Stellenbosch Voedselwetenskap Kultuur
Versameling te ondersoek vir geskikte metaboliet produksie en tradisionele Maas
met 'n kenmerkende suurheid en tradisionele geur met 'n geskikte kultuur
kombinasie te produseer.
Die toonaangewende 25 enkelstamme is Lactococcus lactis subsp. leetis
biovar diacetylactis (12 stamme), L. lactis subsp. lactis (vier stamme) en L. lactis
subsp. cremoris (nege stamme). Hierdie stamme was in gepasteuriseerde volroom
melk geïnokuleer en geaktiveer vir 8 h teen 22°C. 'n Inokulum van die onderskeie
geaktiveerde stamme is hierna in gepasteuriseerde volroom melk geplaas, vir 16 h
teen 22°C geïnkubeer en hul vermoë om suur te produseer (pH = 4.6) onder
beheerde tyd-temperatuur kondisies is bepaal. Die resultaat van die studie het
aangedui dat nege enkelstamme, naamlik L. leetis subsp. lactis biovar diacetylactis
(S1, S2, S3 en S5), L. lactis subsp. leetis (S13, S15 en S16) en twee L. leetis subsp.
cremoris (S 17 en S22), geskikte suurheidsvlakke vir die produksie van Maas bereik
het. 'n pH vlak van 4.3 - 5.1 is na 16 h teen 22°C deur hierdie nege enkelstamme
bereik.
Twee-stam kombinasies is onderskeidelik gevorm tussen die geskikte enkel
L. lactis subsp lactis biovar diacetylactis, L. lactis subsp. lactis en L. lactis subsp.
cremoris stamme. Die gevolgtrekking gemaak uit die data, is dat aanvaarbare Maas
voorberei kan word met vier van die twee-stam kombinasies (S3S17, S3S22, S5S17
en S5S22) op grond van suurvorming, metaboliet produksie en sensoriese
evaluasie. Hierdie vier kombinasies het genoegsame suur geproduseer om 'n pH
vlak van 4.6 - 4.8 bereik, hoë metaboliet konsentrasies geproduseer en 'n dik,
gladde en romerige tekstuur aangeneem na 16 h teen 22°C.
Drie-stam kombinasies is gevorm tussen die onderskeie twee-stam
kombinasies en L. lactis subsp. lactis stamme (813,815 en 816) en ook geëvalueer.
Die tekort aan 'n skerp Maas geur in die drie-stam kombinasies het daartoe gelei dat
Leuconostoc mesenteroides subsp. dextranicum (stam L1) en L. mesenteroides
subsp. citrovorum (stam L2) bygevoeg is. Vier kultuur kombinasies (A, B, C en D) is
gevorm deur die geselekteerde Leuconostoc stamme (L1 en L2) te kombineer met
die mees gepaste Lactococcus stamme (83, 817, 813 en 822). Hierdie
kombinasies het genoegsame suur geproduseer wat 'n pH vlak van 4.5 - 4.6 na 14 h
teen 22°C bereik het. In die Maas wat met bovermelde kombinasies gemaak is, was
die asetaldehied die mees geproduseerde geur metaboliet teen konsentrasies van
26.6 - 89.3 mg.l ̄ ¹. Ander geur metaboliete (etanol, asetoon, diasetiel, 2-butanoon)
is in laer konsentrasies geproduseer. Daar is gevind dat drie uit die vier kultuur
kombinasies (A, C en D) 'n superieur, delikate geur wat 'n tipies karakteristiek van
die Maas gehad het.
Vrugte gegeurde Maas geproduseer met die drie kultuur kombinasies (A, C
en D) deur 11 geursels te gebruik, is sensories geëvalueer. Die statistiese
geëvalueerde data het getoon dat die voorkoms, gladheid, geur intensiteit, soetheid
en die algehele aanvaarbaarheid beïnvloed is deur die tipe vrugte geursels en die
kultuur kombinasies. Die vrugte geursel 4 (piesang) het voorkeur geniet. Die
sensoriese paneellede het ook aangedui dat kultuur kombinasie C die algehele
mees aanvaarbare Maas geproduseer het oor die studie periode van drie weke.
Data van die rakleeftyd van die natuurlike ongegeurde Maas wat geproduseer
is met die drie kultuur kombinasies (A, C en D) het aangedui dat die Maas na 15 d
by yskas temperatuur steeds 'n aanvaarbare voorkoms, smaak en goeie
mikrobiologiese kwaliteit gehad het.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51906 |
| Date | 03 1900 |
| Creators | Arendse, Garron Mark |
| Contributors | 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 | English |
| Type | Thesis |
| Format | 150 p. : ill. |
| Rights | Stellenbosch University |
Page generated in 0.0024 seconds