In order to study the decrease of yogurt fermentation time, the effects of a wide range of
supplements on yogurt fermentation time were evaluated. YE was identified as the only
supplement which showed potential. Unfortunately it resulted in a product with an
unacceptable flavour. It was therefore important to identify and isolate the specific
component responsible for the decrease in yogurt fermentation time.
YE was fractionated with size exclusion chromatography and it was subsequently
determined that the accelerating fraction had a low molecular weight.
It was important to establish whether the accelerating component was of mineral, vitamin or
amino acid origin. Three cocktails containing the most common minerals, vitamins and
amino acids were prepared and their respective effects on yogurt fermentation were
determined. Results indicated that when compared to the respective controls, no decrease in
fermentation time was observed with the mineral and vitamin cocktails. A decrease in
fermentation time was observed with the amino acid cocktail, indicating that the accelerating
component present in YE was of amino acid origin. It was however not clear whether it was
a single amino acid or a peptide.
The accelerating fraction was further analysed by SDS-PAGE and due to no visible bands in
the respective region (<1kDa), it could not be analysed with mass spectrometry. The fraction
obtained directly after size exclusion chromatography was however analysed by using mass
spectrometry in order to determine the total amino acid content of the accelerating fraction
after which it was evident that the fraction containing the accelerant contained an abundance
of peptides.
The individual effects of the 17 identified amino acids were determined in respective yogurt
fermentations. Results indicated that no single amino acid was responsible for the decrease
in yogurt fermentation time. Although a combination of the 17 amino acids in one
fermentation run resulted in a decrease in fermentation time in comparison to
unsupplemented yogurt, the decrease was not as considerable as that of the accelerating
fraction obtained after size exclusion chromatography. Due to the fact that it was not practical to evaluate the effect of all possible combinations of
the 17 amino acids, the combinations that were evaluated were based on literature reports
on stimulation of Streptococcus thermophilus growth. Focus was placed on the growth of
Streptococcus thermophilus due to this organism being the growth limiting organism
between the two starter organisms used for yogurt fermentation. None of the evaluated
amino acid combinations decreased yogurt fermentation time, and it was therefore
concluded that the accelerating component was a peptide and not a free amino acid.
In order to establish the mechanism of acceleration of the isolated YE fraction, it was
important to determine whether the addition of YE to milk increased the rate of starter
bacteria growth or whether it completed the growth requirements of starter bacteria. The
latter could either result in earlier initiation of lactic acid production or in increased levels of
lactic acid production. Results indicated that YE had no effect on the total growth rate of the
starter bacteria. However, when examining the effect on the respective bacteria individually,
it became clear that YE increased Streptococcus thermophilus cell numbers in comparison
to the unsupplemented control. Using resazurin, it seems YE increased the metabolic rate of
the starter bacteria.
Although supplementation of yogurt with YE did not influence combined starter bacteria
growth, it influenced lactic acid production. The addition of YE to yogurt resulted in increased
lactic acid levels as well as an increase in lactic acid production rate. Lactic acid was also
initiated earlier in the fermentation process, resulting in higher lactic acid levels in
comparison to unsupplemented yogurt.
It was therefore evident from this study that YE did not provide nutrients that are not already
present in milk, but rather provided nutrients in a readily available form at the beginning of
the yogurt fermentation process resulting in the reduction of the lag phase of lactic acid
production.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-08202014-124636 |
| Date | 20 August 2014 |
| Creators | Smith, Esti-Andrine |
| Contributors | Dr M de Wit, Prof G Osthoff, Dr J Myburgh |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-08202014-124636/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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