Thesis (MSc Food Sc)--University of Stellenbosch, 2011. / Includes bibliography. / ENGLISH ABSTRACT: Maize is an important crop for both human and animal consumption. Maize kernel texture
(kernel hardness) is an important quality trait for many sectors in the South African maize
industry, where a harder texture is desired. Both total protein content and the main storage
proteins, zein, have been associated with kernel texture. The zein profiles of South African
white maize hybrids, from a breeding program, grown at three localities together with their
respective inbred parent lines were evaluated to determine the difference in zein expression.
For only the hybrids, total protein content, zein content and degree of hardness (kernel texture)
was determined to establish possible relationships.
Zein consists of four main classes, α-, β-, γ-, and δ-zein, which can further be divided into
sub-classes. Zein was characterised using matrix-assisted laser desorption ionisation time-offlight
mass spectrometry (MALDI-TOF MS) after optimisation of the zein extraction and matrix
preparation procedures. Two matrices [2-(4-hydroxyphenylazo)benzoic acid (HABA) and α-
cyano-4-hydroxy-cinammic acid (CHCA)] and three pH levels (<1.5, 1.7 and 2.9) for matrix
solutions were investigated. Two solvent concentrations (50% and 70% acetonitrile (ACN) were
also investigated. Parallel to this investigation, a zein extraction procedure was optimised. Zein
was extracted from non-defatted (NDF) and defatted (DF) maize meal at ambient temperature
and 60°C and meal with different particle size distributions. Particle size of maize meal did not
influence the quality of spectra. Regardless of matrix conditions used, zein extracted at 60°C
from NDF meal produced spectra with a low signal-to-noise (S/N) ratio. When only HABA was
included (pH<1.5), not all γ-zein sub-classes were observed. This was also true for zein
extracted at ambient temperature from NDF and DF meal. Good S/N ratios for all zein classes
were obtained when zein was extracted from NDF meal at ambient temperature using a matrix
solution containing both matrices in 70% ACN at pH 2.9. MALDI-TOF MS provided accurate
detection and good profile resolution for zein characterisation. Spectral profiles of hybrids were
a combination of their respective inbred parent lines.
Zein proteins were quantified using reverse-phase high performance liquid chromatography
(RP-HPLC). Total protein content was determined and kernel texture assessed using a particle
size (PSI) method. Significant (P<0.01) differences were observed for total protein content and
degree of hardness between certain hybrids as well as average values for localities.
Correlations and principal component analysis indicated that hybrids with a higher protein and
total zein content had a harder kernel texture. The β- and γ-zein contents also correlated
positively with kernel hardness. However, when expressed as percentage of total zein the
opposite was observed. Collectively the α-zeins and most individual α-zeins correlated positively
with hardness. Scanning electron microscopy micrographs showed differences between the floury
endosperm of harder and softer maize kernels; illustrating starch types (amylose and
amylopectin) should also be analysed in future hardness studies.
The correlations obtained were not strong (r<0.6) and the variation explained by first two
principal components was low. Other maize constituents, more hardness measurements should
be considered in future studies to improve this. / AFRIKAANSE OPSOMMING: Mielies is a belangrike gewas vir beide mens- en dierlike inname. Mieliepittekstuur (pithardheid)
is ‘n belangrike kwaliteitseienskap vir baie sektore in die Suid Afrikaanse mielieindustrie, waar ‘n
harder tekstuur verlang word. Beide totale proteïeninhoud en die hoof opbergingsproteïen, zein,
is al geassosieer met pittekstuur. Die zein profiele van Suid- Afrikaanse witmielie basters, van ‘n
teel program, wat by drie lokaliteite verbou is sowel as hul onderskeie ingeteelde ouerlyne is geevalueer
om verskille in zein uitdrukking te bepaal. Die totale proteïeninhoud, zeininhoud en
graad van hardheid is bepaal om verhoudings vas te stel.
Zein bestaan uit vier hoof klasse, α-, β-, γ-, en δ-zein, wat verder onderverdeel word in subklasse.
Zein is gekarakteriseer met matriks-ondersteunende laser desorpsie ionisasie tyd-vanvlug
massa spektrometrie (MBLDI-TVV MS) na die zein ekstraksie en matriks
voorbereidingprosedures geoptimaliseer is. Twee matrikse [2-(4-hydroksiephenylazo)benzoë
suur (HABA) en α-cyano-4-hydroksie-kaneelsuur (CHCA)] en drie pH vlakke (<1.5, 1.7 and 2.9)
vir matriksoplossings was ondersoek. Twee oplossingkonsentrasies [50% and 70% asetonitriel
(ACN)] is ook ondersoek. Zein ekstraksie kondisies is ook geoptimiseer. Zein is geëkstraheer
van nie-ontvette (NOV) en ontvette (OV) mieliemeel by omgewings temperatuur en 60°C. Die
partikelgrootte van die mieliemeel het nie die kwaliteit van spektra beïnvloed nie. Ongeag watter
matrikskondisies gebruik is het zein wat van NGV meel by 60°C ge-ekstraheer is, spektra met ‘n
lae sein-tot-geraas (S/G) verhouding geproduseer. As die HABA alleenlik gebruik (by pH<1.5)
is, is nie alle γ-zein klasse waargeneem nie. Dit was ook waar vir zein wat by omgewings
temperatuur van NGV en OV mieliemeel ge-ekstraheer is. Goeie S/G verhoudings is
waargeneem met zein, ge-ekstraheer van NGV mieliemeel by omringende temperatuur, met die
bebruik van beide matrikse in 70% ACN by pH 2.9. (MBLDI-TVV MS) het akkurate en goeie
resolusie van profiele vir zein karateriseering verksaf. Spektrale profiele van basters was ’n
kombinasie van hul onderskeie ouer lyne.
Zeinproteïene is met omgekeerde-fase hoë prestasie vloeistofchromatografie
gekwantifiseer. Totale proteïeninhoud is bepaal en die hardheidsgraad was bepaal met ‘n
partikelgroote indeks (PGI) metode. Beduidende verskille tussen proteïeninhoud en
hardheidsgraad is waargeneem tussen sekere basters sowel as gemiddelde waardes by die
verskeie lokalieteite. Korrelasies en hoofkomponent analise het aangedui dat basters met ‘n
hoër proteïeninhoud en totale zein ‘n harder tekstuur gehad het. Die β- en γ-zeininhoud het ook
positief gekorreleer met hardheid. Alhoewel, wanneer die proteïene as persentasie van totale
zein uitgedruk is, is die teenoorgestelde waargeneem. Gesamentelik het α-zein asook die
meeste indivduele α-zeins positief gekorreleer met hardheid.
Skandeer elektron mikroskopie mikrograwe het verskille tussen die meelerige endosperm
van harder en sagter pitte aangedui; meer proteïenliggame was aanwesig in die harder pitte en die stysel was digter gepak. Dus moet stysel tipes ook in ag geneem word in toekomstige
hardheidsstudies.
Korrelasies wat verkry is, was nie hoog (r<0.6) nie en die variasie verduidelik deur die
eerste twee hoofkomponente was laag. Ander miielie samestellende dele as ook meer
hardheidsmetings moet in toekomstige studies in ag geneem word om dit te verbeter.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6784 |
| Date | 03 1900 |
| Creators | O'Kennedy, Kim |
| Contributors | Manley, Marena, Fox, Glen, University of Stellenbosch. Faculty of AgriSciences. Dept. of Food Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 140 p. : ill. |
| Rights | University of Stellenbosch |
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