|dc.description.abstract||Variability of quality parameters between Australian wheat varieties grown in different locations and seasons causes difficulties in delivering uniform grains with consistent quality to local and international markets and in predicting functional performance in food processing and human nutrition. The objective of this thesis is to assess the relative contributions of genotype (cultivar), environment and their interactions to variability of quality traits such as test weight, grain protein content, β-glucan, fructans, total starch content, total arabinoxylans (T-AX), water extractable arabinoxylans (WE-AX), water un-extractable arabinoxylans (WU-AX), free, conjugated, bound and total phenolic acids.
Three commercial Australian wheat (Triticum aestivum L.) varieties (Gregory, Janz and Peake) grown in 13 different geographic regions of Australia were used to examine wheat whole meal quality parameters. The grain samples were obtained from the National Variety Trials (NVT) conducted by the Australian Grains Research and Development Corporation (GRDC).
Total starch, fructans, β-glucan and total T-AX were determined using Megazyme assay kits (Spectrophotometric analysis), arabinoxylan fractions were analysed using a spectrophotometric technique based on the orcinol-HCl method. Phenolic acid fractions were extracted using liquid nitrogen and analysed using a spectrophotometric technique based on Folin-Ciocalteau reagent and by high pressure liquid chromatography (HPLC) with measurements being made for individual phenolic acids in each fraction. Grain protein content and test weight were provided by NVT. The functionality of hard, soft and waxy wheat starch varieties, with and without the additions of WE-AX, was studied by a series of tests including thermal properties using Differential Scanning Calorimetry (DSC) and pasting properties using the Rapid Visco Analyser (RVA).
All parameters measured and meteorological factors before and after flowering (temperature, rainfall and daily solar exposure) were analysed by statistical methods to deduce which factors influenced grain quality characteristics. The soil characteristics and fertilizers used were not available for all the locations, and because of the large number of missing values which could potentially bias the results of the correlation and regression analysis, these factors were not included in the analysis. Variability of the quality traits and starch functionality was described in terms of the influence of genotype, environmental factors and their interactions.
This study showed that genotype contributed significantly to variability of all the traits tested. Genotype strongly influenced T-AX and WU-AX. Arabinoxylans levels were shown to vary among wheat genotypes. The average ratio of arabinose to xylose was 0.6 for each of the three varieties and this might indicate similarities of the substitution pattern of the xylose backbone by arabinose residues of the three cultivars.
Growth environment was the main contributor to the variability of total starch, grain protein, WE-AX, β-glucan and test weight. Growing conditions had strong significant correlations (α = 0.01 and α = 0.001) with wheat grain protein, total starch, WE-AX, fructans and test weight. Growth conditions had moderately significant correlations (α = 0.05) with T-AX and WU-AX, while variability in WE-AX had an inverse and stronger correlations (α = 0.01 or α = 0.001) with the growing conditions compared to total AX and WU-AX. Arabinoxylan fractions (WE-AX and WU-AX) differed in solubility and in their variability due to environmental factors. These differences might be related to their different molecular weights, the incomplete cross-linking of WE-AX with other components, and to the loose binding of WE-AX to the cell wall surface.
Genotype influenced all of the pasting properties of Gregory, Janz and Peake starches. The effects of growth conditions on starch pasting properties were significant on peak, breakdown and setback viscosities and pasting temperatures. Environmental temperature (minimum temperature days at < 0 ̊C) had negative correlations with pasting viscosities whereas total rainfall and average rainfall after flowering had positive correlations with setback viscosity.
With regards to the addition of WE-AX to several wheat starches (Kukri, QAL2000 and QA-WX-83), the RVA pasting viscosities (peak, trough, final and setback) were decreased, whereas the DSC onset and peak temperatures were increased, but the change in enthalpy was decreased. The pasting and the thermal profiles of Kukri, QAL2000, and QA-WX-83 with WE-AX, have shown that WE-AX compete with starch granules for water.
This study showed that phenolic acids are very variable compounds. The contents of free, conjugated, bound and total phenolic acids of whole meal flour from the same cultivar (Gregory, Janz and Peake) were different between locations and seasons. Cultivar was the main factor influencing free and bound phenolics of Gregory, Janz and Peake samples, which were grown in the 2010 season. Interactions between the genotype and the environment contributed strongly to conjugated and total phenolics. However, when two seasons were involved (2010 and 2012), genotype and all environmental factors had significant contributions to variability of soluble, conjugated, bound and total phenolic acids of Gregory and Janz samples (Peake was not planted in the 2012 season). Gregory cultivar had the highest amount of total phenolics in 2010 and 2012 seasons and its pattern did not change over the two seasons (the mean free phenolic concentrations tended to be consistently higher than bound and conjugated phenolics). Weather conditions in the 2010 season (average temperature before flowering, rainfall and solar exposure before and after flowering) influenced strongly conjugated and total phenolics. Weather conditions influenced all of the phenolic acids in the two seasons involved, 2010 and 2012.
Benzoic acid derivatives (C6-C1) and cinnamic acid derivatives (C6-C3) followed different trends. The conjugated, bound, and free forms of 4-hydroxybenzoic acid, vanillic acid, syringic acid and sinapic acid all followed a similar trend with respect to growth location. The concentrations were highest in the conjugated form, less in the bound form, and least in the free form at all seven locations. On the other hand, the conjugated, bound, and free forms of p-coumaric acid, caffeic acid and ferulic acid followed a consistently different trend to the other four phenolic acids with respect to location. The concentrations were highest in the bound form, less in the conjugated form, and least in the free form at all seven locations.
In conclusion, this study showed that genotype, environment and their interactions influenced grain quality parameters. Both genotype and environmental factors influenced pasting properties of starch. Genotype was the main influencing factor to the variability of T-AX and WU-AX. WE-AX competed with Kukri, QAL2000 and QA-WX-83 starches for water and influenced RVA and DSC parameters. Genotype and all environmental factors contributed significantly to the variability of phenolic acids in wholemeal flour.||en_AU|