Browsing by Author "Kleyn, Megan Elizabeth"

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    Influence of waxy wheat flour blends on dough and bread baking quality as well as shelf life
    (Stellenbosch : Stellenbosch University, 2018-03) Kleyn, Megan Elizabeth; Manley, Marena; Du Plessis, Anton; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Waxy wheats are a naturally occurring genetic mutation of the hexaploid bread wheat Triticum aestivum. They contain only amylopectin starch due to the absence of the protein responsible for producing amylose, called granule bound starch synthase (GBSS). The amylopectin content retards starch retrogradation as amylopectin retrogrades more slowly than amylose. This can be utilised to increase the shelf life of bread by slowing down the staling process in which starch retrogradation is involved. One hundred percent waxy wheat cannot be used to make bread because of a resulting undesirable loaf appearance. Blends of waxy wheat and non-waxy wheats were thus used to create a loaf of bread which not only had an extended shelf life but also a desirable appearance. The starch granule morphology and percentage crystallinity of starch isolated from four waxy wheat lines (375, 376, 377 and 378), was determined using a scanning electron microscope and X-ray diffraction respectively. A non-waxy wheat control was used. No differences were seen in granule size and morphology between the lines and the control but more B-type granules were observed in control. The control was found to have an unusually high percentage crystallinity (36.5%) but was still lower than, or equal to, the waxy wheat lines (36.5 – 38%). Flour of each line was blended with the control in ratios of 10, 15, 20 and 25% waxy wheat to non-waxy wheat. Pasting properties were determined by the Rapid Visco Analyser (RVA). Blends of lines 375, 376 and 377 were found to have a lower peak viscosity, a faster peak time and a lower final viscosity than the control, while line 378 was similar in values to the control. No significant differences were seen between the blends and the control for the arrival time, water absorption, and stability as determined by the Farinograph. Likewise, no significant differences were seen for the peak time, peak height and tail height determined by the Mixograph between all blends and the control. Biaxial extension of the dough from each blend using the Alveograph showed no significant differences from the control for the P, L, P/L and W parameters. The blends were baked into loaves of bread to determine final loaf quality and shelf life. The C-Cell showed no significant differences for the cell and hole number, cell area and slice brightness between the blends and control. Lines 375 and 377 had the highest percentage concavity and therefore the worst appearance. Line 376 and 378 had the best appearance with the highest amount of waxy wheat. The texture analyser showed that waxy wheats create a softer initial loaf. On day six, only blends from line 376 successfully decreased the firmness compared to the control. The addition of up to 25% waxy wheats to non-waxy wheats marginally affects the processing properties of dough but negatively affects the outward appearance of bread. Bread baked with blends of 20 – 25% of line 376 had an improved shelf life, whilst still being visually appealing.