Please read the abstract in the section 00front of this document / Thesis (PhD (Food Science))--University of Pretoria, 2006. / Food Science / unrestricted

Bread flour quality, which is directly related bread quality, varies from time to time. It is therefore almost impossible to obtain bread with consistent quality without determining the flour's suitability for bread-making and the addition of bread improvers. Rheological tests such as the farinograph and the mixograph which are commonly used by bakeries to predict flour quality are empirical in nature which makes fundamental interpretation of the results difficult. The stress relaxation test, a more fundamental rheological test, was used in combination with the mixograph to determine if the stress relaxation test can provide additional information to the mixograph on prediction of the effect of ascorbic acid and DATEM on bread-making quality of three different flour samples. In this test, an optimally developed ball of dough was compressed between parallel plates of a TA-XT2 texture analyser. The 20 g dough was compressed to a load of 1.5 N and thereafter allowed to relax at constant deformation. The relaxation time (RT) was recorded as time taken for the compression force to decay to a force of 0.65 N. Longer RT indicated better flour quality. RT was compared with the mixograph peak time and peak height as predictors of the effect of ascorbic acid and DATEM on bread quality. Test bakes were carried out, and concentrations of ascorbic acid and DATEM were varied as in the stress relaxation test and the mixograph test. At the various stages of the baking process several dough and bread properties were assessed subjectively and scored according to a standardised scoring system. The mixograph was successful in characterising untreated flours in terms of bread-making quality and the stress relaxation test did not provide additional information in this regard. The mixograph was better able to predict the effect of improvers on the stronger Lelie while the stress relaxation test was better at predicting improver effect (especially of DATEM) on the weaker flours, Tiger and Silver Queen. The mixograph predicted the improving effect of DATEM on Tiger and Silver Queen up to a peak, followed by no further improvement. The stress relaxation test predicted improvement beyond the peak, and this continued improvement was observed in the test bake and strong correlation (p<O.05) was found between effect of DATEM on RTs and these important test bake parameters: baking height, loaf volume, drop baking height and the bread score. In addition to information on mixing properties provided by the mixograph, RT seemed to be predicting dough's stability, related to its gas-retaining properties. This stability which can be enhanced by DATEM may be related to both the extensibility of dough's gluten matrix and the stability of the liquid film surrounding the gluten matrix. / Dissertation (MSc (Agric) Food Science and Technology)--University of Pretoria, 2005. / Food Science / unrestricted

Supplemented and unsupplemented white breads were baked and toasted at three different toaster settings, light, medium, and dark. Organoleptically, products were highly accepted when toasted at the light and medium temperatures. Biological tests with rats resulted in a decline in the efficient utilization of the protein with toasted white bread diets, evidenced by poor weight gain, low liver weight, Serum protein, PER (protein efficiency ratio - weight gain/protein intake) and percent digestability. Increased toasting temperatures reduced the amino acides essential for growth in white bread diets. Supplementation with soybean improved the quality of the bread, possible due to destruction by heating of the trypsin inhibitor in soybean.

No description available.

Soy peroxidase enzyme obtained from isoelectic precipitation procedures was added to all-purpose flour (APF) to assess its effects on the rheological properties and consumer acceptability of yeast bread. A pH 4.8 isoelectrically precipitated fraction from soybeans was used because it produced the most precipitate and had about the same peroxidase activity as the other fractions. Gluten strength was determined using a farinograph for seven treatment groups: control (all-purpose flour), bread flour, all-purpose flour + soy flour, bread flour + soy flour, all purpose flour + pH 4.8 precipitate, all-purpose flour + 15 mg soybean peroxidase, and all-purpose flour + 25 mg soybean peroxidase. Four types of yeast bread were baked for loaf volume determination, texture analysis, and consumer acceptability: a control loaf using only all-purpose flour, a reference loaf using all bread flour, a loaf with all purpose flour + whole soy flour, and a loaf with all-purpose flour + pH 4.8 soy precipitate. The APF+soy flour, bread flour, bread flour + soy flour, and the APF + pH 4.8 precipitate produced an improvement in the gluten strength and mixing tolerance compared to the control (p<0.05). However, the improvement by the addition of the pH 4.8 precipitate cannot be attributed to the peroxidase enzyme because peroxidase needs hydrogen peroxide as a substrate and no hydrogen peroxidase could be added to the farinogragh; therefore, it was concluded that the increase in gluten strength produced by the pH 4.8 soy precipitate was due to an unknown component present in the pH 4.8 fraction. No significant differences (p<0.05) were found in crumb or crust texture for any of the treatment groups. The addition of pH 4.8 precipitate to APF significantly decreased (p<0.05) loaf volume compared to bread made from bread flour. The results from sensory analysis showed there was no difference in preference for any of the breads. This study showed no conclusive evidence that peroxidase enzyme improved gluten strength or loaf volume of yeast bread, but further research is warranted. / Master of Science

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Call number: LD2668 .T4 1980 J85 / Master of Science+Q4675

Call number: LD2668 .T4 1984 W8 / Master of Science

Call number: LD2668 .T4 1955 B36 / Master of Science

Call number: LD2668 .T4 1964 R89 / Master of Science