Ph.D. Dissertation:

Study the modeling influence of storage condition (temperature and relative humidity) of wheat seeds and Sangak bread made on bread making quality

Wheat is one of the most important products in the world and the main source of carbohydrates and protein in human nutrition. Wheat is harvested in a short period, but usually takes several months to be processed and used. However, due to the fluidity of wheat gluten, the obtained flour and bread don’t possess the required quality and a great loss will be occurred. Therefore; wheat must be stored in good condition to maintain its nutritional and rheological properties for milling and bakery industry. In the first phase of this study, the influence of moisture content (16, 18, and 20 %), Storage temperature (30, 40 and 50 0C) and storage duration of wheat seeds (2, 5 and 8 days) on characteristics of wheat grain such as germination, seed vigor index, germination index, respiration rate of wheat seeds, adsorption and desorption isotherms of wheat, absorption binding energy and disposal and entropy of adsorption and desorption were studied. Results showed that the Oswin model showed the best fit with adsorption and desorption isotherm data of wheat grain. Binding energy was calculated using the formula Klazyvs- Klapyrn. The binding energy of freshly harvested wheat was high in low moisture content, and it decreased by increasing moisture content. Germination rate increased by increasing moisture content and progressing storage time of freshly harvested wheat, while it decreased by increasing storage temperature. In the second phase of study, the effect of moisture content, storage time and temperature was evaluated on the rheological, thermal and chemical properties of wheat flour and the structure of gluten was studied. Results showed that the rheological properties of wheat flour were improved by increasing storage temperature up to 40?. This is due to oxidation and rearrangement disulfide bonds between different protein chains or reaction of -SH groups and disulfide bonds resulting in increasing strength and improving the quality of flour. These changes cause the flour to be aged. As a result, the quality and technological properties of flour will be improved. In the third phase of study the influence of ageing treatments on the texture, color and organoleptic characteristics of Sangak bread was evaluated and the structural changes in bread were investigated. Results showed that by increasing moisture content the stiffness index of bread decreased in the first and second regions of TPA curve, while increasing in storage temperature led to increasing in this parameter by a slight trend up to 40°C and then it surged by increasing temperature to 50°C. By increasing moisture content and storage time of grain, the overall rating index of bread improved. While increasing storage temperature up to 40? resulted in increasing in this index, higher temperatures caused a fall in overall rating index of bread.

Keywords: Wheat Pishgam,thermal properties, adsorption and desorption isotherms, rheological properties