الفهرس 
ACKNOWLEDGMENT
Beta glucanOnly 14 pages are availabe for public view
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Abstract
Recently, barley had received increase attention as a healthy cereal for human consumption, due to its many beneficial constituents. So many studies tried to increase the human consumption of barley grains, by incorporate the grains in daily human diet, especially in bread making. Indeed, barley flour caused a negative influence on bread volume and appearance; as the presence of husks lacks of the gluten proteins and the dark gray color of the barley final products negatively affected consumer acceptability and limited its use in bread making. So this investigation was designed to study plenty points to gain knowledge that could lead to improvement baking characterization of barley bread to increase consumer acceptability for these breads. This research has investigated the impact of increasing the conditioning moisture content of barley grains prior to milling on quality attributes of barley flours from hulled and hull-less barley grains, besides the evaluation of physical and sensory properties of bread baked from these barley flours. In addition, in the present study, the barley flour extracted from germinated barley grains were used as improver to improve the gas production during baking process. Moreover, the additions of xylanase and hemicellulase enzymes during barley bread making and its influence on the solubility of pentosans and β-glucan were studied. Furthermore the influence of natural and sourdough fermentation on the quality of bread were investigated.
The obtained data could be summarized as follows:
1. Flour extraction rate was decreased as the tempering moisture of grains prior to milling increased. In all conditioning treatments, the flour yield was lower in hulled than in hull-less variety. The flour color was significantly improved (become white) as the conditioning moisture of hull-less barley grains before milling increased, while the hulled barley showed slight improving. The chemical composition of flours including protein, fat, crude fiber, ash, pentosan, β-glucan, bond and total phenolic compound and phytic acid contents showed decreasing, whereas starch, reducing sugar and free phenolic contents were raised as the conditioning moisture of the grains prior to milling in both varieties increased. A slight raise in solubility of protein and starch with substantially increasing in the solubility of pentosan and β-glucan was observed in all flours from both barley varieties as the tempering moisture of grains before milling increased. The solubility of β-glucan was higher in flours from hulled than that corresponding flours from hull-less variety and this reflected the higher values of relative viscosity of flour water extract from the former than the latter. The Rapid Visco Analyser (RVA) measurements for the flours obtained from hulled and hull-less barley indicated that the values for pasting temperature, time to gelatinization, time to peak, peak viscosity, trough viscosity and final viscosity were decreased as the moisture content of barley grains prior to milling increased.
2. The results indicated that the specific volume of breads baked from barley flours and wheat-barley composite flours were enhanced with increasing conditioning moisture of barley grains prior to milling; therefore baking loss values decrease. On the other hand, increase the moisture content of barley grains prior to milling lead to improve all the tested parameters of sensory evaluation and retarded the staling rate of barley pan bread and wheat-barley breads.
3. The specific volume of bread increased significantly in wheat-hulled barley bread samples after addition of 20% flour from germinating barley grains (samples S18 and S19). On the other hand, the results of sensory evaluation of pan breads baked from wheat-hulled barley composite flour containing 20% flour from germinating barley grains showed that the sample S18 (bread baked from 50%wheat-30%hulled barley composite flour-20% flour from germinating barley grains) recorded the best scores in general appearance, crumb grain distribution, flavor and taste parameters. On the other hand, the results indicated that both samples S18 and S19 had lower staling rate than control.
4. The data revealed the positive effects of hemicellulase and xylanase enzymes in increasing the soluble pentosan contents and the solubility of β-glucan.
5. The loaf volume of breads increased significantly with the increase of hemicellulase and xylanase enzymes dosages. The results concerning sensory evaluation of enzymes-treated samples recorded higher overall scores than control in both barley varieties. While the increase of hemicellulase dosage with wheat-barley samples caused a gradual decrease in the scores of general appearance and taste; on contrary, increase the xylanase dosage caused positive effects on the same parameters. On the other hand, increase of hemicellulase dosage retarding the staling rate of the baked pan bread.
6. After 24 hours of natural fermentation, the content of reducing sugars decreased; while free and total phenolic compounds increased with natural fermentation process due to the degradation of the most of cell walls. Furthermore, the phytic acid content decreased and inorganic phosphorus increased after 24 hours of fermentation. The results showed an increase in soluble protein and soluble pento.