الفهرس 
Physicochemical properties of wheat flourOnly 14 pages are availabe for public view
Abstract
Bread is the main source of energy in the diet of many people all over the world, especially in developing countries. The quality of bread depends on the quality of wheat flour, which is strongly affected by the activity of endogenous enzymes. On the other hand, consumers demand bread with better quality and shelf life.
The bread industry faces some technological problems including bread staling, which is responsible for losing large amount of bread. The technology of dough freezing is widely used to reduce the economic losses resulting from bread staling, providing fresh bakery products for the consumers at any time of the day. The quality attributes of bread produced from frozen dough are strongly affected by dough formulation, freezing rate, storage time, thawing conditions.
Malt flour (MF) is one of the preferred natural improvers as it has a positive impact on the technological, nutritional and sensory characteristics of bread.
The objective of the present work was to shed light on the relationship between the enzymatic activity and the quality characteristics of both pan bread produced from frozen dough, as well as balady bread prepared from wheat flour with 82% extraction (control), and its blends with wheat MF with 1 and 2% levels as dough improver.
The obtained results could be summarized as follows: Part 1. Quality attributes of pan bread made by frozen dough:
Pan bread samples were prepared with the flours (72% ext.) of Egyptian wheat varieties, Shandaweel 1 (F1) and Sakha 94 (F2), a flour of Amoun Co. (F3) and a mixture of F1 and F2 with 1:1 ratio (w/w) (F4). Eight bread formulas were prepared using the same quantity of all ingredients, four of them were prepared from F1, F2, F3 and F4 with the active dry yeast (A, B, D and AB, respectively) whereas, the other four were prepared with the compressed yeast (AC, BC, DC and ABC, respectively). Then, dough samples were frozen at 18±2°C. After completely freezing, the dough samples were stored at -18±2°C for 70 days.
1. Physicochemical properties of tested wheat kernels: Shandaweel 1 variety had test weight and TWK of 82.68 kg/hl and 44.60g, respectively. Whereas, the test weight and TKW for Sakha 94 variety were 80.23 kg/hl and 44.20g, respectively. The moisture contents for tested wheat varieties were 6.78 and 7.26% for Shandaweel 1 and Sakha 94 varieties, respectively. Moreover, the ash content of Shandaweel 1 was higher than that of Sakha 94.
2. characteristics of wheat flours (72% ext.):
• The moisture content of F3 was significantly (p≤0.05) lower than that in the other flours. The mixing of F1 and F2 didn’t affect significantly the moisture content. The tested flours had protein content in the range of 11.48 to 11.71%. The protein content was significantly (p≤0.05) higher in F1 and F4 than in F3 and F2 samples. The ash content for tested wheat flours ranged from 0.43 to 0.50%.
• The wet gluten content for tested wheat flours ranged from 23.03 to
29.47%. The F3 significantly (p≤0.05) recorded the highest value of
GI (96.21%) followed by F4 (91.53%), F2 (88.79%) and F1 (86.48%).
• The FN of different tested wheat flours ranged between 365 sec )F3) to 451 sec (F1). The DS content varied from 4.73 to 6.67%. The DS level in F4 and F1 was significantly (p≤0.05) higher than that in F2 and F3. However, F4 had lower FN, and higher LN and DS level compared to F1 and F2.
• The F3 significantly (p≤0.05) recorded the highest L* value followed by F4, F2 and F1, respectively. The highest values of b* and SI were for F2. Whereas, F1 had significantly (p≤0.05) the lowest b* and SI. F2 and F4 were the most reddish.
• At room temperature (25°C), F3 displayed higher WAI and SP than the other flour samples. However, it had the lowest value of WS. The mixing of F1 and F2 provides higher values of WAI and SP than those of F1 or F2. The water hydration properties of different wheat flours were significantly (p≤0.05) increased as the temperature increased from 25 to 100°C.
• The wheat flours required 56.7 to 66.5% water absorption to reach the optimum dough consistency. F4 had the highest stability time (6.5 min). F3 had the lowest values of MTI (40 BU).
• A reduction in dough extensibility and an increment in the maximum resistance to extension were observed when F1 was mixed with F2. Moreover, F3 recorded the highest value of energy as compared to the other flours. However, F4 had the highest value of ratio No.
• α-amylase activity for the tested wheat flours ranged from 0.144 to
0.450 U/ml. The F4 had the highest α-amylase activity followed by F2, F3 and F1, respectively. α-amylase activity of F2 was approximately more than two times comparing with the α-amylase activity in F1. The mixing of F1 and F2 significantly (p≤0.05) increased the activity of α-amylase compared with F1 which had the lowest activity of α-amylase.
• Xylanase activity for the tested wheat flours ranged from 0.083 to
0.123 U/ml. It was significantly (p≤0.05) higher in F1 than in the other tested flours. Also, there were non-significant (p≥0.05) differences in xylanase activity between F2 and F3 samples.
3. characteristics of fresh and frozen doughs:
• The freezing point (tf) values of the doughs contained active dry yeast were in the range of -1ºC for AC, BC and DC to -5ºC (B and AB). The end freezing point (te) ranged from -16ºC (B) to -9ºC (AC). The proportion of freezable water (α) varied from 60% (A) to 50% (D and AC samples). Enthalpy values (∆H) ranged from 34 to 39 Kcal/kg.
• pH values: The initial pH values of different prepared doughs ranged from 5.25 (A) to 5.49 (ABC). After 14 days of frozen storage at -
18±2°C, a slight decrease in pH values was noticed for all prepared doughs. A significant (p≤0.05) increase in pH values was observed for different doughs by increasing the time of frozen storage at -18±2°C up to 70 days.
• The dough samples had a higher α-amylase activity than that of the wheat flours from which they were made. The dough samples prepared from F4 recorded higher α-amylase activity than those made from F1 or F2. A significant (p≤0.05) increase in α-amylase activity was noticed by extending the frozen storage period of dough up to 70 days at -18±2ºC. The linear regression analysis indicated that there was a strong correlation between the time of frozen storage and α- amylase activity.
• Xylanase activity was higher in all prepared doughs comparing with that of the wheat flours from which they were made. The activity of xylanase for unfrozen doughs lies between 0.167 till 0.211 U/ml. Using the compressed yeast in dough preparation caused a significant (p≤0.05) rise in xylanase activity compared to the use of active dry yeast despite using the same type of flour, except for the dough prepared from F4. After 14 days of frozen storage at -18±2ºC, a significant (p≤0.05) increase in xylanase activity was noticed for all prepared doughs. Subsequently, a significant (p≤0.05) decrease in xylanase activity was observed by extending the frozen storage period of doughs up to 70 days at -18±2ºC. After 70 days of storage, the doughs prepared with active dry yeast had higher xylanase activity than those prepared with compressed yeast.
• The initial counts of yeast cells ranged from 6.98 to 7.59 Log CFU/g for dough samples prepared by active dry yeast, while ranged from
7.34 to 7.65 Log CFU/g for those prepared by compressed yeast. Moreover, the yeast viability decreased significantly (p≤0.05) by increasing the frozen storage time at -18±2ºC. The slowest rates of yeast loss occurred during frozen storage were observed in B sample. While, D sample had the highest rate of yeast loss.
• An increase in the volumes of different freshly prepared doughs was observed by increasing the fermentation time up to 180 min. While, beyond 14th day of frozen storage, the decrease in the dough volume ranged from 1.8% (D) to 5.7% (A). Thereafter, the loss of dough volume
increased significantly (p≤0.05) by increasing the time of frozen storage. The losses after 70 days of frozen storage ranged between 23.9% (ABC) to 36.9% (DC).
• An increase in CO2 volume was observed by increasing the
fermentation time up to 180 min. While, there were significant (p≤0.05) increases in the loss of gas production by increasing the time of frozen storage at -18±2ºC. Also, when using the same type of flour, the gassing power loss in doughs prepared using compressed yeast was lower than those prepared using active dry yeast. After 70 days of frozen storage, the gassing power decreased by 21.4 to 35.3% for doughs prepared by active dry yeast whereas 16.9 to 28.2% for those prepared by the compressed yeast.
4. characteristics of pan bread made by frozen dough:
• The fresh ABC sample exhibited significantly (p≤0.05) higher LSV value (3.79 cm3/ g) than the other fresh pan breads under investigation. While, the lowest LSV value (3.46 cm3/ g) was recorded for D sample. Subsequently by extending the time of frozen storage for different dough samples at -18±2ºC up to 70 days, the LSV of pan bread baked from various prepared doughs were significantly (p≤0.05) decreased.
• The α-amylase activity of pan breads was affected by the flour and yeast types, as well as the frozen storage time of dough at -18±2ºC. Where, pan bread made from F2 significantly (p≤0.05) recorded higher α-amylase activity than those prepared from F1 or F3 whether yeast was used in compressed or active dry form. Also, when using the same type of flour, α-amylase activity was significantly (p≤0.05) higher in pan bread prepared using compressed yeast than those prepared using active dry yeast. By increasing the frozen storage time at -18±2ºC of all dough samples up to 70 days, a significant (p≤0.05) reduction in α- amylase activity was investigated for all pan bread samples. A clear reduction in α-amylase activity for all fresh pan breads was observed by increasing the storage time of bread up to 72 h at 25±2ºC.
Such decrease was strongly depending on the wheat variety and the type of yeast. There was a significant (p≤0.05) decrease in the residual activity of α-amylase in pan bread (after 72 h of storage at 25±2ºC ) made by frozen dough by increasing the frozen storage period of the dough at -18±2ºC up to 70 days.
• Xylanase activity for pan bread made by unfrozen dough ranged between 0.290 U/ml (AC) to 0.261 U/ml (B). Pan bread made from F1 had higher xylanase activity than those of F2. Using the compressed yeast in dough preparation with F1, F2 and F3 (AC, BC and DC samples) significantly (p≤0.05) increased the activity of xylanase in baked bread compared to its activity when using active dry yeast (A, B and D samples). By extending the time of storage for frozen doughs up to 70 days at -18±2ºC, the activity of xylanase decreased significantly (p≤0.05). There was a significant (p≤0.05) reduction in xylanase activity in pan bread after 72 h of storage at 25±2ºC compared to its activity in pan bread after 1 h of baking. Pan bread made from F1, F2 and F3 with compressed yeast retained higher xylanase activity compared to those with active dry yeast. In addition, the longer the frozen storage time of dough at -18±2ºC, the higher the decrease of xylanase residual activity in pan bread. The highest values of residual xylanase activity were found in A and B samples. While, DC and D samples had the lowest values (0.53 and 0.60%, respectively) where the residual xylanase activity was about 74 and 47 times respectively lower compared to that in the bread made by unfrozen dough.
• The crust color and summitry of form scores for pan bread made by unfrozen dough ranged from 7.3 to 9.5 and 12.8 to 14.3, respectively. Pan breads produced from F2 had significantly (p≤0.05) better crust color and more symmetrical shape than those produced from F1. Moreover, when using the same type of flour, the crust color scores of pan bread prepared using compressed yeast were significantly (p≤0.05) higher than that of breads prepared using active dry yeast. The increase in frozen storage time of pan bread doughs at -18±2 ºC up to 70 days
had no significant (p≥0.05) effect on the sensory evaluation of crust color. However, it caused a significant (p≤0.05) decrease in the summitry of form scores. Generally, the mean scores of internal sensory attributes for pan breads produced from F2 were significantly (p≤0.05) higher than those produced from F1. Also, pan breads made by the dough samples prepared using compressed yeast had higher scores than those prepared using active dry yeast. Overall acceptability scores of tested pan breads indicated that F4 was more suitable for producing frozen doughs, as it provided pan breads with better sensory properties compared to the other tested flours. Also, pan breads made by the dough samples prepared using compressed yeast had better acceptability than those prepared using active dry yeast.
• The L*, a*, b*, WI and BI values for pan bread made by unfrozen doughs ranged between 61.47 to 71.25, 1.90 to 8.51, 26.97 to 35.40,
46.22 to 58.74, and 53.29 to 88.97, respectively. The AB sample significantly (p≤0.05) presented the lowest L* value (61.94), whereas BC sample had the darkest crust color. In general, pan bread obtained from frozen doughs presented significantly (p≤0.05) lower L*, and b* values, while higher a* values than breads obtained from unfrozen doughs, indicating a decrease in crust lightness with the frozen storage at -18±2 ºC. Consequently, by increasing the time of frozen storage, there was a significant (p≤0.05) decrease in WI values and an increase in BI.
• The alkaline water retention capacity (AWRC, %) of pan bread made from F4 were significantly (p≤0.05) higher than those of pan breads prepared from the other tested flours whether yeast was used in compressed or active dry form. Also, when using the same type of flour, AWRC were significantly (p≤0.05) higher in pan bread prepared using compressed yeast than those of breads prepared using active dry yeast. Noticeably, the frozen storage time of dough at -18±2 ºC significantly (p≤0.05) affected the AWRC values of different produced pan breads. Where, the longer the time of frozen storage of dough,
the lower the values of AWRC. The AWRC of all produced pan breads were reduced by increasing the storage period at 25±2ºC.
Part 2. Quality attributes of balady bread:
Egyptian balady bread was prepared using wheat flour with 82%
ext. (control) and its blends with malt flour (MF) at 1 and 2% levels.
1. Proximate chemical composition of MF: The MF contained 2.07,
12.73, 1.70, 2.57 and 80.93% for moisture, crude protein, ash, lipids and total carbohydrates contents, respectively.
2. characteristics of wheat flours (82% ext.):
• There were non-significant (p≥0.05) differences in the contents of moisture, lipids and total carbohydrates among all tested flours. The crude protein content was in the range of 10.43 to 12.15%. The wheat flour with 1% MF had significantly (p≤0.05) the highest content of crude protein (12.15%), while the crude protein content decreased significantly (p≤0.05) with increasing the MF level to 2% (10.43%). The ash content of flour affected significantly (p≤0.05) by the MF level, where it increased from 0.65 to 0.90 and 1.82% when the MF level was 1 and 2%, respectively.
• The control flour contained 26.07 and 8.85% of wet and dry gluten contents. The addition of MF caused a significant (p≤0.05) increase in the wet gluten content compared to the control flour. But it didn’t affect significantly (p≥0.05) the dry gluten content. Adding MF with
1% level significantly (p≤0.05) increased the GI from 84.33 to 90.00%
in comparing with the control flour. While, increasing the MF level to
2% had no significant (p≥0.05) effect on the GI.
• The addition of MF led to a significant (p≤0.05) decrease in the FN value, consequently an increase in LN compared to the control flour. Flour with 2% MF had significantly (p≤0.05) the lowest value of FN, and the highest LN and DS content.
• Analysis of variance showed that the addition of MF caused a significant (p≤0.05) decrease in L* value compared to the control flour. Wheat flour with 1% MF was less yellowish and had lower color intensity than the other tested flours. Whereas, it had the highest a* value, meaning that it was the most reddish.
• Adding MF with 1% level didn’t affect significantly (p≥0.05) the WAI and SP values compared to the control flour, but there was significant (p≤0.05) decreases in WAI and SP when increasing the addition level to 2%. While, the addition of MF to wheat flour with 1 and 2% levels caused a significant (p≤0.05) increase in the %WS in comparing to the control flour. The water hydration properties of all tested wheat flours were increased as the temperature increased from 25 to 100°C. The control flour had significantly (p≤0.05) the highest values of WAI and SP, while the lowest value of WS compared to the other tested flours.
• The water absorption of the control flour was 56.8%. Adding MF with
1 and 2% decreased the amount of water needed to reach the optimum dough consistency (500 BU) to 56 and 55.5%, respectively. The addition of MF didn’t affect the DDT, where it was 2.0 min for all tested flours. Whereas, it promoted a decrease in the stability time compared to that of control flour. The dough of the control flour had the highest stability time (9.5 min), while it decreased to 7.5 and 5.5 min when the MF level was 1 and 2%, respectively. The time of breakdown was reduced by the presence of MF. Where, it was higher in the control sample (12 min) followed by the blends contained 1 and 2% MF, respectively (9.0 and 6.5 min). Furthermore, the dough of the control flour had the lowest values of MTI and softening degree (10 and 40
BU, respectively) which means that it was more resistant to mixing than that of the flour contained MF.
3. Effect of MF on the characteristics of dough and balady bread:
• The dough yield ranged from 145.99 to 147.68. The addition of MF
didn’t affect significantly the dough yield.
• The pH values ranged between 6.03 to 6.41 after 15 min of dough resting. The pH value of dough prepared from wheat flour with 2% MF was significantly (p≤0.05) lower compared to the other prepared doughs. After 30 min of dough fermentation, pH values reduced to the range of 5.76 to 5.94. The control dough recorded the highest value, while the dough prepared from wheat flour with 2% MF had significantly (p≤0.05) the lowest pH value. Also, there were non- significant (p≥0.05) differences in the pH values between the control dough and that contained 1% MF.
• The flour, dough and balady bread samples contained MF had significantly (p≤0.05) higher α-amylase activity than the control samples. Moreover, α-amylase activity of balady bread doughs was higher than that of flours from which they were made, especially during the fermentation period. α-amylase activity of balady breads was lower than that of the doughs from which they were baked. The residual activities of α-amylase after 72 h of storage at 25±2ºC were approximately 10.0, 12.9 and 19.6% for the control then balady breads produced using 1 and 2% MF, respectively compared to that of the breads after 1 h of baking.
• The activity of xylanase in flour samples ranged from 0.071 to 0.073
U/ml. Xylanase activity of the control flour was significantly (p≤0.05) higher than that contained MF. Moreover, xylanase activity of balady bread doughs was higher than that of flours from which they were made, especially during the fermentation period. Xylanase activity of balady breads was lower than that of the doughs from which they were baked. Also, balady bread samples contained MF had significantly (p≤0.05) lower activity of xylanase compared to the control bread. The activity of xylanase was decreased by extending the storage time of balady bread at 25±2ºC to 72 h. The residual activity of xylanase was almost 5.85, 5.46 and 2.56% for the control then balady breads produced using 1 and 2% MF, respectively compared with that of breads after 1 h of baking.
• Balady bread weight and diameter varied from 130.58 to 135.41 g and
16.77 to 18.08 cm, respectively. Adding MF to balady bread dough formula significantly (p≤0.05) increased the weight and diameter of produced breads in comparing to that of the control bread. There were non-significant (p≥0.05) differences in the thickness of the upper and lower layers of all balady breads under investigation.
• Using MF in balady bread making significantly (p≤0.05) affected the all investigated sensory characteristics of produced breads, except the bread roundness. Where, balady breads baked from the doughs contained MF had better appearance, crust color, crumb texture, odor and taste than the control bread. Also, the separation of layers became more acceptable. There were non-significant (p≥0.05) differences in the mean scores of all sensory attributes for balady breads baked from the doughs contained MF at 1 and 2% levels.
• A significant (p≤0.05) increase in AWRC of balady breads was observed when MF used in the bread manufacturing. This means that, balady breads baked from the doughs contained MF had higher ability to retain water comparing with the control bread. The AWRC of all produced balady breads were significantly (p≤0.05) reduced by increasing the storage period at 25±2ºC.
• Generally, the obtained results indicated that there was a positive effect of using MF in balady bread preparation where it significantly (p≤0.05) improved the AWRC of bread during storage, considerably reduced the staling rate and can provide relatively fresh balady bread.