Effects Of Baking Temperature, Time And Humidity On Bread Crust And Crumb Properties

The main objectives of this study are to investigate the effects of baking temperature, time and humidity on bread qualities and subsequently find the relationship between bread crust and crumb properties. The bread samples were prepared following the straight-dough method. In determining crust and crumb, the difference in colour between these two regions was used. The colour of crust and crumb were measured using a chromameter. The colour range obtained for crust based on top crust colour of commercial bread samples is L <66.0, a > 2.4 and b >22.3 while crumb has a range of L >66.0, a <2.4 and b< 22.3. This colour range is used as a guideline in determining crust thickness of baked loaf samples. Bread slices were scanned to obtain its L a b values and the crust thickness was determined from the crumb region when the L a b values are met. The evaluation of crumb moisture content and firmness were conducted following the standard method of American Association of Cereal Chemist (AACC) 14-5A and American Institute of Baking (AIB), respectively. Experimental results were statistically analyzed using Analysis of Variance (ANOVA). Various combination of baking temperature, time and humidity affected the organoleptic properties of bread. Baking temperature and time significantly affect bread crust colour (P<0.001), thickness (P<0.001), initial moisture content (P<0.05) and firmness (P<0.001). Baking temperature has larger effect on crust colour and thickness compared to baking time. Higher baking temperature produced darker and thicker crust. Rate of thickness increment was also higher at high baking temperature (0.0465 mm/min) compared to low baking temperature (0.0085 mm/min). Increasing baking temperature produces crumb of high initial moisture content with high firmness value. The effect of baking time (P<0.01) is less significant than temperature however increasing baking time would also darken the crust colour and increases the thickness, increases crumb firmness and reduces crumb moisture content. The application of humidified baking has no significant impact on crust coloration (P>0.05) however it causes a decrease in crust thickness (P<0.05), retain moisture (P<0.01) and reduce firmness (P<0.05). Humidified baking also reduces moisture migration (P<0.01) and firming rate (P<0.01) of breads during storage. Besides humidified baking, the usage of baking lid also have potential in increasing L and b values (P<0.001) and reducing a value and crust thickness (P<0.001). However, the application of lid prevents bread expansion and causes high firmness value in bread. Sandwich bread has lower moisture content compared to open bread. Three important correlations were obtained from the study that are between top crust colour difference (ΔE) and thickness, ΔE and firmness and finally crust thickness and firmness. The correlation between ΔE and thickness for non-humidified (NH) baking is represented by yNH = 0.1724x and yH = 0.1712x for humidified (H) baking. The coefficient of correlation, R2, for correlation between ΔE and thickness for non-humidified baking and humidified baking are given by 0.9467 and 0.9341, respectively. A simple model of T = kΔE derived from the correlation between ΔE and thickness indicates that the crust thickness (T) can be predicted by the changes in crust colour (ΔE). The heating constant, k, is dependant of baking temperature. The correlation, ΔE and firmness has the R2 of 0.8306 for non-humidified baking and 0.8025 for humidified baking. The correlation between ΔE and firmness for non-humidified baking is represented by yNH = 0.8375x + 20.824 and yH = 0.8127x + 25.035 for humidified baking. The other correlation, thickness and firmness has the R2 of 0.7436 and 0.6915, for non-humidified and humidified baking, respectively. The correlation of thickness and firmness for non-humidified baking is represented by yNH = 4.0385x + 26.952 and yH = 3.921x + 30.852 for humidified baking. The high value of R2 shows that there is a strong relationship between colour, thickness and firmness. Crust colour can be used in predicting crust thickness and crumb firmness In conclusion, the results show that the bread crust and crumb properties are highly dependent of baking temperature and time. The moisture content and firmness in crumb are also affected by crust formation. This research also produces several significant contributions for bakery study; new method of measuring crust thickness using colour, humidified baking application for improving the storage quality of bread and finally establishment of correlations and linear model that can be used to estimate crust thickness and probably anticipate crumb behavior during storage.

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