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Title: Quantification of bread crust crispness including the effects of selected additives
Author: Al-Hebeil, Salah Ali I.
Awarding Body: University of Newcastle Upon Tyne
Current Institution: University of Newcastle upon Tyne
Date of Award: 2013
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Bread crust crispness is one of the most important and desirable characteristics that express the level of freshness and quality for bread classified as ‘crispy’. Several approaches have been used to determine food crispness; however no reliable objective method for bread crispness has been reported yet. To understand and quantify bread crust crispness, standard procedures for both instrumental and sensory measurements should be developed. Therefore, the first part of this research aimed to investigate both mechanical and acoustic parameters that relate to bread crust crispness determination and correlate them with sensory evaluation using expert panels at 4, 24, 48 and 72 hours post baking. A texture analyser (TA-XT plus) fitted with an acoustic envelope detector was used to determine mechanical and acoustic parameters. Five different bread formulae were evaluated at 4 and 24 hours post-baking, predominantly for crust crispness Two new experimental parameters were investigated in an attempt to standardise instrumental and sensory evaluations to improve consistency in the outcomes of the studies. Several mechanical and acoustic parameters either separately or in combination were tested and the results were compared with sensory evaluations. The ratio of sound pressure level and maximum force (SPL/Forcemax) along with the ratio the number of sound peaks and maximum force (AUX/Forcemax) were chosen as instrumental crispness indicators due to their significant positive correlations with sensory evaluations at 4, 24, 48 and 72 hours post baking. SPL refers to sound pressure level (dB) which is the highest sound recorded during the fracture of the sample at a certain threshold, AUX refers to the number of sound peaks resulting from the pressure of the wedge probe on the surface of bread during the process of penetration, and the Forcemax is the maximum force (Kg) required during the fracture of the crust. Then the influence of selected additives on bread crispness and crumb firmness were studied. For crust crispness, both experimental parameters SPL/Forcemax and AUX/Forcemax were used as instrumental crust crispness, while crumb firmness was tested using compression test as reported by AACC (74-09). Abstract II Polydextrose, sodium alginate, and enzymes dough conditioner (EDC), citrus fiber and mono and di-glycerides (M&D-G) were used as additives to modify the bread formulation, each in three different ratios. The migration of water from wet crumb to dry crust is considered as the main reason of bread crust loss, therefore the main reason of choosing those additive was based on their highly water binding capacity. The addition of 1% polydextrose, 0.25% and 0.5% sodium alginate and 1% enzymes dough conditioner (EDC) increased the sensory measures of crispness significantly above the control bread, and in most cases both SPL/Forcemax and AUX/Forcemax were also significantly higher than the control. Other concentrations were similar to the control or less crisp. The addition of M&D-G to the dough formulation did not show any effect on bread crust crispness. Neither did the addition of citrus fibre. Both experimental parameters showed high correlations with the sensory analysis when comparing bread of the same age, either 4 or 24 hours after baking. However conducting the sensory analysis at two different time points in the absence of score references lead to similarity in scores awarded at 4 and 24 hours, which did not fully reflect the loss of crispness occurring during this period. To allow the evaluation of both instrumental and sensory analysis at the same time, a follow on experiment was conducted using two different bread recipes at two different ages (4 and 24 hours) baked at the same time within two consecutive days. In conclusion, this work demonstrated that both experimental parameters relatively corresponded with the sensory evaluations even when the time factor was compensated for. AUX/Forcemax showed more accuracy in reflecting the level of crispness than SPL/Forcemax while SPL/Forcemax seems to measure the of crust staling values. Polydextrose, sodium alginate and EDC in ratios of 1%, 0.25% and 1-2% respectively showed better enhancement both for bread crust crispness and crumb softness. Further work regarding the effects of polydextrose, sodium alginate and EDC was recommended to determine the optimal amount of these ingredients to ensure a better crispy product.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available