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In bread-making, the baking process is one of the key steps to produce the final product quality attributes including texture, color and flavor, as a result of several thermal reactions such as non-enzymatic browning reaction, starch gelatinisation and protein denaturation. These thermal reactions are dominated by heat and mass transfer mechanisms inside an oven chamber as well as inside the dough pieces. In this study, an industrial baking process was divided into 4 zones. Experiments were conducted, and mathematical models were developed to account for the heat and mass contribution as well as their consequent impacts on the product qualities. Monitoring systems were developed and installed inside an industrial oven to evaluate oven performance, including temperature profile and airflow pattern. Many other tests and experiments were conducted and results given in some detail. To deal with the complexity of a continuous baking process, a three dimensional transient-state CFD model with moving grids was established to account for the effect of oven load on heat transfer in the oven chamber. The dynamic response of the travelling tin temperature profiles could be predicted in accordance with a change in the oven load. The modelled tin temperature profiles showed a good agreement with the measured tin temperature profiles from the actual industrial baking process. Finally, the three-dimensional CFD model could provide guidance in manipulating the oven condition to achieve the optimum temperature profile in the industrial travelling-tray baking oven. / Doctor of Philosophy (PhD)

Master of Science / Food Science Institute / Fadi Aramouni / β-(1,4)-endoxylanases, commonly referred to as xylanases, have become integral to the industrial breadmaking process. This enzyme is known to cause improvement in dough rheology, loaf volume, and crumb grain. Significant research has been conducted regarding the structure, function, and inhibition of xylanases, but there is currently no quick and reproducible method to evaluate their effect in baking. The goal of this research was to develop a quantitative method for this purpose and to determine why the effect of xylanases varies with different wheat flours. The currently used methods of test baking, dough stickiness, and spectrophotometric analysis for reducing sugars were evaluated, and failed to provide reproducible results. Therefore, a new method was developed to measure the Flour Water Expression Rate (FWER) with the addition of xylanases. Commercially available enzymes from Aspergillus niger and Bacillus subtilis were evaluated in this study. The FWER method measures the amount of water released by the xylanase over a set period of time. This method consistently provided statistically significant data (p<0.05), which was able to provide a comparison of xylanases from A. niger and B. subtilis in different flours. The results indicated that the xylanase from A. niger tends to release more water, have a higher FWER value, than the xylanase from B. subtilis. In one flour, A. niger xylanase resulted in an FWER of 15.18 compared to B. subtilis xylanase that resulted in an FWER of 9.57 at equivalent activities. However, inhibitors in the wheat appeared to cause an impact on the FWER, which was evaluated with an uninhibited xylanase from B. subtilis. This new method for the evaluation of xylanases in baking suggests varying levels of xylanase inhibitors in wheat may be the reason xylanases effect wheat flours differently.

The staling of baked products remains a significant cause of economic loss due to the loss of enjoyment seen as crumb firming occurs. The aims of the current project have been to investigate the stability of amylases in bakery formulations. In addition, the impact of partial hydrolysis products of starch on staling is investigated. Specific assays were used to measure ƒÑ-amylase and ƒÒ-amylase, in the presence of the other potentially interfering activity. ƒÑ-Amylase activity levels appeared to gradually increase during the proofing stages and then to decline upon heating of the dough. However, the activity remaining in the final baked loaf was readily measurable indicating that not all of the enzyme had been inactivated. Free and total ƒÒ-amylase activities were also measured and most was found to be in the free form. ƒÒ-Amylase was unstable with only relatively low activities remaining in the final baked loaf. It appears that of the two amylolytic enzymes, ƒÑ-a mylase is sufficiently stable that it may exert some impact on the crumb characteristics in the freshly baked product and during subsequent storage. In order to assess the likelihood that amylolysis is of significance to crumb characteristics, HPLC was used to analyse aqueous extracts for sugars. Commercial flours were found to contain low levels of sugars with maltose being the predominant sugar present. A number of commercial breads were also analysed and the composition found to vary between the different samples. Typically maltose was present at higher levels than the other sugars. When experimental loaves were analysed, the patterns showed that other sugars declined during proofing whereas maltose remained at readily measurable levels. Upon baking and subsequent storage the amounts of maltose increased. These results are consistent with the findings that some amylolytic activity remains in the baked product. In the third phase of this study, a potential means of investigating the role of particular carb ohydrates in product textures and staling rates was examined. The approach of spray drying was used to prepare microencapsulated maltodextrin. The encapsulating agents used were based upon rice starch and guar galactomannan. When these microcapsules were incorporated into the breadmaking formulation and baked, it appeared that softer crumb characteristics were achieved. The data also indicates an effect of delay in the staling rates. In a preliminary evaluation of the potential of two X-ray scattering methods, it was found that both techniques appear useful. The differences seen for samples of bread crumb analysed at various stages of storage did not show large differences in the intensity patterns. Of the two approaches, small angle analysis (SAXS) appears to show greater potential for application in ongoing studies of staling. In conclusion, cereal grain ƒÑ-amylase may be more stable during breadmaking than previously thought. There appears to be an increase in the level of some low molecular weight sugars in the final, baked product. Microencapsulation may offer a useful technique for the study of the role of specific carbohydrates during baking and storage of breads.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniversitet, 2004. / Härtill 5 uppsatser.

A enzima lipoxigenase através da farinha integral de soja é amplamente utilizada na panificação com objetivos de branqueamento e melhora da reologia. Com base nesse pressuposto, o objetivo inicial deste estudo foi de observar a ação oxidante dessa enzima na presença de dois outros oxidantes (ácido ascórbico e peróxido de benzoíla) nas propriedades reológicas e sensoriais de pães. Sete misturas com diferentes combinações dos três compostos foram elaboradas utilizando-se um delineamento experimental do tipo \"centroide-simplex\", sendo aplicadas à farinha de trigo para o preparo de pães. A enzima apresentou sinergia com o ácido ascórbico na elasticidade da massa, sugerindo uma inter-relação bioquímica entre os dois compostos no fortalecimento da matriz protéica do glúten. A mesma sinergia entre a lipoxigenase da soja e o acido ascórbico foi observada na redução da tonalidade amarela dos pães medida instrumentalmente. A partir desses resultados, buscou-se avaliar a ação da enzima frente a variações tanto na força da farinha como no tempo de fermentação, reproduzindo as condições reais de processamento. Desta vez, um planejamento experimental do tipo Box-Behnken com três fatores (atividade da enzima, força da farinha e tempo de fermentação) em três níveis de variação, foi aplicado no preparo das amostras. Os resultados mostraram que a lipoxigenase da soja (fração 1) é uma enzima oxidante de ação rápida e seu efeito no branqueamento dos carotenóides da farinha de trigo exibiu interação positiva tanto com a força da farinha como o tempo de fermentação. Respostas reológicas e sensoriais decorrentes da ação conjunta de diferentes oxidantes e condições de processamento em pães foram pela primeira vez descritas através de modelos polinomiais com capacidade preditiva. / Soy lipoxygenase enzyme through soy flour is widely used in breadmaking for bleaching and rheological improvement. Based on this fact, the initial objective of this study was to observe the enzymes\' action in the presence of two other oxidants (ascorbic acid and benzoyl peroxide) in the rheological and sensory properties of breads. Seven mixtures with different combinations of the three compounds were prepared using a \"centroid-simplex\" design and applied to wheat flour for breadmaking. The enzyme showed synergism with ascorbic acid in the dough elasticity suggesting a biochemical interrelation between the two compounds in strengthening the gluten protein matrix. The same synergy between soy lipoxygenase and ascorbic acid was observed with the yellow hue reduction of breads measured instrumentally. From these results, the enzyme action was evaluated with wheat strength and proofing time variations reproducing real processing conditions. This time, a Box-Behnken experimental design with three factors (enzyme activity, wheat strength and proofing time), and three variation levels were applied in the sample preparation. The results showed that soy lipoxygenase (type 1) is a fast-acting oxidizing enzyme and its bleaching effect on wheat flour carotenoid exhibited a positive interaction with wheat strength and proofing time. Rheological and sensory results attributed to the combined action of the different oxidants and breadmaking conditions were for the first time described through polynomial models with predictive capacity.

Author also know as S M Loveday / Fresh bakery products have a very short shelf life, which limits the extent to which manufacturing can be centralised. Frozen doughs are relatively stable and can be manufactured in large volumes, distributed and baked on-demand at the point of sale or consumption. With appropriate formulation and processing a shelf life of several months can be achieved.Shelf life is limited by a decline in proofing rate after thawing, which is attributed to a) the dough losing its ability to retain gas and b) insufficient gas production, i.e. yeast activity. The loss of shelf life is accelerated by delays between mixing and freezing, which allow yeast cells the chance to ferment carbohydrates.This work examined the reasons for insufficient gas production after thawing frozen dough and the effect of pre-freezing fermentation on shelf life. Literature data on yeast metabolite dynamics in fermenting dough were incomplete. In particular there were few data on the accumulation of ethanol, a major fermentation end product which can be injurious to yeast.Doughs were prepared in a domestic breadmaker using compressed yeast from a local manufacturer and analysed for glucose, fructose, sucrose, maltose and ethanol. Gas production after thawing declined within 48 hours of frozen storage. This was accelerated by 30 or 90 minutes of fermentation at 30;C prior to freezing.Sucrose was rapidly hydrolysed and yeast consumed glucose in preference to fructose. Maltose was not consumed while other sugars remained. Ethanol, accumulated from consumption of glucose and fructose, was produced in approximately equal amounts to CO2, indicating that yeast cells metabolised reductively.Glucose uptake in fermenting dough followed simple hyperbolic kinetics and fructose uptake was competitively inhibited by glucose. Mathematical modelling indicated that diffusion of sugars and ethanol in dough occurred quickly enough to eliminate solute gradients brought about by yeast metabolism.