An instrumented oven for the monitoring of thermal reactions during the baking of sponge cake

An electric convective oven was conceived and equipped to allow monitoring thermal reactions during the baking of sponge cake. High total heat fluxes of between 6000 and 9000 W m⁻² were recorded under baking temperatures of 140-200 °C. The mapping of thermal conditions indicated satisfactory thermal homogeneity, with average temperature variations of 5 °C and maximum relative variations of the convective heat transfer coefficient of 15% on the thermal domain investigated. Internal heat and mass transfers, the extent of thermal reactions within the sponge cake and repeatability of the baking operation were all characterized by experimental measurements. Some of the main operating variables were monitored in the cake (core and surface temperatures, moisture content, levels of chemical reactants and products) and others in the baking atmosphere (temperature, humidity and concentrations of volatile compounds). Specific non-disruptive sampling devices were designed to extract data from cakes and the oven atmosphere in order to follow the kinetics of thermal reactions during the baking operation. Three phases could be identified during baking, corresponding to the relative importance of conductive and evaporative internal heat transfer regimes and to macroscopic changes in the cake structure with formation of a crust. The progress of thermal reactions was monitored with satisfactory precision in both the cake and the baking vapors: relative standard deviations of 2% and 8.7% were obtained respectively for the water content and hydroxymethylfurfural (HMF) content of three replicates during a baking operation.     

A generic procedure to monitor Maillard-derived fluorescent compounds in cookies by flow-injection analysis

Flow-injection analysis is proposed for routine measurement of Maillard-derived fluorescent compounds (FC) in cookies as a marker of the extent of baking. In addition, procedure was applied to investigate the formation of free and total (bound to protein free) FC in cookie-resembling models and in commercial wheat-based cookies as well. FC accounts for the overall fluorescence response of Maillard-derived fluorescent compounds (bound or not to protein) formed during baking but not for a single compound. Free and total FC values increased exponentially during baking at 200, 210 and 220 °C and an induction period of 10 min was observed for free FC. In the complex scenario of the progress of the Maillard reaction (MR) during baking, formation of FC (347/415, ext/emm) was not the limiting step for browning development at the advanced stage of the reaction. Furthermore, the formation of Maillard-derived fluorescent compounds and browning during baking were a consequence of parallel reactions apart from the classical MR scheme of consecutive reactions. Total/free FC ratio was dependent on the baking conditions applied and ratio was significantly decreased at severe baking conditions. Total/free FC ratio could be used as a reference marker for monitoring the process and to identify potential over-processing situations during baking. In addition, fluorescent residues were originally bound to protein because total/free FC ratio decreased drastically as increased the temperature and time of the process. Levels of total FC were nearly 20-fold of free FC in commercial samples. Values of FC were positively correlated with acrylamide, a Maillard-derived food processing contaminant.     

Increment Kinetics of Acidity in French Bread and Critical Control Point Analysis During Baking and Storage

This study analyzed the increment kinetics of acidity in French bread during baking and storage and discussed some critical control points based on the acidity of French bread. The reactions of acidity increments in baking and storage were first order reactions and the relationship between reaction rate and temperature fitted the Arrhenius equation. The activation energy of acidity increment during baking was 16.80 kJ/mol. Furthermore, by adding antioxidants, the activation energy of acidity increment in the storage increased from 14.50 to 19.25 kJ/mol. Antioxidants, such as 3-tert-butyl-4-hydroxyanisole, could be used to control the acidity increment in French bread. Finally, some critical control points in the production of French bread, which are important to the property of bread, include adjusting fermentation temperature, checking oil quality, adding appropriate amount of salt, and checking the cleanness of baking molds.     

Browning development in bakery products – A review

This paper presents a review regarding several aspects of the development of browning during baking of bakery products, mainly from an engineering point of view. During baking, the formation of colour is due to the Maillard reaction, and caramelization of sugars. Besides the major influence of this phenomenon on the initial acceptance of products by consumers, it is the responsible for other relevant changes occurring in food during baking, i.e. production of flavour and aroma compounds, formation of toxic products (e.g. acrylamide), and decrease of nutritional value of proteins. As well as baking, the development of browning in bakery products is a simultaneous heat and mass transfer process that occurs mostly in a non-ideal system under non-ideal conditions. In addition, the mechanisms of chemical reactions involved are still not elucidated completely, so the process is difficult to control and represents a major challenge for food engineers. Effects of browning on properties of products and experimental, modelling and technological aspects of colour formation during baking are reviewed.     

Bread baking and its color kinetics modeled by the spatial reaction engineering approach (S-REA)

Baking is a relatively complex process involving simultaneous heat and mass transfer coupled with reactions and structural changes. An accurate and physically-meaningful model of baking is useful to assist process design and product quality improvement. The reaction engineering approach (REA), which has been proven to accurately model the drying rate of porous foods, is implemented here to describe the local evaporation/condensation rate during bread baking for the first time. The REA is coupled with a set of equations of conservation of heat and mass transfer to yield the spatial reaction engineering approach (S-REA). The results of modeling match well with the experimental data. The S-REA can also model the browning kinetics during bread baking accurately. The S-REA is readily implemented for process design by implementing it in computational fluid dynamics (CFD)-environment. The S-REA can also be used for optimization to determine baking trajectories to achieve the desired product properties.     

Comparative studies on physicochemical and baking properties of newly harvested and stored indian varieties of wheat

Comparative studies on the progressive changes in distribution pattern of proteins, and in rheological and baking properties, were carried out with seven newly harvested and stored wheat varieties. Freshly harvested wheat contained a larger amount of low molecular weight gliadins, which were aggregated during storage in air. This resulted in improvement of the rheological and baking properties of stored grains. Thus, gluten content in wheat or, more precisely, the interchange reactions between thiol and disulphide during storage, governed the dough rheology. The same effects could be achieved by addition of an oxidising agent such as KBrO₃. Radiation treatment (up to 200 krad) also improved the baking quality of newly harvested wheat by modifying some of its rheological properties. A significant correlation between SS/SH ratio and loaf volume was observed. Lower loaf volume in newly harvested wheat was associated with its low SS/SH ratio, high maximum gelatinisation viscosity and low gas retention capacity.     

Two-dimensional CFD modeling and simulation of crustless bread baking process

A special type of baking oven was developed where crustless bread was made by gently baking the dough at controlled temperature by spraying water at prefixed intervals on the surface of the dough. In this study, a two-dimensional (2D) CFD model for crustless bread during baking has been developed to facilitate a better understanding of the baking process. Simultaneous heat and mass transfer from the bread during baking was successfully simulated. It was found that core temperature of the bread reached at 95 °C at the end of baking where as moisture of the bread satisfies the normal bread quality. The model can be successively applied to study the unsteady heat and mass transfer from the crustless bread during baking.     

Changes in carbohydrates and amino acids during baking of Vicia faba

Chemical changes in carbohydrates, proteins and amino acids of the broad bean Vicia faba which occur during the production of the baked beans “foul midamis” were studied. During baking part of the sugars and amino acids of the beans were involved in discolouration reactions with subsequent decrease of the components studied.     

Determination and prediction of thermal conductivity of frozen part baked bread during thawing and baking

The thermal conductivity of food is usually measured in isothermal conditions with a line-heat source probe. The thermal conductivity of bread during the baking phase is function of temperature and is an important parameter to assess. This work aims at (i) developing a measurement method of thermal conductivity in pseudo-non-isothermal conditions, usable during the part baked bread thawing–baking phase, and (ii) establishing models to predict the change of the thermal conductivity as function of the temperature. The line-heat source probe method has been used, the probe temperature being corrected by subtracting the temperature increase due to the baking. Values obtained in pseudo-non-isothermal conditions during the thawing–baking phase are similar to these ones obtained in isothermal conditions. A parallel model has been successfully used to fit the experimental values of the thermal conductivity of bread during the baking phase.     

The fate of furfurals and other volatile markers during the baking process of a model cookie

This work investigates the generation and the evolution of some neoformed compounds formed during the baking of a model biscuit. Thank to their physicochemical properties of volatility and hydrophobicity, furfurylic compounds were followed by a double approach: the analysis of the volatile fraction extracted from food matrix and from the vapours released during the thermal process. 5-Hydroxymethylfurfural (HMF) was the main furfurylic compound formed, it followed an exponential kinetic in both the matrix and the vapours of baking biscuits. However, at the very final stage of baking a drop in HMF was observed in the cookie matrix whereas increasing amounts of HMF were still found in the vapours of baking. Moreover, some degradation products of HMF such as furaldehyde (F) and 2-methylfurfural (MF) were also detected. These observations support the hypothesis of a concomitant volatilization and degradation of HMF during the baking of the model cookie, under our experimental conditions.     

Effect of Flour Type and Baking Temperature on Cake Dynamic Height Profile Measurements During Baking

A dynamic height profile method using digital imaging of cakes at 2 min intervals during baking was used to analyze changes in volume during baking for cakes made with three different flour types (plain flour, heat-treated cake flour, and strong white flour) and baked at three different temperatures (175°C, 190°C, and 205°C). The cakes made from the different flours showed, with some exceptions, a similar trend in the shape and development of the top contour during baking. In the first 4–6 min of baking, there was relatively little expansion followed by a period of rapid expansion to the maximum volume and a period of contraction up to the end of baking. For the three flour types, volume peaked at 16–17 min for the medium and high baking temperatures and at 20 min for the low baking temperature. Cakes made from heat-treated cake flour and strong white flour baked at low and high temperatures produced cakes where the center of the cake was lower than the surrounding pins resulting in a final undesirable dimpled cake contour. A higher baking temperature caused the cake to rise more rapidly. Baking at high temperature produced cakes which shrank the most (P < 0.001) during cooling. Among all combinations of flour type and different temperature treatments, cake made from heat-treated cake flour baked at the middle temperature produced the best final cake in terms of a final dome-shape contour, an appreciable volume during baking, less volume shrinkage during baking, and maximum cross-sectional area of the half cake after 1 h cooling.     

闽南乌龙茶烘焙的研究进展

激烈市场环境下,闽南清香型乌龙茶销售陷入困境,浓香型乌龙茶开始回归,"清转浓"正如火如荼地进行。烘焙是形成浓香型乌龙茶风味的关键工艺,具有提升茶叶品质的重要作用。烘焙型茶叶通过褐化反应形成乌润色泽;烘烤香由褐化反应产生,焙火前已形成的花果香在烘焙中得以保留和提升;多酚类物质异构化减少茶汤苦涩味,糖类物质通过分解、参与褐化反应的方式增加甜醇滋味。本文对焙火提高乌龙茶色、香、味等方面品质的研究进行了综述,总结了已发现的呈香、呈味物质,为探索烘焙对茶叶品质形成的化学机制提供理论依据和参考。     

Image analysis of structural changes in dough during baking

The bakery market is developing new technologies based on dough partial baking and the study of the changes that dough undergoes through the whole baking process could help in the selection of baking times. The aim of this work was to study the changes of dough structure and their relationship with dough temperature, mass loss and loaf height during baking by applying image analysis techniques. Results showed that during baking, bubble coalescence was presented, observing a maximum at the first stages of baking (<250 s). This phenomenon was associated with an increment in dough height without a significant change in dough centre temperature. Fractal dimension of texture of crumb, fractal dimension of contour of cells and crumb grain features were useful indicators of coalescence as well as to distinguish the baking time needed for crumb features remain invariable.     

TEXTURAL AND VISCOELASTIC CHANGES OF CANNED BISCUIT DOUGH DURING MICROWAVE AND CONVENTIONAL BAKING

Textural changes of canned biscuit wheat dough during microwave and conventional baking were described and contrasted using empirical methods. Drastic increases of specific volume and modulus of elasticity were observed in the beginning and the ending periods of both baking processes. Weight loss showed a significantly (p < 0.001) linear relationship with baking time for both baking methods, but the weight loss rate constant for microwave baking was 0.36%/s significantly (p<0.01) higher than conventional baking. Multi-dimensional Scaling showed that microwave baking for 50 s best resembles the textural characteristics of wheat dough under conventional baking for 10 min. Stress relaxation modeling indicated that microwave baking produced higher viscosity and modulus of elasticity values which translates into baked biscuits with undesirable tougher texture.     

Overall and Local Bread Expansion,Mechanical Properties,and Molecular Structure During Bread Baking: Effect of Emulsifying Starches

In order to determine the relationship between molecular structure of wheat bread dough, its mechanical properties, total and local bread expansion during baking and final bread quality, different methods (rheological, nuclear magnetic resonance, magnetic resonance imaging and general bread characterisation) were employed. The study was extended on wheat dough with starch modified by octenyl succinic anhydride (OSA) in order to generalise the results. The interest of investigating multi-scale changes occurring in dough at different phases of baking process by considering overall results was demonstrated. It was found that OSA starch improved the baking performance during the first phase of baking. This feature was due to a higher absorption of water by OSA starch granules occurring at temperatures below that of starch gelatinization, as confirmed by NMR, and consecutive higher resistance to deformation for OSA dough in this temperature range (20–60 °C). This was explained by a delayed collapse of cell walls in the bottom of the OSA dough. In the second phase of baking (60–80 °C), the mechanism of shrinkage reduced the volume gained by OSA dough during the first phase of baking due to higher rigidity of OSA dough and its higher resistance to deformation. MRI monitoring of the inflation during baking made it possible to distinguish the qualities and defaults coming from the addition of OSA starch as well as to suggest the possible mechanisms at the origin of such dough behaviour.     

On-line dynamic HS-SPME for monitoring endogenous aroma compounds released during the baking of a model cake

This work shows that using a dynamic SPME device combined with an instrumented oven, it is possible to monitor the release of a large amount of volatile compounds generated during the baking process of a real cereal product (sponge cake model) by directly sampling its baking vapours. The steam assisted dynamic SPME device made it possible to extract volatile compounds with very different volatility and hydrophobicity, such as 5-hydroxymethylfurfural and 2-methyl-propanal. Time dependent analyses of baking vapours made it possible to simultaneously follow the release of several odour compounds and thermal reaction markers at different stages of their generation in the sponge cake model. The release of newly formed aroma compounds during baking significantly affected the odour quality of baking extracts as shown by odour profiles and sensory preferences evaluated by Direct-GC–Olfactometry. GC–Olfactometry analysis was carried out on the final baking fractions to gain an understanding of the compounds which could contribute to overall odour quality.     

Impact of the Baking Duration on Bread Staling Kinetics

This paper presents a study on the impact of the duration of the baking plateau on staling kinetics in the case of bread crumb made of sourdough; it follows Le-Bail et al. Journal of Cereal Science 50:235–240, (2009)a previous study proposed by Le-Bail et al. Journal of Cereal Science 50:235–240, (2009) on the impact of heating rate during baking on staling parameters. Degassed bread dough was baked in a miniaturized baking system with baking plateau of 0, 4, and 8 min at 98 °C corresponding to a total baking time of 10, 14 and 18 min respectively (simulating from underbaked to fully baked bread). Results showed that longer baking time resulted in the higher Young’s modulus of the baked dough at the end of staling was. It was observed as in Le-Bail et al. Journal of Cereal Science 50:235–240, (2009) that the crystallization of amylopectin occurred a few days before the hardening of the baked crumb during staling. The amount of freezable water decreased during staling (over 10 days period), which was in agreement with the increase in amylopectin crystallites during staling which trap water. The amount of soluble amylose increased with increasing duration of the baking plateau at 98 °C, indicating that for prolonged baking, an increasing amount of amylose is leached outside of the starch granules. This was proposed as an explanation for the higher Young’s modulus of the crumb at the end of staling.     

Furan quantification in bread crust: development of a simple and sensitive method using headspace-trap GC-MS

To study reactivity in bread crust during the baking process in the pan, we followed furan mainly resulting from Maillard and caramelisation reactions in cereal products. Furan quantification is commonly performed with automatic HS-static GC-MS. However, we showed that the automatic HS-trap GC-MS method can improve the sensitivity of the furan quantification. Indeed, this method allowed the LOD to be decreased from 0.3 ng g^–1 with HS-static mode to 0.03 ng g^–1 with HS-trap mode under these conditions. After validation of this method for furan quantification in bread crust, a difference between the crust extracted from the bottom and from the sides of the bread was evident. The quantity of furan in the bottom crust was five times lower than in the side crust, revealing less reactivity on the bottom than on the sides of the bread during the baking process in the pan. Differences in water content may explain these variations in reactivity.     

Cake baking in tunnel type multi-zone industrial ovens Part II. Evaluation of quality parameters

In addition to characterization of baking conditions during industrial cake baking, some important quality parameters, such as texture, color, density and viscosity of the cake batter were evaluated during baking in two different multi-zone industrial scale ovens: gas fired band oven and electric powered mold oven. The flow behavior of all batters was pseudo-plastic with a yield stress. The average moisture removal rates (3.59×10⁻⁴–1.40×10⁻³ kg H₂O/kg solid s) of cakes fell between those of cookies and breads. During baking, pH increased and then decreased at the late stage of baking. Batter positions (side or center) on the band were not critical for quality parameters with the exception of moisture content. Most color changes occurred 1/4–3/4 way through the baking. After 21 days of storage, the hardness of all cakes increased 1.8–3 times the original value.     

Chemical stability of encapsulated aspartame in cakes without added sugar

Encapsulated aspartame (APM), developed to protect the APM molecule during baking, has not been evaluated for stability during baking and subsequent product storage. Thus, the objectives of this project were to determine the APM recovery in various cake formulations after baking and to evaluate APM degradation kinetics during product storage. The recovery of encapsulated APM after baking was 33–34% while that of non-encapsulated APM was 22%. The addition of the acidulant glucono-delta lactone (GDL) to the formulation increased the recovery of encapsulated APM to 58%. The rate constants of APM degradation in the cakes with and without GDL at 22 °C were 0.0085 and 0.035 day⁻¹, respectively. By using 2.5% encapsulated APM in cupcake mixes for home preparation, enough APM should remain to provide adequate sweetness during typical product shelf life.