Identification of Baking Expansion Phases of Leavened Dough Using an Experimental Approach

Food Bioprocess Technol (2016) 9:892–903 DOI 10.1007/s11947-015-1669-7 ORIGINAL PAPER Identification of Baking Expansion Phases of Leavened Dough Using an Experimental Approach Antoni Miś 1 & Agnieszka Nawrocka 1 & Dariusz Dziki 2 Received: 28 April 2015 / Accepted: 28 December 2015 / Published online: 22 January 2016 # The Author(s) 2016. This article is published with open access at Springerlink.com Abstract A measurement system was designed to study changes in the volume, pressure, and viscosity of dough leavened by baking powder during model baking. Analysis of the volume changes demonstrated two baking stages, i.e. dough expansion and crumb shrinking. Through the analysis of pressure and viscosity extremes, the expansion stage was divided into five phases: stress relaxation (R) characterised by a mild pressure decline; gluten matrix softening (S), during which the decrease in viscosity is accompanied by a gradual pressure rise contributing to substantial dough expansion (by ∼54 %); starch gelatinisation and protein aggregation (G) characterised by rapidly increasing viscosity; gas bubble opening (O) reflecting a rapid pressure reduction; and boiling of water in dough (B), which ends at initiation of crumb shrinking. The study showed that enrichment of the dough with carob fibre increased the contribution of phases S and O to dough expansion at the cost of phase G. A similar contribution of the expansion phases was reported for the Bombona cultivar, which exhibits the highest gluten content. In contrast, the Finezja and Katoda cultivars, which have a lower gluten level, were characterised by an approximately two-fold higher impact of phase G on the increase in dough expansion. The results indicated that the developed method for identification of baking expansion phases of leavened * Antoni Miś 1 2 Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, 20-290 Lublin, Poland Department of Thermal Technology, University of Life Sciences, Doświadczalna 44, 20-280 Lublin, Poland dough can be useful in baking characteristics of raw materials and bakery additives. Keywords Leavened dough . Fibre-rich additions . Wheat cultivars . Model baking . Expansion phases . Baking characteristics Abbreviations t Baking time, s t0 Moment of start of baking, s Moment of finish of baking expansion stage, s tE tML Higher time limit for mathematical modelling P(t) and η(t), s ρ Density of gas-free dough, g cm−3 Rp Radius of heating plates, cm H Width of gap between heating plates, cm Initial dough sample weight at t0, g mI D Dough disc diameter, cm FN Normal force exerted by dough to upper plate, N γA Shear strain amplitude, k Calibration factor of Newtonian viscosity, Pa s V Specific volume of dough, cm3 g−1 P Pressure exerted by dough to upper plate, Pa η Newtonian viscosity of dough, Pa s RV dV/dt, cm3 g−1 s−1 RP dP/dt, Pa s−1 Rη dη/dt, Pa Subscripts Minimum Min Maximum Max Food Bioprocess Technol (2016) 9:892–903 Introduction A baking temperature induces a variety of physical and chemical processes that transform viscous-liquid dough into bakery product with solid and cellular-structured crumb (Mondal and Datta 2008). The most readily observable symptom of these processes is dough expansion accompanied by externally invisible changes in its cellular structure. In chemically leavened dough, expansion is possible thanks to accumulation of high amounts of CO2 in aqueous phase of the dough. The gas is produced at the stage of dough mixing, when the leavening agent, mostly sodium bicarbonate, reacts with water (Bellido et al. 2009). During baking, the temperature rise increases CO2 saturation, forcing its diffusion from the liquid to gaseous phase of dough. Consequently, air bubbles serving as nucleation sites are filled with carbon dioxide and their volume gradually increases. During the growth, gas bubbles coalesce and, as a result, become more diverse in terms of size, and their number is substantially reduced (Babin et al. 2006). In addition to the amount of the gas accumulated in the bubbles, the increase in its pressure induced by the rising temperature enhances gas bubble expansion. Inhibition of expansion begins at the time of cell opening, which leads to rapid release of the gases and a simultaneous decline in their pressure in dough (Singh and Bhattacharya 2005). At the end of baking when the dough temperature in the peripheral zone reaches the water boiling point, the produced water vapour pressure is an additional force maintaining the further dough expansion process until the end of the thermosetting of the crumb cellular structure (Wang and Sun 1999). Continuation of baking is associated with formation of an increasingly thicker bread crust and considerable drying of crumb. Consequently, the loaf volume begins to decrease (Rouillé et al. 2010; Sommier et al. 2005; Wagner et al. 2007). Besides the above-mentioned physical and structural changes, chemical transformations take place, with starch gelatinisation (Besbes et al. 2014; Chevallier et al. 2000) and gluten protein aggregation (Singh 2005) as the most important processes. During gelatinisation, starch granules absorb water and change in size and shape due to swelling and crystal melting (Fessas and Schiraldi 2000). The gluten proteins, i.e. gliadins and glutenins, form a continuous three-dimensional network, which ensures viscoelastic properties of the dough and determines the proper transformation thereof into crumb. During baking, the gluten network is strengthened through formation of additional cross-links, mainly disulphide bonds (Wieser 2007), which ultimately leads to thermosetting of the bread crumb. The major symptoms of thermal modifications include an increase in molecular weights of gluten proteins and their reduced solubility (Schofield et al. 1983; Singh 2005). The starch and protein transformations as well as changes in dough temperature and moisture have a 893 significant effect on dough rheology during baking. At the early stages of baking, dough consistency gradually softens as an immediate effect of gluten protein weakening by an increasing temperature (Ahmed 2015). When dough reaches a temperature of 55–60 °C initiating the processes of starch gelatinisation and gluten protein aggregation, viscosity increases rapidly (Rouillé et al. 2010; Singh and Bhattacharya 2005) until dough reaches ca. 75 °C. A further temperature rise leads to a decrease in dough viscosity (Dreese et al. 1988; Vanin et al. 2010) related to disruption of swollen starch granules and melting of remaining crystallites (Ahmed et al. 2013; Keetels et al. 1996). No decline in viscosity is observed when the moisture of the crust zone decreases below 37 % and a long-lasting plateau of viscosity is evident (Vanin et al. 2013). In the final baking stage when dough reaches the water boiling point, viscosity increases proportionally to the rate of the decrease in the water content. Given the considerable co (...truncated)