Determination of extensibility for certain types of pretzels dough

. Determination of pretzels dough is essential to analyse the technological process, the dough handling behaviour and properties of the finished product. In various processing steps such as kneading, dividing, shaping and baking the dough undergoes different mechanical deformation, including the extent, compression or shear. In the literature there are several methods for analysing these properties. These include empirical rheological methods, such as recording dough evolution during kneading, extensibility measurement or fundamental rheological methods. The study in this paper propose to investigate the behaviour of different types of test dough extensibility and make estimates of the values of the moment (time) and maximum force that wick dough is deformed to appearance of fracture. The maximum elongation of the dough wick is determined for the same values of its initial geometry as well as the other test parameters for two types of dough, one with a composition of 45% water, 10% oil and 45% flour, and another with a composition of 55% water, 10% oil and 35% flour. Preliminary results have found that a dough with more water has a greater tensile strength than the dough with the same amount of oil and less water.


Introduction
The dough extensibility is a rheological property which begins to form even during the dough kneading. If during kneading the elastic properties are not formed, then the dough will not have the proper rheological behaviour in fermentation, modelling or baking processes, [1]. In more general terms, the extensibility of the dough is its property of stretching, without breaking, [2,3]. This property does not depend only on the quality and amount of gluten in wheat flour, depends also on the amount of water added in the mixture, [4,5]. The main method for determining the dough extensibility is standardized with AACC Method no. 54-10.01/ ISO 5530-2/ ICC-Standard no. 114/1 and involves stretching a dough wick and drawing extensographic curves with the help of Brabender Extender, [6]. Results on dough stretching help determine its rheological properties, the amounts of ingredients to obtain it, including the possibility of processing and baking, [7]. A very extensible dough is used in the bread making process because it is considered easier to process, and the less extensible dough is used for other bakery products such as pretzels, sticks, grissins, [6]. The tensile strength of the dough is recorded in the Brabender Extender system data recorder. The recording system has the role of plotting extensographic curves which allow the determination of certain characteristics: -resistance to stretching due to maximum resistance, Rm and resistance to constant deformation corresponding to the time of stretching at 50 mm, R50. Each of the average values is expressed by approximately 5 UE; -the extensibility is due to the displacement of the dough from the time of the curve recording until the moment the sample breaks and is indicated on the extensogram by a smooth fall to zero or by a sudden fall; each of the mean values is expressed by approximately 1 mm; -energy is defined as the area under the curve recorded and describes the effort required to stretch the dough wick; where: ma represents the dough mass [mm].

Methodology
To quantify the extensibility of the dough, the Brabender extensograph is generally used or other comparable test devices, [6,9,11]. In all situations, the force used to stretch the dough wicks up to breakage, when it is reached at the maximum dough extensibility level, [12,13]. The dough used to determine extensibility with the Brabender extensograph is obtained with the help of the Brabender farinograph, by the method AACC 54-21 (2000) and must have the characteristics of a normal consistency dough [5,14]. The dough is prepared from 300 g flour, water and 1,2 % salt, and a 150 g sample is divided from the total dough which is shaped like a wick (long form). The wick of dough is placed on racks dough and let rest in thermostat for 45, 90, 135 and 180 minutes. After the thermostat period, the dough wick is subject to stretching until it breaks, [6,8]. Determinations result in an extension curve whose characteristics indicate the rheological properties of the dough (figure 1). The rheological properties of the dough depend on the next steps in the established technological flow, [8]. Two types of dough were prepared for the proposed study: -type I -dough with composition of 45% water, 10% oil from the total amount of flour; -type II -dough with composition of 55% water and 10% oil from the total amount of flour. Besides the amount of water and oil, to obtain each type of dough was also added the flour purchased from the trade (1 kg), kitchen salt (0.012 kg), yeast (0.005 kg), sugar (0.010 kg). Flour had a moisture of 9,56 % and a hydration capacity of 65,7 % which was determined with the help of the Brabender farinograph. For blending the ingredients and kneading the dough was used spiral arm and planetary motion kneader, DitoSama. Mixing the ingredients was done for 2 minutes in the first velocity stage of the kneading arm, and subsequently switched over for 10 minutes in the second stage of the velocity to carry out the kneading process of the dough. After completing the kneading, the dough was divided into pieces whose mass was 100 g.
To perform the extensibility test, pieces of dough were moulded in the form of wicks with a length of 400 mm and a diameter of about 16 mm and placed on the fixed crosspiece of the HOUNSFIELD H1KS Mechanical Testing Machine. The apparatus used during the experiments was equipped with a hook, a force cell of 10 N and a clamping system for the end of wicks on the fixed crosspiece of the device. To record the maximum force that has been applied for stretching to break the dough wick was used a computer on which the Qmat software was installed. After attaching wick on the fixed crosspiece and hanging the hook on the movable traverse, the wick was lifted vertically at a speed of 50 mm / min. The movement of the hook was made until the dough wick broke into one of the tear areas a, b, c, d, e from figure 2. At the time of breaking the dough wick in the Qmat software acquisition system the maximum force at which the breakage occurred and the hook movement vertically was recorded for each wick sample ( figure 3).
where: L-length of the wick after stretching; A0 -the initial area of the wick section. Fig. 4 Diagram "stress-strain" [15] To determine the length of the dough corresponding to the moment of reaching the maximum force the value of the angle β formed by it at the point "c" in Figure 1 was first found, applying the calculation scheme in Figure 5 and it was taken into account to drop 100 mm of the length of the wick, since the ends of the wicks have been inserted into the holder of the dough wicks.  (4) and (5). namely,

Results and discussions
Experimental results recorded for maximum strength, respectively the displacement of the hook corresponding to the maximum force is shown in Table 1 and in the graphs of Figures  6 and 7. Graphs have been processed using Excel. Elastic modulus values (E) determined by linear regression, the length of the wick after stretching (L), the deformation values (ε) and the resistance of the dough to the stretch (σ) are shown in Table 2. Dough with 55% water

Conclusions
The experimental data show a deformation of the dough within the limits of 0.66 -0.88 until it reaches the breaking strength for dough with 45% water and within 0.6 -1.7 for a dough with 55% water. Modulus of elasticity of dough with 45% water and 10% oil has much lower values compared to 55% water and 10% oil. It can be concluded that a greater amount of water in the dough leads to an increase in dough extensibility, respectively, to easier handling of the dough wicks without breaking or thinning during moulding. A dough with less water will break faster than one with a higher water content.