Structural and sensory changes in short-dough biscuits: addition thaumatin and sucrose reduction effects

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INTRODUCTION
Sucrose, popularly known as sugar, is an essential ingredient in many kinds of food, including bakery products such as cakes and biscuits. Short dough biscuits are characterized by high-fat and sugar content and "low amount of water", where the role of sugar and fat within the dough is well understood (Maache-Rezzoug et al., 1998).
Sucrose contributes significantly to the energy content of bakery products and is responsible for providing sweetness, texture, flavor, and color. Sucrose characteristics, including type, the amount on formulation, and particle size influence the product quality, mainly on the development of the gluten network and starch gelatinization (Manley, 2011).
However, in recent years, due to the high consumption of the sucrose and its association with health issues, public health agencies have already recommended the reduction of sugar in the human die ( Van der Sman et al., 2022).
Currently, food industries have expressed a growing interest in sucrose substitutes as a response to the public interest in low-calorie products, in this context, searching for alternative natural sources is indispensable (Jafari et al., 2021;Mariotti and Alamprese, 2012).
The sucrose replacement by natural or artificial sweeteners in biscuit has been the focus of several studies.
Thaumatin is a vegetal low-calorie protein sweetener, extracted from Katemfe, the fruit of the West African plant Thaumatococcus daniellii and considered as the sweetest substance on nature. The sweetener power of Thaumatin is 1600 -3000 times higher compared to sucrose power, and it also presents health benefits to consumers that are related to the amino acids chain. The benefits include mask metallic and bitter tastes, ability to enhance certain flavors and aromas as peppermint and coffee, improvement of mouthfeel, stability on adverse conditions of pH and temperature.
Thaumatin is an innocuous substance, classified as GRAS (Generally Recognized As Safe), allowing its industrial use on food and showing no consumption restriction by any populational group in different countries. In some countries, Thaumatin food use was allowed without limits (quantum satis) but, high usage levels contribute to licorice-like after taste (Bassoli and Merlini, 2003).
Biscuits can be described as a matrix in which air bubbles are incorporated. Rheologically, biscuit dough is a dense solid-liquid paste, with complex flow behavior.
The short-dough biscuit is brittle and for this type of dough, it is important to avoid gluten network development, ensuring the product characteristics. During the manufacturing process the dough rheological properties are changed by the loss of water, thermal denaturation, and melting of its components. Furthermore, flour type, sucrose concentration, sucrose replacers, and fat can also influence the mechanical properties of the dough (Baltsavias et al., 1997(Baltsavias et al., , 1999Chevallier et al., 2002), and, consequently, the physical and sensory properties of biscuit (Biguzzi et al., 2014). Furthermore, sucrose content in biscuits influences the sensory attributes, providing flavor, spreadability, gluten mobility, and coloring to the surface of the final product due to the browning reaction (Pareyt et al., 2009). Due to these functions, the sucrose replacement is rather difficult to achieve. Therefore, it is important to carry out studies that present solutions in relation to the reduction of sucrose with the maintenance of the structural characteristics of the dough and the biscuits. In this context, the aim of this work was to study the mechanical and sensory properties of the biscuit dough and baked biscuits, with reduction of the sucrose and addition of thaumatin.

Biscuits Production
Short-dough biscuits were prepared by the creaming method formulated according to the information in Table 1.

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The first step consisted of manually mixing the butter and sucrose until a homogeneous mixture was obtained. The second step consisted of adding the other ingredients: powdered milk, soy lecithin, water, thaumatin, salt, and ammonia bicarbonate in the butter/sucrose mixture. This mixture was whipped manually for 7 minutes until a homogeneous mixture was formed, being called "cream mixture." The third and final step was the addition of enriched white wheat flour, sodium acid pyrophosphate, and sodium bicarbonate to the cream mixture. Then, it was mixed manually for 7 minutes until a homogeneous mass was obtained. In samples containing thaumatin, 2 ppm of this protein was diluted in water, forming a solution, as suggested by the manufacturer, and then added in the second formulation step, following the procedure described above. The sucrose-reducing samples were named as follows: RED 25%, RED 35%, RED 50%, and RED 65%, based on the standard formulation, totaling five formulations. The biscuit mold standardization was performed in a manual molding machine; each biscuit weighed approximately 5g. The cooking process was carried out in an industrial oven at 180°C for 20 minutes.

Back-extrusion
The dough's firmness, consistency, cohesiveness, and viscosity index were obtained by the back-extrusion deformation test using a TA-TX plus Texture Analyzer (Stable Micro Systems, England). The sample was placed inside an acrylic cylindric cell, and a 40mm diameter disc probe (A/BE) was used. The experimental conditions were: measure force in compression, test speed, 2 mm/s; distance, 25 mm; sample dimensions: 40g x 2cm x 5cm (weight x height x diameter). The test was performed in triplicate.

Texture Profile Analysis (TPA)
The test consisted of compressing two times a baked biscuit in a reciprocating motion that imitates the jaw's action. The TPA was performed using a TA-TX plus Texture Analyzer (Stable Micro Systems, England).
The baked biscuit was placed on the center of a base and compressed with a 100mm diameter metal disc probe. The experimental conditions were: test speed, 1mm/s; target mode strain, 20%; time, 3 sec; trigger force, 5g. Sample dimensions: 5cm x 3cm x 2cm (Length x Width x Height). The mechanical textural characteristics of hardness, cohesiveness, springiness (elasticity), adhesiveness, fracturability (brittleness), chewiness, and gumminess were obtained. The test was performed in decaplicate.

Structural Analysis -Scanning Electron Microscopy (SEM)
The biscuit samples were fractured naturally and then immediately analyzed by Scanning Electron Microscope (Hitachi TM-3000, Japan), and viewed under vacuum, at a magnification of x1000 and voltage of 15kV.

Sensory Analysis
The test was approved by the Human Research

Statistical Analysis
One-way analysis of variance (ANOVA) followed

Mechanical Properties of the Dough and Baked Biscuits Back extrusion
Biscuit dough is considered a low-water content matrix of starch, protein, and lipid paste that embeds gas bubbles of different sizes and dimensions.
The knowledge of the mechanical properties of the dough is essential, as they are directly associated with the workability and sensory characteristics.
Understanding the mechanical properties of short doughs and their corresponding biscuits can guide specific phases of the production process, such as handling the biscuit on the production line, packaging, and distribution, during which the biscuit has to resist mechanical stresses (Brennan and Samyue, 2004;Cairano et al., 2021). found for sample RED 25%, followed by RED 60% and the lowest firmness in sample RED 35%.
The consistency, property related to dough density and consequently to the amounts and combinations of the formulation ingredients and development of gluten network, indicated higher value for the control sample.
For this parameter, RED 50% was statistically lower than the control (p<0.05). Nevertheless, other sugar reduced samples showed same profile as for firmness with lowest value found for RED 35%. These results show that this property may not be only related to the sucrose content.
Cohesiveness and viscosity properties for semi-solid samples, as the short dough, are related to flowability. 4248 ± 157 c 10537 ± 485 cd -1729 ± 248 b -838 ± 53 b Means followed by different letters in the same column are significantly different by Tukey test (p<0.05).

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are associated. On the other hand, the viscosity indicates the tendency to flow resistance. According to Table 2 dough cohesiveness increases (in module) according to the sucrose reduction in the formulation, and the viscosity index indicates the same behavior (in module). In this context, lower sucrose content leads to a greater interaction of the dough ingredients, which contributes to the gluten network development, resulting in a higher dough viscosity index. However, the 25% and 35% sucrose reductions did not differ significantly (p>0.05) from the control sample, indicating that these concentrations do not change the brittle structure characteristic of the short dough biscuit.

Texture Profile Analysis (TPA)
Double compression test mimics the mouth's biting action and determines the texture parameters, such as cohesiveness, chewiness, adhesiveness, fracturability, resilience, springiness and hardness. Table 3 presents the results of TPA and show the influence of sucrose content on texture properties of the biscuits.
Hardness represents the maximum force needed to compress the sample. Springiness corresponds to the capacity of the sample recovery after the application of the deformation force. Resilience is defined as the recovery energy necessary to return to its original form.
Cohesiveness is the measure of sample deformation before the rupture. Chewiness is the force required to chew a solid sample until the deglutination process (Chen and Opara, 2013). According to the results, hardness was not significantly different among all the samples (p>0.05), showing that sucrose content did not influence on it. Same profile was found for parameters such as adhesiveness, springiness and chewiness were not significantly different among samples.
Fracturability, in general, is a characteristic of products with high levels of hardness and low cohesiveness.
The results show lower values for the control sample and the sample with 65% sucrose reduction. The cohesiveness results confirm this behavior.

Structural Analysis
The scanning electron microscopy (SEM) (Figure 1) revealed a higher compaction of the biscuits with sucrose reduction. These samples also showed a greater amount of free starch (white halos), which was not properly incorporated into the mixture. The sucrose content can also influence this behavior, shifting the starch gelatinization point to a higher temperature, therefore samples with sucrose reduction have more apparent white halos (Manley, 2011). This possibly influenced the texture of the dough and the baked biscuits. On the other hand, porosity was

Sensory Analysis -Rate All That Apply (RATA)
Based on sensory analysis results, RED 25% had the highest overall acceptance value ( Figure 2). According to the attributes analysis, this sample is crunchy, with a buttery flavor and sweet taste. For tasters, the RED 25% sample generally has better sensory characteristics than the others. Figure 3 shows the three samples and the sensory attributes that characterize them. In the first canonical variable, it is observed that the control sample and the sample with 25% reduction of sucrose were very similar, while the sample with 35% reduction was at the other end of this canonical variable showing itself completely different. The control sample was perceived as "hard", "buttery", and "crunchy", while the sample with 25% reduction was perceived as "sweet" and "artificial".
The attributes artificial, metallic, and bitter indicate that the addition of thaumatin influenced the intensity of these attributes in the samples with reduction of sucrose, despite this, these samples presented satisfactory intensity as the texture attributes.

CONCLUSION
The results of the study indicated that the sucrose content in the biscuit formulation plays an important role in the rheological characteristics of the dough and the products. The extent of the effects is correlated with the level of sucrose reduction since, in the formulations tested, the 25% and 35% sucrose reductions produced minor changes in the rheological characteristics. This provided better physical quality of the biscuit dough, such as firmness, consistency, and hardness. These attributes positively influenced the sensory quality, as greater crunchiness and mouthfeel. The results obtained in this study show that it was possible to maintain the technological and sensory quality of the biscuits, from formulations containing less sucrose in combination with thaumatin. Means followed by different letters in the same column are significantly different (p<0.05).