Introduction

Burger buns are sweet yeast-leavened bread products that are highly appreciated by consumers for their good taste and soft texture. Sucrose is a principal ingredient in sweet baked goods. In particular in burger buns amount of sugar ranges generally between 70 and 120 g kg−1, and can be even higher depending in which country they are sold [1]. It is well known that increased consumption of added sugar is linked to numerous health problems such as obesity, cardiovascular disease, diabetes and dental caries. According to the WHO, the consumption of added sugar should not exceed 25 g day−1 to reduce the risk. As a result of the above mentioned conditions the demand for sugar-free or sugar-reduced products is increasing steadily [2].

Bakery is one of the leading sources for added sugar. In yeast-leavened bakery products sugar is an energy source for the baker’s yeast. It contributes to a higher CO2 and ethanol production, which leads to a faster and more efficient fermentation process [3]. Furthermore, sugar increases the gelatinisation temperature, which then affects volume and appearance of the final product [4]. This increase is caused by the interaction of the starch chains and sugar. Sugar stabilizes the amorphous regions of the starch and, consequently, restrict its flexibility [5]. Additionally, since sugar competes with gluten for water, the protein hydration is restricted and a dispersion of gluten polymers occurs, which results in less cross-linking of the protein network [6].

Regarding the product quality criteria sugar contributes to the colour formation in baked goods and Maillard reaction, which also influences flavour formation [7]. Finding a sucrose substitute is challenging, as the alternative needs to be able to mimic all of its attributes.

Scientific literature in sugar-reduction in burger buns is scarce. This study provides a fundamental understanding of the role of sugar in sweet yeast-leavened products, to provide pivotal principals to produce sugar-reduced or even sugar-free baked goods.

Materials and methods

Materials

Baker’s flour (Odlums Group, Dublin, Ireland) with a protein content of 120 g kg−1 and a moisture of 13.5%, tap water, sunflower oil (Musgrave Wholesale Partners, Dublin, Ireland), instant active dried baker’s yeast Saccharomyces cerevisiae (Puratos, Groot-Bijgaarden, Belgium), salt (Glacia British Salt Limited, Cheshire, UK), wheat gluten (Roquette, Lestrem, France), ascorbic acid (Storefast Solutions, Northfleet, UK), sodium-stearoyl-lactylate (Danisco, Copenhagen, Denmark) were used in this study. Sucrose (Siucra, Dublin, Ireland) was replaced by wheat starch (Roquette, Lestrem, France) as a bulking agent. The control burger bun, containing 100 g kg−1 added sucrose, was produced using these ingredients according to the recipe (Table 1).

Table 1 Recipe for the control burger bun containing 100 g kg−1 added sucrose based on flour
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Adjustment of the water content

To ensure the same dough consistency for each sucrose level, the water content of the sugar-reduced recipes was adjusted to the control using Farinograph E (Brabender OHG, Duisburg, Germany). The chamber temperature was kept at 30 °C. The sucrose content was reduced from 100 to 0 g kg−1 in 10 g kg−1 steps.

Dough analysis

Dough preparation

Instant active dried baker’s yeast (Saccharomyces cerevisiae) was activated for 10 min in tap water (25 °C). All solid ingredients were mixed for 1 min at minimum speed using Mixer Titanium Major (KM020) (Kenwood, Havant, UK), followed by the addition of oil and activated yeast solution to the solid ingredients, and kneaded for 8 min at speed one. For the evaluation of the viscoelastic properties of the dough and for the imaging of the protein network by confocal laser scanning microscopy, yeast was omitted.

Fermentation quality

The fermentation quality of the dough was determined using Rheofermentometer F3 (Chopin, Villeneuve-la-Garenne, France). 300 g of dough was prepared as described in 2.4.1 and placed in the fermentation chamber at 30 °C. A weight of 1500 g was placed on the dough and the dough was fermented for 3 h.

The dough development and the gas release were detected and the time needed to achieve the maximum height (T1), the total volume of the dough reached by carbon dioxide production (V tot), the maximum height of the dough (Hm), and the height of maximum gas formation (Hm′) were evaluated.

Viscoelastic properties of the dough

The viscoelastic properties of the dough were determined using the Rheometer Physica MCR 301 (Anton Paar GmbH, Ostfildern, Germany). Parallel plates’ geometries, serrated to prevent slippery, were used. The temperature of the lower plate was set to 30 °C and used in conjunction with a 50 mm diameter upper plate. The linear viscoelastic region was determined by performing an amplitude sweep as described by Hager et al. [8]. Frequency sweeps were conducted using a target strain of 0.01% and a frequency range from 100 to 0.1 Hz. Before each test, the sample rested for 5 minutes to allow equilibration. The viscoelastic properties were determined by the damping factor which represents the ratio between the lost (G″) and stored (G′) deformation energy of the system, tan (G″/G′).

Gluten-network development

The influence of sugar on the gluten-network development was determined using GlutoPeak (Brabender, Duisburg, Germany). For these measurements, the standard ratio of 50/50 (solid/liquid) regarding the recipe was used. The torque of the sample was measured running a constant speed of 2750 min−1 and a chamber temperature of 36 °C for 300 s.

Extensibility and resistance to extension

The Extensograph (Brabender, Duisburg, Germany) was used to analyse the extensibility of the dough. Dough pieces of 150 g were moulded and put in the proofing chamber at 30 °C and the extensibility of the dough was measured after proofing for 60 min.

Ultrastructure of the dough

Confocal laser scanning microscopy (CLSM) was used to analyse the gluten network visually. Dough containing 0, 50 and 100 g kg−1 added sucrose was prepared as described in 2.4.1. The gluten network was dyed by the addition of rhodamine B (Sigma-Aldrich, St Louis, MO, USA), using the method of Jekle and Becker [9]. After mixing the dough it was frozen overnight. A slice of one millimetre thickness was cut off the frozen dough using a scalpel and placed on the slide, covered with a glass cover slip. Dough samples were viewed using Olympus IX81 inverted laser microscope (Olympus, Center Valley, PA) with FluoView FV3-256 scanning unit under 20× objective. Proteins were monitored using λ exc = 543 nm and λ em = 590/50 nm.

Quality characteristics of burger buns

Burger bun preparation

Dough (80 g) was moulded and placed on a burger bun tray with a diameter of 105 mm and a height of 15 mm. The buns were fermented at 85% relative humidity and 30 °C in a proofer (KOMA SunRiser, Roermond, The Netherlands) for 1 h. After proofing, the burger buns were baked for 14 min at 200 °C using a deck oven (MIWE condor, Arnstein, Germany), cooled down for 2 h at room temperature and packed in plastic bags. The specific volume, the crumb texture, the crumb structure, and the colour of three buns per batch per sucrose level were analysed 2, 24, 48 and 120 h after baking.

Specific volume

The specific volume of the burger buns was determined using VolScan Profiler (Stable Micro Systems, Godalming, UK).

Crumb hardness and staling

For the determination of the crumb texture, the bottom and the top of the burger buns were cut to a resulting height of 35 mm. The texture was analysed using TA-XT2i texture analyser (Stable Micro Systems, Godalming, UK) as described by Dal Bello et al. [10].

Crumb structure

The crumb structure was analysed by a C-cell Bread Imaging system (Calibre Control International Ltd., Warrington, UK). The slice area [mm2] and the area of cells [%] were evaluated.

Crust and crumb colour

The colour of the crumb and crust was measured using Colorimeter CR-400 (Konica Minolta, Osaka, Japan). The CIE L* a* b* colour system was used for the evaluation of the measurements; the L*-value, which shows the lightness, was evaluated.

Water activity and microbial shelf life

The water activity of the crumb was measured with a water activity metre (HygroLab, Rotronic, Bassersdorf, Switzerland). The influence of sugar on the shelf life of burger buns was evaluated using the mould environmental challenge method indicated by Dal Bello et al. [10]. Burger buns were halved horizontally and put on a sterile metal rack. The crumb-side of each half was exposed to the environment for 5 min before they were packed separately in a sterile plastic bag and heat sealed. Two filter pipettes were inserted in each bag to ensure comparable aerobic conditions. The samples were stored in a room with an average temperature of 20 ± 2 °C and the mould growth was monitored for 14 days. The mould growth was visually evaluated and rated as “mould-free”, “<10% mouldy”, “10–24% mouldy”, “25–49% mouldy”, “>50% mouldy”.

Sensory evaluation

Burger buns containing different amounts of added sucrose were evaluated regarding their sweetness-intensity and hedonic, which included appearance, flavour, aroma, texture and sweetness by a trained sensory panel of 12 people. The crust of the buns was removed to prevent optical influences. The panellists judged the samples on a scale from 0 to 10. Regarding the sweetness-intensity 0 was “not sweet” and 10 described as “very sweet”, whereas the scale for the hedonic ranged from 0 for “extremely dislike” to 10 for “extremely like”, with 5 indicating “neither like nor dislike”. The sensory evaluation was performed in duplicates on two different days. The evaluated samples were burger buns containing 0–100 g kg−1 sucrose in 20 g kg−1 steps. In addition, the panel was asked for their favourite sample.

Statistical analysis

Dough analysis and burger bun analysis were performed in triplicates. A variance analysis (one-way ANOVA, p ≤ 0.05, Tukey test) was performed using Minitab 16. Additionally, correlation analysis between all results and the sucrose level was conducted using Microsoft Excel 2010 and PCA analysis was performed using R. For the PCA analysis the sensory evaluation was left out.

Results

To understand the role of sugar in the burger bun system, the added sucrose content was replaced by wheat starch and dough attributes as well as burger bun properties were investigated. The sweetness-intensity and other sensory properties were determined by a sensory panel. For a deeper inside a correlation analysis, as well as, a PCA was performed.

Adjustment of the water content

In this study sugar was reduced from 100 to 0 g kg−1. The sugar was replaced by wheat starch as a bulking agent. Preliminary studies (data not shown) revealed that wheat starch was the most suitable replacement. Nevertheless, starch has a higher water holding capacity than sugar. Therefore, the water level of the various formulations needed to be adjusted using farinograph (Table 2). A total replacement of sucrose by wheat starch required 12.5% more water addition to ensure the same dough consistency of the control recipe.

Table 2 Results of dough analysis
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Dough analysis

Fermentation quality

The characterisation of the dough development and gaseous release during fermentation was performed using the rheofermentometer and included an evaluation of Hm, Hm′, V tot and T1. Dough without any addition of sucrose showed the lowest Hm in the dough development curve (Table 2), whereas the highest Hm was achieved by adding 10 g kg−1 sucrose, followed by the addition of 100 g kg−1 sucrose. Furthermore, the longest time needed for the dough to achieve the maximum height (T1) was recorded for the dough, where no sugar was added while the fastest dough development occurred when 20 g kg−1 sucrose was added.

The gas release curve gives the values Hm’, and V tot. The curve of dough containing little amounts of added sucrose (0–20 g kg−1) increased at the beginning of the fermentation, followed by a decrease and a second increase. Dough containing more than 20 g kg−1 added sucrose did not show any decrease of gas release. Hm′ and V tot showed the highest values for dough containing 70 g kg−1 added sucrose. The lowest values were measured when no sucrose was added.

Viscoelastic properties

Viscoelastic properties of the dough are evaluated by determining the behaviour of G′ and G″ during a frequency sweep. All measurements showed G′ > G″ in the dough system. Consequently, the dough system is more elastic than viscous. Since, the damping factor increased with increasing sucrose content and reached the highest value, when 100 g kg−1 sucrose was added (Table 2), the viscous portion increased with the addition of sucrose.

Gluten-network development

Figure 1 shows the effect of sucrose on the gluten-network formation measured under shearing over time in the GlutoPeak. By increasing the sucrose level, the torque force decreased (Table 2) indicating a progressive delay in gluten-network development.

Fig. 1
figure 1

Illustration of the gluten network development of recipes containing 0, 50 and 100 g kg−1 added sucrose. The graph shows the mean torque of the recipes (duplicates) during shearing and the standard deviations are shown as error bars. The micrographs show the gluten network (white pattern) taken by a confocal laser scanning microscope of dough with, a 0 g kg−1 added sucrose, b 50 g kg−1 added sucrose and c 100 g kg−1 added sucrose

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Extensibility and resistance to extension

The extensibility and the resistance to extension were measured to characterise the dough strength and the gluten-network quality after fermentation (Table 2). Extensibility increased with increasing sucrose level and reached the highest value, when 80 g kg−1 sucrose was added. Except for doughs containing 60 and 100 g kg−1 added sucrose, the resistance to extension did not show significant differences. Dough containing 60 g kg−1 sucrose resulted in the highest resistance to extension, whereas an addition of 100 g kg−1 sucrose led to the lowest value.

Ultrastructure of the dough

CLSM was applied to visualise the influence of added sucrose on the gluten network of the dough (Fig. 1). Micrograph (A) shows dough without any addition of sucrose and exhibits an interconnected and compact network of protein filaments (white), whereas a change in the compactness of the network is clearly recognizable by the addition of 50 g kg−1 sucrose in micrograph (B). The addition of 100 g kg−1 sucrose resulted in a fairly weak network, indicated by occasionally occurring protein aggregates [micrograph (C)].

Quality characteristics of burger buns

Specific volume

Since the specific volume is an important attribute of baked goods, the effect of sucrose on the specific volume of burger buns containing different levels of sugar was determined (Table 3). In general, a high specific volume with a dense crumb structure is desired for burger buns. In small to moderate amounts of added sucrose (10–40 g kg−1) the specific volume increased, followed by a decrease, when higher amounts of sucrose (50–100 g kg−1) were added. The specific volume of the sucrose-free burger bun was the lowest, whereas the highest value was measured, when 40 g kg−1 sucrose was added.

Table 3 Results of the quality characteristics of burger bun
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Crumb hardness and staling

The crumb texture is another very important characteristic for bakery products. The changes in crumb hardness over time allow prediction staling behaviour of the product. Furthermore, a commercial burger bun is characterized by a soft, but dense crumb.

The crumb of the sucrose-free burger bun showed the highest hardness after baking. 10 g kg−1 added sucrose resulted in a significant decrease in crumb hardness, which decreased with the addition of more sucrose up to 50 g kg−1. The addition of more sugar resulted in a harder crumb. The second highest crumb hardness was measured, when 100 g kg−1 sucrose was added. Regarding the staling rate, burger buns containing sucrose showed a very low staling rate up to 48 h, followed by a significantly harder crumb after 120 h. Interestingly, the crumb hardness of buns containing 100 g kg−1 added sucrose did not differ significantly from no-added-sucrose buns after 120 h.

Crumb structure

The crumb structure is an important parameter for the evaluation of the burger bun quality. Ideally, the crumb of a commercial burger bun is dense with many small cells and without any holes. The values for the slice area and the area of cells of the burger buns were evaluated (Table 3). The crumb structure showed no significant differences between the data after 2 h and after 120 h. Consequently, the analysis after 2 h are described and discussed. Figure 2 shows the appearance of the crumb structure. The addition of 40 g kg−1 sucrose caused an increased cell area compared to a no-added burger bun (Table 3). The highest area of cells occurred, when 60 g kg−1 sucrose was added. The difference in cell area of buns containing 20–100 g kg−1 added sucrose was not significant.

Fig. 2
figure 2

Crumb structure (first row) and crust appearance (second row) of burger buns containing 0–100 g kg−1 (A–K)

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Crust and crumb colour

Commercial burger buns are characterized by their golden-brown crust-colour. Due to the fact that sugar contributes to browning, the L*-value, as an indicator for lightness, was evaluated. The higher the L*-value, the lighter the analysed product. Regarding the colour of the crumb, the amount of sucrose did not affect the L*-value. In contrast, the sucrose level showed a significant effect on the colour of the crust (Table 3). Without added sucrose the burger bun showed the palest crust, whereas the darkest crust occurred, when 80 g kg−1 sucrose was added. This value did not differ significantly from the L*-value of the 40 g kg−1-sucrose-bun. The effect of sucrose on the crust-colour is illustrated in Fig. 2.

Water activity and microbial shelf life

The water activity (a w) reflects the amount of free water in the system, which has an impact on the shelf life of the product. The addition of sucrose caused decrease in water activity. The crumb of the burger buns without any added sucrose resulted in a water activity of 0.948 ± 0.004 and differed from the control significantly (Table 3). Figure 3 reveals the effect of added sucrose on the shelf life of burger buns. Sucrose prolonged shelf life significantly from 4 (no-added-sucrose) to 10 days (control) (Table 3).

Fig. 3
figure 3

Shelf life evaluation of burger buns containing 0 g kg−1 (a), 50 g kg−1 (b) and 100 g kg−1 (c) added sucrose. The number of slices for each mould group (“mould-free”, “<10% mouldy”, < 10-24% mouldy”, “<25-49% mouldy” and >50% mouldy”) was counted on each day over 14 days. The graph shows mean values with standard deviations as error bars

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Sensory evaluation

An investigation of the sweetness-intensity of burger buns containing different amounts of added sucrose was performed. Burger buns without added sucrose showed an average sweetness-value of 1.6 ± 1.3 and differed from the other samples significantly (p ≤ 0.05). The panel judged the sweetness of buns with 20 g kg−1 added sucrose with 3.4 ± 1.6, which differed also significantly from the other samples tasted. Burger buns containing 40 and 60 g kg−1 added sucrose could not be distinguished from each other (40 g kg−1=5.3 ± 1.4; 60 g kg−1=6.1 ± 1.2). Additionally, 100 and 80 g kg−1 added sucrose differed significantly from the other samples regarding sweetness-intensity, but not from each other. Thus, the panel could distinguish between samples containing little amounts of sucrose, but with the increase of sucrose the perception of sweetness decreased. No significant differences occurred in the hedonic evaluation regarding appearance, flavour, aroma, and texture. The evaluation of the sweetness preference showed that burger buns without any sucrose addition and buns with 100 g kg−1 added sucrose were disliked the most. Regarding this evaluation buns with 20 g kg−1 (6.0 ± 1.7), 40 g kg−1 (6.0 ± 2.0) or 60 g kg−1 (5.4 ± 2.0) added sucrose did not differ significantly from each other.

The most preferred burger bun regarding all attributes contains 40 g kg−1 sucrose (33.33% of the panellists), followed by the addition of 60 g kg−1 sucrose (29.17% of the panellists).

Principal component analysis (PCA)

PCA analysis was performed for all dough characteristics as well as for burger bun characteristics. Dough characteristics resulted in three groups: 0 g kg−1 added sucrose formed one group (Group 1), 10–70 g kg−1 added sucrose belonged to Group 2 and Group 3 included 80, 90 and 100 g kg−1 added sucrose dough.

PCA for burger buns resulted as well in three groups. Group A is represented by 0 g kg−1 added sucrose; Group B is formed by 10–60 g kg−1 added sucrose buns. 70–100 g kg−1 added sucrose buns are defined in Group C.

Discussion

This study examined the impact of added sucrose on the dough quality, physical properties, shelf life and sensory characteristics of burger buns.

Depending on the added amount, sucrose can increase the fermentation quality, as well as decrease it by inhibiting the yeast metabolism. Indeed, on the one hand yeast needs monosaccharides for the growth and the production of CO2 [1]. On the other hand sugar can slow down the yeast’s metabolism due to high osmotic stress [11].

Hm indirectly describes the performance of yeast and the quality of the microstructure of the dough. A high Hm is the result of a dough system characterized by a combination of high gas production and firm microstructure [12]. Regarding Hm and T1, dough containing different sucrose levels did not differ significantly from each other. Nevertheless, the lowest Hm and the longest T1 occurred in dough with no-added-sucrose. A low Hm and a long T1 could be attributed to a reduced metabolic activity of the yeast. High sucrose levels (90 and 100 g kg−1) could cause hyperosmolarity, which results in osmotic stress for the yeast negatively influencing the dough development [13].

The gas release curve showed the gas formation during fermentation resulting in Hm′ and V tot. Sucrose levels between 50 and 100 g kg−1 are negatively correlated to Hm’ (r = −0.86, p ≤ 0.05), which can be explained by the reduction of fermentation activity due to hyperosmolarity in the dough system caused by sucrose [11]. Sucrose concentration of 0–40 g kg−1 correlated positively with V tot (r = 0.97, p ≤ 0.01), but negatively, when 50–100 g kg−1 was added (r = −0.87, p ≤ 0.05). Reduced fermentation led to a decreased CO2 production, resulting in a lower V tot [1].

The results of the viscoelastic properties for the different doughs revealed a positive correlation between sucrose level and damping factor (r = 0.868, p ≤ 0.001). Gluten competes with sugar for water; consequently, a high sugar level reduces the hydration of the protein and delays the protein-network development, resulting in an increase of viscous properties of sugar-rich dough [14].

GlutoPeak measurements showed a positive correlation between the amount of added sucrose and the peak maximum time (PMT) (r = 0.913, p ≤ 0.001) as well as a negative correlation between the amount of added sucrose and the torque maximum (TM) (r = −0.989, P ≤ 0.001). With increasing sucrose level a decrease of gluten hydration is observed resulting in a slower gluten-network formation, (which caused the delayed PMT), and to a weaker gluten network, (which is highlighted by the decreased TM). This emphasises the fact that sucrose delayed and weakened the gluten network [15]. Further evidence for a weaker protein network caused by sugar is shown in the CLSM micrographs (Fig. 1).

The weak gluten network caused by the addition of sucrose affected also the extensibility and the resistance to extension of the dough. Dough is characterized as strong, if its extensibility is low and its resistance to extension is high at the same time [16]. The dough extensibility positively correlated with the sucrose level (r = 0.831, p ≤ 0.005). The resistance to extension correlated negatively with sugar additions of 50–100 g kg−1 (r = −0.96, p ≤ 0.005), which means the dough became weaker [17].

In addition to the effect of sucrose on the dough characteristics, sugar also affected the quality of the burger buns.

Due to a combination of high CO2 production and decreasing resistance to extension in the dough, the highest specific volume was achieved by an addition of 40 g kg−1 sucrose. Correlation analysis exhibited a negative correlation between sucrose levels of 50–100 g kg−1 and the specific volume of the buns (r = 0.90, p ≤ 0.05). The decrease of the specific volume of buns containing more than 50 g kg−1 sucrose could be due to the inhibited yeast activity during fermentation. The results of Hm′ (all sucrose levels) during fermentation and the specific volume of the buns correlated positively with each other (r = 0.840, p ≤ 0.005).

The specific volume and the crumb hardness are often related to each other. A positive correlation between sucrose level and crumb hardness occurred, when 50 g kg−1 sugar or more were added (r = 0.897, p ≤ 0.05). A less efficient gas formation (Hm’) resulted in a harder burger bun (r = −0.929, p ≤ 0.0001). According to D’Appolonia and Morad [18] bread staling is mostly characterized by the retrogradation of the starch molecules. Sucrose was replaced by wheat starch in recipes containing less than 100 g kg−1 sucrose. However, the crumb hardness of no-added-sucrose buns and the control did not differ significantly from each other after 120 h. Hence, sucrose contributed to the staling process, which is in fact not desired.

Sucrose delays starch gelatinisation and protein denaturation during the baking process, which results in an expansion of the gas cells by CO2 and water vapour before the dough becomes a set structure [19]. Sucrose addition of 0–40 g kg−1 in the burger buns correlated positively with the area of cells (r = 0.929, p ≤ 0.05). This increasing amount of cells is most likely the result of more extensible dough in combination with a weak protein network, which allows the dough to rise and avoids a collapse of cells. As expected, the slice area correlated positively with the specific volume (r = 0.979, p ≤ 0.0001) and Hm′ (r = 0.899, P ≤ 0.0005).

The formation of a golden crust is influenced by the level of Maillard reaction and caramelisation in which sugars are involved, and has an effect on the lightness of the final product [20, 21]. Burger buns containing 0–30 g kg−1 added sucrose differed significantly in the L*-value, whereas no significant difference in lightness occurred, when 30 or 100 g kg−1 sucrose was added. The L*-value of the crust correlated negatively with the amount of added sucrose up to 70 g kg−1 (r = −0.888, p ≤ 0.005). The addition of 30 g kg−1 sucrose is the minimum amount of sugar to be added to achieve a desired brown crust (Table 3).

Sugar also impacts on the water activity of a product and, therefore, the microbial shelf life. Water activity correlated negatively with the amount of added sucrose (r = −0.927, p ≤ 0.0001). Since sugar is known to lower the water activity in a system [22], a significant decrease in aw from 0.948 ± 0.004 in sugar-free burger buns to 0.915 ± 0.006 in buns containing 100 g kg−1 sucrose was expected. The water content had to be adjusted for each sucrose level, to achieve the same dough consistency. Hence, the lower the sucrose content, the higher the amount of wheat starch and the higher the adjusted water in the dough system (Table 2). Consequently, the water activity could reflect the higher amount of added water. However, sucrose is a hygroscopic agent and binds free water, which contributed more likely to the lower water activity of crumbs containing higher amounts of sucrose. Additionally, water activity correlated negatively with PMT (r = −0.944, p ≤ 0.0001), but positively with TM (r = 0.893, p ≤ 0.0005). The more water available in the dough system, the higher and faster the gluten hydration and the stronger the network is. According to Mathlouthi [23] not all water-activity-depressors extend microbial shelf life. Shelf life of buns containing 10 g kg−1 added sucrose did not differ significantly from the ones with 90 g kg−1 added sugar (Fig. 3). Sometimes a hygroscopic ingredient, such as sugar, does not bind water strongly enough, which results in mobile water allowing microbial growth [1]. Nevertheless, a shelf life extension from 4 ± 1 day for buns without added sucrose to 10 ± 1 day for 100 g kg−1 added sucrose buns occurred.

One typical attribute of sugar is its sweet taste. The threshold for sweetness in solution is 6.8 g/L, which is lower than in solid systems [24]. Regarding sweetness preference, there are four different types of panellists defined: Type I individuals show an inverted U-function with increasing sucrose concentration, whereas Type II individuals prefer sweetness in a monotonic increasing way. People belonging to Type III dislike high concentration of sugar, and show a monotonic decrease with increasing sugar level, and Type IV individuals experience a flat relationship between sweet preference and sugar concentration [25]. The sensory evaluation showed that some panellists preferred sweet samples and could be categorized as Type II, whereas on the other hand other panellists liked non-sweet samples more and belonged to Type III. Considering all individual results together the group could be categorized as Type I.

The overall preference of the burger buns showed that the panellists liked the burger buns containing 40 or 60 g kg−1 sucrose the most.

The results of this study provide a deep insight of the impact of sucrose on sweet yeast-leavened products. The desired attributes regarding product quality could be achieved by a reduced sucrose addition of 40 to 60 g kg−1. However, PCA analysis showed that an addition of at least 70 g kg−1 sucrose is necessary to ensure the same burger bun quality considering all attributes. Based on this result, future studies might deal with alternative replacement of sugar by other bulking agents with functional activities. When functional bulking agents are considered as sugar replacer in bakery products, those characterized by low water absorption/water holding capacity are preferred, since high water addition in the recipe will significantly compromise dough rheology and bakery quality parameters.