Introduction

Bread quality is characterized by flavor, nutritional value, texture, and shelf life. In the bakery industry, these properties are achieved by adding bread improvers or enzymes. Alternatively, the use of sourdough affects all aspects of bread quality and meets consumers’ demands for fewer additives [1]. Although whole grain foods are known to be beneficial to health, their sensory properties are a limiting factor for consumption. It is known that the use of whole grains or adding bran fractions affects the bread process and end product properties. Compared to wheat bread, the addition of bran fractions results in a darker color, specific flavor, lower specific volume, and denser crumb texture, and these effects are generally considered negative by consumers [2]. The development of a porous crumb is primarily caused by the components in the dough, the conditions during processing, the activity of the yeast, the temperature during fermentation, and the formation of gas bubbles. A bread product with a well-developed porous crumb structure might have a better gas retention capacity, which leads to a volume increase and a decrease in crumb hardness with enticing sensory qualities [3]. The low gas holding capacity and coarser crumb structure of whole grain dough are usually attributed to the inhibition of the gluten network or dough foam structure by bran particles [2].

The sourdough ecosystem consists of a mixture of flour and water fermented by yeasts and lactic acid bacteria (LAB) [4]. The sourdough fermentation remains poorly understood due to its complex biological system and the numerous factors influencing its final characteristics. They distinguish between exogenous and endogenous factors. The composition of the cereal substrate (fermentable carbohydrates, N-sources, minerals, vitamins, lipids, growth inhibitors, enzyme activity), and the grains’ native microbiota are the endogenous factors. The process parameters that are used, such as temperature, oxygen content, dough yield, quantity of backslopping, sodium chloride addition, fermentation time, number of propagation steps, and starter cultures are the exogenous factors [5].

During sourdough fermentation, the synergistic effects of various organic acids, enzymes and pH reduction causes hydrolysis and dissolution of large molecules (e.g., gluten proteins, non-starch polysaccharides, and cell wall polysaccharides) in whole wheat flour. The increase in free amino acids and the production of flavor precursors results with an improvement in flavor. By the hydrolysis of polysaccharides, the rheological quality of whole wheat dough and the texture of the product can be improved [6]. The sourdough inhibits microbial spoilage due to the acidification and various antimicrobial compounds such as organic acids and bacteriocins and also can delay staling due to the production of exopolysaccharides and enzymatic activities related to the hydrolysis of starch and the disruption of the continuous gluten protein matrix [7].

The development of starter culture in the bakery industry is initially based on the isolation of natural microflora from sourdough, biochemical and taxonomic characterization of microorganisms (predominantly lactobacilli), and selection of suitable strains as starter cultures through time-consuming application trials [8]. The advantage of commercial starters is that they provide reliable quality in bread production while improving control of sourdough production and enabling sourdough production in a one-step process. The performance of starter cultures in the fermentation process has been reported as a decrease in pH value, and an increase in total titratable acidity and organic acid production [9]. With the development of new sourdough products and equipments that makes them easy to use, sourdough technology is becoming more and more common in both small-scale and industrial bakeries [10].

One of the microorganisms that is most frequently used in the food industry is LAB. Infinitive viewpoints for technological processes are provided by LAB because of their diversity and variability. Lactiplantibacillus plantarum is a facultative heterofermentative bacteria that is commonly used in baking and is known for the structure and acidity it gives to the cereals used for fermentation [11]. Fructilactobacillus sanfranciscensis, a heterofermentative LAB, is perfectly adapted to the sourdough environment. Maltose, which is continuously produced with glucose by flour amylases from starch, is its preferred carbohydrate [12]. Since the metabolic properties of LAB are strain-specific, the choice of starter LAB for sourdough is one of the most important factors in sourdough bread making [13]. The overall taste of bread is affected by its lactic and acetic acid content. Homofermentative LAB can almost completely convert hexoses to lactic acid (> 85%), whereas heterofermentative LAB can reduce hexoses to lactic acid, acetic acid/ethanol, and CO2. In addition to the starter culture, temperature affects the ratio of lactic acid to acetic acid. Lactic and acetic acids are also produced by heterofermentative LAB from pentoses [14].

The aim of this study is to investigate the effects of the wheat variety (Tosunbey, Kenanbey, İkizce-96, Bezostaja-1), sourdough treatment (Spontaneous fermentation (SP), Fructilactobacillus sanfranciscensis (LS) and Lactiplantibacillus plantarum (LP)) and sourdough level (0–10-20–30%) on technological characteristics of whole wheat bread. Total titratable acidity, pH, specific volume, crust and crumb color, textural and sensory properties of whole wheat sourdough breads were determined.

Materials and methods

Materials

The wheat varieties (hard white winter: Tosunbey and Kenanbey, hard red winter: İkizce-96 and Bezostaja-1) used in the study were grown in İkizce, Ankara,  Türkiye. For sourdough preparation, the LAB strains (Fructilactobacillus sanfranciscensis (DSM 20663) and Lactiplantibacillus plantarum (DSM 20174)) were supplied from DSMZ-German Collection of Microorganisms and Cell Cultures in lyophilized form and whole wheat flour from a local market.

Milling

Wheat samples were milled by using a Chopin CD 1 laboratory mill (Villeneuve La Garenne, France) after conditioning. The bran fractions were ground by a hammer mill (Perten 3100, Huddinge, Sweden) equipped with a 500 μm sieve. The fine ground bran, and flour obtained from the roller mill were mixed to get whole wheat flour.

Flour analysis

The moisture, protein, gluten content, falling number and farinograph parameters were determined according to the official methods of AACC 44-15A, 46–30, 38-12A, 56-81B and 54–21, respectively [15]. The ash content and Zeleny sedimentation were determined by ICC Method 104/1 and 116/1, respectively [16]. Modified Zeleny sedimentation was performed by incubating at 37 °C for 2 h after the addition of bromophenol blue [17].

Preparing sourdough

The LAB strains of Fructilactobacillus sanfranciscensis  and Lactiplantibacillus plantarum were prepared as described in our previous work [18]. Briefly, the strains stored at -80 °C in de Man Rogosa Sharpe (MRS) broth (Merck) containing 30% (v/v) glycerol, were incubated at 30 °C overnight. After the second overnight incubation, the inoculum was centrifuged. The pellet was resuspended (LAB: 2 × 109 CFU/mL) and mixed with commercial whole wheat flour to obtain a dough yield (DY) of 250. DY = [(g flour + g water)/g flour] × 100. The mixture was fermented at 30 °C for 18 h. Spontaneous sourdough was obtained by fermenting the mixture of whole wheat flour and water in the same conditions.

Bread making

The process of bread making was performed according to AACC Method No: 10–11 [15] with some modifications, as described in our previous work [18]. Briefly, the bread recipe included 1.5% salt, 2% fresh yeast, 100 ppm ascorbic acid, 0.004% α-amylase and sourdough at the levels of 0–10-20–30%, based on 100 g flour. The flour and water content (according to farinograph water absorption) in the formula were calculated considering the amounts in the sourdough, and approximately 170 g of dough was obtained. After fermentation (30 + 30 min) and proofing (45 min), the baking was performed at 215 °C for 25 min.

Specific volume of bread

The volume of bread was determined according to AACC Method No: 10–05 (by displacement of rapeseed) after 2 h from baking [15]. The specific volume was calculated as the following equation: Specific volume (cm3/g) = Volume (cm3) / Weight (g).

Color analysis

The color of whole wheat flour, crumb and crust were determined using a Hunterlab Mini Scan XEplus (USA) according to the CIE L*a*b* system.

pH and total titratable acidity (TTA)

The pH of sourdough, dough and bread samples was determined according to AOAC Method No: 943.02 [19], and TTA was determined according to Özkaya and Özkaya [20]. For TTA, 5 mL acetone was added to 10 g of sample and homogenized with 95 mL of distilled water. TTA was expressed as ml of 0.1 mol/L NaOH needed to achieve a final pH of 8.5.

Texture profile analysis (TPA)

TPA of bread crumbs was performed using a texture analyzer (Stable Micro Sytems, TA-XT plus, Godalming, Surrey, England) equipped with a 5 kg load cell and 36 mm cylindrical probe (P/36). A stack of two slices (12.5 mm thickness) was compressed under the following conditions: pre-test speed: 1.0 mm/s, test speed: 2.0 mm/s, post-test speed: 2.0 mm/s, compression ratio: 40%, trigger force: 20 g, time: 5 s. Hardness, springiness, cohesiveness and chewiness were determined on the first (24 h) and third days (72 h) of storage.

Sensory evaluation

Sensory evaluation was performed by ten semi-trained panelists based on texture, color, flavor, taste, and overall acceptability. The panelists were asked to evaluate the coded bread samples according to a 9-point hedonic scale (1. Extremely bad, 2. Very bad, 3. Bad, 4. Somewhat bad, 5. Neither likeable nor bad, 6. Likeable at an acceptable level, 7. Highly liked, 8. Very highly liked, 9. Exceptionally liked). The results are given as a polar coordinate graph with the average scores for each criterion.

Statistical analyses

In the study wheat variety (Tosunbey, Kenanbey, İkizce-96, Bezostaja-1), sourdough treatment (spontaneous fermentation, Lactiplantibacillus plantarum, Fructilactobacillus sanfranciscensis), and sourdough level (0–10-20–30%) were taken as factors. The experimental design was 4 × 3x4 factorial in a randomized block trial design with three replicates. The results were evaluated by analysis of variance (ANOVA), and differences between means were evaluated by Duncan’s multiple range test using XLSTAT 2020.

Results and discussions

Quality analysis of whole wheat flour

Quality analysis of whole wheat flour is presented in Table 1. The differences between whole wheat flours in terms of ash, protein, wet and dry gluten content, gluten index, sedimentation, falling number, farinograph parameters and color (L*, a*, b*) were significant (p < 0.05). Whole wheat flour of the Kenanbey had the highest ash content (1.50%), while there was no statistically significant difference between other varieties (1.46%). The protein content of samples ranged from 12.2 to 15.6% and İkizce-96 had the highest value. Zeleny sedimentation and modified Zeleny sedimentation varied between 11–19 mL and 20–29 mL, respectively. The highest Zeleny sedimentation value was obtained in İkizce-96 and the lowest in Tosunbey. Sedimentation value is one of the important methods used to determine protein quality in wheat. The wet and dry gluten content and gluten index varied between 25.0–37.3%, 8.3–12.2% and 41.6–97.6%, respectively, also Tosunbey had the lowest gluten content. Gluten plays a dominant role in the formation of the viscoelastic structure of bread dough, which depends on its kneading, processing and gas-holding capacity. The falling number indicates the amylase activity present in the flour. Low amylase activity causes the amount of sugar usable by yeast cells to be insufficient, which causes the bread volume to be low. When the enzyme activity is too high, the pore structure of the crumb is disrupted, the bread volume is not at the desired level and the crumb shows sticky properties. In bread production, the falling number is required to be between 200–250 s. If the falling number is < 150 s, amylase activity is considered extremely high, and if it is > 300 s, amylase activity is considered very low [17]. Falling number of whole wheat flours varied between 367–414 s, consequently the alpha-amylase activity of the flours was low for bread making. The farinograph development time varied between 2.6–6.4 min, water absorption between 64.4–67.0%, stability between 2.6–8.4 min, and farinograph quality number (FQN) between 56–129 mm. Tosunbey had the highest development time, stability, FQN and the lowest water absorption. Flour with a development time and stability of ≤ 1 min is classified as weak, while flour with a development time of 3–5 min and stability of 8–14 min is classified as strong [21]. The color of the whole wheat flours varied between 85.83–89.67, 1.71–2.62, and 11.79–13.61, respectively for L*, a*, and b* values.

Table 1 Quality analysis of whole wheat flour
Full size table

pH and TTA

The pH and TTA of the sourdoughs after mixing (0th hour) and after fermentation (18th hour) are given in Table 2. No statistically significant difference was observed between sourdoughs in terms of pH and TTA after mixing (p > 0.05). The pH of sourdoughs for SP, LP and LS treatments were 6.35, 6.27, and 6.26 after mixing and 4.80, 3.70, and 3.71 after fermentation, respectively. The TTA of sourdoughs increased after fermentation. While SP had the lowest TTA, there was no statistically significant difference between LP and LS treatments (p > 0.05). The TTA of SP, LP and LS treatments were 2.88, 3.15, 3.13 after mixing and 6.09, 14.62, and 15.28 after fermentation, respectively.

Table 2 pH and total titratable acidity (TTA) of the sourdough
Full size table

The effects of wheat variety, sourdough treatment and sourdough level on the pH and TTA of dough and whole wheat bread are given in Table 3. WV, ST, SL factors, and WVxST, WVxSL interactions had a significant effect on pH after kneading (p < 0.01). Also, the effect of all factors and STxSL interaction on pH was significant after fermentation (p < 0.01). For whole wheat breads all of the factors, WVxSL, STxSL (p < 0.01) and WVxST interactions (p < 0.05) had significant effects on the pH value. In bread samples among the wheat varieties, the highest pH and the lowest TTA were determined at Tosunbey (5.79 and 5.50), among the sourdough treatments at SP (5.93 and 5.28), and among the sourdough levels at 0% (6.02 and 4.93), while the lowest pH and the highest TTA were determined at İkizce-96 (5.64 and 6.76), LS (5.61 and 6.75) and 30% (5.41 and 7.10). The complexity of the microbial ecology, or its metabolites, and the compounds present in the raw material have an impact on pH and TTA values, even if variables like fermentation time and temperature, and dough yield are held constant [22]. Considering the LAB used in this study is homofermentative (LP) and heterofermentative (LS), the sourdough process could have an impact on the levels of organic acids, and finally on pH and TTA.

Table 3 Effects of wheat variety, sourdough treatment and sourdough level on pH, TTA, volume and specific volume of whole wheat bread
Full size table

The effects of significantly important interactions for pH are given in Fig. 1. WVxST interaction showed that Tosunbey and SP had the highest pH for dough (after kneading) and bread (Fig. 1a). STxSL interaction showed that as the sourdough level increased, pH decreased, and the rate of decreasing was lowest in SP for dough (after kneading and after fermentation) and bread. Also, the lowest pH was determined with LS and 30% (Fig. 1b). WVxSL interaction for whole wheat bread showed that pH decreased as the sourdough level increased, and 0% sourdough level of Tosunbey and Kenanbey had the highest pH (Fig. 1c).

Fig. 1
figure 1

The effects of the interactions of wheat variety and sourdough treatment (WVxST) for dough (after kneading) and bread (A), sourdough treatment and sourdough level (STxSL) for dough (after kneading, after fermentation) and bread (B), wheat variety and sourdough level (WVxSL) for bread (C) on pH. a-h: Different lower case letters indicate significant differences between samples for dough after kneading, a-h: Different lower case letters in italics indicate significant differences between samples for dough after fermentation, A–H: Different capital letters indicate significant differences between samples for bread

Full size image

The effects of significantly important interactions for TTA are given in Fig. 2. STxSL interaction showed that the TTA of dough (after kneading and after fermentation) and bread samples increased as the sourdough level increased, and the increasing rate was the lowest in SP. The highest TTA was obtained with a 30% sourdough level of LS (Fig. 2a). As shown in the WVxST interaction graph of dough samples after kneading, LS had the highest TTA with İkizce-96, while SP had the lowest TTA with Bezostaja and Tosunbey (Fig. 2b).

Fig. 2
figure 2

The effects of the interactions of sourdough treatment and sourdough level (STxSL) for dough (after kneading, after fermentation) and bread (A), wheat variety and sourdough treatment (WVx ST) for dough (after kneading) (B) on TTA. a–h: Different lower case letters indicate significant differences between samples for dough after kneading, a–h: Different lower case letters in italics indicate significant differences between samples for dough after fermentation, A–H: Different capital letters indicate significant differences between samples for bread

Full size image

Volume and specific volume of breads

The effects of wheat variety, sourdough treatment and sourdough level on volume and specific volume of whole wheat breads are given in Table 3. The bread volume varied between 348–369 cm3, 361–370 cm3 and 355–373 cm3 for WV, ST and SL factors, respectively. İkizce-96 (2.56 cm3/g) and Tosunbey (2.38 cm3/g) had the highest and the lowest specific volume, respectively. The lower specific volume of Tosunbey was the probable result of lower protein content, Zeleny sedimentation, and gluten content (Table 1). SP had the highest specific volume (2.52 cm3/g), while the difference between LP and LS was not statistically significant (2.46 and 2.48 cm3/g, respectively) (p > 0.05). The specific volume varied between 2.55 and 2.42 cm3/g for sourdough levels of 0–30%. The amount of gas created during fermentation and the dough’s ability to hold gas are the primary factors influencing loaf-specific volume. Since proteins have a positive net charge in an acidic environment, there are more intramolecular electrostatic repulsion forces. This causes the gluten proteins to unfold, increasing their solubility and weakening their structure [22].

The effect of significantly important interactions for the specific volume of whole wheat bread is given in Fig. 3. WVxST interaction showed that LS treatment of İkizce-96 had the highest specific volume, while LP and LS treatments of Tosunbey had the lowest values (Fig. 3a). WVxSL interaction showed the 0% sourdough level of İkizce-96 had the highest, and the 30% sourdough level of Tosunbey had the lowest specific volume (Fig. 3b). As seen in the ST x SL interaction graph (Fig. 3c), increasing levels of sourdough caused a decrease in specific volume and the decreasing occurred less in SP than in other sourdough treatments. While the highest specific volume was obtained with 0% sourdough level, the lowest specific volume was at 30% sourdough level of LP treatment. Similarly Tomic et al. [22] determined that 25 g and 50 g/100 g wheat sourdough produced bread had a lower specific volume compared to control bread. But there are conflicting results in the literature regarding the effect of sourdough on bread quality. The sourdough decreases or increases the bread volume according to previous studies [23]. To explain the effects of sourdough on dough and bread quality, several hypotheses have been proposed as the direct effect of pH on dough structure, the effect of acid on grain enzymes, and the effect of microorganisms alone [24]. When the acidity of sourdough increases too much, the volume of bread decreases. Quantitative analysis of gluten in sourdough and chemically acidified dough showed that gliadins and glutenins were hydrolyzed. Especially high-molecular glutens break down completely, which leads to strong gluten softening. Weak gluten increases dough expansion but also reduces gas retention. Therefore, the acidity level of sourdough and bread dough should be carefully controlled to increase the volume [1].

Fig. 3
figure 3

The effects of the interactions of wheat variety and sourdough treatment (WVx ST) (A), wheat variety and sourdough level (WVx SL) (B), sourdough treatment and sourdough level (STxSL) (C) on specific volume of whole wheat breads

Full size image

Color of crumb and crust

The effects of wheat variety, sourdough treatment and sourdough level on the color of crumb and crust of whole wheat bread are given in Table 4. In terms of crust L*, Tosunbey had the highest (65.13) and Bezostaja-1 had the lowest value (52.98). There was no statistical difference between LP and LS (57.31 and 57.07, respectively) (p > 0.05), while SP had the lowest L* (56.00). The effect of sourdough level on crust L* was not statistically significant (p > 0.05). Kenanbey had the highest (9.68) and Tosunbey had the lowest (7.25) crust a* value. SP had the highest a* (56.00), while the difference between LP and LS was not statistically significant (8.55 and 8.38, respectively) (p > 0.05). For the sourdough levels of 0–30%, the crust a* was varied between 8.85 and 8.22. In terms of crust b*, Kenanbey had the highest (23.89) and İkizce-96 had the lowest value (20.23), while there was no significant difference between sourdough treatments (p > 0.05). The b* varied between 22.49 and 21.66 for the sourdough levels of 0–30%. While the crust colors (L*, a*, b*) of İkizce-96 and Bezostaja-1 (hard red winter wheats) were similar, Tosunbey and Kenanbey (hard white winter wheats) had quite different crust colors from each other. It is thought that the difference in protein content (12.19% and 14.53%, respectively), and falling number indicating α-amylase activity (414 and 367 s, respectively) may cause differences in the crust color of Tosunbey and Kenanbey. Reducing sugars and nitrogen in the α-amino group of proteins are the substances that play a major role in the Maillard reaction, which is of great importance in the formation of crust color [25]. Kenanbey had the highest crumb L* and b* values (67.31 and 24.48 respectively), while Bezoataja-1 had the highest crumb a* (6.30). SP had lower crumb a* and b* values (5.35 and 22.01) than other sourdough treatments, and there was no statistical difference between LP and LS (p > 0.05). The crumb L* and a* values varied between 64.30–62.90 and 5.31–5.62, respectively for 0–30% sourdough levels.

Table 4 Effects of wheat variety, sourdough treatment and sourdough level on crust and crumb color of whole wheat bread
Full size table

The effects of significantly important interactions for the crumb and crust color of whole wheat bread is given in Supplementary Fig. 1. As the sourdough level increased, the crumb L* value decreased slightly in SP, while increased in LP and LS treatments. While the highest L* value was obtained at a 30% sourdough level of LP, the lowest value was at a 30% sourdough level of SP (Supplementary Fig. 1a). As the sourdough level increased the crumb a* value of wheat varieties slightly increased except for Kenanbey (Supplementary Fig. 1b). Also, the increasing sourdough levels increased the crumb a* value for sourdough treatments similar in LP and LS, but very little in SP (Supplementary Fig. 1c) The crumb b* value of Tosunbey and Kenanbey (white colored varieties) decreased as the sourdough level increased, but İkizce-96 and Bezostaja -1 (red colored varieties) had slightly increased (Supplementary Fig. 1d). Sanz-Penella et al. [26] reported that the addition of sourdough did not show significant changes in the crust and crumb color of whole wheat bread compared to the control. It was stated that the total color difference between the samples with sourdough addition and the control sample in terms of bread crumb and crust color was less than 5 units (from 0.67 to 3.16), indicating that no difference could be detected visually.

Texture profile analysis (TPA)

TPA is a technique that attempts to use a common basis for both subjective and objective assessment of product eating qualities. In this technique, two consecutive compressions with force are applied on the same sample, causing some irreversible changes in the tested food [27]. Hardness is the force required to achieve a certain deformation; springiness is the rate at which a deformed material returns to its undeformed state after removing the deforming force; cohesiveness is the strength of the internal bonds that make up the body of the product, and chewiness is the energy required to prepare a solid product to be swallowed [28]. In many studies, it has been stated that there is a negative relationship between firmness, gumminess, chewiness, and bread quality, while springiness and cohesiveness are positive features [29]. The effects of wheat variety, sourdough treatment and sourdough level on TPA of whole wheat bread on the first and third days of storage are given in Table 5. The hardness and chewiness of all the bread samples significantly increased with the storage time, while the cohesiveness and springiness decreased.

Table 5 Effects of wheat variety, sourdough treatment and sourdough level on texture profile of whole wheat breads on the first and third days of storage
Full size table

Hardness

All the examined factors (WV, ST, SL) and interactions (WVxST, WVxSL, STxSL, WVxSTxSL) had significant effect on hardness (p < 0.01). Considering wheat varieties, the hardness of crumb varied between 15.5–24.5 N and 19.3–31.0 N on the first and third days, respectively. Tosunbey had the highest and İkizce-96 had the lowest hardness, with an inverse relation to specific volume. For the sourdough treatments, the hardness varied between 17.3–20.0 N and 22.3–26.1 N on the first and third days, respectively. SP had the lowest and LP had the highest hardness values. The hardness values for 0–30% sourdough levels varied between 17.6 and 20.8 N on the first day, and between 22.7 and 26.9 N on the third day. The rise in hardness was more for the breads produced with lactic starters and the increasing sourdough levels, during storage. Several studies have shown that the anti-staling effect of sourdough is related to a wide range of parameters, including strain specificity, the degree of acidification, a combination of organic acids, the breakdown of protein and starch, and the interaction between starch and protein [30]. Generally, it was determined that the crumb hardness was related to the bread volume, and the hardness of the bread with lower spesific volume increased as a result of denser structure. Katina et al. [23] determined that using 20% sourdough in bread production, produced with low ash content flours, reduced the hardness of the bread during the 4-day storage period, and the hardness increased as the ash content in the flour increased. It has been reported that fermentation time and bread volume also have an effect on the hardness of bread, and as the fermentation time increases and the bread volume increases, softer bread crumbs are obtained. As seen in the WVxSTxSL interaction graph (Fig. 4), the lowest hardness value was obtained with the SP sourdough treatment of İkizce-96 at 30% sourdough level, and the highest hardness value was obtained with the LP sourdough treatment of Tosunbey at 30% sourdough level.

Fig. 4
figure 4

The effects of the interactions of wheat variety, sourdough treatment and sourdough level (WVx STxSL) on hardness of whole wheat breads. a–v: Different lower case letters indicate significant differences between samples on the 1st day of storage, A–U: Different capital letters indicate significant differences between samples on the 3rd day of storage

Full size image

Springiness

The springiness of crumb varied between 0.881–0.892 and 859–0.894 on the first and thirds day of storage, respectively, for wheat varieties. Tosunbey and Bezostaja-1 had the highest springiness (0.892 and 0.891) on the first day. The springiness varied between 0.883–0.890 and 0.871–0.875 for sourdough treatments on the first and third day, respectively. As the sourdough level increased, the springiness of the bread decreased. The springiness varied between 0.873–0.898 on the first day and 0.863–0.879 on the third day respectively, for 0–30% sourdough levels. Karaman et al. [31] found the springiness of whole wheat bread as 0.88, 0.76, and 0.77–0.88 respectively, using commercial yeast, spontaneous fermentation, and sourdough made with nine different starter cultures. Springiness is associated with a fresh and elastic product; therefore high-quality bread will be associated with high springiness values. Low springiness is indicative of brittleness, reflecting the bread’s tendency to crumble when sliced [32]. On the first day, WV, ST, and SL factors (p < 0.01) and WVxST, WVxSL (p < 0.05) interactions had a significant effect on springiness. On the third day WV, SL (p < 0.01) and ST (p < 0.05) factors, and WVxST, WVxSL (p < 0.01) interactions had a significant effect. The highest springiness was obtained with SP sourdough treatment of Bezostaja-1 on the first day of storage, and LP of Bezostaja-1, SP and LS sourdough treatments of Tosunbey were in the same group statistically. LP sourdough treatment of Tosunbey had the highest springiness on the third day (Supplementary Fig. 2a). Additionally, on the first day of storage, the 0% sourdough level of Bezostaja-1 had the highest springiness and it was in the same group statistically with the 0% and 10% sourdough levels of Tosunbey. Also, 10% and 20% sourdough levels of Tosunbey had the highest springiness on the third day (Supplementary Fig. 2b).

Cohesiveness

The cohesiveness of crumb varied between 0.633–0.658 and 0.528–0.591 on the first and third days, respectively, for wheat varieties. Bezostaja-1 had the highest and Tosunbey had the lowest cohesiveness. For the sourdough treatments, the cohesiveness varied between 0.640–0.651 and 0.564–0.570 on the first and third days, respectively. SP had the highest and LP had the lowest cohesiveness. The cohesiveness ​​varied between 0.665–0.618 on the first day and between 0.594–0.634 on the third day, for 0–30% sourdough levels. Cohesiveness characterizes how much a material can deform before breaking and reflects the material’s internal cohesion. Bread with high cohesiveness is desirable because it forms a lump rather than crumbling during chewing, while low cohesiveness indicates increased susceptibility of bread to fracturing or crumbling. Low cohesiveness implies that lower compression energy is required and consequently those breads are more easily crumbled [32]. The higher cohesiveness values were obtained with SP and LS sourdough treatments of Bezostaja-1 and İkizce-96 on the first day of storage. There was no statistically significant difference between the cohesiveness of SP and LS of Bezostaja-1, and SP and LP of İkizce-96 on the third day (Supplementary Fig. 3a). As the sourdough level increased, the cohesiveness of the crumb decreased for wheat varieties and sourdough treatments (Supplementary Fig. 3b, c). Similarly, Casoda et al. [33] reported higher cohesiveness and springiness for bread not incorporating sourdough, while hardness, gumminess, resilience, and chewiness were greater in bread made with sourdough.

Chewiness

The chewiness of crumb varied between 8.94–13.78 N and 9.78–14.62 N on the first and third days of storage, respectively, for wheat varieties. The bread samples with higher specific volumes had softer crumb texture and lower chewiness. In this regard, Tosunbey had the highest and İkizce-96 had the lowest chewiness. During storage, the chewiness for SP, LP and LS sourdough treatments varied between 10.01–11.05 N, 11.22–12.75 N, 11.16–12.33 N, respectively. The chewiness values ​​for 0–30% sourdough levels varied between 10.50–11.14 N and 11.75–12.29 N on the first and third days of storage, respectively. The highest chewiness was determined at the 30% and 20% sourdough levels of LP treatment for Tosunbey, as shown in the WVxSTxSL graph (Supplementary Fig. 4). Crowley et al. [34] reported the chewiness values ​​of breads with control, 20% and 40% sourdough added changed between 500–672 g, 506–637 g and 506–693 g, respectively, during the storage period of 26–74 h, and the chewiness value increased during storage. The chewiness is the amount of energy needed to masticate a solid food product [35] and the low chewiness value is expressed as the easy breaking of the bread in the mouth like a biscuit [32]. As the bread crumb becomes harder it requires more energy to break down and longer time to chew (increased chewiness) [36].

Sensory evaluation

The images of whole wheat breads and polar coordinate graphs for the sensory properties are given in Figs. 5 and 6, respectively. All the bread samples have acceptable scores by receiving more than five, the midpoint of the 9-degree hedonic scale. For Tosunbey except LP 30%, all the sourdough treatments had higher overall acceptability, and except LS 30%, all the sourdough treatments had higher scores for texture than 0% sourdough level. It determined that 30% of sourdough treatments were less liked in terms of smell for Tosunbey, and increasing sourdough levels generally had a positive effect on taste, with LS 20% and 30% being the highest-scoring applications. For Kenanbey, SP 30% had the lowest score in terms of taste and smell, and overall acceptability was highest for SP 10%, LP 20%, and LS 10%, respectively. LP 10% and SP 20% had the highest score for the crust color of Kenanbey. For İkizce-96, SP 20% and 30% had the lowest scores in terms of taste and smell, and LP 30% had the lowest score for texture. In terms of overall acceptability, LP 10% was the most appreciated application for İkizce-96. For Bezostaja-1, LS 30% had the lowest score in terms of texture and taste. LP 30% received the highest score, and SP 30% had the lowest score in terms of smell. In all sourdough applications for Bezostaja-1, the overall acceptability was higher than 0%. Sourdough treatments had diverse effects on the sensory characteristics of breads produced with different whole wheat flours, associated with the microbiota and metabolites. When whole-meal flour is used for both the starter and breadmaking, the bacteria have more nutrients to grow and feed on, increasing the effectiveness of fermentation and the resulting byproducts. The final product’s texture, sensory attributes, and nutritional composition are significantly influenced by the sourdough process [37].

Fig. 5
figure 5

Images of the whole wheat sourdough breads [Tosunbey, Kenanbey, İkizce-96, Bezostaja-1 from top to down; SP: Spontaneous fermentation, LP: Lactiplantibacillus plantarum, LS: Fructilactobacillus sanfranciscensis from left to right with increasing sourdough levels (10–20-30%)]

Full size image
Fig. 6
figure 6

The polar coordinate graphs for the sensory properties of whole wheat breads. SP: Spontaneous fermentation, LP: Lactiplantibacillus plantarum, LS: Fructilactobacillus sanfranciscensis

Full size image

Conclusions

Considering that acidity affects all bread quality, it is important to optimize the process conditions to ensure standard quality production. Sourdough can be prepared in ovens by spontaneous fermentation with natural microbial flora or by using starter cultures. Spontaneous fermentation makes production variable due to variations in natural microbial flora depending on the raw material and process conditions. The use of lactic starters to produce sourdough with appropriate microorganisms is important for bread production with standard quality. Although the increasing demand for sourdough bread is associated with health benefits, it is restricted to traditional and artisanal baking in the world. The popularization of sourdough bread particularly by industrial bakeries with new technologies, different flours and microorganisms can be beneficial for consumers to reach more nutritious bread.

This study shows that wheat variety, sourdough treatment (spontan fermentation, Lactiplantibacillus plantarum, Fructilactobacillus sanfranciscensis) and sourdough level have a significant effect on pH, TTA, specific volume, color, and texture profile analysis (hardness, springiness, cohesiveness, chewiness) of whole wheat bread. İkizce-96 had a higher potential to produce whole wheat sourdough bread regarding the higher protein content and Zeleny sedimentation value. However, the breads produced with SP treatment had better technological properties than LP and LS due to the lower acidity, but the breads of SP were less appreciated in terms of smell. The increasing sourdough levels resulted in a lower specific volume and higher hardness. Consequently, wheat varieties with high protein content and protein quality had better potential in whole wheat bread making, and sourdough produced with selected lactic starters (LP and LS) could be used at 10–20% levels to have acceptable technological and sensory characteristics.