Yeast Flakes as a Technological Ingredient for Salt Reduction and Flavor Enhancement in Bread

Abstract

Excessive sodium intake is a major public health concern, and bread is one of the main dietary sources of sodium chloride. This study evaluated the potential of inactive yeast flakes as a functional ingredient for the partial replacement of sodium chloride in bread formulations. Bread samples with reduced salt and increasing levels of yeast flakes were analysed in terms of physicochemical properties, texture profile, colour, crumb structure, and sensory characteristics. The substitution of NaCl with yeast flakes significantly influenced bread quality. A reduction in crumb porosity, water activity, and springiness, as well as an increase in hardness and acidity, were observed. Colour analysis revealed crumbs with higher redness (a*) and yellowness (b*). Colour changes were confirmed by total colour difference values. Sensory evaluation showed a decrease in saltiness compared to the control sample, however, bread containing a moderate level of yeast flakes maintained acceptable sensory quality and flavour perception. Correlation analysis demonstrated strong relationships between selected instrumental and sensory parameters, particularly for colour, hardness, springiness, and porosity, confirming the consistency of both evaluation approaches. The results indicate that yeast flakes may represent a promising, naturally derived alternative for partial sodium chloride reduction in bread.

1. Introduction

Salt (sodium chloride) is one of the most fundamental seasoning agents used in food production, including industrial food processing, gastronomy, and domestic cooking. Its widespread application results from a wide range of functional properties. Technologically, salt contributes to texture modification, enhances the solubility of meat proteins, exhibits antimicrobial activity, and provides the characteristic salty taste. Moreover, sodium chloride enhances overall flavor perception and improves the sensory attributes of many food products. Beyond its technological importance, the sodium contained in salt plays a key physiological role in maintaining homeostasis and supporting essential metabolic processes. Together with potassium, sodium regulates osmotic pressure, acid–base balance, and the distribution of body fluids, and it is involved in the proper functioning of the cardiovascular and neuromuscular systems [1]. Sodium ions also participate in oxidation–reduction reactions and act as cofactors in numerous enzymatic processes. Thus, maintaining appropriate sodium levels is critical for human health [2]. Although sodium deficiency (resulting in hyponatremia) is relatively rare, excessive sodium intake is common and poses significant health risks. Chronic overconsumption of sodium is associated with an increased risk of hypertension, cardiovascular diseases, obesity and metabolic syndrome, kidney disorders, skeletal demineralization, cancer, and disruptions of the intestinal microbiome [3,4].

Excessive sodium intake is a global public health concern. Although consumption levels vary across countries, they commonly exceed the recommendations of national and international health authorities. According to a WHO analysis, the average daily salt intake in Poland exceeds 11 g/day (approx. 4.4 g/day of sodium) [5], in Middle Eastern countries it reaches approximately 10 g/day (approx. 4.0 g/day of sodium) [3], in USA over 3.4 g sodium/day [4]. In contrast, WHO and EFSA recommends a maximum intake of 5 g/day (2.0 g/day of sodium) [6,7], while the United States National Academy of Science, Engineering, and Medicine suggests an adequate intake of 3.75 g/day (1.5 g/day of sodium) [8]. In general, food and health authorities recommend sodium chloride consumption in the range of 1.25–5.0 g/day (0.5–2.0 g/day of sodium), meaning that actual intake in many populations is approximately twofold higher than advised.

The primary dietary sources of sodium differ by socioeconomic context. In industrialized countries, 75–80% of sodium intake comes from processed foods (mainly from added salt), whose sodium content may be over 100-fold higher than that of home-prepared dishes [9,10,11,12,13]. An additional 5–10% derives from naturally occurring sodium in foods, and 10–15% from salt added during cooking or at the table. In contrast, in developing countries, the proportion of sodium added during food preparation is considerably higher [2].

Bread is one of the oldest and most universally consumed foods worldwide [14]. It is a staple that provides both energy and essential nutrients [10,15], and it is compatible with diverse dietary patterns, including vegetarian, vegan, and culturally or religiously motivated elimination diets [16]. Despite its long-standing dietary significance, bread has recently been implicated in several health concerns, including associations with excessive caloric intake, type 2 diabetes, and cardiovascular disease. These concerns are partly related to contemporary dietary trends (e.g., low-carbohydrate diets) and perceived links between bread consumption and gastrointestinal discomfort [17]. Another significant issue is the high salt content of bread. In many European countries, major contributors to dietary sodium include bread, cereal products (including breakfast cereals), bakery items, processed meats, cheeses, and other dairy products [3,4,18]. Because these foods are consumed daily or nearly daily, their salt content plays a critical role in population-level sodium intake [13].

Lowering the salt content in bread poses a notable technological challenge. Salt fulfills several important functions in breadmaking: strengthening the gluten network, improving dough elasticity and reducing stickiness, influencing the textural characteristics of the final product, and affecting crust and crumb coloration as well as sensory perception. Additionally, salt modifies osmotic pressure, thereby influencing key biological processes during dough development, including fermentation dynamics, enzyme activity, and water activity [3,4,10]. Salt also plays a crucial role in imparting desirable sensory characteristics to food. Therefore, reducing salt levels in food products may lead to negative consumer perception of the modified products [4].

Given the growing public health need to reduce sodium intake and the technological challenges associated with lowering salt levels in bread, there is increasing interest in strategies and ingredients that can compensate for the sensory and functional roles of sodium chloride. Existing approaches include the use of hollow salt crystals, heterogeneous salt distribution, salt replacers and various flavor or salt enhancers such as amino acids and plant-based substitutes [2,3,10,11,13]. In parallel, increasing consumer demand for natural and clean-label solutions has intensified the search for multifunctional ingredients capable of improving sensory quality while supporting nutritional objectives [19]. In this context, yeast flakes constitute a promising alternative due to their naturally low sodium content and their richness in flavor-active compounds, including glutamic acid, 5′-nucleotides (e.g., GMP, IMP), peptides, and amino acids linked to umami and kokumi taste [20], which contribute to enhanced flavor intensity, mouthfulness, and overall palatability, particularly in reduced-sodium food systems. Their technological and functional potential is further supported by the wide availability of raw materials, a well-developed production infrastructure, and diverse applications across the food, pharmaceutical, and cosmetic industries. Yeast flakes are typically produced from food-grade strains of Saccharomyces cerevisiae, industrially cultivated on nutrient media using carbon sources such as sugarcane or beet molasses. Following biomass growth, the yeast is deactivated, harvested, washed, dried, and processed into flakes or powder, facilitating broad availability, economic feasibility, and sustainable use as a food ingredient [21]. Beyond human nutrition, the animal feed sector represents a major area of application due to the nutritional and functional benefits of inactive yeast, including support for digestive health, immune function, and overall animal well-being [22,23]. As livestock production increasingly prioritizes sustainable practices and natural feed additives, demand for inactive dried yeast continues to rise.

The broad applicability of inactive dried yeast is also reflected in strong market growth. The global inactive dried yeast market is projected to reach USD 2234.6 million by 2035, with a compound annual growth rate (CAGR) of 11.9% between 2025 and 2035 [24]. Inactive dried yeast is rich in high-quality protein, dietary fiber, and B-complex vitamins, which has led to its increased use in functional foods and value-added nutritional products [21,25,26]. Despite their favorable sensory profile and frequent use as flavor enhancers in other food categories, the potential application of yeast flakes in breadmaking—both as a partial salt replacer and as an ingredient influencing dough rheology and final product quality—has not yet been comprehensively examined. Therefore, the aim of this study was to evaluate the feasibility of incorporating inactive, non-fermentative yeast flakes into bread formulations to reduce sodium chloride content while maintaining acceptable technological, sensory, and physicochemical properties. Additionally, the study examines whether yeast flakes can enhance flavor, support dough development, and mitigate the adverse effects of salt reduction, offering a viable strategy for producing bread with improved nutritional value.

2. Materials and Methods

2.1. Materials

The following ingredients were used for bread preparation: wheat flour type 550 (with moisture content 13.97%; water absorption 60%; α-amylase activity 391 s; gluten content 26.08%; gluten spreadability 6 mm; acidity 4.9°A), water supplied by a local water treatment plant (source: Czyżkówko, Bydgoszcz, Poland), baker’s yeast—leavening agent (Saccharomyces cerevisiae), sodium chloride, and—depending on the formulation—yeast flakes—flavour enhancing ingredient (derived from Saccharomyces cerevisiae—inactive and non-fermentative; PRIMÄR, Salutaguse, Estonia, with composition: 5% fat, 39% carbohydrates, 47% protein, 0.25% sodium chloride). Flour, baker’s yeast, sodium chloride and yeast flakes were purchased from a local retail store in Bydgoszcz, Poland. Prior to dough preparation, all ingredients were stored at room temperature (approximately 20 °C).

2.2. Methods

2.2.1. Bread Preparation

For bread preparation, sodium chloride alone or in combination with yeast flakes was hydrated in half of the total water (he flakes were gently stirred until a uniform dispersion was obtained, ensuring that no lumps remained), after which the baker’s yeast was added. The sieved flour was then mixed with the prepared solution using a planetary mixer (Kenwood Titanium Chef Baker, Kenwood, Havant, UK). The resulting dough was placed in a fermentation chamber (T = 30 °C, humidity 75–80%, t = 23 min). Subsequently, the dough was punched down for the first time and returned to the fermentation chamber (T = 30 °C, humidity 75–80%, t = 23 min). After a second punching, the dough was divided into 250 g portions with an accuracy of 0.01 g.

The dough pieces were placed in greased moulds measuring 80 mm in height, with a 75 mm × 75 mm base and an 80 mm × 80 mm top. The moulds were then transferred to the fermentation chamber for final proofing until the dough reached the rim of the moulds (about 5 min). The surface of the fermented dough was lightly moistened with water and baked in an oven at 230 °C for 30 min.

After 10 min of baking, steam was injected into the oven for 10 s. The loaves were removed from the moulds and allowed to cool for 1 h at room temperature. Subsequently, the bread was stored at 20 °C for 24 h (humidity 65–70%) before physicochemical, textural and sensory analyses were performed. The complete recipe is presented in

Table 1. List of raw materials used for samples preparation [g/100 g of flour].

Raw Material	Sample Name
	CS (Control Sample)	YS1 (25% NaCl Reduction)	YS2 (50% NaCl Reduction)
Flour	100.00	100.00	100.00
Water	48.00	48.00	48.00
Baker’s yeast	1.78	1.78	1.78
Sodium chloride	1.40	1.05	0.70
Inactive yeast flakes	0.00	4.39	6.58

.

To increase the reliability of the results, the baking process was carried out twice. In each baking process two breads per sample were obtained).

2.2.2. Physicochemical Analysis

Dry Mass Determination

Bread samples for dry matter determination the bread crumbs were weighted with an accuracy of 0.01 g. Moisture content was determined using the loss on drying (LOD) method with a moisture analyser (model MA 50.R, RADWAG, Radom, Poland) at 120 °C until constant mass was achieved. For each sample, six measurements were performed (three per one baking process—two per one loaf) [27,28].

Water Activity

The water activity (Aw) of bread samples was measured after storage at 20 °C for 24 h. The crumb was cut to fit the measuring cell and placed into a 40 mm-deep Rotronic sample cup, which was then inserted into the measuring chamber of the device (HC2-AW-USB, Rotronic AG, Bassersdorf, Switzerland). For each sample, six measurements were performed (three per one baking process—two per one loaf).

Crumb Porosity

Crumb porosity was determined with method described by Korus et al. [29] with slight modification. Crumb cubes of 3 cm were cut and divided into five equal parts. Each part was subsequently compressed into small balls in order to expel air from the pores. The balls were then immersed in oil within the measuring cylinder. Crumb porosity, expressed as a percentage, was calculated according to the following formula:

$$\mathrm{X}={\displaystyle \frac{\left(\mathrm{a}-\mathrm{b}\right)\times 100\mathrm{\%}}{\mathrm{a}}}$$

where:

• a—volume of the cube with pores—27 [mL]
• b—volume of the crumb without pores [mL].

For each sample, six measurements were performed (three per one baking process—two per one loaf).

Crumb Acidity

Crumb acidity was determined using the titration method with sodium hydroxide (NaOH) as the titrant. A 25 g portion of bread crumb was weighed to the nearest 0.001 g, finely ground, and transferred to a volumetric flask. Subsequently, 250 mL of distilled water was added and the flask was tightly sealed. The mixture was shaken vigorously for 2 min and then shaken again every 15 min over the course of one hour.

After extraction, the suspension was filtered and 50 mL aliquots of the filtrate were transferred into three conical flasks. A few drops of phenolphthalein (Chempur, Krupski Młyn, Poland) indicator were added, and titration was performed using a 0.1 M NaOH solution (Chempur, Krupski Młyn, Poland). For each sample, six measurements were performed (three per one baking process—two per one loaf).

The results were expressed as degrees of acidity (°A), defined as the volume of 0.1 M NaOH required to neutralize the acids present in 100 g of crumb.

2.2.3. Colorimetric Measurements

The colour of the bread crumb was evaluated according to the guidelines of the Commission Internationale de l’Eclairage (CIE) using the L*, a*, b* and C* colour coordinates. The colorimeter lens was placed directly on the crumb surface, and each measurement consisted of three flashes. For each sample, six measurements were performed (three per one baking process—two per one loaf).

Colour parameters were recorded using a colorimetric spectrophotometer (Konica Minolta Chroma Meter CR-410, Tokyo, Japan). The total colour difference (ΔE) was calculated according to the following equation [30]:

$$\mathsf{\Delta }\mathrm{E}={[{\left(\mathsf{\Delta }{\mathrm{L}}^{\mathrm{*}}\right)}^2+{\left(\mathsf{\Delta }{\mathrm{a}}^{\mathrm{*}}\right)}^2+{\left({\mathsf{\Delta }\mathrm{b}}^{\mathrm{*}}\right)}^2]}^{1/2}$$

where:

• ΔL*—the difference of L* between analysed samples,
• Δa*—the difference of a* between analysed samples,
• Δb*—the difference of b* between analysed samples.

The ΔE value was used to assess the effect of formulation modification on colour changes in bread.

2.2.4. Texture Analysis

Bread texture was analysed using the Texture Profile Analysis (TPA) test, performed with a universal testing machine equipped with an Xforce HP load cell (500 N) (Zwick/Roell, Ulm, Germany) and a cylindrical probe (Ø58 mm). Measurement data were collected and analyzed using TestExpert II V 3.1 software (Zwick/Roell, Ulm, Germany). Crumb samples with dimensions of 3 × 3 × 3 cm (depth × width × height) were cut and subjected to a double compression to 50% of sample deformation, at a test speed of 5 mm/s and with a 5-s relaxation time between compressions. For each sample, six measurements were performed (three per one baking process—two per one loaf).

Based on the TPA curves, the following parameters were determined: hardness I, hardness II and springiness.

2.2.5. Organoleptic Tests

The sensory evaluation was carried out by a trained panel consisting of ten participants (five women and five men aged 20–45 years). All panelists were nonsmokers and declared no sensory impairments.

The selection, training and supervision of the panel were conducted in accordance with the PN-EN ISO 8586:2014-03 standard [31], while the evaluation procedure followed the guidelines of PN-ISO 4121:1998 [32].

The assessments were conducted under controlled laboratory conditions at approximately 1:00 p.m., at least two hours after the last meal or consumption of beverages other than water, in order to minimise potential effects on sensory perception [33]. Samples were coded with random identifiers and presented in a randomized order to each panelist. All samples were evaluated at a comparable post-baking time and serving temperature (with size 3 × 3 × 3 cm (depth × width × height)). The sensory evaluation was conducted in a room illuminated with artificial light, at an ambient temperature of 20 ± 2 °C. Before each evaluation and between successive samples, panelists rinsed their mouths with water at 20 ± 1 °C. The sensory analysis was designed as a comparative descriptive assessment relative to the control sample (CS). For each sample, two independent baking processes were evaluated, and each panelist assessed one sample from each baking process, resulting in n = 20 sensory observations per variant.

A 10-point linear scale was used for the organoleptic assessment. The definitions of all evaluated attributes are presented in

Table 2. Description of the assessed organoleptic properties.

Parameter	Description of Point 1 on Scale	Description of Point 10 on Scale
Springiness	permanently deformable	perfectly elastic
Softness	very hard	very soft
Taste	very undesirable	very desirable
Flavour	very undesirable	very desirable
Colour	very undesirable	very desirable
Cross-sectional appearance	very undesirable	very desirable

. Additionally, saltiness perception was evaluated using a 10-point scale ranging from −5 (“less salty”) to +5 (“more salty”), with 0 representing the control sample (CS).

2.2.6. Statistical Analysis

The presented results are expressed as the mean values of six measurements (three per one baking process—two per one loaf) (mean ± standard deviation, SD). Normality and homogeneity of variances were verified with Shapiro-Wilk test. Statistical differences between samples were assessed using one-way analysis of variance (ANOVA). When a significant main effect was detected (p < 0.05), pairwise comparisons between means were performed using Tukey’s test. In cases where ANOVA indicated no significant differences, no post hoc tests were applied. All statistical analyses were performed using Statistica 13 software. Differences were considered statistically significant at p < 0.05. Furthermore, a correlation analysis was conducted to examine the relationships between selected instrumental measurements (a*, b*, hardness, springiness, and porosity) and the corresponding sensory scores. Pearson’s correlation coefficient (r) was used to assess the strength and direction of the linear relationships between variables, with the significance level set at p < 0.05. For these correlations, n = 3 represents the number of independent formulations (loaf numbers), while n = 20 corresponds to the total number of sensory panel measurements obtained from two loaves per formulation, evaluated by ten panelists.

3. Results and Discussion

3.1. Physicochemical Properties

In all analysed samples, the dry matter content ranged from 59.70% to 60.85%. Both samples supplemented with yeast flakes exhibited a lower dry matter content than the control sample. However, the differences between CS and YS1 were not statistically significant. In contrast, the dry matter content of YS2 was significantly lower compared with the other samples (

Table 3. Physicochemical properties of bread samples.

Sample Name	Dry Mass [%]	Aw	Crumb Porosity [%]	Crumb Acidity [°A]
CS	60.85 ± 0.625 b	0.93 ± 0.018 a	60.49 ± 2.176 a	1.27 ± 0.115 a
YS1	59.93 ± 0.070 b	0.91 ± 0.001 a	58.03 ± 2.211 a	1.80 ± 0.001 b
YS2	59.70 ± 0.010 a	0.91 ± 0.001 a	56.79 ± 2.136 a	2.40 ± 0.001 c

a, b, c—samples with the same letter in the column do not differ significantly.

).

The water activity of all analysed samples ranged between 0.91 and 0.93 (Table 3). The addition of yeast flakes combined with a reduction in NaCl content caused a decrease in water activity. Water activity is a crucial factor influencing microbial growth and, consequently, the microbiological stability and shelf life of food products. The observed decrease in water activity in samples where sodium chloride was partially replaced with yeast flakes can be attributed to the presence of hydrophilic components derived from yeast cell walls, such as β-glucans, mannoproteins, and dietary fibre. These compounds exhibit a high water-binding capacity, which reduces the amount of free, microbiologically available water in the dough matrix. As a consequence, the dough becomes less plastic and less extensible, limiting gas cell expansion during fermentation and baking, and ultimately resulting in a denser crumb structure with reduced porosity. However, the observed changes in water activity were not statistically significant, therefore its impact on the shelf-life stability cannot be confirmed. In the case of a one-directional recipe modification involving only salt reduction, water activity usually increases, which is an unfavourable phenomenon. In food systems, salt acts as a preservative by reducing water activity and, through increased osmotic pressure, disrupting microbial metabolism and growth [34,35]. Therefore, the observed reduction in water activity in the present study may be considered beneficial in terms of bread shelf-life improvement.

Increasing the concentration of yeast flakes combined with decreasing sodium chloride content caused a reduction in crumb porosity from 60.49% to 56.79%, however no statistical significant difference was observed (Table 3). Bread crumb porosity refers to the air-filled spaces within the crumb that are created by gas expansion during fermentation and baking and subsequently stabilised by the dough matrix. The decrease in crumb porosity observed after the partial replacement of sodium chloride with yeast flakes can be the result of a weakened gluten network [36], increased competition for water caused by the presence of yeast flakes, and the presence of insoluble yeast-derived components that interfere with gas cell formation and stability. Although yeast flakes may enhance flavour, in combination with a reduced sodium chloride concentration they act as structural disruptors and modify fermentation dynamics, leading to the development of a denser and less porous crumb structure. Additionally, low-salt dough exhibits more fragile gas cell walls, which can promote cell coalescence and, consequently, lower porosity [37].

Crumb acidity increased with increasing yeast flake concentration and decreasing NaCl content, from 1.27°A in CS to 2.40°A in YS2 (Table 3), and all observed changes were statistically significant. The increase in acidity in samples may be attributed to the presence of naturally acidic compounds in the yeast flakes, including organic acids, phosphates, and products of nucleotide degradation. The concomitant reduction in water activity may have further concentrated these compounds within the crumb matrix, resulting in higher measured acidity values. Changes in crumb acidity may influence several quality attributes of bread. Increased acidity can contribute to shelf-life extension by delaying starch retrogradation through the inhibition of protease and amylase activity, thereby reducing the staling rate [38], as well as by inhibiting microbial growth [39]. In addition, organic acids contribute to sour taste development and may enhance perceived saltiness, partially compensating for sodium chloride reduction [40]. In this context, the observed increase in crumb acidity may be considered a beneficial effect. On the other hand, excessive acidity may negatively affect bread quality by reducing loaf volume and increasing crumb hardness, due to its impact on gluten network development and gas retention [41].

3.2. Colourimetric Measurement

The colour coordinates of all samples changed after reducing the sodium chloride content and adding yeast flakes (

Table 4. Colour coordinates of bread samples.

Sample Name	L*	a*	b*	C*
CS	75.37 ± 0.685 b	0.25 ± 0.082 a	18.29 ± 0.143 a	18.29 ± 0.142 a
YS1	71.21 ± 0.101 a	1.42 ± 0.082 b	20.08 ± 0.095 b	20.13 ± 0.092 b
YS2	70.37 ± 0.791 a	1.70 ± 0.125 c	20.40 ± 0.393 b	20.47 ± 0.398 b

a, b, c—samples with the same letter in the column do not differ significantly.

). The highest L* value was recorded for the CS sample (75.37), which was significantly higher than in both YS samples. Modification of the bread formulation caused a decrease in L* to 71.21 and 70.37 for YS1 and YS2, respectively. No statistically significant difference was observed between YS1 and YS2 in terms of L*. In contrast, the a* coordinate increased from 0.25 to 1.42 and 1.70 for CS, YS1 and YS2, respectively. Both the differences between CS and the YS samples and between YS1 and YS2 were statistically significant. Similarly, the b* coordinate increased from 18.29 to 20.08 and 20.40 for CS, YS1 and YS2, respectively. However, in the case of b*, the changes were statistically significant only between CS and the YS samples, with no significant difference between YS1 and YS2. The C* value also increased following sodium chloride reduction and yeast flake incorporation, from 19.29 to 20.13 and 20.47 for CS, YS1 and YS2, respectively. Even the addition of yeast flakes at a level of 4.39% resulted in a noticeable colour change. Thus, the partial replacement of sodium chloride with yeast flakes produced darker bread with a higher proportion of red and yellow colour tones. Similar results were reported by Jiménez-Maroto et al. [42], who investigated the partial replacement of sodium chloride with fermented soy ingredients and obtained darker and redder bread, with changes positively correlated with the concentration of the flavour enhancer used. The observed changes in crumb colour following partial substitution of sodium chloride with yeast flakes are likely the result of multiple, interacting mechanisms. In addition to the intrinsic colour of yeast flakes occurring due to the naturally beige–brown pigments present in yeast flakes, including melanoidins and other compounds formed during the thermal processing of yeast [43], thermal reactions occurring during baking—most notably the Maillard reaction—may have contributed to the observed colour shift. The presence of additional amino compounds supplied by yeast flakes can intensify non-enzymatic browning reactions, leading to increased redness and yellowness. Change of the yellowness was observed by Grasso et al. [44], which observed increase of the b* coordinate in hybrid beef meatballs after yeast flakes addition. In their paper no changes of a* were observed, however the internal temperature of the meatballs was 75 °C, therefore, only the initial stage of the Maillard reaction has occurred. On the other hand, Öztürk et al. [45] observed the same situation like observed in this paper—decrease of L*, increase of both a* and b* after inactive yeast cells addition. What has been associated with the occurrence of the Maillard reaction. On the other hand, single-factor reformulation involving the replacement of sodium chloride with another salt may also affect color parameters. For example, when NaCl was replaced with CaCl₂ or CaCO₃, the resulting crumb was characterised by higher L* and b* values and lower a* values [46].

Differences in the CIELab colour coordinates resulted in changes in the total colour difference (ΔE). Depending on the ΔE value, a difference may be imperceptible, noticeable, or perceived as two distinct colours. As shown in

Table 5. The total colour differences (ΔE) between bread samples.

Sample Name	CS	YS1	YS2
CS	0.00 +
YS1	4.68 ++	0.00 +
YS2	5.62 +++	0.94 +	0.00 +

⁺ the observer does not notice the difference; ⁺⁺ the observer notices the difference; ⁺⁺⁺ the observer gets the impression of two different colors [49].

, a high total colour difference was observed when CS was compared with both YS samples. In the comparison between CS and YS1, the ΔE value was 4.68, whereas for CS and YS2 it reached 5.62. In the first case, ΔE was higher than 3.0 but lower than 5.0, indicating that the colour difference was noticeable to the observer. In the second case, a ΔE value of 5.62 exceeded 5.0, allowing the samples to be classified as having distinctly different colours. In contrast, when YS1 and YS2 were compared, the ΔE value was 0.94, indicating that no visible difference in colour was perceived between these samples. The obtained ΔE values clearly indicate that the modification of the recipe had a significant impact on bread colour. In contrast, Monteiro et al. [47], who investigated the effect of sodium reduction combined with inhomogeneous salt distribution using salt–waxy starch agglomerates, did not observe significant changes in colour coordinates. This may further confirm that the colour changes observed in the present study were not primarily caused by the reduction in sodium chloride content itself, but rather by the incorporation of yeast flakes. This suggests that yeast flakes could be deliberately used as a natural colouring enhancing ingredient in reduced-sodium formulations [48].

3.3. Texture Analysis

Bread texture parameters changed following the modification of sodium chloride and yeast flake concentrations. In all cases, decreasing the NaCl concentration followed by increasing yeast flakes concentration resulted in a significant increase in both hardness I and hardness II (

Table 6. TPA parameters of the bread samples.

Sample Name	Hardness I [N]	Hardness II [N]	Springiness [mm]
CS	21.10 ± 0.500 a	18.00 ± 0.700 a	0.96 ± 0.003 b
YS1	38.90 ± 0.900 b	31.45 ± 0.850 b	0.95 ± 0.010 ab
YS2	41.15 ± 0.950 c	33.35 ± 1.050 b	0.94 ± 0.008 a

a, b, c—samples with the same letter in the column do not differ significantly.

). The lowest values of hardness I and hardness II were observed in the CS sample (21.10 N and 18.00 N, respectively), while the highest values were recorded in YS2 (41.15 N and 33.35 N, respectively). Deepening the degree of reformulation from CS to YS2 caused an almost twofold increase in hardness I and an approximately 1.8-fold increase in hardness II. Similar findings confirming that the change may be due to a decrease in sodium chloride concentration were reported by Lynch et al. [50], who observed that low-salt bread was harder than the control and that hardness increased further as salt content decreased. In contrast, Bassett et al. [46] found that a reduction in sodium chloride combined with fortification using calcium salts (CaCl₂ and CaCO₃) led to a decrease in hardness. Additionally, Arena et al. [51] reported a significant increase in hardness with decreasing levels of sea salt addition. A statistically significant decrease in springiness was also observed, from 0.96 to 0.95 and 0.94 for CS, YS1, and YS2, respectively (Table 6).

In a TPA test, springiness is defined as the ability of a sample to recover its original shape after the removal of a deforming force and is calculated as the ratio of the distance travelled by the sample during the second compression cycle to that of the first. In bread crumb, springiness reflects the integrity and elasticity of the gluten network as well as the structure and distribution of gas cells. In the present study, a bread recipe reformulation resulted in a significant decrease in crumb springiness between CS and YS2 samples. No significant changes were observed between CS and YS1 and between YS1 and YS2. It is also necessary to point out that although the difference is significant, it involves a change in springiness from 0.96 to 0.94 mm, which is a small difference. However, similar observations were reported by Barroca et al. [18], who investigated the use of halophyte powder as a sodium chloride substitute. However, the changes depended on the level of halophyte powder addition, and the powder itself contained over 7600 mg/100 g of sodium ions, which is much higher than the sodium content of yeast flakes (0.25 g of sodium chloride, which is approximately 98 mg/100 g). Sodium ions play an important role in dough development and handling, and reduced Na⁺ availability may interfere with gluten network formation [52], thereby affecting bread texture parameters. This effect can be primarily attributed to a weakening of the gluten network, as salt normally enhances protein–protein interactions and strengthens the viscoelastic structure of the dough. Moreover, hydrophilic components of yeast flakes, such as β-glucans, mannoproteins, and dietary fibre, compete for the available water, thereby limiting proper gluten hydration and further impairing structural development. The concomitant reduction in porosity and water activity additionally contributes to the formation of a denser and less elastic crumb.

Changes in bread hardness correlated with crumb porosity: samples with lower porosity exhibited higher hardness and lower springiness, indicating a denser structure [53]. As described in Section 3.1, reducing the salt concentration and incorporation of yeast flakes can lead to a decrease in crumb pore volume, which significantly affects the textural properties of bread.

3.4. Organoleptic Tests

The results of the organoleptic evaluation are presented in

Table 7. Organoleptic tests results for analysed bread samples.

Parameter	CS	YS1	YS2
Springiness	8.50 ± 1.309 c	6.38 ± 1.685 b	3.78 ± 1.394 a
Softness	6.75 ± 1.389 c	5.40 ± 1.075 b	3.88 ± 1.126 a
Taste	7.50 ± 2.068 b	5.88 ± 1.246 b	4.40 ± 1.350 a
Flavour	7.13 ± 1.885 b	6.11 ± 1.616 ab	5.56 ± 0.882 a
Colour	8.44 ± 1.236 b	7.67 ± 1.225 ab	6.56 ± 1.509 a
Cross-sectional appearance	7.00 ± 1.195 a	6.06 ± 1.130 a	6.50 ± 1.604 a

a, b, c—samples with the same letter in the line do not differ significantly.

. For all analysed parameters, reducing the sodium chloride concentration and increasing the level of yeast flakes led to changes in the assigned scores.

In the case of springiness, the highest score was recorded for the control sample CS (8.50), while both modified samples, YS1 and YS2, received significantly lower scores (6.38 and 3.78, respectively) (Table 7). Moreover, a further modification of the formulation resulted in a statistically significant decrease in the springiness score of YS2 compared to YS1. In practical terms, the modified bread was perceived as less elastic than the control sample. These results are consistent with the texture profile analysis (TPA), which also indicated a decrease in springiness.

Similar trends were observed for softness (Table 7). All changes were statistically significant. The highest score was noted for the control sample (6.75), whereas the lowest was recorded for YS2 (3.88). According to the sensory scale applied in this study, lower softness scores reflect a higher perceived firmness of the bread. Consequently, these findings are in agreement with the TPA results, which demonstrated an increase in instrumental hardness.

A reduction in sodium chloride concentration combined with an increase in yeast flake content resulted in a gradual decrease in taste scores, from 7.50 for CS, to 5.88 for YS1 and 4.40 for YS2 (Table 7). However, the difference between CS and YS1 was not statistically significant. A lower score indicates a less desirable taste; nevertheless, the results suggest that the addition of 4.39% yeast flakes still allows the production of bread with acceptable sensory properties. Increasing the yeast flake content to 6.58% led to a pronounced decline in taste scores, indicating that higher substitution levels may negatively affect sensory perception.

Only slight differences were observed in flavour scores (Table 7). Although a decreasing tendency was recorded, the differences between CS and YS1 and between YS1 and YS2 were not statistically significant. The obtained values ranged from 7.13 (CS) to 5.56 (YS2). The absence of significant differences confirms that, similarly to the taste evaluation, the addition of yeast flakes up to 4.39% together with a reduction in sodium chloride to 1.05% did not result in a marked deterioration of flavour quality.

In the case of colour, statistically significant differences were observed only between CS and YS2 (Table 7). The lack of a significant difference between CS and YS1 is not fully consistent with the colourimetric measurements, which indicated a noticeable ΔE between these samples. This discrepancy highlights the importance of combining instrumental analysis with sensory assessment, as even detectable visual changes may not be perceived by consumers as undesirable.

No statistically significant differences were found between the samples in terms of cross-sectional appearance (Table 7). The obtained scores ranged from 7.00 to 6.06, indicating that, despite a slight reduction in porosity, the recipe modifications did not result in an unacceptable change in the sensory quality of the crumb structure.

Based on the saltiness perception results, no statistical significance between samples were observed, however, both YS1 and YS2 samples were evaluated as less salty than the control sample (Figure 1). Among the modified breads, YS1 (containing 4.39% yeast flakes and 1.05% sodium chloride) was perceived as less salty than YS2 (containing 6.58% yeast flakes and 0.7% sodium chloride). These results indicate that increasing the concentration of yeast flakes probably can enhance the perception of saltiness, confirming the ability of yeast flakes to act as flavour enhancers and partially compensate for reduced sodium chloride levels [48]. Nevertheless, taking into account that all samples containing yeast flakes were still evaluated as less salty than the control and no statistical significance was observed large population studies are necessary to confirm this thesis.

Sensory properties play a crucial role in product acceptance. Modifications to bread formulations, especially those involving a reduction in sodium chloride, inevitably influence sensory characteristics. Raffo et al. [54] reported a reduction in saltiness when sodium chloride was replaced by Pansalt^® (Oriola Corporation, Espoo, Finland), although no significant changes in texture and mouthfeel were observed. Similarly, Pasqualone et al. [55] demonstrated that decreasing sodium chloride levels from 20 g/kg to 10 g/kg resulted in a significant decline in sensory attributes such as salty taste, toasted colour, crumb consistency and crust colour. In a study by Spina et al. [56], the partial replacement of sodium chloride (from 2% to 1%) with yeast extract led to a decrease in softness (an increase in hardness), saltiness, elasticity and aroma, which ultimately reduced overall acceptability. These findings are consistent with the results obtained in the present study and highlight the crucial role of sodium chloride in shaping both the technological and sensory characteristics of bread. However, when yeast extract was used as a sodium chloride replacer in baked crackers, a reduction of NaCl from 7.50% to 3.75% while maintaining the same level of yeast extract resulted in products with acceptable sensory properties. In contrast, Filipović et al. [57] observed a deterioration in overall sensory quality following the addition of yeast extract, whereas the incorporation of sugar improved sensory attributes and increased consumer acceptability. However different perceptions of products with different types of inactivated yeast forms may depend on additives composition. Yeast extract is a hydrolyzed product obtained by autolysis or enzymatic treatment of yeast cells, resulting in the release of intracellular compounds such as free amino acids, peptides, and nucleotides, which are readily available and exhibit strong umami-enhancing properties [20]. On the other hand, yeast flakes consist of inactivated, non-hydrolyzed yeast cells, in which these compounds remain largely entrapped within the cell structure. They are a source of protein and vitamins, especially B-complex, low in fat and sodium [20]. As a consequence, the flavor-modulating effects of yeast flakes may be less immediate or intense compared to yeast extract and may depend on processing conditions, hydration, fermentation dynamics, and thermal treatment during baking, which can promote partial release of taste-active compounds. This distinction is particularly relevant when comparing sensory outcomes between studies using yeast extract and those employing yeast flakes. While both ingredients can enhance flavor perception and partially compensate for sodium reduction, their mechanisms of action, intensity of umami contribution, and interactions with the dough matrix differ substantially.

As demonstrated both in the literature and in the present study, sensory properties undergo substantial changes as a result of recipe modification. Nevertheless, because not all differences observed between CS and YS1 were statistically significant, the use of yeast flakes appears to hold promising potential for application in the reformulation of reduced-salt bread.

3.5. Result Correlations

In order to verify the consistency between the results of instrumental analyses and sensory evaluation, a correlation analysis of selected parameters was performed. Strong relationships were observed between instrumental measurements and sensory scores.

Sensory colour scores showed strong negative correlations with redness (a*) and yellowness (b*) (r = −0.90 and r = −0.88, respectively), indicating that samples with more intense red–yellow hues were perceived by the panel as less desirable in terms of colour (

Table 8. Correlations value of selected results (p < 0.05).

Parameter	a*; n = 3	b*; n = 3	Springiness TPA; n = 3	Hardness I (TPA); n = 3	Softness (Organoleptic Test); n = 20
Colour (organoleptic test); n = 20	−0.90	−0.88	-	-	-
Springiness (organoleptic test); n = 20	-	-	0.99	-	-
Softness (organoleptic test); n = 20	-	-	-	−0.90	-
Crumb porosity; n = 3	-	-	-	−0.97	0.97

).

In the case of springiness, a very strong positive correlation was obtained between sensory assessment and TPA results (r = 0.99) (Table 8). Both methods consistently indicated a decrease in springiness as a result of the formulation changes.

A strong negative correlation was observed between sensory softness scores and hardness I determined by the TPA test (r = −0.90) (Table 8). Although the correlation was negative in numerical terms, this is consistent with the applied sensory scale, in which lower scores correspond to higher perceived hardness (1 = very hard, 10 = very soft). Therefore, the negative correlation confirms that an increase in instrumental hardness was accompanied by an increase in perceived hardness.

Crumb porosity was also strongly related to hardness (Table 8). The correlations between crumb porosity and hardness I (TPA) and between crumb porosity and sensory hardness were r = −0.97 and r = 0.97, respectively. This indicates that a decrease in porosity resulted in higher instrumental hardness and, simultaneously, in lower sensory hardness scores (i.e., greater perceived firmness). These findings confirm that the denser crumb structure formed in the reformulated samples directly contributed to increased hardness and reduced textural softness.

Overall, despite the limited number of formulations (n = 3) and the corresponding sensory panel replicates (n = 20), the correlation coefficients demonstrate clear agreement between instrumental and sensory measurements, suggesting that the applied analytical methods reflect the actual changes in bread quality resulting from partial sodium chloride replacement with yeast flakes.

4. Conclusions

The results of this study demonstrate that yeast flakes can be considered a promising technological ingredient for the partial replacement of sodium chloride in bread formulation. Their application allowed for a reduction in salt content while maintaining acceptable sensory quality by enhancing saltiness perception at moderate substitution levels, but did not improve overall flavor.

At the same time, the partial substitution of NaCl with yeast flakes significantly affected several physicochemical and structural properties of the bread. A decrease in crumb porosity, water activity, and springiness was observed, indicating a harder and less elastic crumb structure. These changes can be attributed to the weakening of the gluten network resulting from reduced ionic strength, as well as to competition for water between gluten proteins and the hydrophilic components of yeast flakes, including β-glucans and mannoproteins. An increase in crumb acidity, likely caused by organic compounds present in the yeast flakes and possible modifications in fermentation dynamics, was also observed.

Despite these structural changes, the overall sensory scores of the bread were remained satisfactory, particularly for the sample containing 4.39% yeast flakes, for which most sensory attributes did not differ significantly from the control. Interestingly, although instrumental colour measurements (ΔE values) indicated a noticeable difference between the control and the modified sample, this change was not perceived as significant by the sensory panel. This discrepancy highlights the importance of combining instrumental and organoleptic methods when evaluating product quality, as not all measurable changes are necessarily perceived as negative or undesirable by consumers.

Considering the observed reduction in crumb porosity and textural changes associated with the incorporation of yeast flakes, their application may be particularly suitable for bakery products in which a dense and less elastic structure is not only acceptable but technologically desirable. Such products include dense whole-grain loaves, flatbreads, crackers, and other low- or non-leavened bakery products. In these categories, a compact crumb structure and reduced elasticity do not compromise product quality and may even contribute positively to textural and sensory attributes. Therefore, the use of yeast flakes as a sodium chloride reduction and flavour enhancing ingredient may offer greater technological advantages in these bread types.

Nevertheless, further research is required to optimize the level of substitution and to better understand the interactions between yeast flakes, gluten proteins, and fermentation processes. Future studies should also focus on consumer acceptance in a broader population, shelf-life stability, and the long-term technological performance of yeast flakes in different bread formulations. Future research should also explore these alternative applications to better define the technological potential of yeast flakes across different bakery matrices. Overall, the findings of this work provide a foundation for further research and indicate that yeast flakes have considerable potential as a technological ingredient for sodium chloride reduction in bread. Given the current lack of comprehensive data on their application for this purpose, the present study represents an initial step toward filling this research gap.