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Frontiers in Food Science and Technology ·

Volume 6 - 2026 | https://doi.org/10.3389/frfst.2026.1906637

Effects of glycerol and water addition on the texture profile and consumer acceptance of protein bars

  • Vitor Andre Silva Vidal1*corresponding author
  • Even Sørvåg Hauge1
  • Ida-Johanne Jensen1
  • Jørgen Lerfall1
  1. Department of Biotechnology and Food Science, NTNU-Norwegian University of Science and Technology, Trondheim, Norway
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Abstract

Protein bars are widely consumed worldwide, primarily due to their nutritional properties and convenience. This study investigated the effects of glycerol and water addition on the physicochemical and textural properties of protein bars. Four formulations were developed with two levels of glycerol (3% and 3.5%) and with or without added water (0% or 2%). Moisture and ash contents were not significantly affected by reformulation, however, glycerol addition significantly reduced a w below the threshold for microbial growth, ensuring product stability. Sensory evaluation revealed that the addition of water decreased firmness and crispiness, while increasing stickiness and chewiness. Overall, the findings emphasize the functional role of glycerol as a humectant and its influence on the textural profile, while also demonstrating that water addition, although contributing to softness, may negatively affect consumer preference for protein bars. These results provide valuable insights for optimizing protein bar formulations to enhance textural quality and consumer acceptance.

Keywords

1 Introduction

The increasing demand on high-protein diets has driven the expansion of protein-enriched food products beyond athletic populations to a broader health-conscious consumer base (Abdel-Salam et al., 2022). Among these products, snack bars have gained prominence as a practical delivery system for nutrients, offering convenience, compactness, and suitability for on-the-go consumption (Vidal et al., 2026). Their technological design allows them to maintain stability under room-temperature storage conditions while providing important sources of macronutrients and energy (Aljaloud et al., 2020; Ayad et al., 2020; Jetavat et al., 2020). Taking these into account, the marketplace currently includes a wide variety of bar formulations, particularly protein-fortified options developed to balance functional nutritional benefits with desirable organoleptic qualities (Duda-Seiman et al., 2025; Vidal et al., 2026).

Protein bars are among the fastest-growing categories of functional foods and are designed to provide high protein content together with desirable sensory characteristics and extended shelf stability. These products commonly contain dairy- or plant-based proteins, carbohydrates, fats, fibers, vitamins, and minerals, offering a convenient and nutritionally balanced food option (Aljaloud et al., 2020; Jetavat et al., 2020). Despite their growing popularity, maintaining desirable textural properties remains a major challenge in protein bar development, as excessive hardness and other unfavorable textural changes can negatively affect consumer acceptance and ultimately limit product acceptance (McMahon et al., 2009; Liu et al., 2009; Kamei et al., 2024; Prescott et al., 2022).

To overcome these challenges, humectants such as glycerol are frequently incorporated into protein bar formulations (Chen et al., 2019; Loveday et al., 2009). Protein bars are generally classified as intermediate-moisture foods and typically exhibit water activity (aw) values below 0.80, characteristics that contribute to microbial stability and shelf life (Hassan, 2020). In this context, humectants play an important role in regulating aw and moisture content, while also contributing to the stabilization of protein structures and modification of textural attributes (Liu et al., 2009; Aung and Nam, 2024). Among these ingredients, glycerol has received considerable attention due to its ability to control water migration, maintain product quality, and reduce hardening phenomena during storage (Hassan, 2020). Although the effects of humectants on the stability of high-protein nutrition bars have been investigated, limited information is available regarding the combined influence of glycerol concentration and water addition on the physicochemical properties, texture profile, and consumer acceptance of protein bars.

The present study investigates the effects of different levels of glycerol (3% and 3.5%) and water content (0% and 2%) on the physicochemical composition, textural properties, and consumer acceptance of protein bars. The novelty of this work lies in the combined assessment of glycerol and water contents as formulation variables, integrating instrumental analyses with sensory evaluation to provide comprehensive insights for optimizing texture and enhancing consumer acceptability of protein bars.

2 Materials and methods

2.1 Materials

The raw materials used in this study were purchased from commercial retailers located in Trondheim, Norway. All ingredients and additives met appropriate hygienic and quality standards required for food production. The protein bar formulations were prepared using pea protein flour (approximately 80% protein and 4% fat) as primary protein source, peanut butter (approximately 25% protein and 50% fat), oatmeal (approximately 13% protein and 7% fat), glucose syrup, rapeseed oil, cashew nuts (approximately 18% protein and 44% fat), pumpkin seeds (approximately 30% protein and 49% fat), chia seeds (approximately 17% protein and 31% fat), taco seasoning, sodium chloride (NaCl), water (H2O), monosodium glutamate, and glycerol.

2.2 Processing

All formulations were prepared according to a standardized manufacturing procedure. The base composition comprised pea protein flour (35.1%), peanut butter (21.7%), oatmeal (5.9%), glucose syrup (11.9%), rapeseed oil (8.6%), cashew nuts (5.9%), pumpkin seeds (3.5%), chia seeds (2.3%), taco seasoning (1.2%), sodium chloride (0.2%), and monosodium glutamate (0.2%). Glycerol was incorporated at either 3% or 3.5%, while water was added at 0% or 2%, depending on the formulation design (Table 1). The variations in glycerol and water levels were compensated by proportionally adjusting the amounts of the remaining ingredients while maintaining their relative proportions. This approach ensured a constant formulation basis across all treatments.

TABLE 1. Bars performed with different contents of glycerol and water.

TreatmentGlycerol (%)H2O (%)
G3W03%0
G3.5W03.5%0
G3W23%2
G3.5W23.5%2

Dry and semi-solid ingredients were first manually blended to ensure preliminary homogenization. The mixture was then mechanically processed in a planetary mixer equipped with a paddle tool for 5 min at low rotational speed until a cohesive mass was obtained. Individual portions (58.0 ± 0.5 g) were weighed and shaped in silicone molds. Compaction was achieved by applying a controlled 10 kg force using a rectangular compression plate (110 × 40 mm), with the applied load monitored on a calibrated scale to ensure consistency.

The molded samples were baked in a preheated oven at 200 °C for 15 min. After thermal processing, the bars were allowed to cool under ambient laboratory conditions before being vacuum-sealed in polyethylene pouches for storage prior to analysis. A schematic representation of the processing sequence is presented in Figure 1.

Flowchart of processing steps for bar samples.
Figure 1. Flowchart of processing steps for bar samples.

Three independent production trials were conducted at the Department of Biotechnology and Food Science, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.

2.3 Physicochemical characterization

2.3.1 Moisture, ash, and water activity

Moisture and ash contents in the protein bar samples were determined following the procedures described by Horwitz (2010). Aw was assessed at 20 °C using a LabMaster instrument (Novasina, Switzerland).

2.3.2 Shear force

Shear force analysis was performed according to Małecki et al. (2020). Samples were prepared in cubic portions of approximately 2 × 2 × 2 cm. Measurements were carried out using a TA-XT 2i texture analyzer (Stable Micro Systems Ltd., Surrey, United Kingdom) fitted with a Warner-Bratzler blade (1 mm thickness). Prior to testing, the equipment was calibrated using a 5 kg standard weight. The operating conditions were set to a crosshead speed of 2 mm/s during both the upward and downward movements, with a platform travel distance of 25 mm. Each sample was subjected to a single cut, and the resulting shear force values were reported in Newtons (N).

2.4 Sensory evaluation

The sensory study was performed under ethical approval granted by the Department of Biotechnology and Food Science, Norwegian University of Science and Technology (NTNU), Norway (protocol IBT0225), and complied with established Good Practice principles (Civille et al., 2024). All assessors participated on a voluntary basis and provided written informed consent prior to the session.

Sensory testing was conducted in a single evaluation session in which each participant analyzed all formulations. Prior to serving, the bars were cut into standardized portions (approximately 4 × 3 × 2 cm). Samples were presented individually in identical plastic cups labeled with randomly generated three-digit numerical codes to prevent identification bias (in Figure 2). To minimize order and carry-over effects, the presentation sequence was systematically balanced across panelists.

Set up for sensory test for an individual panelist.
Figure 2. Set up for sensory test for an individual panelist.

Each serving was accompanied by water at ambient temperature to allow palate cleansing between samples, as well as a disposal container. The evaluations took place in a controlled sensory facility specifically designed for food testing at NTNU, Trondheim, Norway. The laboratory layout and environmental conditions complied with ISO 8589:2007 requirements for sensory analysis facilities.

2.4.1 Identification and selection of texture descriptors

A semi-trained panel of ten assessors (aged 22–50 years), all with prior experience and familiarity with sensory evaluation, was engaged to establish the texture profile of the samples. The Repertory Grid method (Rocha and Bolini, 2015) was employed to identify similarities and differences in texture-related attributes. Following this procedure, a group discussion was held to refine the terminology by retaining the most frequently cited descriptors that accurately represented the samples while discarding those rarely perceived by the panelists. The final set of texture descriptors was: chewiness, crispiness, stickiness, firmness, dryness, and sandiness. These descriptors were subsequently applied in the intensity scale assessment (Vidal et al., 2019).

2.4.2 Acceptance test and intensity scale method

On the same day and within a single session, a consumer panel consisting of 70 participants, including students and staff from the Norwegian University of Science and Technology (NTNU), Trondheim, Norway, evaluated the bar samples. The assessment combined an acceptance test with an intensity scaling method. The acceptance test was measured using a nine-point structured hedonic scale, where 1 represented “extremely disliked” and 9 corresponded to “extremely liked” (Vidal et al., 2020). Subsequently, participants rated the intensity of selected descriptors (chewiness, crispiness, stickiness, firmness, dryness, and sandiness), previously selected through the Repertory Grid method, using a 9 cm unstructured line scale, with the term “little” on the left end and “far” on the right end (Vidal et al., 2019).

2.5 Statistical analysis

The experiment followed a 2 × 2 factorial arrangement with two glycerol levels (3% and 3.5%) and two water levels (0% and 2%), resulting in four treatment combinations. Three independent production batches were prepared on separate days under identical processing conditions. For each batch, at least three samples were analyzed for each response variable. Statistical differences among treatments were evaluated using one-way analysis of variance (ANOVA) followed by Tukey’s post hoc test at a significance level of 5% (P < 0.05). In the statistical model, formulation was treated as a fixed effect, whereas batch variation was considered a random effect. All analysis were performed using SPSS Statistics (version 29.0.1.0, IBM Corp., New York, United States).

Consumer acceptance results were processed separately using EyeOpenR software (version 6.0.4.2, West Malling, United Kingdom). Mean comparison plots were generated using the “bar chart of means” function, and differences among samples were further examined through ANOVA followed by Tukey’s multiple comparison test (α = 0.05). Multivariate relationships between acceptance and intensity attributes were explored by Principal Component Analysis (PCA), also conducted in EyeOpenR.

3 Results and discussion

3.1 Moisture and ash contents

The results for the moisture and ash contents of the protein bar samples with varying levels of added glycerol and water are presented in Table 2.

TABLE 2. Moisture (%), ash (%), water activity (aw) and shear force (N) of bars performed with different formulations.

TreatmentMoisture (%)Ash (%)AwShear force (N)
G3W06.56 ± 0.01 b3.29 ± 0.13a0.407 ± 0.011c72.61 ± 8.18b
G3.5W06.79 ± 0.04 b3.31 ± 0.04a0.387 ± 0.004c92.71 ± 9.61a
G3W27.42 ± 0.08a3.32 ± 0.16a0.471 ± 0.017a30.48 ± 7.02d
G3.5W27.70 ± 0.27a3.31 ± 0.14a0.433 ± 0.006b51.13 ± 5.35c

Values are means ± standard error. Means in the same column with different superscript letters are significantly different by the Tukey test (P < 0.05). G3W0: 3% glycerol and no addition of H2O; G3.5W0: 3.5% glycerol and no addition of H2O; G3W2: 3% glycerol and 2% H2O; G3.5W2: 3.5% glycerol and 2% H2O.

Moisture content ranged from 6.56% to 7.70%, closely aligning with the values reported for similar products (Allai et al., 2022; Souiy et al., 2022), and no significant differences (P > 0.05) were observed among the samples. Interestingly, the addition of 2% water did not significantly (P > 0.05) increase the moisture content compared to the samples without added water (G3W0 and G3.5W0). This outcome may be attributed to the humectant properties of glycerol (Basiak et al., 2018). Glycerol is a well-known humectant that strongly binds free water molecules through hydrogen bonding, thereby reducing their availability for evaporation or migration within the matrix (Chen et al., 2022). In this way, the addition of glycerol promotes redistribution of water rather than an overall increase in total moisture content.

The ash content of the samples ranged from 3.29% to 3.32%, slightly exceeding the values reported by AlJaloudi et al. (2024), who found ash contents of 1.77%–2.28% in high-protein bars. The higher values obtained in the present study may be attributed to the greater mineral contribution of the ingredients used. In particular, the formulations likely contained higher proportions of seeds such as chia and pumpkin seeds, which are recognized for their substantial ash fractions. Ikumi et al. (2022) reported that chia seeds contain 4–6 g of ash per 100 g dry matter, while Devi et al. (2018) found that pumpkin seeds provide approximately 4.4 g per 100 g dry matter. These findings demonstrate the role of seed addition in increasing the ash content of the protein bar samples. Moreover, since no significant differences (P > 0.05) in ash content were observed among the formulations, this suggests that variations in water (0% and 2%) and glycerol (3% and 3.5%) additions did not affect either moisture content or the accumulation of inorganic residues.

3.2 Water activity

Aw plays a crucial role in food safety, as lower aw values are associated with an extended shelf life (Fadiji et al., 2023). Aw can also have a substantial impact on the perception of texture-related properties. According to Ibrahim et al. (2021), aw values can be used to predict hardness in snack bars supplemented with varying concentrations of date paste during storage. Similarly, You et al. (2024) reported that higher aw values in protein bars were associated with lower instrumental hardness. Furthermore, Hassan (2020) reported that the addition of glycerol in protein bars was effective in reducing aw values and contributed to a softer texture.

The aw results are presented in Table 2. As expected, the protein bar samples with added water (G3W2 and G3.5W2) exhibited the highest (P < 0.05) aw values. Moreover, the glycerol content influenced (P < 0.05) the aw of the formulations containing added water, as observed when comparing G3W2 (3% glycerol) and G3.5W2 (3.5% glycerol). This effect can be attributed to the role of certain polyols, such as glycerol, in decreasing the aw values due to the relatively low viscosity of glycerol (Hassan, 2020).

Aw serves as a critical parameter in assessing the potential for microbial proliferation, defining packaging requirements, and guiding the establishment of food preservation standards (Samakradhamrongthai et al., 2021). All protein bar samples exhibited very low aw, ranging from 0.387 to 0.471, values that are well below the threshold required to support microbial growth. For products stored under vacuum at ambient temperature, such as protein bars, an aw value below 0.85 is required to achieve microbiological stability and ensure shelf life (Beuchat et al., 2013; Ingham et al., 2006). According to You et al. (2024), protein bars classified as intermediate-moisture products, with an aw ranging from 0.60 to 0.80, demonstrate microbial stability, thereby enabling a shelf life of 6–12 months. Nonetheless, suggested that maintaining aw below approximately 0.75 contributes to enhanced microbial stability during extended storage at ambient temperature (Juneja et al., 2016; Leistner, 1994; Mediani et al., 2022; Shi et al., 2020; Zapata et al., 1990). In the present study, all formulations exhibited very low aw values (0.387–0.471), which are substantially below the minimum requirements reported for the growth of most spoilage microorganisms. These results indicate a favorable condition for microbiological stability and support the classification of the bars as intermediate-moisture products with low aw.

3.3 Shear force

Texture parameters play a crucial role in consumer acceptance (Kowalska et al., 2023). Furthermore, the product’s composition generally influences the texture profile, thereby affecting the overall quality (Peleg, 2019).

The addition of glycerol and water significantly (P < 0.05) influenced the shear force values (N). Increasing the glycerol content added in the formulation from 3% to 3.5% led to a significant (P < 0.05) increase in shear force, both with and without added water, as observed when comparing samples G3W0 with G3.5W0 and G3W2 with G3.5W2. In contrast, as expected, the addition of water significantly (P < 0.05) decreased the shear force values.

The increase in shear force values observed in protein bar samples with higher glycerol content can be attributed to specific interactions between glycerol and protein molecules. The hydroxyl groups of glycerol interact with the surface of protein layers through hydrogen bonding, while glycerol exhibits fewer interactions with other glycerol molecules compared to water (Chen et al., 2019). This reduced intermolecular interaction among glycerol molecules enhances the entropic effect on the hydrophobic regions of proteins, promoting aggregation of protein layers and resulting in a firmer texture (Chen et al., 2019; Hassan, 2020). Consequently, the combination of glycerol and protein interactions and the inherent protein content explains the observed increase in shear force values in protein bar samples with higher glycerol content. In contrast, the addition of water significantly reduced shear force values, suggesting a softening effect on the protein bar matrix. Water acts as a plasticizer by increasing molecular mobility within the food system and reducing intermolecular forces among proteins and other macromolecules (Lamp et al., 2022). Consequently, the matrix becomes less rigid and requires lower force to undergo deformation. In addition, water may compete with glycerol for hydrogen-bonding sites on protein surfaces, partially weakening protein-glycerol interactions and limiting the formation of a compact structure (Yang et al., 2024). Similar plasticizing effects of water on protein-rich matrices have been reported in previous studies (Lamp et al., 2022; Matveev et al., 2000), where increased water availability resulted in reduced hardness and improved deformability of the product matrix.

These results are important for understanding the effect of glycerol and water addition on the shear force of protein bars. They are crucial for the development of snack bars with an improved texture profile and enhanced consumer acceptance.

3.4 Sensory evaluation

3.4.1 Intensity scale method

The evaluation of the intensity of different textural properties is essential to enhance the understanding of the impact of glycerol, a widely used humectant in the food industry, and the addition of water in protein bar formulations. To evaluate the textural properties of the protein bar samples, six descriptors were selected by the panelists: chewiness, crispiness, stickiness, firmness, dryness, and sandiness. These were used for the application of the intensity scale method, and the results are presented in Table 3. Interestingly, among the descriptors, only dryness did not show a significant difference (P > 0.05) between the samples.

TABLE 3. Intensity of texture properties of bars samples prepared with different formulations.

PropertiesG3W0G3.5W0G3W2G3.5W2
Chewiness1.59 ± 0.18c2.05 ± 0.21b2.35 ± 0.25b3.07 ± 0.29a
Crispiness5.25 ± 0.28a4.86 ± 0.27ab4.24 ± 0.27b3.57 ± 0.25c
Stickiness1.39 ± 0.19b1.88 ± 0.25a1.83 ± 0.22a1.96 ± 0.25a
Firmness5.87 ± 0.28a5.45 ± 0.28ab4.75 ± 0.28b4.99 ± 0.24b
Dryness6.37 ± 0.27a6.54 ± 0.26a6.96 ± 0.26a6.24 ± 0.28a
Sandiness5.97 ± 0.31b6.26 ± 0.30ab6.87 ± 0.27a6.09 ± 0.31ab

Values are means ± standard error. Means in the same row with different superscript letters are significantly different by the Tukey test (P < 0.05). G3W0: 3% glycerol and no addition of H2O; G3.5W0: 3.5% glycerol and no addition of H2O; G3W2: 3% glycerol and 2% H2O; G3.5W2: 3.5% glycerol and 2% H2O.

As expected, the addition of water to the protein bar formulations significantly reduced (P < 0.05) the intensity of crispiness and firmness. However, varying glycerol content (3% and 3.5%) did not affect (P > 0.05) the intensities of firmness and sandiness when comparing samples G3W0 with G3.5W0 and G3W2 with G3.5W2. Only sample G3W0, containing the lowest glycerol level (3%) and no added water, differed from the other protein bar formulations with respect to stickiness, exhibiting the lowest values. Furthermore, the incorporation of glycerol and water did not influence dryness values.

3.4.2 Acceptance test

A nine-point structured hedonic scale was employed to assess consumer acceptance, as this method ensures an even distribution of responses across the extremes (extremely disliked and extremely liked) while incorporating a midpoint that enables participants to express neutrality toward the product (Lawless and Heymann, 2010). The outcomes of the acceptance evaluation for the different protein bar formulations are illustrated in Figure 3.

Acceptance of bar treatments. The participants rated the samples for overall liking using a 9-point structured hedonic scale (1 – extremely disliked to 9 – extremely liked). Values are means (n = 70) ± standard error. The superscript letter (<sup>a, b</sup>) indicates statistically significant difference according to Tukey’s test (*P < 0.05*). G3W0: 3% glycerol and no addition of H<sub>2</sub>O; G3.5W0: 3.5% glycerol and no addition of H<sub>2</sub>O; G3W2: 3% glycerol and 2% H<sub>2</sub>O; G3.5W2: 3.5% glycerol and 2% H<sub>2</sub>O.
Figure 3. Acceptance of bar treatments. The participants rated the samples for overall liking using a 9-point structured hedonic scale (1 – extremely disliked to 9 – extremely liked). Values are means (n = 70) ± standard error. The superscript letter (a, b) indicates statistically significant difference according to Tukey’s test (P < 0.05). G3W0: 3% glycerol and no addition of H2O; G3.5W0: 3.5% glycerol and no addition of H2O; G3W2: 3% glycerol and 2% H2O; G3.5W2: 3.5% glycerol and 2% H2O.

The sample containing 3% glycerol and 2% water (G3W2) received the lowest acceptance value (P < 0.05) from consumers. Interestingly, although no statistically significant difference (P > 0.05) was observed, the sample with 3.5% glycerol and 2% water (G3.5W2) obtained the second-lowest mean acceptance values. These findings suggest that the incorporation of water into protein bar formulations may reduce consumer acceptance. In contrast, Barakat and Alfheeaid (2023) reported that cereal bars with higher moisture levels generally received higher sensory acceptance from consumers. Aramouni and Abu-Ghoush (2011) emphasized that consumer expectations for cereal energy bars involve a balance between softness and crispiness. Their findings further suggest that products with a predominantly soft and pliable texture may be less appealing in terms of overall texture and consumer preference.

3.4.3 Intensity x acceptance correlation

The two-dimensional PCA plot accounted for 95.06% of the total variance, with the first component explaining 61.35% and the second component 33.71% (Figure 4). Analysis of the sample distribution in the PCA plot, together with the intensity and acceptance test results, indicates that the addition of glycerol and water had a marked influence on the textural profile and consumer acceptance of the protein bar samples.

Principal Component Analysis (PCA) bi-plot from acceptance and intensity scale results conducted by 70 assessors of the bar treatments. G3W0: 3% glycerol and no addition of H<sub>2</sub>O; G3.5W0: 3.5% glycerol and no addition of H<sub>2</sub>O; G3W2: 3% glycerol and 2% H<sub>2</sub>O; G3.5W2: 3.5% glycerol and 2% H<sub>2</sub>O.
Figure 4. Principal Component Analysis (PCA) bi-plot from acceptance and intensity scale results conducted by 70 assessors of the bar treatments. G3W0: 3% glycerol and no addition of H2O; G3.5W0: 3.5% glycerol and no addition of H2O; G3W2: 3% glycerol and 2% H2O; G3.5W2: 3.5% glycerol and 2% H2O.

The PCA bi-plot indicates that dryness and sandiness attributes vary independently in relation to the firmness and crispiness dimension, which opposes the stickiness and chewiness dimension. G3W0 and G3.5W0 samples, which clustered with the firmness and crispiness attributes, tended to obtain higher acceptance values. Conversely, G3W2 and G3.5W2 samples, aligned with the opposing stickiness and chewiness cluster, tended to receive lower acceptance values. Moreover, it is important to note that sample G3W2 (formulated with 3% glycerol and 2% water) obtained the lowest acceptance values and was characterized by the highest intensities of dryness and sandiness texture attributes. These results suggest that consumers prefer protein bars with lower intensities of dryness and sandiness.

These findings from the PCA analysis indicate which attributes drive consumer acceptance. Protein bar samples exhibiting higher intensities of firmness and crispiness, together with lower intensities of stickiness, sandiness, chewiness, and dryness, are predicted to achieve greater consumer acceptance.

4 Conclusion

This study demonstrated that the addition of glycerol and water significantly influenced the textural attributes and consumer perception of protein bars. While moisture and ash contents remained within the expected range and were not markedly affected by the reformulation, aw values were low (ranging from 0.387 to 0.471), with these values being reduced by the addition of glycerol, ensuring microbial stability and extended shelf life. Increasing glycerol content from 3% to 3.5% enhanced shear force values, resulting in firmer textures, whereas the incorporation of water reduced firmness and crispiness but increased stickiness and chewiness. Sensory evaluation and PCA analysis further revealed that consumer acceptance was closely associated with bars characterized by higher firmness and crispiness and lower levels of dryness, sandiness, chewiness, and stickiness.

Consumer acceptance results indicated that the effect of water addition depended on the glycerol concentration. While the formulation containing 3% glycerol and 2% added water exhibited the lowest acceptance values, increasing glycerol to 3.5% appeared to mitigate this effect. These findings suggest that optimizing the balance between glycerol and water may be an effective strategy for maintaining desirable sensory characteristics and consumer acceptance in protein bar formulations. Since protein bars are susceptible to physicochemical and textural changes during storage, future research should investigate the effects of glycerol and water addition on moisture migration, hardening behavior, sensory characteristics, and overall product stability throughout shelf life.

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Footnotes

Edited by: Marcello Alinovi, University of Parma, Italy

Reviewed by: Gaigai Niu, Beibu Gulf University, China

Porntip Wiriyawattana, Ramkhamhaeng University, Thailand

Statements

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding

The author(s) declared that financial support was received for this work and/or its publication. We thank the Research Council of Norway (grant number: 332249) for funding this research.

Data availability

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics approval

The studies involving humans were approved by All research-related activities performed at NTNU are regulated under the Research Ethics Act 2017, and must follow relevant guidelines from national and international advisory bodies, conventions and agreements (cf. National Committee for Research Ethics in Science and Technology (NENT), National Committee for Research Ethics in Social Sciences and the Humanities (NESH), the European Group on Ethics in Science and New Technologies (EGE)/European Commission, the International Committee of Medical Journal Editors, and ICMJE (the Vancouver Convention). The study, Effects of glycerol and water addition on the texture profile and consumer acceptance of protein bars, was conducted following The Research Ethics Act of 2017 (https://lovdata.no/dokument/NL/lov/2017-04-28-23 (accessed on September 4th 2023). Ethical considerations and potential risks were considered when participants were selected, and the legal data was handled. Informed consent was obtained from all subjects and/or their legal guardian(s) before the study was conducted. The study collected no personal data; all participants were anonymous, without any trackable connections between the subject and the collected data. The Norwegian University of Science and Technology, Department of Biotechnology and Food Science, ethically approved the study (protocol approval number IBT0225, dated February 2025). The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

Author contributions

VV: Conceptualization, Investigation, Methodology, Validation, Writing – original draft. EH: Formal Analysis, Investigation, Methodology, Writing – original draft. I-JJ: Conceptualization, Resources, Supervision, Visualization, Writing – review and editing. JL: Conceptualization, Data curation, Funding acquisition, Project administration, Resources, Supervision, Validation, Writing – review and editing.

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Citation

Vidal, V. A. S., et al. (2026). Effects of glycerol and water addition on the texture profile and consumer acceptance of protein bars. Frontiers in Food Science and Technology, Volume 6. https://doi.org/
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6 - 2026

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Copyright © 2026 Vidal, Hauge, Jensen and Lerfall.

License: https://creativecommons.org/licenses/by/4.0/

*Correspondence: Vitor Andre Silva Vidal

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