Effect of Apple, Chestnut, and Acorn Flours on the Technological and Sensory Properties of Wheat Bread

Abstract

The increasing interest in fibre-enriched and functional bakery products has led to the exploration of novel plant-based ingredients with both technological functionality and consumer acceptance. This study evaluates the effects of incorporating flours derived from apple (Malus domestica cv. Oberländer Himbeerapfel), sweet chestnut (Castanea sativa), horse chestnut (Aesculus hippocastanum), and red, sessile, and pedunculate oak (Quercus rubra, Q. petraea, and Q. robur) into wheat bread at 5%, 10%, and 15% substitution levels. The impact on crumb structure, crust colour, textural parameters (hardness, adhesiveness, springiness), and sensory attributes was assessed. The inclusion of apple and sweet chestnut flours resulted in a softer crumb, lower adhesiveness, and higher sensory scores related to flavour, aroma, and crust appearance. In contrast, higher levels of oak- and horse-chestnut-derived flours increased crumb hardness and reduced overall acceptability due to bitterness or excessive density. Apple flour preserved crumb brightness and contributed to warm tones, while oak flours caused more intense crust darkening. These findings suggest that selected non-traditional flours, especially apple and sweet chestnut, can enhance the sensory and physical properties of wheat bread, supporting the development of fibre-rich, clean-label formulations aligned with consumer trends in sustainable and functional baking.

1. Introduction

Innovations in wheat bread production, involving the enrichment of traditional formulations with various functional ingredients, are gaining increasing popularity among both researchers and consumers [1]. The incorporation of flours derived from alternative sources such as acorns, chestnuts, and apples has been intensively studied in recent years due to their impact on the nutritional value, technological properties, and sensory characteristics of bread. The use of such ingredients can improve the nutritional profile of bread by increasing its content of dietary fibre, minerals, and bioactive compounds, while also affecting texture, flavour, and consumer acceptance [2,3].

Today, acorns, chestnuts, and other wild-derived natural additives have nearly disappeared from the modern human diet as standalone foodstuffs and are mainly associated with animal feed. However, for thousands of years, they constituted a significant component of traditional diets across various cultures. For example, acorns were consumed in Sardinia, Spain, Turkey, Asia, North America, and Poland, prepared in the form of porridges, bread, cakes, oils, and beverages [4,5,6,7,8]. Similarly, edible chestnuts and fruit by-products such as apple pomace played an important role in traditional diets and are now regaining attention in the context of sustainable food processing and the circular economy [9,10].

Flours produced from acorns (Quercus spp.), sweet chestnuts (Castanea sativa), horse chestnuts (Aesculus hippocastanum), and apples (Malus domestica) possess high nutritional value, and their application in baking aligns with current health-oriented trends. All these raw materials are rich in dietary fibre, phenolic compounds, antioxidants, and essential minerals [11,12,13]. Chestnut flour contains substantial amounts of complex carbohydrates as well as vitamins and volatile compounds that enhance the flavour and aroma of bread [14,15]. Apple flour, particularly that derived from apple pomace—a by-product of juice production—is naturally gluten-free and represents a valuable ingredient in the manufacture of functional baked goods [3]. Acorn flour, in turn, aside from its high phenolic and starch content, may exhibit a characteristic astringent aftertaste due to the presence of tannins [16].

Acorn flour is obtained from the nut after removing the hard seed coat (pericarp), which constitutes up to 34% of the fruit’s mass and is not used in processing [17,18,19]. To date, no studies have addressed the use of whole acorns, including the pericarp, in flour production, despite their potential to promote the more complete utilisation of the raw material [20].

Globally, fruit juice production generates several million tonnes of apple pomace annually. In some countries, such as India, only about 1% of this residue is utilised as animal feed or dried product. The vast majority is discarded in landfills or spread on fields, which may lead to serious environmental issues and soil contamination [10]. In this context, the incorporation of apple flour into bakery products represents an important strategy for waste valorisation and the sustainable use of agro-industrial by-products.

Seeds of horse chestnut (Aesculus hippocastanum) contain escins—a group of biologically active saponins with antibacterial, antiviral, antifungal, anti-inflammatory, and anti-oedematous properties [21]. Raw or naturally dried seeds require prolonged soaking in water or plant-based lye solutions to eliminate their characteristic soapy taste and to reduce toxicity. Alternatively, slow roasting of the seeds deactivates escins and renders them edible while preserving their nutraceutical potential [22]. These features make horse chestnut a promising ingredient in the development of functional breads with potential immune-supporting effects.

The chemical composition of alternative flours may vary significantly depending on the plant species, environmental conditions, raw material maturity, and processing methods. This variability affects the levels of fibre, phenolic compounds, starch, and volatile aroma compounds [7,23]. For instance, the detergent fibre content in acorn flour may be up to twice as high as in wholemeal flours [24], while horse chestnut may contain substantial amounts of saponins that influence the biological activity of the final product [21].

All the flours included in this study affect the technological properties of dough, such as water absorption, development time, stability, and loaf volume. Due to their limited ability to support gluten network formation, they may reduce the final bread volume [25,26]. However, at the same time, they enrich the product with bioactive compounds exhibiting antioxidant activity, thereby enhancing its functional value and potential health benefits.

The introduction of alternative flours into wheat bread production opens new possibilities for developing innovative products with improved nutritional composition and distinctive sensory characteristics. Previous studies have demonstrated that flours derived from acorns, chestnuts, and apples—particularly in the context of gluten-free products—increase dietary fibre, mineral content, and phenolic compounds, resulting in enhanced antioxidant activity [27,28,29,30]. Their use aligns with the principles of sustainable processing, waste valorisation, and the growing demand for clean-label foods.

The aim of this study was to conduct a comparative assessment of the technological and sensory properties of wheat bread enriched with flours derived from underutilised plant materials: red oak (Quercus rubra), pedunculate oak (Q. robur), sessile oak (Q. petraea), horse chestnut (Aesculus hippocastanum), sweet chestnut (Castanea sativa), and a traditional apple cultivar (Malus domestica cv. Oberländer Himbeerapfel). Unlike previous studies, uniform substitution levels (5–15%) were applied to all flour types, and a systematic evaluation was performed to assess their effects on crumb texture, crust colour, and sensory perception. The novelty of this research lies in the integrated comparison of rarely studied ingredients—particularly flours from red oak and horse chestnut—and in the use of whole seeds for flour production, including entire acorns and chestnuts. This approach offers a sustainable and nutritionally enriched strategy for bread formulation while reducing raw material losses.

2. Materials and Methods

2.1. Plant Materials

This study utilised plant materials for flour production, including apples (Malus domestica cv. Oberländer Himbeerapfel) [31,32], sweet chestnuts (Castanea sativa), horse chestnuts (Aesculus hippocastanum) [12], and acorns from red, sessile, and pedunculate oak (Quercus rubra, Q. petraea, and Q. robur) [16]. Apples were collected from trees growing in abandoned human settlements within Wolin National Park, while the chestnuts and acorns were gathered in various locations across the West Pomeranian Voivodeship.

2.2. Preparation of Flour from Acorns, Chestnuts, and Apples

Fruits of Quercus rubra (red oak), Q. robur (pedunculate oak), Q. petraea (sessile oak), Aesculus hippocastanum (horse chestnut), and Castanea sativa (sweet chestnut) were collected in autumn from natural forests and rural areas in north-western Poland. Apples (Malus domestica cv. Oberländer Himbeerapfel) were harvested from abandoned orchards located within the territory of Wolin National Park. All collected fruits were manually sorted to remove damaged or pest-infested specimens.

Apple flour was obtained by slicing the apples into 5 mm pieces and subjecting them to freeze-drying (lyophilisation) to preserve colour and bioactive compounds. The dried slices were then ground using a WŻ-1 laboratory grinder (Zakład Badawczy Przemysłu Piekarskiego, Bydgoszcz, Poland), which is designed for the dry milling and homogenisation of food-grade materials in bakery and confectionery applications.

Acorns and horse chestnuts were air-dried at 25–30 °C in a well-ventilated space until they reached a safe moisture content of approximately 10%, which was confirmed using a halogen moisture analyser (MA 110.R, Radwag, Radom, Poland). These values are consistent with previously reported safe storage ranges: 7.8–11.5% for acorns [20] and 8.1–9.7% for chestnuts [33]. After drying, the fruits were ground into flour using the WŻ-1 grinder.

To remove biologically active bitter and soapy-tasting compounds, acorn and horse chestnut flours underwent a debittering process involving repeated rinsing with distilled water until the water became clear. For chestnut flour, a foam test was additionally applied: samples were shaken in water-filled test tubes and observed for foam stability. Persistent foam lasting ≥5–10 min indicated the presence of saponins; rinsing was repeated until foaming ceased, suggesting effective saponin removal. After rinsing, the flours were re-dried in a laboratory convection dryer at 30 °C.

All prepared flours were stored in sealed containers at room temperature in a dry environment. Prior to the baking experiments, the flours were milled again using the WŻ-1 grinder to obtain a homogeneous powder with consistent granulation.

2.3. Colour Measurement

As described by Błaszak et al. [34], the colour parameters of the samples in the CIE Lab* system were determined using a photocolorimetric method with a Konica Minolta CM 700D spectrophotometer (Tokyo, Japan). Measurements were performed with a 3 mm aperture diameter, 10º observer type, and D65 illuminant. The L* value indicates lightness, ranging from 0 (black) to 100 (white). The a* value represents the position within the green–red spectrum, where negative values indicate green and positive values indicate red. The b* value corresponds to the blue–yellow axis, with negative values indicating blue hues and positive values indicating yellow tones.

For each bread sample, 25 independent measurements were taken at different points on the crust surface. Results are reported as mean values.

2.4. Laboratory Bread Baking

Commercial wheat flour type 650 (Młyny Stoisław S.A., Stoisław, Poland) was used for bread production. The rheological properties of the wheat flour were determined using a Brabender farinograph and included water absorption of 59.1%, a dough development time of 1.7 min, a dough stability of 3.1 min, and a degree of softening of 75.5 FU [12].

Additional flours used for partial substitution (at 5%, 10%, and 15% levels) were obtained from the following plant materials:

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Red oak (Quercus rubra);

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Pedunculate oak (Q. robur);

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Sessile oak (Q. petraea);

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Horse chestnut (Aesculus hippocastanum);

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Sweet chestnut (Castanea sativa);

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A traditional apple cultivar (Malus domestica cv. Oberländer Himbeerapfel).

Each bread sample was prepared using 250 g of a flour blend with equalised moisture content. Dough preparation was performed with a Hobart KitchenAid mixer (Greenville, OH, USA). The ingredients included water (120–200 mL, depending on the type of flour), baker’s yeast (3% relative to flour weight; compressed Saccharomyces cerevisiae), and salt (1.5%).

The final dough temperature was maintained at 32 °C. The fermentation process included a first proofing phase for 60 min at 32 °C and 75–80% relative humidity (Unox S.P.A. fermentation chamber, Cadoneghe, Italy), followed by moulding and final proofing at 35 °C for 20–40 min under moderate ambient humidity (approximately 50–55%) (Figure 1). These conditions were established based on preliminary trials performed to optimise the fermentation process for the specific composition of dough enriched with the acorn, chestnut, and apple flours used in this study. Baking was performed in an electric oven (Unox S.P.A., Italy) at 230–240 °C for 35–40 min, with 3 s steam injections applied every 5 min during the first 15 min of baking.

2.5. Instrumental Texture Analysis of Bread

The texture profile analysis (TPA) of the bread crumb was performed using a Texture Analyser TA-XT2/25^® (Stable Micro Systems, Godalming, UK), operated with Texture Expert for Windows^® v. 1.22 software (Figure 2). Measurements were conducted using a cylindrical probe (SMS P/0.5″) that compressed the crumb samples to 50% of their original height. The pre-test speed was 2 mm·s⁻¹, and both test and post-test speeds were set at 5 mm·s⁻¹.

The following parameters were determined:

Hardness (maximum compression hardness [N]);

Adhesiveness (negative hardness following probe retraction);

Elasticity (distance between the peaks of the first and second compression).

Each measurement was repeated five times per sample. Data were processed using the Texture Expert for Windows^® 3.2 software, and the results were presented as mean values.

2.6. Sensory Evaluation

Sensory evaluation of the bread samples was conducted 6–8 h after baking in accordance with the Polish Norm [35] and ICC Standard [36]. A trained panel consisting of 31 assessors performed an organoleptic evaluation of the bread samples, assessing crust and crumb characteristics using a 5-point hedonic scale. The crust was evaluated for appearance, colour, thickness, and other attributes, which included crispiness, surface uniformity, and roughness. The crumb was assessed for elasticity, porosity, flavour, and aroma, as well as other attributes, such as moisture, cohesiveness, gumminess, and overall freshness perception.

Each attribute was rated using a 5-point hedonic scale:

• 1 = very poor;
• 2 = poor;
• 3 = acceptable;
• 4 = good;
• 5 = very good.

Panellists assessed each sample individually under standardised conditions. Results are presented as mean values.

2.7. Statistical Analysis

All statistical analyses were performed using Statistica 13.1 (StatSoft Polska, Kraków, Poland). Differences between means were analysed using variance homogeneity and normality tests, followed by ANOVA with Tukey’s post hoc test. Significance was set at p < 0.05.

3. Results and Discussion

3.1. Changes in the Colour of Flour and Baked Product Crumb as Affected by Additives

This study investigated the effect of flours obtained from underutilised plant materials, including Oberländer Himbeerapfel apple flour, sweet chestnut flour (Castanea sativa), horse chestnut flour (Aesculus hippocastanum), and acorn flours from red, sessile, and pedunculate oaks (Quercus rubra, Q. petraea, Q. robur), on the colour parameters of flour blends and the crumb of the baked products in the CIE L*a*b* colour space. Particular attention was given to changes in lightness (L*) and the chromatic coordinates a* (red–green) and b* (yellow–blue), which reflect the overall colour tone and hue of the samples (Figure 3a–f,

Table 1. L* colour parameters of wheat flour blends supplemented with 5%, 10%, and 15% of alternative flours (oak, chestnut, horse chestnut, apple) and of the crumb of the baked products prepared from them.

Type of Flour	Proportion	Flour (L*)	Crumb of the Baked Product (L*)
Wheat flour	100%	91.9 h *	72.8 k
	5%	88.4 fgh	51.0 fg
Wheat flour + red oak	10%	78.4 b	48.3 def
	15%	73.4 a	43.2 ab
	5%	87.0 efg	55.4 h
Wheat flour + pedunculate oak	10%	82.5 cd	49.7 efg
	15%	79.6 bc	43.7 bc
	5%	85.4 def	55.5 h
Wheat flour + sessile oak	10%	82.3 cd	47.2 de
	15%	78.1 b	46.0 bcd
	5%	87.2 efg	58.8 i
Wheat flour + horse chestnut	10%	85.2 def	52.5 g
	15%	82.5 cd	40.6 a
	5%	90.1 gh	59.4 i
Wheat flour + sweet chestnut	10%	88.5 fgh	56.5 hi
	15%	86.8 efg	46.4 cd
	5%	90.9 h	68.4 j
Wheat flour + apple	10%	89.6 gh	58.7 i
	15%	84.7 de	50.6 fg

* Mean values in the same column followed by different letters indicate statistically significant differences according to NIR test (p ≤ 0.05).

).

The additives reduced the lightness of both the flour and the baked products. For wheat flour without additives (L* = 91.9), the addition of apple flour caused moderate darkening, reducing the L* value to 90.9 (5%), 89.6 (10%), and 84.7 (15%) (Table 1). Sweet chestnut flour exhibited a similar but milder effect, with L* reaching 86.8 at a 15% concentration. In contrast, oak flour, particularly from red oak, resulted in a more pronounced reduction in lightness, with L* decreasing to 73.4 at a 15% addition, indicating a significantly darker shade.

After baking, a further reduction in lightness was observed due to the intensification of the Maillard reactions and sugar caramelisation. Among the tested samples, the bread enriched with 15% apple flour retained a relatively high L* value of 50.6, compared to 58.7 and 68.4 for the 10% and 5% levels, respectively. This confirms that higher concentrations of apple flour contribute to progressive crumb darkening, although to a lesser extent than oak or chestnut flour. The visual effect of apple flour was therefore the mildest among all tested additives.

A similar trend was observed in earlier studies using apple pomace as a flour substitute. For instance, Rocha Parra et al. [37] reported that increasing the content of apple-derived material led to a clear reduction in the brightness of both the crumb and crust, with lightness values ranging from approximately 62.6 to 47.2. These observations align with our findings, confirming that the addition of apple-based components, although rich in fibre and polyphenols, generally results in darker baked products.

This darkening effect is most likely due to enhanced non-enzymatic browning occurring during the baking process, particularly Maillard reactions and caramelisation, which are intensified by the presence of reducing sugars and phenolic compounds. This phenomenon has also been observed in the final baked products by Korus et al. [28], Skendi et al. [38], and Beltrão Martins et al. [29], especially in gluten-free and fibre-enriched breads, where darker crumb and crust colours were reported as a result of such reactions.

Chromatic coordinates (a* and b*) were measured in wheat flour blends enriched with alternative flours and in the crumb of the corresponding baked products.

Changes in the chromatic coordinates a* and b* further highlighted the visual differences caused by the tested additives. Apple flour increased both the a* and b* values, shifting the colour towards warmer yellow-red hues. In the case of the composite flour blend containing 15% apple flour, the a* value reached 3.0 and the b* value 12.7, indicating a dominance of intense yellow-orange tones. In the crumb of the baked product enriched with the same amount of apple flour, the a* value increased further to 9.4 and the b* value to 25.8, reflecting an even more pronounced shift in crumb colour towards saturated red-yellow hues. This intensified colouration is attributed to enhanced non-enzymatic browning reactions—such as Maillard reactions and caramelisation—occurring during the baking process. These results are consistent with the findings of Rocha Parra et al. [37,39], who reported that in baked bread products containing flours derived from apple pomace—rich in natural sugars and phenolic compounds—there was a noticeable increase in both a* and b* values. This colour shift towards red and yellow tones was attributed to the intensification of non-enzymatic browning reactions, such as Maillard reactions and caramelisation, occurring during baking.

Sweet chestnut flour caused a balanced increase in a* and b* values, albeit to a lesser extent than apple flour. At a 15% concentration, the a* value reached 2.4 and the b* value 9.9, resulting in mild warm tones dominated by red-yellow hues. These colour coordinates are comparable to those observed by Demirkesen et al. [40] in final gluten-free bread products containing chestnut flour, where similar chromatic shifts were reported as a result of flour pigmentation and baking-induced browning reactions.

In contrast, oak flours—particularly red oak flour—significantly increased a* values while reducing b*, producing darker, cooler, reddish-brown tones. For flour with a 15% addition of red oak flour, the a* value increased to 7.6, while the b* value dropped to 3.3. This observation corroborated the findings of Beltrão Martins et al. [29], who demonstrated that acorn flour intensifies red and brown shades due to its high tannin and phenolic content, affecting both the dough during preparation and the colour characteristics of the final baked bread.

The inclusion of apple flour led to lighter, warmer hues, enhancing the visual appeal of baked products and making it a suitable option for consumers seeking aesthetically pleasing, functional bakery goods. Sweet chestnut flour imparted mild and balanced warm tones, while oak flours, particularly red oak, introduced darker and cooler reddish-brown hues. These effects are advantageous in the production of artisan-style bread, where darker colour profiles are often preferred.

The results confirm that the type and concentration of flour additives allow for the controlled modification of baked product colour, which is a critical aspect of visual appeal and market acceptance. By leveraging the distinct colour properties of apple, chestnut, and oak flours, it is possible to create diverse bakery products that align with consumer preferences and current food trends.

3.2. Effect of Fruit- and Tree-Based Flours on the Textural Properties of Wheat Bread

This study assessed the effect of flours obtained from underutilised plant materials—including apple, sweet chestnut, horse chestnut, and oak flours—on the textural properties of wheat-based baked products. The parameters measured included hardness (N), adhesiveness, and springiness to determine the structural and functional changes induced by these additives (

Table 2. Effect of fruit and tree flour additives on bread texture parameters.

Type of Flour	Proportion	Hardness (N)	Adhesiveness	Springiness
Wheat flour	100%	12.01 hi *	0.469 b	0.974 f
Wheat flour + red oak	5%	8.44 c	−0.722 de	0.981 fg
	10%	13.75 jk	−0.490 d	0.952 c
	15%	13.01 ij	0.042 bc	0.944 b
Wheat flour + pedunculate oak	5%	11.72 gh	−0.064 c	0.961 d
	10%	11.71 gh	−0.426 d	0.955 cd
	15%	14.95 k	−0.935 e	0.939 b
Wheat flour + sessile oak	5%	8.78 cd	−0.387 d	0.964 d
	10%	9.94 ef	−0.831 e	0.971 f
	15%	10.16 ef	−0.405 d	0.969 e
Wheat flour + sweet chestnut	5%	5.85 a	−0.396 d	0.987 g
	10%	7.41 b	−1.308 f	0.969 e
	15%	5.91 a	−0.467 d	0.987gh
Wheat flour + horse chestnut	5%	10.77 fg	−0.222 cd	0.967e
	10%	12.81 ij	−0.996 ef	0.966 de
	15%	5.38 a	1.029 a	0.999 h
Wheat flour + apple	5%	11.65 gh	0.379 b	0.949 bc
	10%	9.70 de	−0.789 e	0.972 f
	15%	9.70 de	−1.462 f	0.919 a

* See Table 1.

).

3.2.1. Hardness (N)

The pressing hardness is an indicator of the resistance of baked bread to deformation, directly associated with hardness and compactness. Hardness is one of the key texture parameters affecting consumer acceptance of bread. It not only reflects the initial structure and moisture content of the crumb but also provides insight into the physicochemical changes occurring during storage, such as starch retrogradation and moisture redistribution [28]. In the present study, a clear variation in crumb hardness was observed depending on the type and concentration of flour additive.

The control wheat bread exhibited a hardness of 12.01 N. Lower hardness values were recorded in breads containing horse chestnut flour (5.85–7.41 N) and 15% sweet chestnut flour (5.91 N), indicating a softer, less compact crumb structure. These effects can be attributed to the relatively high sugar content and low fibre concentration in those flours, which promoted a more open and moist crumb network. In particular, bread enriched with 5% chestnut flour exhibited the lowest values for crumb hardness (22.3 units), brittleness (31.7 units), and compactness (23.3 units), indicating a soft and airy crumb structure. These instrumental results align with panellists’ sensory impressions and confirm our findings—chestnut flour significantly improved crumb softness, reduced adhesiveness, and maintained high springiness. In contrast, samples with red oak flour showed increased crumb hardness, with values ranging from 13.01 to 13.75 N for 10–15% supplementation. Similarly, bread with 15% horse chestnut flour reached 12.81 N, close to the control. This increase is consistent with the findings of Korus et al. [28] and Švec et al. [30], who reported increased firmness in gluten-free bread formulations supplemented with acorn flour. They attributed this primarily to the high fibre content, which enhanced water absorption and contributed to a denser structure.

Korus et al. [28] additionally demonstrated that the level of acorn flour incorporation has a significant impact on the evolution of crumb hardness during storage. A 20% acorn flour substitution not only provided comparable hardness on the day of baking but also effectively limited crumb firming over time. After 2–3 days, bread with 20% acorn flour remained significantly softer than all other variants, indicating improved freshness retention. Notably, the same sample was characterised by the highest specific volume and was best accepted in terms of structure and porosity. This supports the often-observed inverse relationship between bread volume and crumb hardness, which was again confirmed in our study, especially for samples with red oak flour, where a lower volume correlated with increased hardness.

These findings suggest that, in addition to fibre content, tannin-rich components such as acorn flour may also influence crumb structure by interacting with the gluten or starch matrix. Although further biochemical confirmation is required, the ability of polyphenols to stabilise the crumb and delay staling may represent a valuable functionality in clean-label bakery formulations.

Zhang et al. [41] demonstrated that tannic acid affects the gluten network—while it weakens disulfide bonds, it also forms new covalent bonds with gluten proteins. Although parameters such as adhesiveness and resilience remained largely unchanged, a noticeable increase in crumb hardness and chewiness was observed, indicating delayed staling and changes in crumb structure. These findings suggest that tannins may play an active role in shaping bread texture, not only through their antioxidant properties but also through their direct interactions with dough proteins.

The densification observed in oak-enriched bread samples is likely related to the high fibre content of these flours, which increases water absorption and dough viscosity. This, in turn, reduces gas retention during proofing and leads to a more compact crumb structure. In contrast, the reduced hardness observed in breads with sweet chestnut and apple flour may be associated with their higher sugar content, which contributes to a softer crumb and improved gas distribution during fermentation.

3.2.2. Adhesiveness

Adhesiveness refers to the tendency of the crumb to adhere to surfaces, primarily affecting the mouthfeel and sensory comfort during consumption. In this study, the control wheat bread exhibited an adhesiveness value of 0.469. The lowest values were recorded for breads enriched with 15% apple flour (–1.462 N) and 10% sweet chestnut flour (–1.308 N), indicating reduced stickiness and enhanced eating comfort. This reduction may be attributed to the presence of soluble fibres and sugars, which help stabilise the crumb structure and limit its stickiness.

Similar effects were reported by Shafi et al. [42] in the context of cookies, where the addition of chestnut flour reduced adhesiveness due to its hydrophilic nature and moisture-retention capacity. Although this study did not concern bread, the mechanical principle may partially apply to the crumb behaviour observed in our experiment.

In gluten-free breads, Beltrão Martins et al. [3] found that the inclusion of acorn flour led to lower adhesiveness and cohesiveness compared to standard GFB loaves. This was explained by the reduced starch content and lower water-binding capacity, which resulted in less sticky crumb textures. These findings suggest that acorn flour may similarly contribute to reduced adhesiveness in wheat bread formulations.

Additionally, Marciniak-Łukasiak et al. [43] observed that the chewiness of gluten-free bread crumb increased with higher levels of chestnut flour from 5% to 20%. While adhesiveness was not directly measured, the rise in chewiness indicates changes in the crumb structure that may also affect the perceived stickiness during eating.

3.2.3. Springiness

Springiness is a key textural parameter that reflects the crumb’s ability to recover its shape after compression, closely related to the internal aeration and elasticity of bread. It plays an important role in consumer acceptance and is often used as an indicator of freshness and structural integrity, particularly during storage.

In the present study, the control wheat bread exhibited a springiness of 0.974. The addition of selected plant-based flours significantly influenced this parameter. The highest springiness was observed in bread with 15% horse chestnut flour (0.999), followed by 5% and 15% sweet chestnut flour (both 0.987). These findings are consistent with Raczyk et al. [44], who demonstrated that sweet chestnut flour preserved high elasticity in wheat bread, supporting its potential as a structure-enhancing additive.

Our results are also aligned with Rao et al. [45], who showed that increasing the level of chestnut powder (5–25%) initially enhanced springiness and cohesiveness in wheat doughs but eventually led to a decline at higher concentrations. Similarly, in our experiment, sweet chestnut flour at 10% produced lower springiness (0.969) than at 5% or 15%, indicating a non-linear response typical of fibre-rich additives.

Apple flour reduced springiness at higher inclusion rates, with the lowest value recorded at 15% (0.919), likely due to the disruption of the matrix structure and moisture retention imbalance. Cantero et al. [46] reported comparable outcomes in gluten-free bread enriched with apple pomace powder—springiness improved at 5% but decreased significantly at 6–8% levels, suggesting a threshold effect beyond which elasticity deteriorates.

Oak-derived flours (from red, sessile, and pedunculate oak) showed intermediate springiness values (0.939–0.981). Although these flours are known to increase crumb hardness and density—due to their high fibre and phenolic content—at moderate substitution levels, they did not negatively affect the bread’s elasticity. This effect was previously characterised by Sikora et al. [12,16,31], who analysed the chemical composition and functional properties of all plant-based flours used in this study, including apple, sweet chestnut, horse chestnut, and oak flours. Their research showed significant differences in the content of phenolic compounds, including tannins, among the additives tested.

Phenolic compounds—particularly tannins—can significantly influence the structural properties of bread. Zhang et al. [41] showed that tannic acid interferes with disulfide bond formation in gluten but forms other covalent interactions with wheat proteins, as evidenced by UV spectroscopy and dynamic rheometry. Texture analysis revealed that, while adhesiveness and resilience remained largely unchanged, increased hardness and chewiness were observed in breads supplemented with tannic acid. These changes suggest that tannins may delay bread staling and contribute to a denser structure. Given the natural presence of tannins in the flours used in this study—especially in oak and horse chestnut flours—their impact on bread structure likely extends beyond the water-binding capacity of dietary fibre alone.

Further support for oak flour’s effect comes from Park et al. [47], who showed that incorporating 5–25% acorn flour into bread formulations led to a significant increase in springiness during both refrigerated and frozen storage. The authors also found that springiness was maintained over time, confirming that acorn-enriched breads have stable and acceptable textural qualities during shelf-life.

Additionally, Beltrão Martins et al. [48] demonstrated that the addition of acorn flour increased springiness in gluten-free bread, regardless of sourdough presence. In their study, acorn level was the primary factor influencing springiness, while storage time and fermentation had no significant effect. These results align with our findings and with Korus et al. [28], who also observed no significant variability in springiness with changing levels of acorn flour or over time in gluten-free systems.

The present data confirm that plant-based flours—especially horse chestnut and sweet chestnut—enhance bread elasticity when used at optimal concentrations (5–15%). Oak-derived flours moderately preserve springiness, even at higher doses, and apple flour reduces elasticity at high concentrations. These results support the potential of chestnut and oak flours as functional ingredients for improving springiness and stabilising bread texture across storage periods.

3.3. Sensory Evaluation of Bread

The sensory evaluation of bread samples was performed by a trained panel of 31 assessors, who assessed crust and crumb quality, including “other attributes” such as crispiness, surface uniformity, roughness, moisture, cohesiveness, gumminess, and freshness (Figure 4). The control wheat bread achieved a crust score of 3.51 and a crumb score of 3.87, indicating a well-balanced structure with satisfactory moisture content and a mouthfeel typical of standard white bread (

Table 3. Sensory evaluation of bread enriched with fruit- and tree-based flours.

	Crust					Crumb
Type of Flour	Proportion	Appearance	Colour	Thickness	Other Attributes	Elasticity	Porosity	Flavour and Aroma	Other Attributes	Total Score
Wheat flour	100%	3.76	3.62	3.43	3.51	3.29	3.48	3.43	3.87	28.39
Wheat flour + red oak	5%	3.95	3.76	3.14	3.30	3.33	3.33	3.05	3.58	27.44
	10%	3.81	3.90	3.00	3.27	3.05	3.33	3.05	3.48	26.89
	15%	3.57	4.10	2.95	3.19	2.67	3.33	3.14	3.32	26.27
Wheat flour + pedunculate oak	5%	3.76	3.52	3.33	3.28	3.00	3.14	3.10	3.35	26.48
	10%	3.67	3.62	2.90	3.13	2.67	2.86	2.95	3.13	24.93
	15%	3.71	3.76	3.10	3.16	2.67	3.14	2.81	3.09	25.44
Wheat flour + sessile oak	5%	3.86	3.81	3.19	3.57	3.29	3.29	3.33	3.43	27.77
	10%	3.71	3.76	3.24	3.35	3.10	3.10	2.71	3.15	26.12
	15%	3.52	3.76	3.05	3.32	3.05	3.05	2.43	3.06	25.24
Wheat flour + sweet chestnut	5%	3.95	3.62	3.62	4.33	3.76	3.62	3.95	3.92	30.77
	10%	4.00	3.86	3.81	3.98	3.71	3.90	4.10	4.40	31.76
	15%	4.29	4.14	3.95	4.02	3.90	4.10	4.14	4.36	32.9
Wheat flour + horse chestnut	5%	3.52	3.33	3.14	2.55	2.76	2.76	1.95	2.70	22.71
	10%	-	-	-	-	-	-	-	-	0
	15%	-	-	-	-	-	-	-	-	0
Wheat flour + apple	5%	3.76	3.76	3.57	3.68	3.48	3.33	3.71	3.83	29.12
	10%	4.10	3.86	3.81	3.77	3.48	3.52	3.90	3.85	30.29
	15%	4.05	4.10	3.86	3.81	3.57	3.52	4.05	3.81	30.77

).

Breads enriched with sweet chestnut flour consistently achieved the most favourable results in all assessed categories. The highest values were observed for the 15% addition, which received 4.02 for crust and 4.36 for crumb. These improvements were attributed to the presence of natural sugars and aromatic volatile compounds in chestnut flour, which positively influenced the bread’s aroma, flavour, texture, and crust colour. Dall’Asta et al. [33] confirmed that chestnut flour contributes a delicate, sweet taste and enhances aroma, while Man et al. [49] and Raczyk et al. [44] reported significant improvement in colour, elasticity, and consumer acceptability at 10–15% supplementation. Similarly, Marciniak-Łukasiak et al. [43] showed that gluten-free breads with 5–10% chestnut flour received the highest ratings in sensory attributes, while higher levels (20%) negatively affected quality.

Our results were further supported by instrumental data and volatile compound analysis, which confirmed a higher concentration of aromatic compounds in chestnut-enriched breads. Moderate additions (5–15%) maintained high sensory appeal, while higher proportions introduced excessive sweetness and diminished porosity, as also reported by Raczyk et al. [44].

Apple-flour-based breads also performed well in sensory analysis. Total scores ranged from 29.12 to 30.77, and the 15% supplementation level yielded the best sensory balance. Bread with apple flour was appreciated for its sweet flavour, pleasant aroma, and darker crust, a result of sugar caramelisation. These findings align with studies by Nisar et al. [50] and Sikora et al. [31], which highlighted the benefits of fruit-derived flours rich in phenolic compounds and natural sugars. Jannati et al. [51] confirmed that apple pomace improved texture, aroma, and water retention, while Pyanikova et al. [52] showed that 10% frozen apple pomace enhanced porosity, elasticity, and flavour. Although Usman et al. [53] focused on cookies, they also demonstrated improved texture and mouthfeel with apple pomace flour.

In terms of flavour and aroma, breads with sweet chestnut (3.95–4.14) and apple flour (3.71–4.05) outperformed the control sample (3.43), confirming that these flours significantly enhance the organoleptic properties of baked goods. Shafi et al. [54] noted similar effects in cookies enriched with chestnut- and fruit-based flours, attributing improvements to the presence of aromatic volatiles.

In contrast, oak-based flours produced less desirable outcomes, particularly at higher inclusion levels. Pedunculate and sessile oak flour led to a progressive decline in sensory quality, with scores falling from 3.10 to 2.81 and 3.33 to 2.43, respectively, as the proportion increased. This effect is attributed to the high tannin content, which imparts bitterness, reduces moisture retention, and affects structure. However, 5% inclusion still provided acceptable results close to the control. Pasqualone et al. [55], and Vinha et al. [56] observed similar limitations with high levels of acorn flour, despite its nutritional value.

Interestingly, red oak flour gave intermediate sensory scores, ranging from 3.05 to 3.14 across all substitution levels, slightly below the control. This suggests a more tolerable profile of bitter compounds compared to other oak flours. At low inclusion levels (5%), all oak variants yielded acceptable total sensory scores of 26.48 (pedunculate), 27.77 (sessile), and 27.44 (red oak) compared to 28.39 for the control. However, at 10–15% supplementation, total scores decreased to 24.93–26.89, confirming the adverse impact of high oak flour content.

It is worth noting that other studies have also demonstrated favourable results for breads with high acorn flour content. For example, Beltrão Martins et al. [57] showed that breads with 23% and 35% acorn flour achieved higher or comparable scores in colour (4.3–4.5), appearance (4.2–4.4), aroma (3.8–4.0), texture (3.6–3.7), and flavour (3.4–3.5) compared to the control bread (3.0 for flavour, 3.5 for overall acceptance). The overall acceptance scores of 3.8 for both 23% and 35% breads clearly surpassed the control’s 3.2. These results suggest that, under certain formulation conditions, even high levels of acorn flour can maintain or improve sensory quality. Capriles et al. [58] noted that although gluten-free breads (GFBs) made with alternative flours often present nutritional benefits, they may compromise on their sensory qualities. However, the findings by Beltrão Martins et al. demonstrate that careful formulation can balance sensory and nutritional attributes.

Additional confirmation comes from Gonzaga et al. [59], who evaluated sensory attributes such as appearance, aroma, taste, texture, and overall appreciation (on a 10-point scale). Their results showed that taste scores for acorn-enriched breads were similar to those of whole-wheat breads (4.4–4.7 range). Although the crust and crumb colour were more intense and less uniform due to acorn flour addition, the breads were well-received. Panellists described the acorn bread as more dense and with higher elasticity compared to the control, indicating that the use of acorn flour may also positively affect bread texture while increasing its nutritional value. The influence of acorn flour on the sensory profile was most apparent in crust and crumb colour and in the appearance of small, less uniform alveoli. Despite this, the overall appreciation of acorn breads remained comparable to whole-wheat variants, confirming consumer acceptance and aligning with the findings of Capriles et al. [58] and Beltrão Martins et al. [57].

Further insights into the effects of acorn flour addition were provided by Mousavi et al. [60], who found that a 30% substitution level achieved the highest overall acceptability score (7.43) among toast breads. Although a 40% substitution improved bread appearance, flavour and texture were most acceptable at 0–30% substitution, and acceptability declined beyond this level. Bread with 50% acorn flour had the minimum acceptable taste, confirming that moderate inclusion offers the best balance between sensory quality and nutritional benefit.

Shiri et al. [61] investigated gluten-free breads and reported that scores for colour, pore structure, symmetry, taste, odour, and general acceptability ranged from 4.80 to 6.98 at lower substitution levels and declined steadily with increased acorn flour content. The 30% inclusion level was associated with improved flavour and colour perception; however, levels above this negatively affected multiple sensory parameters. These findings reinforce the importance of optimising acorn flour levels to avoid undesirable changes in flavour, texture, and colour.

Szabłowska and Tańska [62] further highlighted the technological challenges at higher substitution levels. Acorn flour levels above 30% led to a dense, gummy, and less spongy crumb, with loaf volume reductions up to 52%. While a 30% addition significantly improved ash and fibre content, it also reduced carbohydrate and protein content. These changes confirm the need for balancing sensory acceptability and nutritional enhancement through careful formulation.

Breads enriched with horse chestnut flour obtained the lowest sensory ratings. The 5% variant scored 2.55 for crust and 2.70 for crumb, while flavour and aroma were rated as low as 1.95. These poor results are linked to residual saponins and bitter compounds, which undermine otherwise good instrumental properties such as springiness. Due to pronounced bitterness and poor acceptability, the 10% and 15% horse chestnut samples were excluded from the evaluation, underscoring the importance of proper detoxification processes.

In conclusion, our sensory analysis demonstrated that moderate supplementation with sweet chestnut or apple flour (5–15%) enhances bread’s sensory qualities by improving aroma, flavour, texture, and crust characteristics. These enhancements are well-supported by instrumental data and the literature. Although oak- and horse-chestnut-based flours—especially at high substitution levels—often negatively affect sensory properties due to their bitterness and texture-modifying compounds, selected studies suggest that optimised formulations using acorn flour can overcome these limitations. The integration of new evidence confirms that acorn flour addition of up to 30% can provide a favourable balance between nutritional value and sensory acceptance, while higher proportions require cautious technological adjustments. Therefore, sweet chestnut and apple flours can be recommended as functional and consumer-friendly ingredients for bakery product formulation, while further investigation into acorn flour optimisation remains a promising avenue.

4. Conclusions

The addition of apple and sweet chestnut flours significantly improved the rheological properties of wheat dough, particularly in terms of dough stability and development time, indicating their positive technological potential in bread formulations.

Farinographic analysis showed that increasing apple flour levels reduced water absorption, which was attributed to the lower water-binding capacity of apple starch and fibre compared to gluten-rich wheat flour.

Colour measurements demonstrated that apple and sweet chestnut flours had a less intense darkening effect than acorn and horse chestnut flours, with red oak flour producing the darkest crust due to its high phenolic content.

Textural analysis revealed that sweet chestnut flour maintained crumb elasticity and springiness, while higher levels of acorn and horse chestnut flours increased crumb hardness and adhesiveness.

Sensory evaluation confirmed that apple and sweet chestnut flour additions (especially at 10–15%) resulted in high consumer acceptability, enhancing flavour, aroma, and crust appearance, while higher levels of acorn flour negatively affected taste due to bitterness.

Up to 15% apple or sweet chestnut flour can be successfully used in wheat bread production to improve nutritional value and sensory attractiveness without compromising technological quality.

Acorn flour at 5% substitution can be considered a viable ingredient for rustic or wholegrain-style breads, where darker colour and denser texture are desirable, but higher levels should be avoided due to taste issues.

The use of flours obtained from underutilised plant materials enables the partial replacement of wheat flour in a sustainable and health-oriented manner, supporting the development of clean-label, fibre-enriched bakery products aligned with current consumer trends.

Among all the tested additions, the most acceptable substitution levels were 10–15% for sweet chestnut and apple flour, while the use of acorn flour should be limited to 5%, as higher doses negatively impacted flavour and crumb structure due to increased compactness and bitter notes.