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Article

Usefulness of Rowanberry for Improving the Nutritional Value of Buckwheat Flour Extrudates

by
Robert Iwański
1,*,
Merve Aydin
2,* and
Ismail Tontul
2
1
Department of Fish, Plant and Gastronomy Technology, Faculty of Food Sciences and Fisheries, West Pomeranian University of Technology, Papieża Pawła VI 3, 71-459 Szczecin, Poland
2
Department of Food Engineering, Faculty of Engineering, Necmettin Erbakan University, Koycegiz Campus, Konya 42090, Türkiye
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2025, 15(7), 3656; https://doi.org/10.3390/app15073656
Submission received: 20 February 2025 / Revised: 20 March 2025 / Accepted: 25 March 2025 / Published: 26 March 2025
(This article belongs to the Special Issue New Trends and Advances in the Production of Functional Foods)
Browse Figures
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Abstract

:
Gluten-free snacks are often poor in nutritional value. Increasing the nutritional content and quality of these products is necessary. The present study investigated the effect of adding buckwheat at various levels (0, 30, 40, and 50%), milk powder, and rowanberry on the nutritional content, bioactivity, and quality of the product using extrusion technology. The colour, expansion, nutrient value, texture, total phenolic content, and antioxidant capacity of the samples were examined. The highest phenolic (0.59 mg GAE/g), flavonoid (6.93 mg RE/g), CUPRAC (9.60 mg TE/g), dry matter (92.85%), crude fat (1.01%), and ash (1.16%) values were determined in unexpanded samples containing rowanberry, milk, and 50% buckwheat. The highest DPPH (3.03 mg TE/g) and FRAP (1.43 mg TE/g) activities were indicated in the unexpanded samples containing rowanberry, water, and 40% buckwheat. This study’s results showed that rowanberry could be added as a functional component to enhance the nutritional value and quality of gluten-free extruded samples.

1. Introduction

Extrusion cooking is a process that has been known for over 70 years. Processed raw materials undergo a series of transformations due to the influence of high temperature with a certain amount of water available in the raw materials, high pressure when compressing the material, and rapid expansion after leaving the die. During the processing of food and feed, the following mainly occur: gelatinisation of starch, increasing the viscosity of the processed slurry, protein denaturation, fat hydrolysis, formation of fat–protein and fat–starch complexes, inactivation of unwanted enzymes, and microbiological sterilisation of the material. Food manufacturers increasingly use extrusion to reduce production costs and introduce new and attractive foods to the market. In addition, the extrusion is faster than traditional processing methods [1,2].
Extruded products are especially popular in Asian countries. The quality of the texture of extruded products is significantly influenced by the raw materials and formulation employed in their production. It is also hypothesised that they can have a significant impact on the consumer acceptability and functional properties of these products [1,3]. Products made from wheat flour have excellent structure-forming properties and retain basic rheological features due to the content and properties of gluten. However, gluten is responsible for many health problems because of intolerance, hypersensitivity, and celiac disease [4,5]. Therefore, the gluten-free food and beverage markets are rapidly growing. Gluten-free extruded products are of primary interest to food producers [6]. Buckwheat, a gluten-free pseudocereal, is one of the prominent raw materials used in the production of extruded products because of its suitability for extrusion [7].
Common buckwheat (Fagopyrum esculentum) has been cultivated in Europe for centuries. It is one of the traditional crops cultivated in the world. Poland is fifth in terms of buckwheat production [8]. In recent years, the interest in buckwheat has increased due to the consumers’ interest in traditional foods and local products. In particular, buckwheat flour and groats are an essential source of polyphenolic compounds with high antioxidant activity, vitamins and minerals, starch, protein, fat, and dietary fibre. They are excellent raw materials for producing extruded products [9]. Buckwheat proteins (albumins, globulins, prolamins, and glutelins) are characterised by high biological value. Unlike cereals, buckwheat proteins are rich in lysine, arginine, and aspartic acid but contain less glutamic acid and proline [10]. They are characterised by relatively low digestibility but can prevent obesity and constipation since they act similarly to dietary fibre. Buckwheat is reportedly capable of lowering cholesterol levels and exhibits hypotensive, antibacterial, and antidiabetic effects [11]. In order to improve the structure of buckwheat products, Li et al. [12] and many other authors tried to use gelatinised starch as an effective structuring agent due to its light elastic properties. This process can be replaced by using a low-temperature extrusion process (below the degree of expansion) with the addition of other raw materials, e.g., corn grits. Corn is a gluten-free grain often preferred as a source of corn starch in extruded snacks. Although corn is rich in lutein and zeaxanthin, its nutritional composition is insufficient for a healthy diet [13,14].
Although gluten-free products are generally nutritious, they are inadequate in textural, nutritional (such as low protein and fibre, high-fat content), and sensory properties compared to gluten-containing products [15]. This situation has increased the demand for extruded products with high nutritional value and bioactive properties (such as antioxidant activity) [16]. Adding antioxidant-rich ingredients to extruded products enriches the product with bioactive compounds that are beneficial for health. In general, the production of extruded snacks with plant ingredients rich in bioactive compounds is a new field that has not been fully explored, and the available information is very limited. In previous studies, gluten-free (purple potato, yellow pea, rice, and oat flours) [17,18,19] extruded samples were enriched with antioxidant-rich fruits such as banana, apple, strawberry and tangerine [20], rosehip [21], and chokeberry [22]. However, no study on the enrichment of corn- and buckwheat-based extruded products with rowanberry fruit was found in the literature. The addition of rowanberry, thanks to its many bioactive compounds, increases the nutritional value and stability of food products. It also makes the colour of the final product more attractive [23].
Sorbus aucuparia, commonly known as rowanberry, is a popular ornamental plant widely cultivated in gardens and parks in Europe and North America. Rowanberry fruits are spherical and red. Due to the content of parasorbic acid, they cannot be eaten raw. They have a bitter taste and can cause problems in the digestive system [24]. Rowanberry fruits contain organic acids (malic, tartaric, and parasorbic acids), carotenoids, tannins, carbohydrates, vitamin C (0.2%), and phenolic compounds (quercetin, isoquercitrin, rutin, catechin, etc.) [25,26]. Rowanberry extracts are characterised by a high concentration of phenolic components, namely hydroxycinnamic acids, including caffeoylquinic acid and its derivatives (chlorogenic acid, neo- and crypto-chlorogenic acids), and flavonols, including quercetin and kaempferol conjugates. In addition, p-coumaric and ferulic acids (hydroxycinnamic acids), p-hydroxybenzoic and gallic acids (hydroxybenzoic acids), and catechin, proanthocyanin, and anthocyanin (flavonoids) have also been detected. A review of the available literature showed that 56–80% of the phenolic acids present in rowanberry extract are composed of caffeoylquinic acid, with more than 50% of flavonoid glycosides being composed of quercetin 3-O-(6″-malonyl)-glucoside [25,26]. Furthermore, the rowanberry extract is rich in carotenoids including zeaxanthin, β-cryptoxanthin, all-trans-β-carotene, and organic acids, including malic acid [25]. The rowanberry extracts reportedly have different biological effects such as antioxidants, anti-inflammatory, anti-atherosclerotic, anti-alcohol, and vasodilating effects. Therefore, the extracts are used to treat intestinal obstruction, chronic diarrhoea, and various liver and gallbladder diseases [27]. In addition, due to the content of carotenoids, the addition of rowanberry fruit can make the colour of food products (extrudates, etc.) more attractive. The present study aimed to determine the effect of rowanberry addition and corn–buckwheat ratios on the colour, nutritional value, expansion properties, phenolic content, flavonoid content, antioxidant activity, and textural characteristics of extruded flat cereal crips.

2. Materials and Methods

2.1. Materials

To produce extruded flat cereal crips, buckwheat flour (type 2000), corn grits, whole milk powder (POLMLEK, Warszawa, Poland), water, and rowanberry fruit (Sorbus aucuparia) were procured from Szczecin (Poland). The rowanberry fruit was used after being partially dried and made into a paste in a mortar. In this study, all chemicals were of analytical grade and purchased from Sigma-Aldrich (Steinheim, Germany), Merck (Steinheim, Germany), and Avantor Performance Materials Poland S. A. (Gliwice, Poland).

2.2. Production of Extruded Flat Cereal Crips

Extruded flat cereal crips were produced using the method of Özer et al. [28] with slight modifications (Figure 1). For the corn grits (11.62% moisture), the buckwheat flour (13.13% moisture), and the rowanberry (33.02% moisture), the required water or milk addition was calculated according to Equation (1) so that the moisture content finally extruded to 28%.
X = C ( W % − W C ) + B ( W % − W B ) + R ( W % − W R ) 100 − W %
X: amount of water/milk to be added to the sample (g); C: mass of corn grits (g); B: mass of buckwheat flour (g); R: mass of rowanberry (g); W%: moisture content to be achieved; WC: moisture of corn grits (%); WB: moisture of buckwheat flour (%); and WR: moisture of rowanberry fruit (%).
The content amount calculated as shown in Table 1 was mixed together with water using a mixer (Kitchenaid, Benton Harbor, MI, USA) at the slowest speed. Then, the prepared mixture was extruded by an extruder (Brabender DO-CORDER, Duisburg, Germany) single screw with three heating chambers (85 °C, 93 °C, and 95 °C). The first part is responsible for heating raw materials. Then, the next section is the plasticising section. The last section is the shaping section. The final under-expansion degree and forming pressure were 15 MPa. The obtained extrudates were cut into strips with average dimensions of 2 × 3 cm and then left to dry for seven days at the laboratory temperature (18–22 °C). Then, they were packed with a zipper closure.

2.3. Colour Analysis

The colour of the samples was determined using a colourimeter (D25-2 Hunterlab, Reston, VA, USA). Before measurement, the device was calibrated with a white plate (the standard). L* (0: darkness, 100: whiteness), a* (+a: redness, −a: greenness), and b* (+b: yellowness, −b: blueness) values were recorded for five samples.

2.4. Determining of Expansion Ratio

The degree of expansion was determined by modifying the method of Ruiz-Armenta et al. [29]. A portion was taken from each prepared sample and then expanded for twenty seconds at full power in a microwave oven (Sharp 1800 W/R-23AM, Sakai, Japan). Measurements were made in triplicate, both for samples before expansion and after treatment. In total, 15 g of samples was weighed into a 250 mL measuring cylinder, tap water was added, and the volume change was calculated.

2.5. Determination of Nutritional Value

A variant containing 50% buckwheat was selected for the analysis. The basic chemical composition (total protein, crude fat, crude fibre, total ash, total carbohydrates) was determined according to the method of Schakel et al. [30]. An analytical sample was prepared by pouring the grain of each variety in equal proportions by weight from each of the three places in each experimental plot. Samples were ground in a laboratory mill (KNIFETEC 1095, Foss Tecator, Hoganas, Sweden). To determine the dry weight, the samples were dried at 105 °C until they reached constant weight. Total protein (Nx5.7) was determined by the Kjeldahl method using a Büchi B-324 (Büchi Labortechnik AG, Flawil, Switzerland) distillation unit. The crude fat was determined by the Soxhlet method using diethyl ether as the solvent. Crude ash was determined by burning the sample in a muffle furnace at 580 °C for eight hours. The crude fibre was measured with an ANKOM220 Analyzer (ANKOM Technology, New York, NY, USA). Total carbohydrates (TCs) were determined according to the following Equation (2).
T C = 100 − m o i s t u r e % + c r u d e   p r o t e i n % + f a t % + a s h % + c r u d e   f i b e r %

2.6. Extraction of Samples for Total Phenolic, Total Flavonoid, and Antioxidant Activity Analyses

The extruded sample extract was obtained to define the total phenolic content, flavonoid content, and antioxidant activity capacity according to the method of Eyiz et al. [31]. A total of 20 mL of 80% ethanol solution (80:20 ethanol/water) was added to 2 g of ground extruded sample in a falcon tube. It was homogenised with a homogeniser (WiseTis HG15D, Wertheim, Germany) at 10,000 rpm for a minute. The sample was extracted in a water bath (Nüve, Akyurt, Türkiye) under shaking (200 rpm) at 40 °C for 3 h. After extraction processing, the suspension was filtered with an analytical filter paper.

2.7. Total Phenolic Compound Analysis

A total of 0.5 mL of the extract, 2.5 mL of Folin–Ciocalteu (0.2 N), and sodium carbonate (7.5%) solutions were added to a test tube, respectively. After the mixture was vortexed, it was incubated in a water bath at 50 °C for 5 min. Then, it was cooled to room temperature and read up against the blank (prepared with 80% ethanol instead of extract) at 760 nm with a spectrophotometer (Biochrom Libra S22, Cambridge, UK). The results were calculated as mg gallic acid equivalent (GAE)/kg dry basis [32].

2.8. Flavonoid Analysis

The total flavonoid content of the extracts was assessed by the method of Zhuang et al. [33]. In total, 0.5 mL of extract, 2.5 mL of purified water, and 150 μL of sodium nitrite (NaNO2, 5%) were added to a tube, vortexed, and held for 5 min. Then, 300 μL of aluminium chloride solution (10%) was added to the mixture, vortexed, and stood for 5 min. Finally, 1 mL of sodium hydroxide solution (NaOH, 1 N) was added to it, vortexed, and held for an additional 5 min. The absorbance of the solution was read against the blank (prepared with 80% ethanol instead of the extract) at 510 nm using a spectrophotometer (Libra S60, Biochrom Ltd., Cambridge, UK). The results of total flavonoids were given as mg rutin equivalent (RE)/g dm.

2.9. Antioxidant Capacity Analysis

The antioxidant capacity in the samples was determined using methods of DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity, FRAP (Ferric Reducing Antioxidant Power), and CUPRAC (Cupric Reducing Antioxidant Capacity). All of the assay results were expressed as mg Trolox (6-Hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid) equivalent free radical scavenging activity mg TE/g dm. Trolox solutions were prepared at different concentrations for the preparation of calibration curves.
The DPPH radical scavenging activity was determined according to the method of Tontul and Topuz [32]. Briefly, 950 µL of DPPH solution (60 µM in methanol) was added to a 2 mL Eppendorf tube, and 50 µL extract was added. After vortexing, the mixture was kept in a dark place at room temperature for 30 min. After incubation, the absorbance of the solution was read against the blank (80% ethanol was used instead of the extract) at 516 nm.
To determine the CUPRAC of the samples, 0.5 mL extract, 0.6 mL distilled water, 1 mL calcium chloride solution (10 mM), 1 mL ammonium acetate solution (1 M), and 1 mL neocuproine solution (7.5 mM) were added to a tube, respectively. After the mixture was vortexed, it was held at room temperature in the dark for 30 min. Then, the absorbance values were recorded at 450 nm against a blank (prepared with 80% ethanol instead of extract) [34].
In the FRAP assay, the FRAP reagent was freshly prepared by mixing three different solutions [sodium acetate buffer (300 mM, pH 3.6), 2,4,6-Tri(2-pyridyl)-s-triazine (10 mM in 40 mM HCl solution), FeCl3⋅6H2O (20 mM)] in a ratio of 10:1:1. Then, 75 µL of extract, 2.25 mL of FRAP reagent, and 225 µL of distilled water were mixed in a test tube. After incubating at room temperature for 30 min in a dark place, the absorbance of the solution was read using a spectrophotometer at 593 nm against a blank (prepared with 80% ethanol instead of extract) [35].

2.10. Texture Profile Analysis

The hardness of the samples was determined using a TA-XT 2/25 Texture Analysis Device (Stable Micro Systems TA-XT Plus, Surrey, UK) equipped with a globe-shaped mandrel probe. The test was carried out in a cycle of 50% compression of sample height.

2.11. Statistical Analysis

The extrusion processes were performed in triplicate. Data were subjected to a two-way analysis of variance (ANOVA). Differences between means were calculated using Tukey’s test at p < 0.05. All statistical calculations were performed using Statistica 14.0.0.15 software (TIBCO Software Inc., New York, NY, USA). The Pearson correlation analysis was conducted using SPSS version 21 software (IBM Corp., Armonk, New York, NY, USA). The relevant correlation coefficients indicated that the data were statistically significant at the p < 0.05 and p < 0.01 levels.

3. Results and Discussion

3.1. Colour

The extruded samples prepared with corn–buckwheat in different percentages and rowanberry are demonstrated in Figure 2. The mean L* value for unexpanded samples was 55, while it was 65 after expansion (Figure 3a). An increase in the brightness of the expanded samples was observed, and the highest brightness was characterised by the water-added samples. However, increasing the addition of buckwheat did not significantly change the brightness of the sample. The expansion caused a significant decrease in redness, confirmed by Tukey’s and Sheffe’s tests performed at a significant level of α = 0.05 (Figure 3b). In the case of products before expansion, the lowest parameter a* was recorded for the control samples. The addition of milk in the group of non-expanded products caused a significant increase in the redness of the samples. While the increase in the buckwheat flour content decreased the a* value in the expanded samples containing water, on the contrary, it was observed that the a* value increased as the buckwheat content increased in the expanded samples containing milk. The most intense yellowness was detected in samples containing 30% buckwheat with added water (Figure 3c). The expansion was shown to cause an overall increase in the yellow colour parameter. It was observed that the increase in the content of buckwheat flour caused a decrease in the b* value of most samples.
The colour values of Tartary buckwheat flour were reported as 79.92 (L*), 0.18 (a*), and 20.06 (b*) [36]. While L* values of corn grit extrudates with 10% and 30% buckwheat flour added increased, they decreased in the samples where 20% buckwheat was added. In addition, the a* value increased with the increase in the buckwheat ratio [37]. In a similar study, a* values with an increase in buckwheat content in the extrudate products prepared using corn and buckwheat flours of different ratios (70:30, 50:50, 30:70 corn–buckwheat) rose while the L* and b* values showed a decrease [38]. This finding was associated with a higher amount of reducing sugar and protein because of buckwheat, thereby increasing the Maillard reaction [37,38]. Positive b* values of the samples were attributed to carotenoids in corn grit and buckwheat flour [39]. The results of our samples were found to be compatible with the literature.
The colour values of the rowanberry-added extruded samples prepared with corn–buckwheat in different percentages are shown in Figure 3a–c. No researcher has declared such supplementation of the extruded flat cereal crips with the rowanberry. Adding rowanberry to unexpanded products caused a significant decrease in the L* parameter compared to the control sample (Figure 3a). However, it was observed that the colour of the samples was smooth with the addition of fruit and did not show a significant difference depending on the amount of buckwheat flour. A significantly different brightness result was observed in the sample containing 40% buckwheat flour with milk and rowanberry additives. In the case of expanded extrudates, the increase in the percentage of buckwheat did not significantly affect the brightness of the product. The brightness of the rowanberry-added samples increased by applying the expansion. The sample prepared with the addition of water and milk was characterised by the highest brightness after expansion. While the highest a* value was observed in the samples to which milk and rowanberry were added before expansion, the highest decrease in the a* value after the expansion was observed in the milk-added samples (Figure 3b). The addition of rowanberry increased the a* value of the samples containing both milk and water. A positive effect on redness was also exerted by adding rowanberries, which most intensively increased the level of redness. The correlation between buckwheat flour and the red parameter was most significantly observed in the case of the sample with the addition of water and rowanberry. The lowest b* value was read in the unexpanded sample with 50% buckwheat flour and rowanberry added with water (Figure 3c). It was determined that the addition of rowanberry to the unexpanded samples significantly reduced yellowness. On the contrary, it did not affect the yellowness of the samples after extrusion. The addition of milk increased the yellowness level of the samples containing rowanberry. In the case of products after the expansion process, it was noticed that adding rowanberry reduced the level of yellowness, but to a less significant extent than the untreated counterparts. Overall, the substantial variation in colour observed in the samples can be attributed to the significant unevenness of the extruded sample’s surface and the partial impossibility of crushing the added fruit.
In a study, it was emphasised that the shortbread cookies enriched with rowanberry pomace showed a darker colour than the control sample [40]. An increasing a* value on the surface of the shortbread cookies was observed by Tańska et al. [40] after adding 20% rowanberry pomace. The intense red colour of rowanberry may be responsible for the darkness and redness of the final extrudate products. Adding blueberry, concord grape, cranberry, and red raspberry powders to extruded white cornmeal cereals decreased brightness and increased redness and greenness compared to the control sample. The L*, a*, and b* values of the control sample were determined to be 81.71, 0.34, and 12.21, respectively [41]. Tomato pomace powder-incorporated snacks showed lower lightness but higher redness and yellowness values than the control [42]. On the other hand, the a* (0.7) and b* (6.9) values of the control sample were determined to be lower than the values of the corn extrudate sample enrichment with 10% rosehip by replacing corn flour (6.9 and 21.7, respectively). At the same time, no significant difference was found between the L* values of them (p > 0.05) [43]. Our results were found to be similar when compared with the literature.

3.2. Expansion Ratio

The expansion features of puffed extrudate products are one of their essential characteristics [17]. The expansion ratio of the extruded samples, expanded by microwave and prepared with corn–buckwheat in different percentages, is shown in Figure 4 and Figure 5. The increase in the buckwheat flour ratio exhibited a rise in the expansion ratio of the samples. No effect of milk addition on expansion changes was observed, according to the results. Similarly to our results, Wang and Ryu [44] reported that the higher ratio of corn fibre induced a lower expansion ratio. In contrast to our study results, in another study, the expansion ratio of 100% corn meals decreased with a decline in the corn ratio and an increase in the buckwheat ratio [38]. The dietary fibre content of corn grits was determined to be 3.39% [45]. The starch contents of Tartary buckwheat flour and corn grits were obtained as 77.26% and 88.10%, respectively [36,46]. While the total fibre content of shelled common buckwheat is between 20% and 26% [47], the fibre content of unshelled buckwheat is 2.9% insoluble fibre and 2.4% soluble fibre [48]. As the amount of fibre in an extruded food product decreases the density of the starch in the medium, it shows weaker gelation, prevents the formation of air bubbles by precipitating the cell walls, and causes an increase in mass viscosity, thus inhibiting the expansion rate of the product [29,49]. Similarly, it has been reported that the expansion rate of starch and the degree of gelatinisation increase due to increased starch content [50]. It has been reported that the degree of gelatinisation during the extrusion process affects the degree of expansion [51]. Therefore, our understanding according to these findings is that the fibre and starch composition and amount of the extruded product raw materials (corn and buckwheat), as well as the moisture content, are effective on the gelatinisation and so the expansion of the products [38,52]. Accordingly, the lower dietary fibre content of buckwheat compared to corn grits in our study and the higher expansion ratio were consistent with the literature.
Although the addition of rowanberry showed an increase in the volume of the extrudates, the rise was not at the desired level (Figure 5). It has been reported that adding plant by-products to starch-based extruded products commonly exhibits a lower expansion ratio [49]. In contrast to our study, the expansion value of extruded samples with added fruit powder varied from 209 to 311%, while the control was 550% [20]. In another study, adding mango and papaya peels to corn extrudates decreased the expansion ratio of the samples [53]. Similarly, the expansion ratios of the rice-based breakfast cereal samples using pomelo fruit by-products decreased compared to the control sample [54]. It has been reported that the fibre content of the peels is rich, so adding the pomelo peel to the product decreases the starch content and indirectly reduces its expansion. It may be explained that the fibre will destroy the cell walls and prevent the maximum expansion of air-filled bubbles [13].
In addition to the starch and fibre contents of extrudate samples, moisture content also significantly affects the expansion rate [55]. As a result of the increase in moisture content during the extrusion process, the plasticised melt and dough can reduce flexibility. Therefore, gelatinisation and expansion may be reduced [56]. Ruiz-Armenta et al. [29] reported that pellets with low gelatinisation might not have the desired level of water absorption due to insufficient openings in the starch particles. Therefore, water will be used less in the expansion of the product in the microwave heating process. As mentioned in the literature, the expansion characteristics of our study can be related to the components and moisture contents of rowanberry.

3.3. Texture Profile

The texture is of primary significance for extrudates foods. The major ingredient which determines the texture of these products is flour. In addition, many components affect the general texture of these products [1]. The texture results of extruded samples prepared with corn–buckwheat in different percentages can be seen in Figure 6. According to the results, it was determined that the control and milk-added extrudates had the highest hardness. In unexpanded products containing milk, a decrease was observed in the hardness values of the samples as the buckwheat flour ratio increased. Moreover, an inverse correlation was obtained in the hardness of the samples after expansion. Expanded products showed an average of 50% less hardness than their unexpanded equivalent. The results were also confirmed by Tukey’s and Sheffe’s tests at the significance level of α= 0.05. The usefulness of buckwheat in reducing hardness and other textural features is also demonstrated by Kaur et al. [57]. However, the results obtained in the work are burdened with a high standard deviation caused by the lack of a uniform shape of the extrudates. In contrast, the hardness values of the extruded products prepared using various ratios (70:30, 50:50, 30:70 corn–buckwheat) of corn flour and buckwheat flour increased in parallel with the rise in the buckwheat flour ratio. As the protein (average 12.94%) and fat (about 3%) content of buckwheat are much higher than the protein (6.79%) and fat (0.07%) contents of corn, the differences in hardness can be attributed to these components [10,37]. In addition, the carbohydrate (38.42%), protein (26.32%), and fat (26.71%) contents of milk affected the hardness value of the samples. The high sugar content of the milk powder may have increased firmness by causing the samples to increase in density and decrease in cell size [20]. In addition, the extrusion processing conditions can also show an effect on the hardness of the final product [29]. Ruiz-Armenta et al. [29] reported that the lowest hardness for the extruded samples was at low moisture and high temperature.
As seen in Figure 6, in the group of products before processing, it was established that the addition of rowanberry caused a decrease in the hardness of the samples by approximately 50%. However, adding milk with rowanberry did not significantly change the hardness. In the case of expanded products, the highest hardness was found for the sample containing 50% buckwheat flour with milk, followed by 30% buckwheat flour with water. It was observed that adding milk or rowanberry had no significant effect on hardness. The hardness of the extrudates is also related to the expansion ratio of the product [54]. The increase in air bubbles in the product leads to a rise in ambient pressure, destroying the cell walls and releasing the water vapour to expand the product and reduce its hardness [58]. Thus, the decrease in hardness of rowanberry-added samples compared to the control can be associated with the increase in the expansion volume. Many researchers have investigated the effect on the texture of the used supplements, except for rowanberry in the extruded samples. It was reported that adding rosehip (Rosa canina) powder (10%) to corn extrudate reduced hardness compared to the control sample. In the present study, the hardness results compared to the control are lower than those reported by previous researchers. The hardness values of the extrudate snacks prepared with whole wheat, lycopene, and tomato powder were higher than the control sample [59]. Camire et al. [41] revealed that blueberry, grape, cranberry, and raspberry powders added to breakfast cereals increased the hardness of the product. In a similar study, tomato pomace powder-added extrudate samples (398.85–428.84 N) showed higher hardness values in comparison to the control (364.04 N) [42].
The evaluation of the texture of extruded snacks is a complex issue. Critical extrusion variables such as raw material, temperature, screw speed, and moisture content have a significant influence on the texture of the products [1]. Consequently, the substantial variation in hardness observed in the samples of this study may have been influenced by these parameters as well as their raw material content. Furthermore, it can also be explained by the significant surface roughness of the extruded samples. Overall, the composition, amount, and expansion rates of the raw materials used in the samples and the shape of the samples had an effect on the hardness of the samples.

3.4. Nutritional Value

The nutritional values of extruded samples prepared with 50% buckwheat are shown in Table 2. The highest dry matter, protein, fat, and ash content was characterised in the samples containing milk and rowanberry. This result was attributed to the dry matter contents of milk and rowanberry compared to water. As a result of the expansion, the dry matter, total protein, crude fat, and total ash contents of the samples were increased with expansion, while their total carbohydrate content decreased. Jozinović et al. [38] determined the composition of extruded corn meal as 6.79% (protein), 0.07% (fat), 0.32% (crude fibre), and 0.24% (ash). In addition, in the same study, the protein, fat, crude fibre, and ash contents of extrudate samples containing 50% buckwheat flour were 9.32%, 0.42%, 0.48%, and 0.98%, respectively. An addition of buckwheat flour exhibited an increase in nutritional values. The protein (about 12%), fat (about 3%), and crude fibre (12.7 and 17.8%, respectively, for the two varieties) contents in buckwheat are richer than the corn [10].

3.5. Total Phenolic Contents

The total phenolic contents of the extruded samples prepared with corn–buckwheat in different percentages are shown in Figure 7. Our results indicated that increasing levels of the buckwheat ratio resulted in higher total phenolic content in the extrudates. As expected, the effect of milk addition on the total phenolic content was generally low. It was reported that buckwheat flour has a high polyphenolic compound content (approximately 1.79 mg GAE/g) [9,60]. In the study of Jozinović et al. [38], an increase in the total phenol contents of the extruded products consisting of a mixture of corn flour and buckwheat flour in different ratios (70:30, 50:50, 30:70 corn–buckwheat) was observed with the increase in buckwheat content. As seen in Figure 7, the addition of rowanberry caused an increase in the total phenolic content of the samples compared to the extruded samples containing the same amount of buckwheat. It was reported that rowanberries are the richest source of phenolic acids among berries, followed by chokeberry, blueberry, sweet rowanberry, and Saskatoon berries [61]. The total phenolic content of rowanberry extract prepared with acetone, ethanol, and water as solvents was determined to be 10,936 μg/g, 10,435 μg/g, and 9601 μg/g, respectively [62]. The present results exhibited that rowanberry fruit was the prominent source of phenolic compounds in the samples. Therefore, these results demonstrated that the extruded samples with rowanberry additive had higher polyphenol contents compared to the control sample.
Many researchers have investigated the effect on the total phenolic content of diverse components used in the extrusion process. As a result of the addition of blueberry, concord grape, cranberry, and red raspberry powders to extruded white cornmeal cereals, the highest phenolic content was determined in the blueberry sample (13.85 mg/100 g) [41]. In another study, it was revealed that the addition of rosehip pulp (5.3–8.35 mg GAE/g) and apple pulp powders (3.28–4.61 mg GAE/g) at different rates (10–20%) to corn extrudates increased the total polyphenol content of the samples (especially for 20% rosehip powder) [21]. The highest total phenol content (30–56%) was observed in samples containing carob in rice-based extruded snacks enriched with bean and carob fruit flours [19]. Similarly, Obradović et al. [14] reported that adding carrot powder to corn extrudates increased the total phenolic content compared to the control. Fontes-Zepeda et al. [53] reported that the total phenolic compounds of corn extrudates with 15% mango peel showed increases of approximately fourteen times (from 0.24 to 3.33 mg GAE/g) compared to the control. These results were regarded as compatible with our study.

3.6. Total Flavonoid Content

The total flavonoid contents of extruded samples prepared with corn–buckwheat in different percentages are shown in Figure 8. The rise in the buckwheat content of extruded samples caused an increase in the total flavonoid content of the samples. As expected, the flavonoid content of extruded samples with higher total phenolic content compared to corn was also found to be higher. The total flavonoid content of common buckwheat was found to be 0.67–10 mg/g in the literature [63,64]. Adding milk and rowanberry to the extruded samples containing the same amount of buckwheat increased the total flavonoid content (Figure 8). The flavonoid contents of the samples with a high phenolic content were also high. This is related to the fact that rowanberry is a good source of phenolics and flavonoids. Tańska et al. [40] reported that the total flavonoid value of rowanberry pomace was 0.15 g catechin equivalent/100 g dm. Oniszczuk et al. [22] determined the total flavonoid content of extruded corn porridge enriched with 20% chokeberry fruit (Aronia melanocarpa) as 8.695 and 6.935 mg quercetin equivalent/mL.

3.7. DPPH, CUPRAC, and FRAP Antioxidant Activities

The DPPH, CUPRAC, and FRAP of the extruded samples prepared with corn–buckwheat in different percentages are seen in Table 3. Increasing the buckwheat content of the control and milk-containing samples increased the antioxidant activity. The highest DPPH, CUPRAC, and FRAP were determined as 2.43 mg TE/g, 7.28 mg TE/g, and 1.14 mg TE/g in control samples with 50% buckwheat added, respectively. Buckwheat was reported as a good source of antioxidant compounds. Jozinović et al. [38] reported that the DPPH antioxidant capacity of extruded products produced using corn flour and buckwheat flour in different ratios (70:30, 50:50, and 30:70) increased with the increase in the buckwheat content. Singh et al. [37] investigated the properties of corn grit extrudates containing buckwheat flour at different rates (0, 10, 20, and 30 w/w). They determined the antioxidant activity of extruded products to be between 1.07 and 1.25 µM TE/mg. They also reported a similar trend in antioxidant activity. The increase in the antioxidant activity of the samples may also be associated with the Maillard reaction. Some Maillard reaction products were reported to have high antioxidant activity [65].
The DPPH, CUPRAC, and FRAP of rowanberry-added extruded samples prepared with buckwheat in different percentages are seen in Table 3. The supplementation of rowanberry to the control samples showed the highest antioxidant activity in the 40% buckwheat sample. The DPPH, CUPRAC, and FRAP values of this sample increased by 55%, 30%, and 75% compared to the control sample, respectively. Among the samples containing rowanberry and milk, the 30% buckwheat sample showed the highest DPPH activity, while the 40% buckwheat sample demonstrated the highest CUPRAC and FRAP. According to previous studies, rowanberry fruit is rich in antioxidant compounds [62,66]. In a previous study, the DPPH antioxidant capacity of rowanberry extracts was determined as 73 μmol TE/g, 103 μmol TE/g, and 309 μmol TE/g in acetone, ethanol, and water solvents, respectively. For FRAP, it was determined as 117 μmol TE/g, 118 μmol TE/g, and 323 μmol TE/g [62]. Therefore, this additive in extrudates caused a significant increase in the antioxidant activity of the sample. In addition, it has been reported that antioxidant and antiradical activities in extruded products depend not only on the ratio of bioactive compounds but also on the composition of these compounds [1].
The antioxidant activity of corn and buckwheat extrudates with rowanberry has not been reported in the literature, but the extrudates containing different fruits have been reported. Tańska et al. [40] determined that the rowanberry pomace added to the shortbread cookies at 20% showed remarkably higher DPPH antioxidant activity in the product. Camire et al. [41] determined that blueberry, grape, cranberry, and raspberry powders added to breakfast cereals increased the antioxidant activity of the product. Similarly, Drożdż et al. [21] observed an increase in the antioxidant activity of corn extrudates added with rosehip pomace powder compared to those without additives. In another study, Bhat et al. [59] reported that the antioxidant capacity of extrudate samples enriched with lycopene, tomato powder, and saffron extracts was enhanced. Shi et al. [54] revealed that including pomelo rind in rice-based extruded breakfast cereal products increased the antioxidant activity of the extrudates. Fontes-Zepeda et al. [53] determined that the antioxidant capacity of corn extrudates with 15% mango peel increased approximately 5.3 times compared to the control. Yagci et al. [42] found the antioxidant activity of the extruded sample with the addition of the tomato pomace powder to be between 138 and 313 mg TE/100 g dw according to the CUPRAC method, which is significantly higher than the control (69.4 mg TE/100 g dw).

3.8. Pearson Correlation Analysis

The Pearson correlation coefficients between total phenolic content, flavonoid content, DPPH, FRAP, and CUPRAC antioxidant activities of the extruded samples are shown in Table 4. The correlation between all the parameters was found to be remarkable (p < 0.01). However, a strong correlation was observed between the total phenolic and flavonoid contents compared to the antioxidant activity. The total phenolic content showed the highest correlation with FRAP, while total flavonoids showed the highest correlation with CUPRAC. In another study, the observation of a strong correlation between the total anthocyanin content and the total phenolic content of expanded extrudates prepared with purple potato and yellow pea flours confirmed that flavonoids contribute to the phenolic compounds [17]. In another study, the antioxidant properties of extruded porridge containing chokeberry fruit were found to be closely related to the amount of flavonoids (r = 0.970) and free phenolic acids (r = 0.866). High and positive correlations were found between the phenolic content and antioxidant properties of the samples [22]. The antioxidant capacity of the phenolic compounds varies according to the structure of the compound and the analysis in which it is detected. This phenomenon may be due to the chemical structure of the components, particularly the number and position of OH groups. It has been reported that the antioxidant properties of flavonoid compounds exhibit a nearly proportional relationship with the total number of hydroxyl (-OH) groups present [34].

4. Conclusions

Corn and buckwheat are commonly used in extruded products such as snacks and breakfast cereals due to the growing interest in the gluten-free food and beverage market. Extruded products need to be enriched with raw materials with high phenolic content due to the low polyphenol content of these raw materials. From this point of view, rowanberry fruit rich in phenolic compoundswas added to the extruded products in our study. The increase in the buckwheat flour ratio in the control samples showed a decrease in the brightness and yellowness values and an increase in the redness, expansion, total phenolic, total flavonoid, and antioxidant values. While adding milk did not affect the expansion, it increased the nutritional values (dry matter, protein, fat, and ash content). The increase in the buckwheat ratios of these samples caused a decrease in hardness values and an increase in antioxidant activity. Rowanberry in addition to the control samples showed a tendency to decrease in brightness and hardness values and increase in redness, volume, nutrient content (dry matter, protein, fat, and ash), total phenolic, total flavonoid, and antioxidant activity (DPPH, CUPRAC, and FRAP). Our results are important to highlight that corn–buckwheat samples extruded with water or milk after the addition of rowanberry can be an excellent source of phenols, flavonoids, and antioxidants. In conclusion, including buckwheat and rowanberry in extruded products show great potential as a gluten-free functional food. However, additional research is needed to standardise products, improve sensory qualities, and preserve nutritional and functional properties during commercial processing.

Author Contributions

Conceptualisation, R.I. and M.A.; methodology, R.I., I.T. and M.A.; validation, R.I. and M.A.; formal analysis, M.A. and R.I.; investigation, M.A. and R.I.; writing—original draft preparation, R.I. and M.A.; writing—review and editing M.A., R.I. and I.T.; visualisation, M.A. and R.I.; supervision, R.I., M.A. and I.T.; project administration, R.I. and M.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Science Fund of the Ministry of Science and Higher Education in Poland.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data used to support the findings of this study are available from the corresponding author upon request.

Acknowledgments

The authors gratefully acknowledge M. Tabaszewska from the University of Agriculture in Krakow (Poland) for instructions and theoretical help in performing the analyses.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Production chart of extruded flat cereal crips.
Figure 1. Production chart of extruded flat cereal crips.
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Figure 2. The extruded samples were prepared with corn–buckwheat in different percentages and rowanberry. 30W: 30% Buckwheat + 30% Corn grits + Water; 40W: 40% Buckwheat + 40% Corn grits + Water; 50W: 50% Buckwheat + 50% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 40M: 40% Buckwheat + 40% Corn grits + Milk; 50M: 50% Buckwheat + 50% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry; 50WR: 50% Buckwheat + 50% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 50MR: 50% Buckwheat + 50% Corn grits + Milk + Rowanberry.
Figure 2. The extruded samples were prepared with corn–buckwheat in different percentages and rowanberry. 30W: 30% Buckwheat + 30% Corn grits + Water; 40W: 40% Buckwheat + 40% Corn grits + Water; 50W: 50% Buckwheat + 50% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 40M: 40% Buckwheat + 40% Corn grits + Milk; 50M: 50% Buckwheat + 50% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry; 50WR: 50% Buckwheat + 50% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 50MR: 50% Buckwheat + 50% Corn grits + Milk + Rowanberry.
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Figure 3. Box-whisker plots of L* (a), a* (b), and b* (c) values of extrudate samples. Mean ± 1.96*standard deviation (SD) of the mean describes a 95% confidence interval. E: Expanded; 30W: 30% Buckwheat + 30% Corn grits + Water; 40W: 40% Buckwheat + 40% Corn grits + Water; 50W: 50% Buckwheat + 50% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 40M: 40% Buckwheat + 40% Corn grits + Milk; 50M: 50% Buckwheat + 50% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry; 50WR: 50% Buckwheat + 50% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 50MR: 50% Buckwheat + 50% Corn grits + Milk + Rowanberry.
Figure 3. Box-whisker plots of L* (a), a* (b), and b* (c) values of extrudate samples. Mean ± 1.96*standard deviation (SD) of the mean describes a 95% confidence interval. E: Expanded; 30W: 30% Buckwheat + 30% Corn grits + Water; 40W: 40% Buckwheat + 40% Corn grits + Water; 50W: 50% Buckwheat + 50% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 40M: 40% Buckwheat + 40% Corn grits + Milk; 50M: 50% Buckwheat + 50% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry; 50WR: 50% Buckwheat + 50% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 50MR: 50% Buckwheat + 50% Corn grits + Milk + Rowanberry.
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Figure 4. The expansion ratio of extruded samples, expanded by microwave, prepared with 30% and 40% buckwheat ratios and rowanberry. E: Expanded; 30W: 30% Buckwheat + 30% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40W: 40% Buckwheat + 40% Corn grits + Water; 40M: 40% Buckwheat + 40% Corn grits + Milk; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry.
Figure 4. The expansion ratio of extruded samples, expanded by microwave, prepared with 30% and 40% buckwheat ratios and rowanberry. E: Expanded; 30W: 30% Buckwheat + 30% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40W: 40% Buckwheat + 40% Corn grits + Water; 40M: 40% Buckwheat + 40% Corn grits + Milk; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry.
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Figure 5. The expansion ratio of extruded samples at 30% and 40% buckwheat ratios. E: Expanded; 30W: 30% Buckwheat + 30% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40W: 40% Buckwheat + 40% Corn grits + Water; 40M: 40% Buckwheat + 40% Corn grits + Milk; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry.
Figure 5. The expansion ratio of extruded samples at 30% and 40% buckwheat ratios. E: Expanded; 30W: 30% Buckwheat + 30% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40W: 40% Buckwheat + 40% Corn grits + Water; 40M: 40% Buckwheat + 40% Corn grits + Milk; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry.
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Figure 6. Box-whisker plots of the hardness values of extrudate samples. Mean ± 1.96*standard deviation (SD) of the mean describes a 95% confidence interval. E: Expanded; 30W: 30% Buckwheat + 30% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40W: 40% Buckwheat + 40% Corn grits + Water; 40M: 40% Buckwheat + 40% Corn grits + Milk; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry.
Figure 6. Box-whisker plots of the hardness values of extrudate samples. Mean ± 1.96*standard deviation (SD) of the mean describes a 95% confidence interval. E: Expanded; 30W: 30% Buckwheat + 30% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40W: 40% Buckwheat + 40% Corn grits + Water; 40M: 40% Buckwheat + 40% Corn grits + Milk; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry.
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Figure 7. Box-whisker plots of the total phenolic content values of extrudate samples. Mean ± 1.96*standard deviation (SD) of the mean describes a 95% confidence interval. 30W: 30% Buckwheat + 30% Corn grits + Water; 40W: 40% Buckwheat + 40% Corn grits + Water; 50W: 50% Buckwheat + 50% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 40M: 40% Buckwheat + 40% Corn grits + Milk; 50M: 50% Buckwheat + 50% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry; 50WR: 50% Buckwheat + 50% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 50MR: 50% Buckwheat + 50% Corn grits + Milk + Rowanberry.
Figure 7. Box-whisker plots of the total phenolic content values of extrudate samples. Mean ± 1.96*standard deviation (SD) of the mean describes a 95% confidence interval. 30W: 30% Buckwheat + 30% Corn grits + Water; 40W: 40% Buckwheat + 40% Corn grits + Water; 50W: 50% Buckwheat + 50% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 40M: 40% Buckwheat + 40% Corn grits + Milk; 50M: 50% Buckwheat + 50% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry; 50WR: 50% Buckwheat + 50% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 50MR: 50% Buckwheat + 50% Corn grits + Milk + Rowanberry.
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Figure 8. Box-whisker plots of the total flavonoid content values of extrudate samples. Mean ± 1.96*standard deviation (SD) of the mean describes a 95% confidence interval. 30W: 30% Buckwheat + 30% Corn grits + Water; 40W: 40% Buckwheat + 40% Corn grits + Water; 50W: 50% Buckwheat + 50% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 40M: 40% Buckwheat + 40% Corn grits + Milk; 50M: 50% Buckwheat + 50% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry; 50WR: 50% Buckwheat + 50% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 50MR: 50% Buckwheat + 50% Corn grits + Milk + Rowanberry.
Figure 8. Box-whisker plots of the total flavonoid content values of extrudate samples. Mean ± 1.96*standard deviation (SD) of the mean describes a 95% confidence interval. 30W: 30% Buckwheat + 30% Corn grits + Water; 40W: 40% Buckwheat + 40% Corn grits + Water; 50W: 50% Buckwheat + 50% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 40M: 40% Buckwheat + 40% Corn grits + Milk; 50M: 50% Buckwheat + 50% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry; 50WR: 50% Buckwheat + 50% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 50MR: 50% Buckwheat + 50% Corn grits + Milk + Rowanberry.
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Table 1. The content of extrudate samples.
Table 1. The content of extrudate samples.
Sample CodeContent
30W30% Buckwheat flour + 70% Corn grits + Water
40W40% Buckwheat flour + 60% Corn grits + Water
50W50% Buckwheat flour + 50% Corn grits + Water
30M30% Buckwheat flour + 70% Corn grits + Milk powder
40M40% Buckwheat flour + 60% Corn grits + Milk powder
50M50% Buckwheat flour + 50% Corn grits + Milk powder
30WR30% Buckwheat flour + 70% Corn grits + Water + Rowanberry
40WR40% Buckwheat flour + 60% Corn grits + Water + Rowanberry
50WR50% Buckwheat flour + 50% Corn grits + Water + Rowanberry
30MR30% Buckwheat flour + 70% Corn grits + Milk powder + Rowanberry
40MR40% Buckwheat flour + 60% Corn grits + Milk powder + Rowanberry
50MR50% Buckwheat flour + 50% Corn grits + Milk powder + Rowanberry
Table 2. The nutritional values of extrudate samples.
Table 2. The nutritional values of extrudate samples.
Components (g/100 g Sample)
SampleDry MatterTotal ProteinCrude FibreCrude FatTotal AshTotal Carbohydrates
Unexpanded50W *92.266.830.000.610.9883.83
50M92.499.760.000.731.0780.91
50WR92.588.870.000.721.0481.93
50MR92.859.360.001.011.1681.30
Expanded (E)50WE94.349.210.000.771.0383.31
50ME95.6010.020.000.841.1483.59
50WRE95.649.150.000.911.0584.52
50MRE95.869.880.001.241.1883.54
* 50W: 50% Buckwheat + 50% Corn grits + Water; 50M: 50% Buckwheat + 50% Corn grits + Milk; 50WR: 50% Buckwheat + 50% Corn grits + Water + Rowanberry; 50MR: 50% Buckwheat + 50% Corn grits + Milk + Rowanberry.
Table 3. The DPPH, CUPRAC, and FRAP antioxidant activities of extrudate samples.
Table 3. The DPPH, CUPRAC, and FRAP antioxidant activities of extrudate samples.
SampleDPPH
(mg TE/g)		CUPRAC
(mg TE/g)		FRAP
(mg TE/g)
30W *1.57 ± 0.106.53 ± 0.120.76 ± 0.03
40W1.93 ± 0.146.95 ± 0.070.82 ± 0.01
50W2.43 ± 0.117.28 ± 0.271.14 ± 0.15
30M1.18 ± 0.036.70 ± 0.160.83 ± 0.04
40M2.24 ± 0.117.98 ± 0.090.84 ± 0.03
50M2.58 ± 0.058.61 ± 0.171.13 ± 0.03
30WR1.88 ± 0.057.23 ± 0.160.88 ± 0.06
40WR3.03 ± 0.209.06 ± 0.021.43 ± 0.03
50WR2.78 ± 0.119.45 ± 0.241.18 ± 0.02
30MR2.41 ± 0.177.60 ± 0.291.20 ± 0.03
40MR2.12 ± 0.099.20 ± 0.141.26 ± 0.00
50MR2.97 ± 0.069.60 ± 0.241.28 ± 0.02
* 30W: 30% Buckwheat + 30% Corn grits + Water; 40W: 40% Buckwheat + 40% Corn grits + Water; 50W: 50% Buckwheat + 50% Corn grits + Water; 30M: 30% Buckwheat + 30% Corn grits + Milk; 40M: 40% Buckwheat + 40% Corn grits + Milk; 50M: 50% Buckwheat + 50% Corn grits + Milk; 30WR: 30% Buckwheat + 30% Corn grits + Water + Rowanberry; 40WR: 40% Buckwheat + 40% Corn grits + Water + Rowanberry; 50WR: 50% Buckwheat + 50% Corn grits + Water + Rowanberry; 30MR: 30% Buckwheat + 30% Corn grits + Milk + Rowanberry; 40MR: 40% Buckwheat + 40% Corn grits + Milk + Rowanberry; 50MR: 50% Buckwheat + 50% Corn grits + Milk + Rowanberry.
Table 4. Pearson correlation among the total phenolic content, total flavonoid content, and antioxidant activity of the extruded samples.
Table 4. Pearson correlation among the total phenolic content, total flavonoid content, and antioxidant activity of the extruded samples.
Total PhenolicFlavonoidDPPHFRAPCUPRAC
Total phenolic10.941 **0.833 **0.895 **0.822 **
Flavonoid0.941 **10.859 **0.857 **0.889 **
DPPH0.833 **0.859 **10.810 **0.792 **
FRAP0.895 **0.857 **0.810 **10.777 **
CUPRAC0.822 **0.889 **0.792 **0.777 **1
** Correlation is significant at the p < 0.01 level.
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Iwański, R.; Aydin, M.; Tontul, I. Usefulness of Rowanberry for Improving the Nutritional Value of Buckwheat Flour Extrudates. Appl. Sci. 2025, 15, 3656. https://doi.org/10.3390/app15073656

AMA Style

Iwański R, Aydin M, Tontul I. Usefulness of Rowanberry for Improving the Nutritional Value of Buckwheat Flour Extrudates. Applied Sciences. 2025; 15(7):3656. https://doi.org/10.3390/app15073656

Chicago/Turabian Style

Iwański, Robert, Merve Aydin, and Ismail Tontul. 2025. "Usefulness of Rowanberry for Improving the Nutritional Value of Buckwheat Flour Extrudates" Applied Sciences 15, no. 7: 3656. https://doi.org/10.3390/app15073656

APA Style

Iwański, R., Aydin, M., & Tontul, I. (2025). Usefulness of Rowanberry for Improving the Nutritional Value of Buckwheat Flour Extrudates. Applied Sciences, 15(7), 3656. https://doi.org/10.3390/app15073656

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