Enrichment of White Wheat Bread with Pistachio Hulls and Grape Seeds: Effect on Bread Quality Characteristics

Featured Application

Pistachio hulls and grape seeds are useful by-products of the pistachio and wine industries, respectively. Pistachio hulls and grape seeds can be used as alternative functional ingredients in wheat bread due to their high dietary fiber content and richness in antioxidants and phenolic substances. In this study, the effects of pistachio hulls (fresh and freeze-dried) and grape seeds (fresh and freeze-dried) on bread quality were compared in the 0.5–4% range of addition.

Abstract

In creating sustainable food systems, alternative uses of food waste and by-products as a source of phenolic compounds or dietary fiber in food formulations should be evaluated to reduce food losses and waste. In this study, wheat bread was fortified with agro-industrial by-products, namely, fresh pistachio hull (FPH), pistachio hull powder (PHP), fresh grape seeds (FGS), and grape seed powder (GSP), at different levels (0.5–4%). The effects of this enrichment on moisture content, crust and crumb color, specific volume, baking loss, total phenolic content, antioxidant activity, and textural properties were evaluated and compared with control bread. Fortification with pistachio hulls and grape seeds, especially in powdered form, improved the total phenolic content and antioxidant activity of the bread compared with the control bread. With the increase in the amount of PHP from 0 to 4.0%, the total phenolic content of the bread initially increased from 0.89 to 14.66 mg GAE/g dry weight and the specific volume decreased from 3.59 cm³/g to 2.91 cm³/g. Bread containing PHP showed a significant reduction in baking loss and specific volume, while the addition of FGS and GSP at a low level (0.5%) improved the specific volume. The brightness (L*) of the crumb and crust gradually decreased with increasing levels of all additives. The crumbs of the breads with PHP and FPH were characterized by lower hardness, while GSP and especially FGS had higher hardness. All enriched breads (except those with FGS) were more elastic and easier to chew.

1. Introduction

Bread has always been a traditional staple food for people in many countries around the world. Thanks to its high carbohydrate content, bread is an important source of energy, but it also contains essential elements, such as protein, fat, and minerals. Bread has been the most widely used food for centuries due to its nutritional value and sensory properties [1]. The quality of bread is influenced by the dough composition [2]. However, refined wheat flour, which is commonly used for bread, has a lower nutritional quality because refining the flour results in a significant loss of dietary fiber, vitamins, minerals, and phytochemicals [3]. Therefore, bread is considered the best means of enrichment with bioactive compounds to develop health-promoting products. Since white flour bread is a food with low phenolic content, many scientists focused on fortifying wheat bread with food waste and by-products rich in phenolic antioxidants, such as grape seed powder [4,5], mango peel [6], dry onion skin [7,8], and pomegranate peel powder [9], which are often cheap, functional, and an excellent source of nutraceuticals and bioactive compounds [10].

The amount of waste generated in the food industry is significant, and it is critical to consider alternative recycling options. Grapes are the most widely produced fruit in the world and generate the most waste or by-products (pulp, peel, seeds, and stems). Grape seeds are rich in phenolic compounds, dietary fiber, proteins, vitamins, and organic acids [11]. Pistachio hulls are a major agro-industrial by-product of the pistachio industry and are accumulated in large quantities during industrial postharvest processing. Pistachio hulls are the soft mesocarp and epicarp of the pistachio, which are firmly attached to the hard inner shell. During ripening, it has a pinkish-yellow color that changes to a reddish-light yellow as it matures [12]. Researchers reported that pistachio hulls have antioxidant, antimicrobial, and antimutagenic effects [13,14,15,16]. Goli et al. [15] found that aqueous and methanolic extracts of pistachio hulls are rich in phenols, which effectively retard the deterioration of soybean oil at 60 °C, with efficacy comparable to that of the synthetic antioxidant BHA (butylated hydroxyanisole). Furthermore, pistachio hulls also contain polysaccharides, dietary fibers, essential oils, unsaturated fatty acids, phytosterols, carotenoids, chlorophylls, tocopherols, and triterpene acids [16,17,18]. Due to its antioxidant polyphenolic compounds (phloroglucinol, gallic acid, protocatechuic acid, galloyl-shikimic acid, 4-hydroxybenzoic acid, catechin, vanillic acid, eriodictyol-7-O-glucoside, naringin, and cinnamic acid) [19] and phytochemical contents, such as fatty acids (1500 mg/100 g dried hull), anacardic acids (355 mg/100 g dried hull), phytosterols (21.36 mg/100 g dried hull), carotenoids (0.55 mg/100 g dried hull), chlorophylls (1.14 mg/100 g dried hull), and tocopherols (0.98 mg/100 g dried hull) [16], pistachio hull can be used in bread formulation to improve bread quality. Due to their strong antioxidant activity, pistachio hulls might be an interesting additive to fortify cereal products. In addition, pistachio hulls are currently used as animal feed and have not been considered for food production. Therefore, pistachio hulls have the potential to be used for food upcycling, and there is a need to learn more about the use of pistachio hulls (in fresh or dried form) during this process. The enrichment of white wheat flour with these additives changes the quality of the bread. Therefore, when using non-traditional materials, special attention should be paid to the study of their functional and technological properties.

However, to our knowledge, there is no clear evidence to date for the use of pistachio hulls to enrich bread. In this work, the influence of the addition of fresh or freeze-dried pistachio hulls on the total phenolic content, antioxidant activity, moisture content, crust and crumb color, specific volume, baking loss, and textural and sensory properties of white wheat bread was specifically investigated. In addition, grape seeds, which have been used as an additive for many years, were also used as a fortifying agent and compared with the quality characteristics of breads with pistachio hulls.

2. Materials and Methods

2.1. Materials

Wheat flour with a moisture content of 14.3%, protein content of 11.9%, and ash content of 0.67% was supplied by Özmen Un San. ve Tic. A.Ş., Turkey. Salt and active instant dry yeast were purchased from the local market in Gaziantep, Turkey, while fresh pistachio hull and grape seeds were obtained as by-products from a company in Gaziantep, Turkey. Fresh hulls and grape seeds were stored in ALPE bags at −24 °C until use. Pistachio hulls and grape seeds that were added fresh were coarsely ground using a blender (Arzum, AR1056, İstanbul, Turkey), and those that were added as powder were freeze-dried at −55 °C for 48 h in a freeze-dryer (FreeZone 6, Labconco, Kansas City, MO, USA), and samples were ground after drying. All solvents and chemicals were purchased from Sigma Aldrich (St. Louis, MO, USA). The proximate composition (moisture, protein, oil, and ash) of PHP, FPH, GSP, and FGS was determined [20]. The proximate composition of the additives is shown in

Table 1. Proximate compositions, color values, antioxidant activity, and total phenolic content of fresh and powdered pistachio hulls and grape seeds.

Properties	FPH	PHP	FGS	GSP
Moisture (%, wet basis)	71.40 ± 0.01	6.855 ± 0.09	21.90 ± 0.16	6.035 ± 0.04
Protein (%, dry basis)	10.51 ± 0.08	8.14 ± 0.02	5.36 ± 0.09	7.83 ± 0.026
Oil (%, dry basis)	6.35 ± 0.12	8.79 ± 0.04	9.10 ± 0.12	12.14 ± 0.01
Ash (%, dry basis)	7.88 ± 0.05	9.30 ± 0.18	1.62 ± 0.01	1.65 ± 0.06
L*	48.74 ± 1.23	53.86 ± 1.29	24.26 ± 1.17	31.67 ± 2.10
a*	20.30 ± 2.62	17.09 ± 0.49	15.92 ± 1.34	17.84 ± 0.53
b*	21.61 ± 1.89	21.83 ± 0.52	14.50 ± 0.60	24.09 ± 0.59
Antioxidant activity (mg Trolox/g dry weight)	40.22 ± 0.03	59.39 ± 0.09	32.68 ± 0.01	54.74 ± 0.10
Total phenolic content (mg GAE/g dry weight)	104.9 ± 0.16	137.3 ± 0.25	66.48 ± 0.06	96.73 ± 0.15

FPH: fresh pistachio hull, PHP: pistachio hull powder, FGS: fresh grapeseed, GSP: grapeseed powder.

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2.2. Preparation of Bread

Experiments were performed in a bread-baking machine (Tefal, Pain et Delice, Rumilly, France). The dough recipe was based on the bread standard TS 5000 [21]. For comparison, the control bread (control) was used, which was composed as follows: 400 g wheat flour, 240 mL water, 6 g salt, and 8 g yeast. Fresh pistachio hull (FPH), fresh grape seed (FGS), pistachio hull powder (PHP), and grape seed powder (GSP) were added separately to the bread formulation as additives. Wheat flour was replaced with FPH or FGS or PFP or GSP at five levels (0.5%, 1.38%, 2.25%, 3.13%, and 4% of wheat flour). The selected bread baking program included dough preparation, fermentation, and baking (total 3:30 h). The bread was left to rest for 2 h at room temperature before being prepared for analysis.

2.3. Moisture Content

The moisture content of the bread samples was determined using an infrared moisture analyzer (Daihan Scientific, MA10, Gangwon-do, Korea) at 105 °C.

2.4. Color

The CIE color values L*, a*, and b* were measured at five different points within the crumb and crust regions using a colorimeter (3NH, China). The total color difference (ΔE) of the fortified bread relative to the control bread was calculated for each additive according to Hunter [22].

2.5. Specific Volume and Baking Loss

Baking loss (%) was determined by weighing the bread and the weight of the dough before baking. The specific volume of the bread (cm³/g) was determined by dividing the volume of the bread by its weight. The volume of the bread was determined using the rapeseed displacement method according to the approved method AACC International 10-05.01 [23].

2.6. Total Phenolic Content and Antioxidant Activity

Ground bread samples (1 g) were extracted with 80% methanol (10 mL) in a shaking incubator (Mikrotest, MSC-30, Ankara, Turkey) at 37 °C for 1 h. The mixtures were then centrifuged (PCE Instruments, CFE100, Meschede, Germany) at 6000 rpm for 10 min, and the supernatants were collected.

The total phenolic content (TPC) in the methanol extract of the samples was determined using the Folin–Ciocalteau method and the procedure reported by [24]. All spectrometric measurements were performed in triplicate. The calibration curve was prepared using gallic acid, and the results were expressed as gallic acid equivalents (mg GAE/g dry weight).

The antioxidant activity of the samples was measured using the DPPH (1,1-diphenyl-2-picrylhydrazyl) radical-scavenging method according to Brand-Williams et al. [25] with some modifications. The extracts (0.1 mL) were added to a 2.9 mL DPPH solution (100 ppm). The mixture was shaken vigorously and left in the dark at room temperature for 30 min. Then, the absorbance was measured at 517 nm. The antioxidant activity was expressed as Trolox equivalents (mg Trolox/g dry weight).

2.7. Texture Analysis

Texture analysis of the crumb of bread samples was performed using a texture analyzer (Texture Analyzer TA-XT Stable Micro Systems, Surrey, UK) according to approved method 74-09 [26]. A cylindrical compression probe with a diameter of 36 mm was used for the analysis. Bread slices of 2.5 cm thickness were compressed to 50% of their original thickness at a test speed of 2 mm/s with a 30 s delay between the first and second compressions. Hardness, springiness, cohesiveness, and chewiness properties were measured.

2.8. Sensory Evaluation

A panel of 14 semi-trained panelists consisting of staff and students evaluated the sensory characteristics of the bread samples. The bread was cut into slices (2 cm thick). The sensory evaluation of the samples involved giving grades using a 5-point hedonic scale according to the crust and crumb color, chewiness, taste, flavor, and overall liking.

2.9. Statistical Analysis

The results presented are the average of three replicated observations. The significance of the level and type of additive was determined via an analysis of variance (ANOVA) for each bread quality parameter using SPSS Statics 22.0 (SPSS Inc., Chicago, IL, USA). Tukey’s HSD multiple range test was applied at a 95% significance level to determine the significant differences. In addition, color values were correlated with the total phenolic content and antioxidant activity, and correlation coefficients were calculated.

3. Results

3.1. Moisture Content

The observations of the moisture content of the control and enriched breads are shown in Figure 1a. The values of moisture content of the breads prepared with different additives ranged from 36.89–37.84% for the breads enriched with fresh pistachio hulls (FPH), 38.05–38.53% for the breads enriched with freeze-dried pistachio hulls (PHP), 35.90–36.95% for the breads enriched with fresh grape seeds (FGS), and 37.46–38.45% for the breads enriched with freeze-dried grape seeds (GSP). The minimum moisture content of the enriched bread (35.90%) was found for the bread with the 0.5% addition of FGS and the maximum moisture content (38.53%) for the bread with the 2.25% addition of PHP. A significant increase in moisture content was observed for all enriched bread samples compared with the control (33.70%). It was concluded that the weight loss of the bread decreased with the addition of FPH, FGS, PHP, and GSP. In agreement with our results, the moisture contents of bread samples enriched with broad bean hulls [27], cumin and caraway powder seeds and by-products [28], parsley leaf powder [29], and Plantago ovata husk [30] were increased. This may be attributed to the fact that flours with added dietary fiber prevent water evaporation. According to the ANOVA (Figure 1a), there were significant differences in moisture content between the control bread and all the enriched breads (p < 0.05). In addition, the statistical analysis showed that only the type of additive had a significant effect (p < 0.05) on the moisture content, while the level of additive was not significant (p > 0.05). Figure 1a also shows that the moisture contents of the breads fortified with FHP and FGS increased slightly with the increasing addition levels, while the moisture contents of breads fortified with PHP and GSP decreased slightly with the increasing addition levels. In addition, breads fortified with powdered additives had higher moisture contents than the breads fortified with fresh additives. This was due to the higher water-holding capacity of powder products. Higher moisture content is both economical and necessary to extend the shelf life of bread [31].

3.2. Baking Loss and Specific Volume

Baking loss and specific volume are important quality parameters of bread and are shown in Figure 1b and Figure 1c, respectively. The lowest baking loss of the enriched breads (10.11%) was found for the bread with the 3.13% addition of PHP, and the highest baking loss (14.87%) was found for the bread with the 4% addition of FGS. The baking loss values were lower for all the enriched breads (except for the breads with FGS) than for the control bread. This may be attributed to the fact that flours with fat, fiber, and gluten have free proteins that can bind free water in the dough, which prevents water evaporation and reduces baking loss [3,32]. The baking loss was influenced by the type and level of the additives (p < 0.05), and the control bread was significantly different from the enriched breads, except for the breads with FGS (Figure 1b). Furthermore, the baking loss values did not increase or decrease uniformly as a function of the level of additive; as the FGS content increased from 0.5% to 4%, the baking loss of the breads first decreased and then increased, with only the breads with FGS showing a statistically nonsignificant difference as a function of the change in additive level (Figure 1b). As mentioned above, the change in the other enriched breads was statistically significant (p < 0.05). The comparison of the type and level of additives showed that PHP was the most effective at reducing baking loss. Thus, pistachio hulls can be used to reduce baking loss. This result can be explained by the higher moisture content of the bread samples enriched with pistachio hulls.

The values of the specific volume of the breads enriched with different additives varied between 2.91–3.58 cm³/g for PHP, 3.19–3.56 cm³/g for FPH, 3.30–3.67 cm³/g for GSP, and 3.32–3.76 cm³/g for FGS. When comparing the specific volume of each enriched bread with that of the control bread (3.59 cm³/g), it was found that the addition of pistachio hulls (both fresh and dry) resulted in a decrease in the specific volumes of the breads, while the addition of grape seeds in small amounts increased the specific volumes. There were also significant differences in the specific volume between the control bread and the enriched breads (except for the breads with the 0.5% additions of PHP and FPH) (Figure 1c, p < 0.05). The FGS breads had the highest specific volume, and the PHP breads had the lowest specific volume. Due to the higher water-holding capacity of the pistachio hull, which is a source of polysaccharides and dietary fiber [17], the water requirement of the dough increased, and the achievable volume was limited. In this process, the interaction between gluten and fiber resulted in a decrease in gas retention ability and a decrease in bread volume [33]. The specific volume always decreased as a result of fiber addition, which was previously reported by Ni et al. [27]. In addition, the results of the ANOVA showed that the type and level of additives had a significant effect on the specific volume, and it was clear that the specific volumes of all enriched breads decreased with an increasing level of additive (Figure 1c), and thus, low amounts of additives could be beneficial, while higher amounts could have negative effects on the specific volume.

3.3. Total Phenolic Content and Antioxidant Activity

The results on the effects of the different enrichment levels of FHP, PHP, FGS, and GSP on the total phenolic content and antioxidant activity of the bread samples are shown in Figure 1d and Figure 1e, respectively. Significant increases in the total phenolic content and antioxidant activity of the breads were observed with increasing PHP levels. The total phenolic content and antioxidant activity of the breads initially increased from 0.89 to 14.66 mg GAE/g dry weight and from 5.90 to 16.19 mg Trolox/g dry weight, respectively, when the PHP level increased from 0.5% to 4.0%. When the total phenolic content and antioxidant activity of the control bread were compared, it was found that the addition of FHP, FGS, and GSP also increased them. There was no difference in the total phenolic content between the control bread and the breads with the 0.5% addition of FGS and GSP (p > 0.05), while the total phenolic content and antioxidant activity of all other enriched breads were different from those of the control bread (p < 0.05). Moreover, the total phenolic content and antioxidant activity of breads with powdered additives were higher than those of the breads enriched with fresh additives. This was due to the fact that the total phenolic content and antioxidant activity of powders are intrinsically higher due to the higher extraction yield resulting from the porous surfaces caused by freeze-drying (Table 1). In addition, according to the results from ANOVA, the type and level of additives had a significant effect on the total phenolic content and antioxidant activity, and it was clear that the total phenolic content and antioxidant activity increased with the increasing additive level in all the enriched breads (Figure 1d,e). In agreement with our results, the total phenolic contents and antioxidant activity of wheat bread samples enriched with Moldavian dragonhead [34] and parsley leaf powder [29] increased with increasing additive levels. Dziki et al. [29] found that the total phenolic content of bread to which parsley leaf powder was added at a concentration of 5% increased from 0.23 mg GAE/g (wheat flour) to 0.84 (wheat flour + 5% parsley leaf powder). Moreover, the total phenolic content of enriched bread increased linearly with the percentage (0 to 5%) increase in the addition of dragonhead leaves from 4.8 to 10.1 mg GAE/g dry matter, and the highest radical scavenging activity was obtained in bread with the highest percentage of dragonhead leaves [34]. Therefore, it was concluded in this study that the fortification of wheat flour with PHP significantly improved the functional quality of bread, which could have a positive impact on health.

3.4. Crumb and Crust Color of Bread

Figure 2 shows how the color parameters of the crumb and crust of the bread samples (L*, a*, and b*) changed depending on the PHP, FPH, GSP, and FGS addition levels in the wheat flour. Since the color of bread correlates with its quality and consumer acceptance, the evaluation of color parameters is essential [29]. The L* value of the crumb for all breads was higher than those of the crust. This was due to the fact that the color change of the bread crust was mainly influenced by the Maillard reaction. As a result of the Maillard reaction, brown melanoidins were formed, which darkened the crust. Furthermore, the color of the crumb was influenced by the color of the components added to the wheat flour, especially polyphenols and dietary fiber. Furthermore, statistically significant correlations (p < 0.01) were found between the crumb L* and the total phenolic content and antioxidant activity (r = −0.944 and r = −0.925, respectively). The Maillard reaction had no effect on the formation of the crumb color. The reason for this was that the inside of the bread could not reach the same temperature as the crust [33]. The highest crumb L* value was obtained in the control bread, and the presence of all additives (except the breads with the 0.5% and 1.38% addition of FGS) resulted in a significant reduction (p < 0.05) (Figure 2a). Similarly, the crust L* value of the control bread was different from that of all the enriched breads (p < 0.05) (Figure 2d). The L* value of the crumb and crust of the breads decreased with an increasing level of enrichment (Figure 2a,d). The results from the ANOVA also showed that the level and type of additives had an effect on the L* value of the crumb and crust. In addition, the enrichment of the bread with PHP decreased the lightness of the crumb from 70.01 to 54.30 (bread with the 4% addition of PHP). The bread samples with the addition of pistachio hulls (both dry and fresh) had lower brightness in both the crust and crumb due to the color effects caused by the higher amount of phenolic compounds in pistachio hulls (Table 1).

The a* values of the crumb and crust increased with the increasing levels of additives (Figure 2b,e). The most striking change in the crumb and crust a* values was observed in the breads with PHP. The a* values of the crumbs and crusts ranged from 1.84 and 5.43 (control bread) to 6.92 and 16.61 (for bread with the 4% addition of PHP), respectively. The increase in the redness of the crumb color of bread with PHP was probably due to the phenolic content and the natural color of the pistachio hull powder, which is red to light yellow and affects the color of the bread. In addition, statistically significant correlations (p < 0.01) were found between the crumb a* value and the total phenolic content and antioxidant activity (r = 0.834 and r = 0.898, respectively). Moreover, both enzymatic and non-enzymatic browning could be the reason for higher redness values in the crust color of breads with pistachio hulls than in breads with grape seeds. Similarly, statistically significant correlations (p < 0.01) were found between the crust a* value and the total phenolic content and antioxidant activity (r = 0.737 and r = 0.833, respectively). The a* values of the crumb and crust of the control bread were significantly different from those of the enriched breads, except for the crumb a* value of the breads with 0.5% and 1.38% FGS additions. The b* value of the crumb and crust of all the enriched breads decreased with increasing levels of additives. The crumb b* values decreased from 14.05 in the control bread to 8.87, 8.98, 8.20, and 8.36 when 4% of wheat flour was replaced with PHP, FPH, GSP, and FGS, respectively (Figure 2c,f). In addition, the breads containing pistachio hulls had lower crust b* values than the breads with grape seeds. The analysis of the ANOVA also showed that the types and levels of additives had significant effects on the a* and b* values of the crumbs and crusts.

The total color differences (ΔE) of the crumbs ranged from 7.45 to 17.31% for PHP, 4.52 to 10.29% for FPH, 4.16 to 9.13% for GSP, and 3.05 to 17.31% for FGS. This parameter (ΔE) indicated significant changes in color after the fortification compared with the control. As the amount of additive in the bread dough increased, the ΔE of the crumb increased (Figure 2g). The ΔE values of the crust also decreased with increasing additive levels (Figure 2h). In addition, the highest values for crumb and crust color changes were obtained for bread with PHP, while the lowest values were obtained for bread with FGS. The type of additive used had a significant effect on the color of the breads. The results from the ANOVA also clearly demonstrated that the ΔE values of the crumb and crust changed significantly depending on the type and level of additive (Figure 2g,h).

3.5. Textural Properties of Bread Crumb

The textural properties (hardness, springiness, cohesiveness, chewiness, and resilience) of the breads are shown in Figure 3; these are important quality factors because these properties are strongly related to consumer preferences. Hardness is defined as the loss of softness of the bread crumb and is measured in newtons (N) [35]. The hardness of the control bread was 32.8 N, indicating a firm and dense texture. The highest crumb hardness was found for the bread with the 4.0% addition of FGS (39.65 N), and the lowest was found for the bread with the 0.5% addition of FPH (26.37 N). As can be seen in Figure 3a, PHP and FPH showed softening effects on the crumb hardness, whereas FGS and bread with a higher level of 2.25% GSP had significantly equal and higher hardness values than the control bread. When the level of additives was increased from 0.5% to 4%, the hardness of the enriched bread crumbs (with the exception of FGS) initially decreased and then increased, and the hardness of the PHP and FPH breads to which 4% was added were similar to that of the control (Figure 3a). The hardness of the breads with GSP and FGS additions were higher than those of the breads with PHP and FPH additions. This result can be explained by the higher moisture contents of the breads with PHP and FPH (Figure 1a), the additions of dietary fiber (according to Akbari-Alavijeh et al. [17], pistachio hulls are a source of dietary fiber), and the increase in protein content (Table 1) decreasing the hardness [36,37,38,39]. In addition, the results of the ANOVA showed that the type and level of additives had significant effects on the hardness, and it was clear that the hardness in all enriched breads increased with increased levels of additives (Figure 3a). Similarly, Chen et al. [6], Korus et al. [40], and Dziki et al. [29] found that bread crumb hardness increased with increasing amounts of additives via fortification with mango peel powder, lyophilized kale, and parsley leaf powder, respectively.

Springiness describes the way the crumb of a product springs back following compression and is related to the elasticity of the bread crumb [34]. The lowest springiness of enriched bread (0.57) was found for the bread with the 1.38% addition of GSP and the highest springiness (1.68) was found for the bread with the 4% addition of FGS (Figure 3b). Like hardness, springiness is also strongly influenced by moisture content and water-holding capacity. Hong et al. [41] also reported that breads with mushroom powder were characterized by low specific volumes and springiness due to the high water-holding capacity of the mushroom powder. A similar trend to that observed for hardness was also observed for springiness, and the values for springiness of the bread with FGS were significantly higher than those of the control bread and the other enriched breads. It is also worth noting that consumers preferred bread with higher elasticity, as springiness is associated with freshness and loss of elasticity of the crumb, while bread with low springiness is associated with a crispy crumb [42,43]. The springiness of the PHP and FPH breads, as well as the bread with a higher GSP level of 3.13%, was similar to that of the control (Figure 3b). The results from the ANOVA showed that the springiness values of the bread crumbs changed significantly depending on the level of additive, except for the breads with PHP and FGS (Figure 3b). The results also showed that the type of additive affected the springiness.

Cohesiveness describes the amount of deformation a material can withstand before it breaks, the total strength of the internal bonds holding the product together, and the quantified internal resistance of the food structure [35]. The lowest cohesiveness of the enriched bread (0.263) was found for the bread with 0.5% GSP and the highest cohesiveness (0.565) was found for the bread with 4% PHP (Figure 3c). Based on the obtained results, the cohesiveness of the control bread was 0.507. After the addition of 0.5% PHP, FPH, GSP, and FGS, this value decreased to 0.409, 0.371, 0.263, and 0.340, respectively. When the level of the additive was increased from 0.5% to 4%, the cohesiveness of the enriched bread crumb increased. However, the cohesiveness was higher only in the bread with a PHP addition of 4.0% than in the control bread. In addition, there were no statistically significant differences between the control bread and the breads with a PHP addition of 3.18% (p > 0.05). When comparing the type of additive, it was found that the breads with grape seeds (both dry and fresh) had lower values for crumb cohesiveness than the breads with pistachio hulls (both dry and fresh). This indicates an inverse relationship between the hardness and cohesiveness values of the bread crumb. The loss of cohesiveness could have been due to lower moisture content and intramolecular bonds between bread components [44]. Bread with high cohesiveness is desirable because it is easy to form into a ball in the mouth instead of crumbling when chewed, while bread with low cohesiveness tends to break, which negatively affects consumer acceptance of the bread [45]. The addition of a higher level of 4% PHP improved the cohesiveness of the internal structure of the crumb. In addition, the results of the ANOVA showed that the type and level of the additives had a significant effect on the cohesiveness (p < 0.05).

Chewiness is an important parameter of bread texture that depends on springiness, hardness, and cohesiveness and gives the food the energy needed to require chewing before swallowing [35]. As shown in Figure 3d, the chewiness values of the control bread (12.65 N) decreased to 7.64 N, 5.94 N, and 4.04 N after the addition of PHP, FPH, and GSP, respectively. In contrast, an increase in chewiness (18.82 N) was observed after the addition of FGS. The results of the ANOVA showed that the type and level of additives had significant effects on chewiness, and it was clear that chewiness increased with increasing levels of additives in all the enriched breads (Figure 3d). The chewiness of the breads with FGS and the bread with 4.0% PHP were higher than that of the control bread. The bread with the 4.0% addition of GSP and a higher level of 3.13% FPH had significantly equal chewiness values to the control bread. Since the chewiness values of the fortified breads followed a similar trend to the hardness and springiness: as the hardness and springiness increased, the chewiness of the breads also increased, whereas chewiness was negatively related to the cohesiveness. While lower chewiness is desirable in bread, the current results showed that this parameter was improved by the addition of PHP, FPH, and GSP.

Resilience describes the rate at which the crumb recovers after compression [35] and is an important property related to bread freshness [46]. The resilience values of all enriched breads were not statistically different from those of the control (p > 0.05) and were quite consistent for all the enriched breads (Figure 3e). Thus, the addition of pistachio hulls and grape seeds could have a slight effect on the resilience of the breads, but this did not depend on the level and type of additives. Similar results were obtained by Tong et al. [47] and Dziki et al. [29], where the changes in the resilience of wheat bread due to enrichment with honey powder and parsley leaf powder, respectively, were not significant.

3.6. Sensory Quality of Bread

The appearance of the control bread and the enriched bread is shown in Figure 4. Sensory evaluation is an important parameter for assessing the quality of food products to meet consumer demands. The results of the sensory evaluation of the enriched breads and the control bread are shown in Figure 5. The data were analyzed in terms of the crumb and crust color, chewiness, flavor, taste, and overall liking.

The highest score for the crust and crumb color was obtained by the control bread, and the lowest by the bread with PHP, which was consistent with the results of the color analysis. The results show that the breads that contained pistachio hulls had lower scores compared with the other breads. This may be attributed to the lower brightness of the bread and the higher redness, which may have had a negative effect on the color perception of the panelists. The crust color evaluation was not affected by the type and level of additives, while the crumb color evaluation was affected by the type and ratio of additives (Figure 5a,b). Moreover, it was found that the crust and crumb color scores for all enriched breads (except for bread with 0.5% and 4% additions of GSP and FGS) were different from those of the control bread (p < 0.05). No significant difference was found between the control sample and the enriched breads in terms of chewiness. The lowest chewiness score was found for the bread with 1.38% GSP and the highest was found for the bread with 4% PHP (Figure 5c). Flavor and taste scores were also not influenced by the type and level of additives (Figure 5d,e). The lowest flavor and taste scores were obtained for the breads with PHP; however, the control and all enriched breads did not differ significantly in their flavor and taste scores. Consequently, with a PHP level of 4% in the bread recipe, the flavor and taste scores of the bread were below 4 points. The highest score for overall liking was given to the control bread, and the lowest to the bread with PHP, as well as for all other sensory characteristics tested (with the exception of chewiness). Nevertheless, the control bread and all the enriched breads differed significantly in the overall liking score (except for the breads with 0.5% and 4% added GSP and FGS). The overall liking score was only affected by the type of additive (Figure 5f).

4. Conclusions

Changes in moisture content, crust and crumb color, specific volume, baking loss, total phenolic content, antioxidant activity, and textural properties of bread were studied with respect to the addition of FPH, PHP, FGS, and GSP to wheat flour, and the results showed that the addition of by-products affected the quality characteristics of the bread. The addition of PHP resulted in an increase in total phenolic content and antioxidant activity; however, the specific volume showed the lowest values among the other breads. Although PHP had a decreasing effect on the values of the specific volume of the bread samples, it was found that the overall quality characteristics were not negatively affected. The bread with FGS in the crust and crumb had the lowest value for color change for all additive levels. The lower hardness and chewiness and higher cohesiveness led to the PHP and FPH breads being of good quality. The current results show that most of the bread quality characteristics depended on the level of the additive used, and thus, it is important to control the amount of additives in the bread. The analysis of all these data suggests that pistachio hull powder is an alternative functional ingredient that can be used together with wheat flour for bread making due to its high fiber content and richness in antioxidant and phenolic substances. Although bread with pistachio hull powder caused an increase in total phenolic content and antioxidant capacity, and thus, value-added products were obtained, the sensory quality characteristics were lower than in the control and in bread with grape seeds. Therefore, considering the quality characteristics of bread, pistachio hull powder was found to be a good alternative additive to enrich bread.