Use of Bilberry and Blackcurrant Pomace Powders as Functional Ingredients in Cookies

Abstract

The purpose of the present study was to evaluate the effects of partially replacing wheat flour with bilberry (BIPP) and blackcurrant (BCPP) pomace powders at 2.5%, 5%, and 10% levels on dough texture and rheology and on the proximate composition, color, titratable acidity, pH, spread ratio, total phenolic content, DPPH radical scavenging activity, and textural and sensory properties of cookies. BIPP showed higher protein, fiber, and water absorption capacity while also showing lower fat and titratable acidity as compared with BCPP. The incorporation of BIPP and BCPP in cookies resulted in lower protein and higher fat, fiber, and mineral contents. Dough hardness, consistency, and stiffness increased while the hardness, cohesiveness, and chewiness of the cookies were found to decrease with the increase in pomace levels. A seven-fold increase in the total phenolic content of the cookies was recorded at a 10% replacement level of wheat flour with BIPP, reaching 214.73 mg GAE/100 g, while only a three-fold increase was found for 10% BCPP (90.18 mg GAE/100 g). The enrichment with BIPP and BCPP improved the sensory properties, with the 10% addition level presenting the highest acceptance. The results indicate that bilberry and blackcurrant pomace could be utilized as a sustainable source of fiber and bioactive compounds for adding nutritional, technological, and sensory benefits to the cookies.

1. Introduction

Cookies and biscuits are one of the most popular quick snacks worldwide due to their ready-to-eat nature, affordability, wide availability, relatively long shelf-life, and assortment diversity [1,2]. Although widely appreciated and consumed by different age and socio-economic groups, cookies are rich in sugar, sodium, saturated fats, and energy value and are poor in micronutrients, fiber, and bioactive compounds [3]. As a result, their excessive consumption can lead to chronic non-communicable diseases such as cardiovascular diseases, cancer, and diabetes [4,5]. As consumers become more health-aware and interested in the active role of food to prevent lifestyle diseases, there is a need to improve the nutritional and functional value of these food products while maintaining good sensory and structural qualities [1,6]. Cookies have proven to be a good vehicle for the delivery of dietary fiber and bioactive compounds from the fruit processing industry to consumers [7,8]. The fruit processing industry generates large amounts of by-products with valuable nutritional and functional properties, as justified by their richness in fiber, micronutrients, and bioactive compounds [9]. Currently, there is a growing trend towards their valorization to produce dietary supplements and nutraceuticals or to be used as natural food ingredients [6,10]. A good strategy in cookie and biscuit production involves the inclusion of functional ingredients in their composition by partially replacing the wheat flour with powders from fruit processing by-products [11]. Many studies have been dedicated to the innovation of cookies and biscuits by partially replacing wheat flour with fruit processing by-products such as pomace flour from orange [12], avocado, kiwifruit, pineapple and pomegranate [2,3,13], apple [14,15,16,17,18,19], tomato [20,21], blueberry [1,8,22,23], melon [14], grape [5,24,25,26], grapefruit [6], pear [11], and raspberry, red currants, and strawberry [8,27].

Bilberry (Vaccinium myrtillus L.), also known as huckleberry, whortleberry, or European blueberry, is a perennial dwarf shrub belonging to the Ericaceae family, genus Vaccinium, originating from northern Europe and North America [28]. From ancient times, bilberries, the blue/black fruits of bilberry, are known for their benefits in treating various conditions such as hemorrhoids, vomiting, diarrhea, skin ulcers, and mucosal tissue inflammation [29]. The health-promoting effects of bilberries have been attributed to their phenolic compound content, comprising anthocyanins, terpenoids, flavonols, tannins, coumarins, phenolic acids, and resveratrol. Delphinidin and cyanidin are predominant among anthocyanins, followed by petunidin, peonidin, and malvidin, which are mostly glycosylated by galactose, glucose, and arabinose [30]. Due to the abundance of anthocyanins and of the other health-promoting compounds with antioxidant, antimicrobial, anti-inflammatory, anti-diabetic, cardioprotective, neuroprotective, and anticancer activities, bilberries have been awarded the title of “super food” or “functional food” [31,32,33,34]. Bilberries are available fresh, dried, or frozen, but most often, they are used to produce juices, jams, alcoholic beverages, violet pigments, or food supplements [35]. The residue from bilberry juice processing is the pomace, consisting mainly of skins and seeds, which is a valuable source of vitamins, fibers, and minerals. But what distinguishes bilberry pomace is its huge content of anthocyanins and other phenolic compounds with strong antioxidant properties. Moreover, bilberry pomace was reported to contain significant amounts of polyunsaturated fatty acids (including n-3 PUFAs) from the seed oil [36]. Muceniece et al. [37] obtained the highest yields of polyphenols in extracts from wild bilberries among five Vaccinium spp. berry pomaces and demonstrated the strong antioxidative, hypoglycemic, and hepatoprotective properties of bilberry pomace extract. Other authors reviewed the anti-inflammatory, anti-obesity, antidiabetic, cardioprotective, and antiproliferative effects of bilberry anthocyanins [38,39]. Regardless of their high functional value, pomaces are usually used as animal feed or fertilizer or are even discarded by the food industry, resulting in environmental pollution and increasing the costs of the fruit processing industry [40]. However, after drying to increase shelf life and reduce disposal, pomace could be used in various food applications for enhancing the biological value and functional properties while reducing fruit waste [13,20]. Previously, Syrpas et al. [30] studied the enzyme-assisted extraction of bilberry pomace for further valorization and Nemetz et al. [41] proposed the application of crude bilberry pomace powder as a coloring foodstuff, while Blejan et al. [35,42] developed fruit leathers and corn-based extruded snacks enriched with bilberry pomace powder. Recently, Nour [43] optimized the direct extraction of the bioactive compounds from bilberry pomace in apple juice, while Frum et al. [44] investigated the encapsulation of bilberry pomace powder to produce a new and sustainable dietary supplement.

Blackcurrant (Ribes nigrum L.) is a branched woody shrub from the Grossulariaceae family bearing dark purple bittersweet berries, which are particularly rich in phenolic compounds, including anthocyanins, phenolic acids, flavonoids, and condensed and hydrolyzable tannins [45]. Anthocyanins represent the dominant phenolic group in blackcurrants, accounting for around 80% of the total phenolic content [46]. Several in vivo and in vitro experiments have demonstrated the anti-inflammatory, antimicrobial, anticarcinogenic, vasomodulatory, and immunomodulatory activities provided by the blackcurrant intake [47]. The strong astringency and acid taste and high perishability make blackcurrants seldom eaten in their fresh state, with the fruits mostly being processed in juices, jams, jellies, and alcoholic beverages [48,49]. In blackcurrant juice processing, around 20% of the fruits are discarded as pomace [48,50,51]. Blackcurrant pomace has been recognized as a valuable source of fibers, fruit acids, and phenolic compounds, especially anthocyanins [50,52,53]. Giving the blackcurrant pomace a further use makes it possible to recover its high fiber, vitamin, and bioactive content and to increase the sustainability of the fruit processing industry. Studies regarding potential applications of blackcurrant pomace have mainly been focused on anthocyanins [54] and pectin [55] extraction, as well as on the addition of blackcurrant extracts and powders in crackers [56], fruit leather [35], meat products [57], pasta [58], and yogurt [59].

The purpose of this study was to enhance the fiber and bioactive compound contents of cookies by partially replacing wheat flour with bilberry and blackcurrant pomace powders obtained from by-products of juice production. The influence of the pomace powder addition on dough rheology and processing properties was evaluated, while control and supplemented cookies were analyzed for their physicochemical, bioactive, and sensory characteristics.

2. Materials and Methods

2.1. Raw Materials

Wild bilberries (Vaccinium myrtillus L.) and blackcurrants (Ribes nigrum L.) harvested from the hills of Vâlcea county, Oltenia Region, South-West Romania (44°49′ N 24°15′ E), were processed into juice without enzymatic treatment (juice yields of 57.6% and 49.3% for bilberry and blackcurrant, respectively) in a small-scale fruit juice factory located in Vaideeni (Vâlcea county, Romania). The pomaces (two batches of 3 kg for each berry) obtained as juice by-products were collected, packed in polyethylene bags, transported, and stored at −18 °C until use. The bilberry and blackcurrant pomaces were thawed in the air at room temperature (20 °C) and convectively dried in thin layers at 57 °C in a dehydrator (Deca +SS Design, Profimatic, Cluj-Napoca, Romania). The dried pomaces were thoroughly ground into powders using an electric coffee grinder (Bosch TSM6A011W, Bosch, Munich, Germany), passed through a 0.3 mm sieve, and kept in polyethylene bags at ambient temperature (20 °C) until cookies manufacturing.

The wheat flour type 650 (moisture—13.90%; protein—11.93%; fat—1.42%; and ash—0.65%) used for dough and cookie preparation was produced by the Maripan Cereal S.R.L mills (Tuglui, Dolj County, Romania). Vegetable fat for pastry (99.7% fat, containing refined palm and sunflower oils, emulsifier—E471, and antioxidant—E320, E321) was provided by Shchedro LLC (Zaporizhzhia, Ucraina), while the baking powder (Alpina) used in the formulation was purchased from Zeelandia S.R.L. (Iasi, Romania). Salt (sodium chloride) and granulated sugar were procured from the local market.

2.2. Chemicals

Gallic acid, Folin–Ciocalteu’s reagent, 2,2-diphenyl−1-picrylhydrazyl (DPPH), and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) were purchased from Sigma-Aldrich (Steinheim, Germany), while anhydrous sodium carbonate, sodium hydroxide of analytical grade, and methanol were purchased from Merck (Darmstadt, Germany). Distilled water was used to prepare all the aqueous solutions.

2.3. Preparation of Cookies

The recipe of the control cookies (labeled CC) contained 500 g white wheat flour, 187 g sugar, 218 g vegetable fat, 4 g baking powder, 1 g sodium chloride, and 156 mL water. In the supplemented cookies, 2.5%, 5%, and 10% of the wheat flour was replaced with bilberry (labeled as CBI2.5, CBI5.0, and CBI10.0) and blackcurrant (labeled as CBC2.5, CBC5.0, and CBC10.0) pomace powder, respectively, while keeping all the other ingredients constant. The replacement levels were chosen based on previous works [19,27] and preliminary tests. Cookie dough was manufactured in a planetary mixer (Rohnson R586, 700 W, Praha, Czech Republic). Fat and sugar were thoroughly creamed with the flat beater for 12 min at medium speed; then, water containing the sodium chloride and baking powder was added and mixed for 6 min at high speed to obtain a homogenous cream. Finally, the wheat flour was gradually added to the creaming mass under continuous mixing and further kneaded for 20 min. The dough was sheeted to a thickness of 6.13 mm by using an automatic dough sheeter (Flamic, Waico Group, Isola Vicentina, Italy). Round-shaped cookies were cut from the dough sheet using a cookie cutter of 5 cm in diameter. The cookies were transferred to a baking tray and baked at 200 °C for 10 min in an electrically heated deck oven (MIWE Condo, Arnstein, Germany). After baking, the cookies were left to cool on racks to room temperature (20 °C) and packed in airtight Ziploc bags for further analysis. Cookies from each formulation were manufactured in two independent batches. The determinations of the color parameters, proximate composition, and physical, textural, and sensory properties of the cookies were carried out 24 h after baking.

2.4. Proximate Composition and Physicochemical Properties of Bilberry (BIPP) and Blackcurrant (BCPP) Pomace Powders

The proximate composition of BIPP and BCPP (dry matter, protein, fat, fiber, and ash content) was determined following standard methods [60].

The water solubility index (WSI) of the pomace powders was determined according to the method provided by AACC [61] and was calculated as follows:

WSI (%) = (Weight of dry solids in supernatant/Weight of dry sample) × 100

The water absorption capacity (WAC) was determined following the method described by Jose et al. [2]. Briefly, the mixture of 1 g of the sample and 10 mL of distilled water was kept for 30 min at ambient temperature (20 °C) and were then centrifuged for 30 min at 3000 rpm. The water absorption capacity was calculated as follows:

WAC (%) = (weight of residual/weight of sample) × 100

2.5. Proximate Composition of Cookies

Cookies were analyzed for dry matter, crude protein, crude fat, crude fiber, and ash content according to the methods presented in AACC [61]. The analyses were carried out in duplicate, and the average values are reported.

2.6. Physical Characteristics of Cookies

The thickness and diameter were measured 1 h after baking on ten randomly selected cookies for each formulation using a digital Vernier caliper, as previously presented by De Toledo et al. [14]. Two perpendicular diameters were measured for each cookie sample. The average values were reported in millimeters [61]. The spread ratio was determined based on the ratio of the average diameter and average thickness of the cookies [61]. The weight of the cookies was recorded by using a Kern balance (model ABJ 220 4M, Kern and Sohn Gmbh, Balingen, Germany).

2.7. Color Analysis

Color analysis was conducted 24 h after baking using a PCE-CSM1 reflectance colorimeter (PCE Instruments, Meschede, Germany). The following CIEL*a*b* color parameters were recorded on the upper surface of cookies: L* indicating lightness, a* indicating redness (+) to greenness (−), and b* indicating yellowness (+) to blueness (−). Hue angle (h*) and chroma (C*) were calculated as arctan(b*/a*) and (a*² + b*²)^1/2, respectively. Three randomly selected cookies from each formulation were analyzed, with five readings at different points of the central area of each sample.

2.8. Titratable Acidity and pH

Titratable acidity was measured in the extract made from 10 g of finely ground cookie, homogenized, and diluted to 100 mL with distilled water. The extract was titrated with 0.1 N NaOH until the pH reached 8.1 [60], and the results were expressed as a % of citric acid. Triplicate extracts were prepared for each formulation. The pH measurements were taken in triplicate at 20 °C according to the official method of AOAC [60] by using a Hanna pH-meter HI255 (Hanna Instruments, Padova, Italy).

2.9. Rheological Analysis

The dynamic moduli, storage (G′), loss (G″), and loss tangent (tan δ) were evaluated using a HAAKE MARS 40 rheometer (Termo-HAAKE, Karlsruhe, Germany). For this test, a gap of 2 mm was set and a plate of 40 mm in diameter was used. The dough samples were placed between the rheometer plates after a previous rest of 5 min for relaxation. Frequency sweep tests were performed at 25 °C from 1 to 20 Hz in a range of linear viscoelasticity. For the frequency sweep tests, the dynamic moduli and tan δ were carried out at a constant stress of 15 Pa during heating from 20 to 100 °C at a heating rate of 4 °C per min, a frequency of 1 Hz, and a fixed strain of 0.001.

2.10. Texture Analysis

The textural properties of the doughs were evaluated with a compression test by using the TVT 6700 texturometer (Perten Instruments, Hägersten, Sweden) equipped with a 35 mm diameter cylindrical probe. The sample height was 35 mm, and the starting distance from the sample was 5 mm. The compression was made up to 40% of the initial height of the sample. The trigger force was 20 g, the test speed was 5 mm/s, and the recovery time between compressions was 12 s. Hardness (N), adhesiveness (J), resilience (dimensionless), stringiness (mm), stickiness (g), cohesiveness (dimensionless), chewiness (N), and gumminess (N) were measured.

The textural properties of cookies were determined using a Perten TVT 6700 texturometer (Perten Instruments, Hägersten, Sweden). A double compression test was performed to determine hardness (N), springiness (dimensionless), cohesiveness (dimensionless), gumminess (N), and chewiness (N) parameters. For this test, the texturometer was equipped with a 10 kg load cell and the sample height was 7 mm. The compression was made up to 10% of the initial height of the sample by using a 20 mm diameter cylinder. The starting distance from the sample was 3 mm, the trigger force was 10 g, and the test speed was 2 mm/s. The recovery time between compressions was 5 s.

The fracturability (mm) of the cookies was assessed by a 3-point bend single-cycle breaking test. The geometry used for this test was made up of an aluminum break probe of 70 mm and a 3-point bend rig. The gap was carefully chosen between the support plates so that they could support the sample. The sample height was 7 mm, while the starting distance of the knife was 2 mm above the sample. The test was performed at a speed of 3 mm/s. A trigger force of 50 g was applied. A single-cycle compression test was performed to determine the force required to penetrate the sample (puncture force, N). For these determinations, the texturometer was equipped with a stainless steel cylinder probe, 45 mm in height and 2 mm in diameter. The average sample height was 7 mm, and the starting distance from the sample was 10 mm. The measurement parameters were set as follows: the compression, 2 mm; the initial speed, 1 mm/s; the test speed, 0.5 mm/s; the retract speed, 10 mm/s; and the trigger force, 5 g. The distance above the trigger was 40 mm. The shear force (N) (the force required to cut through the sample to a certain distance) was assessed by a single-cycle cutting test. The texturometer was equipped with a break probe 55 mm high in aluminum. The measurements were made in the center of each sample. The sample height was 7 mm, the starting distance from the sample was 5 mm, the trigger force was 25 g, and the test speed was 2 mm/s.

2.11. Extraction of Phenolic Compounds

After grinding the cookies with a pestle and mortar, 1 g of ground sample was homogenized with 10 mL methanol. After 60 min of sonication in a Bandelin Sonorex Digital 10P ultrasonic bath (Bandelin Electronic GmbH, Berlin, Germany), the homogenates were centrifuged at 2500× g for 5 min. The recovered supernatants were filtered through Whatman No. 1 filter paper and utilized for the subsequent analyses of the total phenolic content and DPPH radical scavenging activity.

2.12. Total Phenolic Content

The total phenolic content was assessed in the extracts by the spectrophotometric Folin–Ciocalteu method given by Singleton et al. [62] using a calibration curve prepared with gallic acid. Aliquots (0.1 mL) of the extract or standard solution of gallic acid were pipetted in a test tube; then, 6 mL of distilled water and 0.5 mL of the Folin–Ciocalteu reagent (freshly diluted 1:1 with distilled water) were added. After 3 to 8 min, 1.5 mL of 20% sodium carbonate solution were added, and a 10 mL volume was made up with water. The content was vortexed for 1 min and stored in the dark for 30 min at 40 °C. The absorbance of the reaction mixture was then measured at 765 nm on a Varian Cary 50 UV spectrophotometer (Varian Co., Cary, NC, USA). The determinations were performed in three repetitions, and the results were reported as milligrams of gallic acid equivalents (GAE) per 100 g.

2.13. DPPH Radical Scavenging Activity

The antioxidant activity of the pomace powders and cookies was assessed as the ability to scavenge the DPPH free radical following the spectrophotometric method proposed by Brand-Williams et al. [63] with slight modifications. This procedure involves reacting aliquots of 50 μL extract with 3 mL of 0.004% DPPH methanolic solution. After shaking them and keeping them in the dark for 30 min, the absorbance was recorded at 517 nm against methanol using a Varian Cary 50 UV spectrophotometer (Varian Co., NC, USA). The DPPH radical scavenging activity was calculated as the percent of inhibition by using the following formula: DPPH scavenging activity (%) = [1 − A_sample/A_control] × 100, where A_sample is the absorbance of the test sample and A_control is the absorbance of the control negative reaction without extract. Trolox was selected as a standard, and the results were expressed as milimoles of Trolox per 100 g of sample.

2.14. Sensory Analysis

A panel of 24 members (15 females and 9 males, aged 24 to 59 years), comprising master’s students and teaching staff from the Department of Horticulture and Food Science, University of Craiova, participated in the sensory evaluation. The cookies were evaluated 24 h after baking for appearance, color, taste, flavor, texture, and overall acceptability. The panelists were invited to complete a nine-point hedonic scale (1 being “dislike extremely” and 9 being “like extremely”). The test was conducted in two sessions, one for each berry pomace added to the cookies. In each session, the panelists received four units of cookies, referring to the pomace powder percentage replacing the wheat flour in the formulation (CC, CBI2.5, CBI5.0, and CBI10.0 in the first session, and CC, CBC2.5, CBC5.0, and CBC10.0 in the second session). The samples identified by code numbers were randomly served to panelists on plastic plates. The analysis was conducted under daylight conditions at 20 °C, water was provided, and the panelists were asked to rinse their mouth between the evaluations. This study was approved by the Committee on Ethics of University of Craiova (no. 482 on 21 February 2025) based on the informed consent from the participants.

2.15. Statistical Analysis

All measurements were carried out at least in triplicate. Mean values and standard deviation were calculated by using Statgraphics Centurion software (version XVI.I) from StatPoint Technologies, Inc. (The Plains, VA, USA). Analysis of variance (ANOVA) was conducted, and the means were compared using Fisher’s Least Significant Difference test (LSD) and the multiple range test with a confidence level set at 5% (p < 0.05). In order to perform principal component analysis (PCA), XLSTAT 2021.2.1 (New York, NY, USA) software was used.

3. Results and Discussion

3.1. Characterization of Wild Bilberry and Blackcurrant Pomace Powders

The results concerning the proximate composition, titratable acidity, total phenolic content, and DPPH radical scavenging activity of BIPP and BCPP are given in

Table 1. Proximate composition, physicochemical, and functional properties of bilberry and blackcurrant pomace powders.

	BIPP	BCPP
Dry matter (g/100 g)	88.97 ± 0.66 a	89.41 ± 0.57 a
Protein (g/100 g)	8.25 ± 0.29 a	6.78 ± 0.26 b
Fat (g/100 g)	8.27 ± 0.26 b	9.32 ± 0.28 a
Fiber (g/100 g)	12.14 ± 0.43 a	10.64 ± 0.58 b
Ash (g/100 g)	1.03 ± 0.15 a	1.07 ± 0.12 a
Titratable acidity (g citric acid/100 g)	4.63 ± 0.19 b	5.82 ± 0.16 a
Water solubility index (WSI, %)	19.32 ± 0.57 a	14.05 ± 0.82 b
Water absorption capacity (WAC, %)	378.31 ± 2.17 a	312.38 ± 2.72 b
Total phenolic content (mg GAE/100 g)	3595.11 ± 0.65 a	953.45 ± 0.37 b
DPPH radical scavenging activity (mmol Trolox/100 g)	11.78 ± 0.17 a	2.35 ± 0.12 b

Different lowercase letters indicate significant differences between pomace powders (p < 0.05); BIPP—bilberry pomace powder; BCPP—blackcurrant pomace powder.

.

Both powders showed low water content (bellow 10%), which suggests the physical and microbiological stability of these ingredients. BIPP showed significantly (p < 0.05) higher protein and fiber but lower fat content as compared with BCPP, while no significant differences were found concerning the dry matter and ash content. A protein content of 6.78% was found in blackcurrant pomace powder, compared to 8.25% in bilberry pomace powder. Górnás et al. [64] also found 6.9% protein contents in blackcurrant pomace flour, while Tarasevičienė et al. [27] reported a protein content of 6.85% in red currant pomace powder. Blejan et al. [36] demonstrated that bilberry and blackcurrant pomace powders are a source of oils rich in mono- and polyunsaturated fatty acids, with BIPP being richer in n-3 PUFA (n-6/n-3 = 0.90) than BCPP (n-6/n-3 = 1.28).

Extremely high values of the total phenolic content were found both in BIPP and BCPP, suggesting that the press cake left after bilberry and blackcurrant juice extraction holds a large fraction of the fruit’s phenolic compounds. Similar values for the total phenolic content have been confirmed in previous studies [36,51]. Bilberries and blackcurrants display high antioxidant activity due to their richness in phenolic compounds, especially anthocyanins [36]. Significantly higher (p < 0.05) values of total phenolic content and DPPH radical scavenging activity were found in BIPP as compared with BCPP. The titratable acidity found in BCPP (5.82 g citric acid/100 g) was significantly higher than in BIPP (4.63 g citric acid/100 g), which will impact the taste and flavor of the supplemented cookies. Similar values of titratable acidity have been reported previously in blackcurrant pomace powders [65].

Table 1 also presents the results concerning the water solubility index (WSI) and water absorption capacity (WAC) of BIPP and BCPP. WAC is defined as the ability of the powdery product to hold or retain water against gravity, comprising bound, hydrodynamic, capillary, and physically entrapped water [66], being a major functional property in food applications. The WAC was found to be the highest for BIPP (378.31%), with 21.1% higher than for BCPP (312.38%). A similar value for the WAC (320%) has been reported previously by Reißner et al. [65] in blackcurrant pomace powder. The higher WAC values of BIPP could be attributed to the higher fiber content in BIPP as compared with BCPP, as it is well known that the hydroxyl groups present in the fiber structure may facilitate the increased water retention through hydrogen bonding [19]. The affinity of the dietary fiber for water due to the increasing number of hydrogen bonds provided by the fiber has previously been reported [17]. The higher protein content in BIPP could also be contributed to its higher WAC as compared with BCPP.

3.2. Proximate Composition of Cookies

The results on the proximate composition of the control and supplemented cookies are presented in

Table 2. Effect of bilberry pomace powder addition on the proximate composition of the cookies.

	CC	CBI2.5	CBI5.0	CBI10.0
Dry matter (g/100 g)	94.67 ± 0.16 a	94.59 ± 0.18 a	94.35 ± 0.21 a	93.45 ± 0.14 b
Protein (g/100 g)	6.86 ± 0.21 a	6.79 ± 0.12 a	6.57 ± 0.17 ab	6.34 ± 0.19 b
Fat (g/100 g)	21.61 ± 0.36 c	22.21 ± 0.31 bc	22.67 ± 0.40 b	23.53 ± 0.56 a
Fiber (g/100 g)	2.79 ± 0.12 d	3.59 ± 0.14 c	4.89 ± 0.25 b	6.76 ± 0.33 a
Ash (g/100 g)	0.29 ± 0.01 d	0.34 ± 0.02 c	0.42 ± 0.02 b	0.57 ± 0.02 a

Different lowercase letters indicate significant differences between cookie formulations (p < 0.05); CC—control cookie; CBI2.5, CBI5.0, and CBI10.0—cookies with 2.5%, 5%, and 10% of the wheat flour replaced by BIPP, respectively.

and

Table 3. Effect of blackcurrant pomace powder addition on the proximate composition of the cookies.

	CC	CBC2.5	CBC5.0	CBC10.0
Dry matter (g/100 g)	94.67 ± 0.16 a	94.81 ± 0.13 a	94.91 ± 0.12 a	94.96 ± 0.20 a
Protein (g/100 g)	6.86 ± 0.21 a	6.69 ± 0.23 a	6.52 ± 0.16 ab	6.28 ± 0.16 b
Fat (g/100 g)	21.61 ± 0.36 b	21.78 ± 0.22 b	22.13 ± 0.38 ab	22.42 ± 0.32 a
Fiber (g/100 g)	2.79 ± 0.12 d	3.31 ± 0.15 c	4.54 ± 0.21 b	6.28 ± 0.28 a
Ash (g/100 g)	0.29 ± 0.01 d	0.35 ± 0.02 c	0.44 ± 0.02 b	0.59 ± 0.03 a

Different lowercase letters indicate significant differences between cookie formulations (p < 0.05); CC—control cookie; CBC2.5, CBC5.0, and CBC10.0—cookies with 2.5%, 5%, and 10% of the wheat flour replaced by BCPP, respectively.

. Although the dry matter content of BIPP is higher than that of wheat flour, the results showed that the increasing proportion of BIPP determined a significant reduction in the dry matter content of the supplemented cookies as compared with the control. However, no significant difference in dry matter content was found for cookies supplemented with BCPP. The difference may be attributed to the higher water absorption capacity (WAC) of BIPP as compared with BCPP, as the moisture content of cookies depends on the moisture retention in the final baked products. Raczkowska et al. [67] also found no significant differences in the dry matter content of the shortbread cookies supplemented with blackcurrant pomace. Tarasevičienė et al. [27] found lower dry matter content in cookies supplemented with raspberry, red currant, and strawberry pomaces at 10% addition level as compared with the control cookies. Andrejko et al. [3] also reported an increase in the moisture content in oat cookies with 5% and 10% carrot and apple pomace additions.

The protein content was higher in wheat flour (11.9%) as compared with fruit pomace powders (8.13% and 6.77% in BIPP and BCPP, respectively). As a result, the protein content in supplemented cookies decreased as the BIPP and BCPP addition level increased. Other authors also attributed the decrease in protein content in cookies supplemented with fruit pomace powders to the difference in the protein content of wheat flour and fruit pomaces [3,14,27,68]. Protein levels between 6.28% and 6.86% were found in cookies in the present study, values close to those reported by Kausar et al. [6] in cookies supplemented with various levels of grapefruit pomace powder. Lower protein values, ranging between 5.20 and 3.30%, were found by Bhat et al. [20] in cookies supplemented with tomato pomace, while De Toledo et al. [14] reported between 8.13 and 8.94% protein levels in cookies made by replacing wheat flour with apple, melon, and pineapple by-products at 5, 10, and 15%.

The cookie fat content was found to be between 21.61 and 23.53% in the present study, in line with the results reported by Bhat et al. [20] in cookies supplemented with tomato pomace (21.70–21.80%) or Kausar et al. [6] (20.19–22.05%) in cookies made with various addition levels (0–15%) of carrot pomace powder. The fat content significantly (p < 0.05) increased with the rise in the BIPP and BCPP addition levels due to the higher fat content in fruit pomace powders (8.21% and 9.35%, respectively) compared to the wheat flour (1.42%).

Bilberry and blackcurrant by-products are richer in fiber and minerals as compared to the wheat flour; as a result, the incorporation of BIPP or BCPP resulted in improved fiber and mineral contents in cookies. Previous studies have also reported that the replacement of wheat flour with grape [24], pineapple [2], grapefruit [6], blueberry [1], or apple [18] pomace powders caused an increase in the fiber and mineral content of the cookies. While the decrease in protein and the increase in fat content represent negative changes in the nutritional profiles of cookies, the increase in the fiber and mineral content is beneficial from a nutritional perspective. More and more scientific evidence supports the important role of dietary fiber in gut motility, body weight, insulin sensitivity and metabolic health, gut microflora and metabolites, chronic inflammation, colorectal carcinoma prevention, and cardiovascular disease [69]. Moreover, fruit fibers are superior to those from cereals as they are associated with bioactive compounds and lower phytic acid contents [22].

3.3. Color Parameters, Titratable Acidity and pH

Color is one of the most important parameters in terms of visual quality evaluation and consumer acceptance. Effects of the incorporation of BIPP and BCPP on the color parameters of cookies are given in

Table 4. Effect of bilberry pomace powder addition on the color, physical parameters, titratable acidity, and pH of the cookies.

	CC	CBI2.5	CBI5.0	CBI10.0
L*	58.70 ± 0.66 a	31.35 ± 0.92 b	23.37 ± 1.23 c	19.49 ± 0.66 d
a*	7.65 ± 0.44 ab	7.97 ± 0.19 a	7.32 ± 0.35 c	3.06 ± 0.44 d
b*	20.41 ± 0.79 a	8.47 ± 0.55 b	3.48 ± 0.47 c	2.60 ± 0.22 d
C*	21.79 ± 0.89 a	9.02 ± 0.46 b	8.71 ± 0.22 b	7.77 ± 0.76 c
h*	69.46 ± 0.41 a	23.55 ± 3.02 b	19.94 ± 3.42 c	19.77 ± 3.27 c
∆E	-	32.17 ± 1.63 c	39.58 ± 1.49 b	42.89 ± 1.21 a
Weight (g)	11.95 ± 0.45 c	13.65 ± 0.69 b	14.63 ± 0.45 a	14.37 ± 0.78 a
Diameter (mm)	49.07 ± 1.28 b	51.12 ± 0.77 a	51.14 ± 0.94 a	51.63 ± 0.76 a
Thickness (mm)	8.48 ± 0.29 c	8.97 ± 0.43 b	9.44 ± 0.28 a	9.29 ± 0.46 ab
Spread ratio	5.79 ± 0.15 a	5.71 ± 0.28 a	5.42 ± 0.23 b	5.57 ± 0.30 ab
Titratable acidity (%, as citric acid)	0.04 ± 0.01 d	0.06 ± 0.01 c	0.09 ± 0.01 b	0.13 ± 0.01 a
pH	6.40 ± 0.08 a	6.20 ± 0.11 b	6.04 ± 0.06 b	4.99 ± 0.09 c

Different lowercase letters indicate significant differences between cookie formulations (p < 0.05); CC—control cookie; CBI2.5, CBI5.0, and CBI10.0—cookies with 2.5%, 5%, and 10% of the wheat flour replaced by BIPP, respectively.

and

Table 5. Effect of blackcurrant pomace powder addition on the color, physical parameters, titratable acidity, and pH of the cookies.

	CC	CBC2.5	CBC5.0	CBC10.0
L*	58.70 ± 0.66 a	47.57 ± 1.20 b	40.74 ± 0.57 c	35.09 ± 1.25 d
a*	7.65 ± 0.44 d	10.55 ± 0.28 c	12.19 ± 0.19 b	14.09 ± 0.29 a
b*	20.41 ± 0.79 a	19.37 ± 0.71 b	19.59 ± 0.42 ab	17.82 ± 0.81 c
C*	21.79 ± 0.89 c	22.06 ± 0.74 bc	23.08 ± 0.43 a	22.72 ± 0.74 ab
h*	69.46 ± 0.41 d	61.43 ± 0.45 c	58.11 ± 0.45 b	51.65 ± 1.11 a
∆E	-	11.63 ± 1.34 c	18.56 ± 0.61 b	24.61 ± 1.21 a
Weight (g)	11.95 ± 0.45 b	12.11 ± 0.71 b	12.46 ± 0.33 b	13.66 ± 1.08 a
Diameter (mm)	49.07 ± 1.28 c	49.93 ± 0.79 bc	50.47 ± 1.77 b	51.59 ± 0.72 a
Thickness (mm)	8.48 ± 0.29 b	8.34 ± 0.50 b	8.63 ± 0.36 b	9.43 ± 0.37 a
Spread ratio	5.79 ± 0.15 a	6.00 ± 0.35 a	5.86 ± 0.37 a	5.48 ± 0.18 b
Titratable acidity (%, as citric acid)	0.04 ± 0.01 d	0.06 ± 0.01 c	0.10 ± 0.01 b	0.15 ± 0.01 a
pH	6.40 ± 0.08 a	6.16 ± 0.08 b	5.77 ± 0.10 c	4.84 ± 0.05 d

Different lowercase letters indicate significant differences between cookie formulations (p < 0.05); CC—control cookie; CBC2.5, CBC5.0, and CBC10.0—cookies with 2.5%, 5%, and 10% of the wheat flour replaced by BCPP, respectively.

, respectively. The partial replacement of the wheat flour both with BIPP and BCPP significantly changed color. Both BIPP and BCPP darkened the color of cookies considering that the L* values significantly (p < 0.05) decreased as the substitution level increased.

The decrease rate of L* values was higher for BIPP than for BCPP due to the dark purple color of BIPP (Figure 1). A similar evolution of L* values has previously been reported in cookies supplemented with carrot [68], apple [3], pineapple, pear [11], or melon by-products [14]. A regular decrease in b* values with respect to the control was also recorded upon increasing the addition level of BIPP and BCPP, with a higher rate of the decrease for BIPP as compared with BCPP. Similarly, yellowness (b* values) decreased significantly in biscuits as compared to the control when apple pear powder [70] or pear pomace [11] were added at levels above 15%, but then increased in cookies fortified with apple by-products [3]. At a 10% BIPP replacement level, an intense dark but attractive purple color was imparted to the cookies. Šarić et al. [8] also reported that the addition of blueberry pomace in cookie formulation led to the decrease in b* values and attributed this evolution to the presence of blue anthocyanins. The addition of BCPP also exerted a positive influence on the color of cookies as the a* values increased progressively with the increasing addition levels, indicating a change in the color chromaticity towards red. At 5% and 10% BCPP substitution levels, the cookies turned a golden-brown color with a pink tint in the central section. Figure 1 presents the appearance of the BIPP, BCPP, control, and supplemented cookies, both at the surface and in the central section. A similar trend of increased redness (a* values) was previously recorded in cookies supplemented with apple [3,18,19] or pear pomace [11]. Lower L* values and higher a* values on the surface of cookies were also observed by Tańska et al. [71] after replacing 20% of white wheat flour with rosehip, rowanberry, and blackcurrant pomaces. The h* value of the control cookies (69.76) means that samples are close to the yellow tone. The addition of BCPP determined the decrease in this parameter; the h* values of the supplemented cookies were between 61.43 and 51.65, which means that as the level of substitution of wheat flour with BCPP increased, the samples slightly moved away from the yellow tone and closer to the red one. BIPP addition resulted in a strong decrease in the h* values as the substitution level increased.

The total color variations were in the ranges of 32.17–42.89 and 11.63–24.61 in BIPP- and BCPP-supplemented cookies, respectively. According to the international perception scale used to compare colors [72], ΔE values between 11 and 49 mean that the samples fit the attribute “colors more similar than opposite”, indicating that the supplemented cookies showed appreciable different colors for the human eye as compared with the controls.

The data on weight, thickness, diameter, and spread ratio of cookies are given also in Table 4 and Table 5. The cookie weight results provide information on the yield of cookies, directly related to the weight loss during baking. The weight of cookies significantly increased as a result of wheat flour replacement with BIPP or BCPP. A similar increase in the weight of cookies has been reported previously after the addition of beetroot [73] or apple [19] pomace powder, and this was attributed to the enhanced water holding capacity of pomace powders given by their rich fiber content. Weight variations were generally higher at higher replacement levels. Enrichment with BIPP resulted in higher weight increases as compared with BCPP, probably as a result of its higher fiber content. The diameter and thickness registered the same increasing trend as a result of wheat flour replacement.

The spread ratio had a decreasing trend as the level of wheat flour substitution increased; however, for BCPP, the decrease was significant (p < 0.05) only at a 10% replacement level. Other authors also found that by-product addition to the cookies reduced the spread ratio values and attributed this variation to the dilution of protein content and to the water absorption capacity of the fibers from the fruit by-products interfering with the formation of the gluten matrix [6,14,70,74]. Jose et al. [2] also reported on the decrease in the spread ratio as a result of wheat flour replacement with pineapple pomace powder in cookies and attributed this to the increase in dough viscosity as a result of the higher fiber content, which limited the cookie spread during baking.

Titratable acidity significantly increased while pH significantly decreased (p < 0.05) as a result of both BIPP and BCPP addition (Table 4 and Table 5). Titratable acidity was higher in cookies supplemented with BCPP as compared with those supplemented with the same level of BIPP due to the higher titratable acidity of BCPP as compared to BIPP. It is generally expected that a higher titratable acidity inhibits bacterial growth, thus increasing cookie shelf life. Moreover, a higher titratable acidity changes the taste and aroma of the cookies and influences the sensory acceptance of the consumers.

3.4. Dough Rheology

The evolution of the storage (G′) and loss (G″) moduli with frequency for the dough samples with different amounts of BIPP and BCPP addition are shown in Figure 2A,C. As may be seen, both moduli increased with the increase in frequency. The storage modulus was higher than the loss one, which indicates a solid-like behavior of all the dough samples [75].

The addition of BIPP and BCPP caused an increase in dough consistency, as may be seen from the increase in G′ and G″ values for the BIPP and BCPP wheat flour mixes as compared to the control sample. The increase is more prominent for the dough samples with high amounts of BIPP and BCPP addition than for those in which low amounts were incorporated. In the case of dough with low amounts of BCPP incorporation (2.5%), G′ and G″ evolution were similar to those of the control, probably due to a low gluten dilution effect. However, when high amounts of BIPP and BCPP were incorporated, the dough becomes more extensible and stiffer. This behavior may be attributed to the fiber content from BIPP and BCPP [35], especially the soluble ones, such as pectin, which act like a thickening agent, having the ability to form gels. According to Šarić et al. [22], the addition of fiber concentrates from blueberry in gluten-free cookies reinforced the dough structure and made the dough harder due to the restricted availability and mobility of water for other components from the dough system. The values of tan δ from Figure 2B,D were less than 1 for all the analyzed samples, indicating that the elastic part was more prominent than the viscous one [76]. Compared to the control dough, the dough samples with different addition levels of BIPP and BCPP presented lower values of tan δ, which indicates a firmer dough with an increasing elastic contribution at a higher frequency. A comparable decrease in the tan δ of the wheat dough as a result of the addition of berry pomace has been reported by other authors [56,77].

The variation in G′, G″, and tan δ with temperature for the dough samples with different BIPP and BCPP addition levels is shown in Figure 3A–D. As may be seen, the moduli values decreased as the temperature increased, leading to lower dough stiffness.

In the first phase, the increasing temperature weakens the protein structure, which denatures and loses its capacity to retain water. The presence of high amounts of lipids may cause incomplete gluten formation and a lack of continuity of the protein network from the dough system. This will lead to lower values of the dough elasticity and viscosity, as may be seen through a drop in the G′ and G″ values, caused by a reduction in the amount of water absorbed by the proteins [76]. Moreover, lipid molecules are absorbed on the surface of protein and starch granules, which may cause their hydrophobicity and a loss of their capacity to bind water, thus slowing down their hydration. The sugar present in the dough recipe leads to its fluidization due to the dehydration action exerted on the flour components. As the temperature increases, starch begins to gelatinize. The process is delayed by the small amount of water available in the dough when it has time to gel. Also, the ingredients present in the dough recipe, such as sucrose, compete for the available water in the dough and delay the swelling of the starch granule, leading to the prevention of viscosity development and gel formation [78].

The gelatinization process begins with a swelling of the starch granules. When the amount of available water is reduced, the gelatinization temperature increases. Moreover, if the amount of water is very low, not all starch granules will gelatinize, even at very high temperatures. Gelatinization manifests as an increase in consistency and viscosity with increasing dough temperature, which may be seen by an increase in G′ and G″ values after 70 °C. Generally, during heating with increasing BIPP and BCPP amounts in the dough recipe, the G′ and G″ moduli presented higher values, most likely due to the presence of the pomace fiber, especially pectin. It is well known that pectin is used as a thickening agent in food products, having the ability to jellify. It may also increase the dough viscosity by interaction with starches during heating. A comparable behavior of dough viscoelasticity has been reported by other authors [56,77] who incorporated dried blackcurrant pomace into their dough recipe. Tan δ increased as the amount of BIPP and BCPP increased, showing an increase in dough elasticity. All the dough samples presented a similar behavior. At the beginning of the heating period, tan δ increased; after which, it decreased; and, at the end of the heating period, it showed a slight upward increasing trend again. This increase in tan δ values may be due to the fact that the release of water by proteins does not coincide with the gelatinization process, and a significant decrease in dough viscosity is produced. Moreover, the presence of other ingredients such as lipids and sugars from the dough recipe maintain a continuous decrease in dough viscosity. Reaching optimal temperatures for the enzymatic degradation of starch maintains the trend of decreasing dough viscosity. After the thermal inactivation of the enzymes, the viscosity of the dough begins to increase slightly, which will lead to a drop in the tan δ values.

3.5. Dough Textural Properties

The results on the textural properties of the doughs made in the manufacturing of the control and supplemented cookies are presented in

Table 6. Effects of bilberry pomace powder addition on the textural properties of the dough.

	CC	CBI2.5	CBI5.0	CBI10.0
Hardness (N)	5.16 ± 0.56 b	5.15 ± 0.48 b	5.86 ± 0.24 a	6.40 ± 0.43 a
Adhesiveness (J)	−3.33 ± 0.70 bc	−2.42 ± 0.32 a	−3.14 ± 0.18 b	−3.92 ± 0.62 c
Resilience (dimensionless)	0.73 ± 0.04 b	0.81 ± 0.03 a	0.79 ± 0.03 a	0.80 ± 0.03 a
Stringiness (mm)	7.08 ± 0.37 b	8.33 ± 0.47 a	8.38 ± 0.23 a	8.76 ± 0.42 a
Stickiness (g)	−89.51 ± 2.50 b	−78.16 ± 3.29 a	−108.38 ± 2.93 c	−107.48 ± 2.22 c
Cohesiveness (dimensionless)	0.35 ± 0.03 a	0.34 ± 0.01 a	0.35 ± 0.02 a	0.29 ± 0.03 b
Chewiness (N)	1.80 ± 0.14 b	1.75 ± 0.10 b	2.07 ± 0.12 a	1.82 ± 0.05 b
Gumminess (N)	1.80 ± 0.14 b	1.75 ± 0.17 b	2.08 ± 0.13 a	1.82 ± 0.05 b

Different lowercase letters indicate significant differences between cookie formulations (p < 0.05); CC—control cookie; CBI2.5, CBI5.0, and CBI10.0—cookies with 2.5%, 5%, and 10% of the wheat flour replaced by BIPP, respectively.

and

Table 7. Effect of blackcurrant pomace powder addition on textural properties of the dough.

	CC	CBI2.5	CBI5.0	CBI10.0
Hardness (N)	5.16 ± 0.56 b	4.45 ± 0.50 c	5.78 ± 0.36 a	6.09 ± 0.31 a
Adhesiveness (J)	−3.33 ± 0.70 ab	−2.84 ± 0.22 a	−3.35 ± 0.41 ab	−3.54 ± 0.27 b
Resilience (dimensionless)	0.73 ± 0.04 a	0.74 ± 0.05 a	0.75 ± 0.05 a	0.73 ± 0.04 a
Stringiness (mm)	7.08 ± 0.37 b	7.76 ± 0.27 a	7.72 ± 0.28 a	7.84 ± 0.60 a
Stickiness (g)	−89.51 ± 2.06 b	−79.38 ± 2.38 a	−100.35 ± 3.57 c	−111.45 ± 2.76 d
Cohesiveness (dimensionless)	0.35 ± 0.05 a	0.33 ± 0.01 ab	0.31 ± 0.04 ab	0.29 ± 0.01 b
Chewiness (N)	1.80 ± 0.14 ab	1.48 ± 0.15 c	1.90 ± 0.16 a	1.69 ± 0.06 b
Gumminess (N)	1.80 ± 0.14 ab	1.48 ± 0.15 c	1.90 ± 0.16 a	1.69 ± 0.07 b

Different lowercase letters indicate significant differences between cookie formulations (p < 0.05); CC—control cookie; CBC2.5, CBC5.0, and CBC10.0—cookies with 2.5%, 5%, and 10% of the wheat flour replaced by BCPP, respectively.

. In good agreement with the results from the rheological analysis, the dough hardness increased as the level of berry pomace powder (both BIPP and BCPP) increased. The rise in hardness became significant (p < 0.05) above the 5% addition level. Previously, Petrović et al. [79] found that the replacement of wheat flour with sour cherry pomace extract encapsulated in soy proteins has led to a significant increase in the hardness of the dough. Dough hardness is strongly dependent on the moisture content in the dough and on the ability of the ingredients to bind water. As a result, the increase in hardness could be attributed to the ability of BIPP and BCPP to bind significant amounts of water. The increase in hardness was higher for BIPP supplementation than for BCPP, probably as a result of the higher water absorption capacity of BIPP as compared with BCPP, as presented above.

Stringiness could be considered as an index of the dough extensibility. In the present study, the stringiness increased as both the BIPP and BCPP addition levels increased. The results of the rheological analysis also showed that when high amounts of BIPP and BCPP were incorporated, the dough becomes more extensible. Almoumen et al. [80] also reported on the increase in hardness and stringiness with increased percentages of high-fiber dietary ingredients (i.e., date fruit pomace) in dough, and they attributed this evolution to the high water absorption by the fiber and the formation of a denser dough structure. In contrast with these results, Boz and Karaoğlu [81] reported on a decrease in the adhesion and stringiness of wheat dough upon rosehip addition.

3.6. Texture Properties of Cookies

The textural properties, especially the hardness of cookies, are critical factors affecting their palatability. Generally, a lesser hardness, leading to softer eating characteristics, is desirable in cookies [11]. The effect of replacing wheat flour with BIPP or BCPP on the textural properties of cookies is given in

Table 8. Effect of bilberry pomace powder addition on the textural properties of the cookies.

	CC	CBI2.5	CBI5.0	CBI10.0
Hardness (N)	72.75 ± 1.09 a	64.71 ± 0.45 b	61.74 ± 1.55 c	59.88 ± 0.31 d
Springiness (mm)	0.97 ± 0.02 a	0.97 ± 0.01 a	0.98 ± 0.01 a	0.98 ± 0.01 a
Cohesiveness (dimensionless)	0.77 ± 0.01 a	0.77 ± 0.01 a	0.77 ± 0.01 a	0.67 ± 0.06 b
Chewiness (N)	53.93 ± 0.81 a	40.65 ± 0.52 c	46.50 ± 0.93 b	39.14 ± 0.67 c
Gumminess (N)	55.72 ± 0.94 a	41.91 ± 0.52 c	47.67 ± 0.82 b	40.01 ± 1.24 d
Fracturability (mm)	0.85 ± 0.03 d	3.53 ± 0.11 c	3.80 ± 0.07 b	3.97 ± 0.14 a
Puncturing force (N)	16.84 ± 0.83 a	9.99 ± 0.18 c	11.44 ± 0.44 b	12.24 ± 0.33 b
Shear force (N)	73.97 ± 3.13 a	57.81 ± 3.53 c	63.65 ± 1.33 b	66.85 ± 0.78 b

Different lowercase letters indicate significant differences between cookie formulations (p < 0.05); CC—control cookie; CBI2.5, CBI5.0, and CBI10.0—cookies with 2.5%, 5%, and 10% of the wheat flour replaced by BIPP, respectively.

and

Table 9. Effect of blackcurrant pomace powder addition on the textural properties of the cookies.

	CC	CBC2.5	CBC5.0	CBC10.0
Hardness (N)	72.75 ± 1.09 a	63.89 ± 0.46 b	58.02 ± 0.72 c	54.73 ± 0.67 d
Springiness (mm)	0.97 ± 0.02 b	0.97 ± 0.01 b	0.98 ± 0.01 b	1.00 ± 0.00 a
Cohesiveness (dimensionless)	0.77 ± 0.01 a	0.77 ± 0.01 a	0.63 ± 0.01 b	0.58 ± 0.04 c
Chewiness (N)	53.93 ± 0.81 a	45.94 ± 0.56 b	34.55 ± 0.94 c	32.22 ± 0.84 d
Gumminess (N)	55.72 ± 0.94 a	49.19 ± 0.77 b	36.43 ± 0.41 c	31.74 ± 0.72 d
Fracturability (mm)	0.85 ± 0.03 c	0.89 ± 0.03 c	1.71 ± 0.17 b	2.84 ± 0.05 a
Puncturing force (N)	16.84 ± 0.83 a	13.90 ± 0.24 b	14.19 ± 0.13 b	14.70 ± 0.18 b
Shear force (N)	73.97 ± 3.13 a	65.84 ± 0.76 b	64.21 ± 0.35 bc	62.67 ± 0.50 c

Different lowercase letters indicate significant differences between cookie formulations (p < 0.05); CC—control cookie; CBC2.5, CBC5.0, and CBC10.0—cookies with 2.5%, 5%, and 10% of the wheat flour replaced by BCPP, respectively.

. The addition of both BIPP and BCPP significantly (p < 0.05) decreased the hardness of cookies compared with the controls. The cookies made with a 10% replacement level showed the lowest hardness. Hardness values were lower in BIPP-supplemented cookies as compared with those supplemented with BCPP: Similar results have been reported by Ahmad et al. [68] for cookies enriched with carrot pomace powder and by Andrejko et al. [3] for cookies supplemented with carrot and apple pomace. Krajewska and Dziki [11] also reported that the hardness of biscuits fortified with pear pomace powder decreased as the pear pomace addition level increased. Naseem et al. [19] found that the hardness decreased in cookies supplemented with apple pomace as compared to the control and attributed this evolution to the high fiber content in apple pomace, possessing higher water holding capacity than wheat flour, which diminishes the water available for gluten development and thus leads to the development of a weaker gluten network.

In contrast, the addition of grape [24] or grapefruit [6] pomace was found to increase the hardness of the cookies. The decrease in hardness has been attributed to the increase in the dietary fiber content, which may disrupt the gluten network structure, resulting in a softer texture, and may act similarly to an emulsifier, promoting a more uniform distribution of fat and other ingredients within the dough, thus leading to a more homogeneous texture and reduced hardness in cookies [11,82]. On the contrary, the increase in hardness reported in other studies has been attributed to the decrease in the protein content in the batter, resulting in a reduction in aeration and the development of a dense structure, as well as to the insoluble fiber content which may increase starch viscosity and delay the short-term retrogradation of starch [83].

The springiness slightly increased as a result of berry pomace addition, but the increase was statistically significant only in cookies made with 10% BCPP; Andrejko et al. [3] also noticed a slight increase in elasticity in cookies supplemented with carrot and apple pomace, but the changes were significant only for the samples containing 5% apple pomace and 5 or 10% carrot pomace.

The cohesiveness and chewiness of the cookies were found to decrease as a result of berry pomace addition. Previously, the studies conducted have shown that the chewiness values did not change significantly after introducing the carrot pomace to the cookie recipe, but the addition of 5% apple pomace resulted in a significant increase in chewiness and no significant changes in cohesiveness [3]. Cohesiveness was described as the strength of the internal bonds holding the product together, while chewiness was defined as the amount of force needed by the consumer during chewing to prepare a bite of food for swallowing. As cookies are usually perceived as fragile products, decreasing the chewiness and hardness of cookies may be positively perceived by consumers.

Fracturability represents the amount (in millimeters) that a cookie sample deforms until it breaks when it is compressed and defines the resistance of the cookie to bend, or its fragility [84]. Fracturability was evaluated by measuring the distance between the probe and the break interface. A sample that breaks at a shorter distance is less compressible and more breakable, so it has higher fracturability [85]. The fracturability values significantly increased with increasing levels of BIPP or BCPP addition, meaning that the control sample showed lower resistance to fracture than the supplemented cookies, with the addition leading to cookies that are softer. The decrease in hardness and the increase in fracturability values could be attributed to the dilution of gluten protein and the increase in the fiber content in the formulation.

3.7. Total Phenolic Content and DPPH Radical Scavenging Activity

The total phenolic content and DPPH radical scavenging activity of the control and BIPP- and BCPP-supplemented cookies are illustrated in

Table 10. Effect of bilberry pomace powder addition on the total phenolic content and DPPH radical scavenging activity of the cookies.

	CC	CBI2.5	CBI5.0	CBI10.0
Total phenolic content (mg GAE/100 g)	30.36 ± 1.67 d	94.73 ± 1.88 c	132.00 ± 3.31 b	214.73 ± 6.11 a
DPPH radical scavenging activity (mmol Trolox/100 g)	0.11 ± 0.01 d	0.44 ± 0.02 c	0.74 ± 0.03 b	1.26 ± 0.05 a

Different lowercase letters indicate significant differences between cookie formulations (p < 0.05); CC—control cookie; CBI2.5, CBI5.0, and CBI10.0—cookies with 2.5%, 5%, and 10% of the wheat flour replaced by BIPP, respectively.

and

Table 11. Effect of blackcurrant pomace powder addition on the total phenolic content and DPPH radical scavenging activity of the cookies.

	CC	CBC2.5	CBC5.0	CBC10.0
Total phenolic content (mg GAE/100 g)	30.36 ± 1.67 d	46.64 ± 1.34 c	65.16 ± 1.55 b	90.18 ± 2.13 a
DPPH radical scavenging activity (mmol Trolox/100 g)	0.11 ± 0.01 d	0.17 ± 0.01 c	0.24 ± 0.01 b	0.38 ± 0.02 a

Different lowercase letters indicate significant differences between cookie formulations (p < 0.05); CC—control cookie; CBC2.5, CBC5.0, and CBC10.0—cookies with 2.5%, 5%, and 10% of the wheat flour replaced by BCPP, respectively.

, respectively. A significant (p < 0.05) progressive increase in the total phenolic content with the increase in the wheat flour replacement level was found both for BIPP and BCPP, along with an increase in radical scavenging activity in cookies. The phenolic content in bilberry pomace powder was very high (around 3.6 g GAE/100 g), primarily due to the high anthocyanin content. The highest replacement level of wheat flour with BIPP (10%) led to a seven-fold increase in the total phenolic content of the cookies, reaching 214.73 mg GAE/100 g, while leading only to a three-fold increase in the total phenolic content when replacing 10% wheat flour with BCPP. The differences could be attributed to the higher phenolic content and antioxidant potential of bilberry as compared with blackcurrant [36]. The antioxidant capacity determined with the DPPH radical was lowest in the control cookies. The increase in pomace powder content led to a strong increase in the DPPH radical scavenging activity, up to 1.26 mmol Trolox/100 g in cookies with a 10% BIPP replacement level. Similar increasing trends of the total phenolic content and antioxidant activity have been reported previously in cookies developed by adding pomace from grape [24,86], grapefruit [6], apple [16,18,19,70], and pear [11].

Šarić et al. [8] also reported that raspberry and blueberry pomace powders increased the bioactive contents and antioxidant capacity of gluten-free cookies, with a total phenolic content six-fold higher in cookies containing blueberry pomace as compared with those made with raspberry pomace.

3.8. Sensory Properties

Results on the sensory analysis of the control and supplemented cookies are given in Figure 4A,B. The replacement of 2.5% of the wheat flour with BIPP resulted in a decrease in the average appearance score as compared with the control, while 5% and 10% replacement levels resulted in a significant increase in it. However, for BCPP supplementation, the appearance score showed an increasing trend as the replacement level increased. The highest appearance score was recorded by the BC10.0 sample. In terms of color, 2.5% BIPP replacement negatively affected cookies’ color scores; however, at 5% and, especially, 10% BIPP replacement levels, the color of cookies turned purple, both on the surface and in the central section, which was positively appreciated by the panelists. However, distinct from the purple color of the middle section, the color of the surface was brownish-purple due to the formation of brown compounds as products of the Maillard reaction occurring between the proteins and reducing sugars in the baking process. Regarding the BCPP supplementation, the cookies turned increasingly brownish as the BCPP replacement level increased, which was also appreciated by the panelists.

The cookie flavor was increasingly appreciated as the BIPP addition level increased due to the intensification of the bilberry aroma. As a result, CBI10.0 samples received the highest average score for flavor. A similar tendency was recorded for taste as the bilberry taste intensified with increasing BIPP addition. The acidity increased as well, and this was appreciated by the panelists. The scores for taste also increased in BCPP-supplemented cookies as compared with the controls due to the specific fruity taste and acidity imparted by BCPP. In a previous study, the grape flavor was indicated by the panelists in cookies supplemented with grape pomace. However, owing to a bitter taste, the overall acceptance of the cookies reduced as the grape pomace percentage increased above 6% [26].

The scores for texture also increased as the level of both BIPP and BCPP increased since the cookies became less hard and less sticky. These results comply with the instrumental data for hardness, cohesiveness, and fracturability, indicating that consumers tend to better evaluate softer and less sticky cookies. Regarding general acceptability, the formulations with 10% wheat flour replacement by pomace powders, both BIPP and BCPP, were the best graded. Ahmad et al. [68] found the highest texture scores for cookies made from wheat flour and 10% carrot pomace powder, attributing this to the reduction in the hardness of the cookies. The general acceptability score for CBC10.0 was higher than that for CBI10.0; however, no significant differences were found between them. Similarly increasing scores for appearance, texture, flavor, color, and overall acceptability have previously been found in cookies supplemented with carrot [68], apple [19], pear [11], or strawberry [27] pomace at levels below 20%. In contrast, other studies have reported that the substitution of wheat flour with pomace powders from avocado, kiwifruit, pineapple, pomegranate [13], or grapefruit [6] at a 10–20% level lowered the ratings of the cookies as compared to the control. De Toledo et al. [14] related the low scores for texture, flavor, and global impression obtained in the sensory analysis for the cookies supplemented with 15% melon by-products to the slight bitterness and acidity from the melon peels, occurring as a result of their high polyphenol content.

The relationships between the sensory and physicochemical characteristics of cookie samples were examined by principal component analysis (PCA), and the results are shown in Figure 5.

The two axes PC1 and PC2 show 44.84% and 30.22% total variance. As may be seen, the PC1 axis distinguished the cookie samples with BIPP and BCPP addition in their recipe, indicating that these samples present large differences among each other. All the samples with BCPP addition are positioned at the bottom of the PCA graph, whereas the samples with BIPP addition are at the top of the PCA graph. The second axis (PC2) shows a close association (p < 0.05) between the control sample and the cookie samples with low addition levels of BIPP and BCPP (2.5%). The sensory characteristics are more closely related to the cookie samples with the highest amounts of BIPP and BCPP addition in their recipe (10%). The total phenolic content and DPPH radical scavenging activity are related to the cookie samples with 5% and 10% BIPP additions in their recipe, whereas the cookie samples with 2.5% BIPP are more closely related with the textural characteristics of the cookie.

4. Conclusions

Bilberry and blackcurrant pomace are plentiful sources of antioxidants, such as anthocyanins and other phenolic compounds, fiber, and minerals, displaying huge potential as a functional ingredient in cookies. The incorporation of BIPP and BCPP in wheat flour resulted in cookies with lower protein but higher fat, fiber, and mineral contents as compared with the controls. Higher weight, diameter, and thickness and a lower spread ratio were found in supplemented cookies. The results on dough rheology indicated an increase in dough hardness, consistency, and stiffness as a result of berry pomace powder incorporation. These changes have been attributed to the dilution of gluten and the increased fiber content interfering with the formation of the gluten matrix in supplemented cookies. The hardness, cohesiveness, and chewiness of the cookies were found to decrease as a result of berry pomace addition. The partial replacement of wheat flour with bilberry and blackcurrant pomace powders led to cookies with enhanced acidity, fruity flavors, and attractive colors, especially at the 10% level. In addition, a progressive increase in the total phenolic content and antioxidant activity was recorded in supplemented cookies with increasing pomace addition levels. This study demonstrated that bilberry and blackcurrant pomace powders could be a sustainable ingredient for producing cookies with improved bioactive, textural, and sensory properties, thus providing more diversity in cookie choices to consumers.