Composition and Physicochemical Properties of Pomace of Various Cultivars of Blackberry (Rubus fruticosus L.)

Abstract

The objective of this study is to assess the proximate chemical composition, and the physical and techno-functional properties of blackberry pomace from different cultivars (‘Polar’, ‘Orkan’, ‘Brzezina’). Blackberry pomace primarily comprises seeds and other parts, such as pulps/skins. It serves as a rich source of bioactive compounds, particularly anthocyanins, and demonstrates notable functional properties, including water holding capacity, oil holding capacity, swelling capacity, and various fiber fractions. Moreover, anthocyanin-rich fruits are interesting due to their health-promoting properties and intensive color. Total anthocyanin content (TAC) ranged from 113.82 mg 100 g⁻¹ d.w. to 129.58 mg 100 g⁻¹ d.w. in blackberry pomace. Fiber fractions, including ADF, NDF, lignin, and WSCs, exhibited significant variations among the different blackberry pomace cultivars as well as color.

1. Introduction

The World Health Organization (2018) for the overall health improvement and reduction of some diseases recommends consuming more than 400 g/day of fruits and vegetables [1]. Berries are delicious, most of them have low calories and are consumed fresh; therefore, they are a good source of bioactive compounds. Bioactive compounds present in the berries in different quantities, but the most amount contain such families as Rosaceae (strawberry, raspberry, blackberry) and Ericaceae (blueberry, cranberry) [2].

Rubus fruticosus belongs to the Rubus genus, which belongs to the family Rosaceae, and is a shrub distributed through Europe, Asia, Oceania, North, and South America [3].

Blackberries contain sufficient amounts of minerals, amino acids, vitamins, and carbohydrates as well as fixed and essential oils, tocopherols, sterols, and polyphenols. It is an important source of ellagic acid, ellagitannins, unsaturated fatty acids, and dietary fiber [3]. The profile and content of these compounds depend on the blackberry variety, meteorological conditions, agronomical practices, and maturity [3]. According to the literature [3], blackberries have 0.49 g of fat, 1.39 g of protein, 5.3 g of dietary fiber, and 0.41 g of ash content in 100 g of their fresh weight. Martins et al. [4] determined that R. fruticosus fruits have 610 mg 100 g of α-tocopherol, 128.0 µg 100 g of β-carotene, and 118.0 µg 100 g of lutein + zeaxanthin. Anthocyanins are red, blue, and sometimes purple pigments, found in different plants, such as vegetables, flowers, and fruits, especially berries. Also, the colored pigments of anthocyanins from berries are strong antioxidants and, moreover, can be used as natural dyes and food colorant, because of their intensive color [5]. The major anthocyanin in blackberries is cyanidin 3-glucoside, which accounts for about 44–95% of the total, the ratios of subsequent anthocyanins vary with cultivar and genotype [6,7]. Blackberries are rich in anthocyanins, but these compounds are very unstable, anthocyanins have low stability in light, temperature, oxygen, pH, enzymes, and other conditions. However, anthocyanins are the most important flavonoids of blackberries, responsible for the color of the fruit and its high antioxidant capacity [8]. The amount of anthocyanins in blackberries reaches 1004.90 mg 100 g⁻¹ DW cyanidin-3-glucoside [9]. According to Pantelidis et al. [10], the number of anthocyanins in blackberries, depending on cultivar, fluctuates from 125.6 to 152.2 mg cyanidin-3-glucoside equivalents 100 g⁻¹ fresh weight, while a total amount of phenols from 1703 to 2349 mg GAE 100 g⁻¹ dry weight [10].

Due to the high content of bioactive compounds, blackberries are proposed as a potential preventive measure against inflammation, cardiovascular diseases, and cancer [11]. Recent studies have demonstrated that blackberry juice stimulated the growth of beneficial Lactobacillus strains [12,13,14]. Moreover, blackberry extract has shown virucidal activity and inhibited the early stages of herpes simplex virus type 1 [13]. Phenolic compounds of blackberry fruits and extracts have been attributed to antioxidant, anti-inflammatory, antidiabetic, and antimicrobial activities. These compounds play a crucial role in preventing oxidative stress and mitigating the risk of diseases such as coronary heart disease and stroke [15].

Blackberries are consumed fresh or are processed as jams, jellies, syrups, juices, wines, beer, desserts, beverage concentrates, sauces, pigments for the food industry, etc. [3]. During the production of juices and other products, industry generates a large amount of waste which consists of pulp, peel, and seeds [16], collectively called pomace, and blackberries’ pomace represents 20% of the total fruit. Blackberry seeds contain oil (fatty acids and other compounds), which is a lipophilic fraction, and the other parts, such as skins and pulp, are rich in polyphenolic antioxidants, antimicrobial agents, and pigments, which makes it a hydrophilic fraction of pomace [17]. Berry pomace is a valuable but little-used by-product of juice production. When processed into a stable fruit powder, the composition is different from the composition of the entire fruit [18].

Growing concerns about food loss, food waste, and related environmental problems have prompted recent actions to reduce and reuse food processing waste. These actions are expected to have an impact on the four Food 2030 priorities: nutrition, climate, circularity, and communities [19].

The generation of food waste is a great concern from social, economic, and environmental points of view. Byproducts and production line waste is the main fruit and vegetable processing waste; therefore, as the economic model changes from linear to circular and food systems become more sustainable, these byproducts are recycled and returned to food chains [20,21]. The valorization of pomace into new reusable products can mitigate environmental problems. Recycling the pomace also reduces the amounts of waste, and thus conserves natural resources [22]. Nowadays, the combined interest in a cleaner environment and a healthier life has led to the development of functionalized materials in many areas [23].

Waste generated after the processing of fruits is a promising source of valuable bioactive compounds. In recent years, researchers have established that pomace is a valuable source of nutrients such as phenolic compounds, pigments, dietary fibers, essential oils, enzymes, vitamins, and fatty acids [2,24,25], and pomace is no longer seen as a waste and can be used as potential dietary additive and natural colorant, nutritional value food supplement or functional ingredient in different food matrices [26,27]. The physicochemical properties of blackberry pomace play a pivotal role in influencing the texture and stability of food products [28]. Furthermore, blackberry pomace, being a rich source of dietary fiber, holds significant importance in human health. Studies have indicated its notable association with the reduction in cholesterol levels and the modification of glycemic reactions [29,30]. Blackberry pomace is a rich source of antioxidants and dietary fiber. Dietary fiber consists of different fractions: cellulose, hemicelluloses, lignins, pectins, and others. Dietary fiber is used for its nutritional, functional and technological properties [31].

The objective of this investigation is to determine the compositional and techno-functional attributes of distinct cultivars (‘Polar’, ‘Orkan’, ‘Brzezina’) of blackberry pomace.

2. Materials and Methods

2.1. Blackberry Pomace Sample Preparation

The blackberries of cultivars ‘Polar’, ‘Orkan’, and ‘Brzezina’ were acquired from a farmer in the Joniškis region (56.30219045284591, 23.603429519328024) in Lithuania in 2023 and juice was extracted using a Stollar Commercial juicer (Riga, Latvia). The pomace was freeze-dried in a lyophilizer ZIRBUS (Bad Grund (Harz), Germany) at −55 °C degrees, for 48 h. Freeze-dried blackberry pomace was ground using a food mill (Model Retsch ZM200, Haan, Germany) to 0.2 mm particle size and stored in hermetic bags at −38 °C degrees for 8 weeks until the analyses (Figure 1).

2.2. Chemicals and Reference Substances

Agricultural-origin ethanol used for extraction was of analytical grade and obtained from the MV group (Kaunas, Lithuania). Demineralized water was sourced from a Milli-Q–Q system (Merck KGaA, Darmstadt, Germany). Hydrogen chloride, petroleum ether, sulfuric acid, sodium hydroxide, sodium sulfite, cetyltrimethylammonium bromide, and Anthrone reagent were obtained from Sigma-Aldrich (Steinheim, Germany).

2.3. Approximate Composition of Blackberry Pomace

The dry matter content of blackberry pomace was determined by drying the sample at 105 °C to constant mass [32]. The ash content was assessed using a muffle furnace at 550 °C for 4 h [33]. Protein content was analyzed according to the Kjeldahl procedure [34], while the fat content was determined using the Randall extraction method [35]. Total fiber content was determined following international standards according to the enzymatic–gravimetric method [36]. All results are expressed as the mass percentage of dry matter.

2.4. Determination of Dietary Fiber Fractions

Blackberry pomace samples were analyzed for acid detergent fiber (ADF comprising cellulose and lignin), neutral detergent fiber (NDF), cellulose, hemicellulose, and lignin using the fractionation method [37]. ADF extraction was carried out with an ANKOM220 Fibre Analyser (ANKOM Technology 2052 O’Neil Road, Macedon, NY) using F57 filter bags (25 μm). The Van Soest analysis method [38], widely recognized as the predominant fiber fractionation system, was employed [38]. NDF analysis was conducted using sodium sulfite, and the results are reported on an ash-free basis. The concentration of water-soluble carbohydrates (WSCs) in the water extracts of the dried samples was determined photocolorimetrically using the Anthrone reagent [39,40].

2.5. Determination of Total Anthocyanin Content (TAC)

The total anthocyanin content was determined using the pH differential method. The extraction of anthocyanins was performed according to Urbonaviciene et al. (2022) [41]. Briefly, one gram of freeze-dried blackberry pomace powder was extracted with 40 mL of aqueous ethanol (70%) and 0.5% HCl ratio 85:15. Extracts were left in the dark for 24 h at 22 °C, then filtered using Whatman paper (retention 8–12 µm). The blackberry pomace extract was mixed with 0.025 M potassium chloride solution and 0.4 M sodium–acetate solution to adjust, respectively, pH to 1 and pH to 4. Cyanidin-3-glucoside (449.2 g/mol) was used as a standard, with a molar absorptivity coefficient of 26,900 (L mol^–1 cm^–1). The sample mixtures were serially measured at λ = 520 and λ = 700 nm wavelengths [6]. Results are expressed as mg 100 g⁻¹ of dry matter.

2.6. Color Parameters of Blackberry Pomace

The color was detected using the Color Flex spectrophotometer (Hunter Associates Laboratory Inc., Sunset Hills Road, Reston, Vt, USA) and recorded in L*, a*, and b* CIE coordinates. The L* (lightness) value ranges from 0 = black to 100 = white, the a* (redness) ranges from green (negative) to red (positive), and the b* (yellowness) values are blue (negative) to yellow (positive). Hue angle (h°) and chroma (C) were also calculated. The spectrophotometer was calibrated with a standard white and black reflective plate [42]. Hue angle (h°) and chroma (C) were calculated using the formulas:

h° = tan⁻¹(b*/a*);

$$\mathrm{C}=\sqrt{({\mathrm{a}}^{\mathrm{*}}{)}^2+{\left({\mathrm{b}}^{\mathrm{*}}\right)}^2}$$

2.7. Determination of Techno-Functional Properties of Blackberry Pomace

2.7.1. Pomace Seed Content

The determination procedure of pomace seed content is described by Reißner et al. (2019) [18]. Frieze-dried pomace was ground for 1 min in a food mill (Model Retsch ZM200, Haan, Germany). The seeds were separated using a 2 mm sieve, weighed, and expressed as a fraction of whole dried pomace.

2.7.2. The Water Holding Capacity (WHC), Swelling Capacity (SC), and Oil Holding Capacity (OHC)

The water holding capacity (WHC), swelling capacity (SC), and oil holding capacity (OHC) of the blackberry pomace were determined following the procedures described by Jurevičiūtė et al. (2022) [28] with slight modifications. For WHC determination, 0.5 g of blackberry pomace was mixed with 10 mL of deionized water and hydrated at 21 °C temperature for 24 h. The samples were centrifuged at 2000 RPM for 20 min (Clinispin Horizon, 755 VES, Drucker Diagnostics Manufacturing, Shady Lane, Philipsburg, PA, USA) and the supernatants were carefully removed. The weight of the residue after hydration was recorded and the WHC was calculated as follows:

WHC (g/g) = (m₂ − m₁)/m₁

where m₁ is the dry sample mass (g) before hydration and m₂ is the sample mass (g) after hydration.

To determine the swelling capacity (SC), 0.2 g of each berry pomace was weighed in a measuring tube with 0.1 mL gradations, and the initial volume (mL) of the samples was measured. Next, the samples were mixed with 5 mL of distilled water and maintained at 21 °C for 24 h. The samples were then centrifuged at 2000 RPM for 20 min (Clinispin Horizon, 755 VES, USA) and the supernatants were removed. The volumes (mL) of the hydrated samples were recorded and the SC was calculated as follows:

SC (mL/g) = (V₂ − V₁)/m

where V₁ is the sample volume before hydration (mL), V₂ is the volume after hydration (mL), and m is the initial weight of the sample (g).

To determine the oil holding capacity (OHC), 1 g of berry pomace was mixed with 20 mL of sunflower oil in a centrifuge tube and was incubated at 37 °C for 1 h. After incubation, the samples were centrifuged at 2000 RPM for 15 min (Clinispin Horizon, 755 VES, USA) and the supernatants were removed. The weight of the berry pomaces was recorded after incubation with the oil, and the OHC was calculated as follows:

OHC (g/g) = (m₂ − m₁)/m₁

where m₁ is the weight of the sample (g) before incubation with the oil and m₂ is the weight of the sample (g) after incubation with the oil.

2.8. Statistical Methods

The data obtained from three replications were analyzed via the one-way analysis of variance (ANOVA) using Statistica software (Statistica 12; StatSoft, Inc., Tulsa, OK, USA). Differences among the means were compared using Fisher’s post hoc test at a significance level of 0.05. Pearson’s correlation coefficient was calculated to determine the relationship between the variables at a significance level of 0.05.

3. Results and Discussion

The results for the proximate composition of blackberry pomace are presented in

Table 1. Proximate composition, fiber fractions and total anthocyanins content of blackberry pomace, d.w.

Composition/Blackberry Cultivar	‘Polar’	‘Orkan’	‘Brzezina’
Dry matter	97.92 ± 0.03 a	97.80 ± 0.03 a	97.14 ± 0.01 b
Protein	9.25 ± 0.02 a	7.26 ± 0.15 c	8.58 ± 0.45 b
Fat	12.25 ± 0.10 a	10.09 ± 0.40 b	9.97 ± 0.25 b
Ash	2.55 ± 0.08 a	3.97 ± 1.71 a	2.49 ± 0.07 a
ADF	35.32 ± 0.51 ab	34.35 ± 0.84 b	36.05 ± 0.69 a
NDF	43.25 ± 0.55 a	38.22 ± 0.35 b	37.57 ± 1.38 b
Lignin	16.57 ± 1.34 a	16.80 ± 0.09 a	16.73 ± 0.4 a
WSCs	36.33 ± 0.37 a	36.24 ± 0.08 a	36.22 ± 0.96 a
Cellulose	18.75 ± 0.83 ab	17.55 ± 0.93 b	19.31 ± 0.64 a
Hemicellulose	7.94 ± 1.06 a	3.87 ± 0.48 b	1.52 ± 0.69 c
Total anthocyanins, mg 100 g−1	115.62 b	129.58 a	113.82 c

Data expressed as means ± standard deviation. Different letters in the rows indicate significant differences between the mean values (p ≤ 0.05). ADF—acid detergent fiber; NDF—neutral detergent fiber; WSCs—water-soluble carbohydrates.

.

The research data reveal significant variations in the main chemical content parameters of blackberry pomace among different cultivars. The ‘Polar’ cultivar exhibited the highest amount of protein (9.25%) and fat (12.25%). The ‘Brzezina’ cultivar pomace displayed statistically significant the lowest amount of dry matter (97.14%), fat (9.97%), and hemicellulose (1.52%). According to Blejan et al. [24], blackberry pomace exhibited 90.33% of dry matter, 7.32 g 100 g⁻¹ d.w. of protein, 9.67 g 100 g⁻¹ d.w. of fat, 44.87 g 100 g⁻¹ d.w. of fiber content, and 1.59 g 100 g⁻¹ d.w. of ash content. Other researchers reported that blackberry pomace has 95.5% dry matter, 10.8% protein, 10.80% fat, 1.70% ash, and 60.30% fiber [43]. Pasquel-Reátegui et al. [44] found that the fat content in blackberry pomace (11.32%) aligned with our results, whereas the ash content (1.62%) was slightly lower than our findings. Seeds are the main source of lipophilic components in blackberry pomace; therefore, the fat content in pomace is high and ash content is also a consequence of the higher seed content. Pomace can contain a higher protein content than the whole fruit due to its elevated seed content [24]. A significant correlation was observed between the seeds and ash content (r = 0.738, p ≤ 0.05) (Table 1 and

Table 2. Physicochemical properties of blackberry pomace.

Blackberry Cultivar	Seed Content, %	Water Holding Capacity (g/g)	Swelling Capacity (mL/g)	Oil Holding Capacity (g/g)
‘Orkan’	48.97 ± 0.9 a	1.14 ± 0.2 b	1.85 ± 0.2 b	0.98 ± 0.1 c
‘Brzezina’	40.61 ± 0.7 b	1.26 ± 0.1 a	1.13 ± 0.6 c	1.12 ± 0.1 b
‘Polar’	38.50 ± 0.6 c	1.13 ± 0.2 b	2.27 ± 0.5 a	1.26 ± 0.04 a

Data expressed as means ± standard deviation. Different letters in the columns indicate significant differences between the mean values (p ≤ 0.05).

). Our findings do not show any relationships between the number of seeds and the higher content of proteins or fats in blackberry pomace (Table 1 and Table 2). Blackberry pomace is rich in dietary fiber because it consists of peels and seeds. There are no significant differences of blackberry pomace lignin and WSCs, and all other dietary fiber fractions in various blackberry cultivars pomace differed significantly. The ‘Brzezina’ cultivar pomace exhibited the highest amount of acid detergent fiber (ADF) at 36.05%, and cellulose exhibited it at 19.31%, while the ‘Polar’ cultivar had the highest neutral detergent fiber (NDF) content at 43.25% and hemicellulose at 7.94%. Additionally, the ‘Orkan’ cultivar pomace showed the highest levels of lignin (16.80%) and water-soluble carbohydrates (WSCs) (36.24%). In comparison, previous research reported that raspberry pomace had similar WSCs and lignin content, respectively, 38.13% and 18.85% [45]. Our findings, however, indicated lower values than those reported by another study, where WSCs were found to be 44.26% in blackberry residue fibers [30]. Mainly, fiber content can vary due to the differences in the variety, cultivation, ripeness, and processing conditions of the berry pomace [28]. After evaluating blackberry pomace functional properties, we can say that fiber from pomace can be used as a potential source of fiber additives to enrich food products.

Blackberries are abundant in anthocyanins, a group of natural pigments belonging to the flavonoid family. These natural water-soluble compounds are widely distributed in fruits and berries including blackberries [26]. Numerous studies not only highlight the potential health benefits of anthocyanins but also indicate their significance in various industries, as natural colorants, providing blue, red, and purple colors [46]. Pomace is one of the sources of natural dyes that can be used not only directly for food pigmentation but also as indicators and sensors of freshness applied for intelligent packaging [47]. The use of natural colorants can be a safe solution for humans and the environment. Total anthocyanins content (TAC) depending on the blackberry cultivar differed in pomace by 15.76 mg 100 g⁻¹ d.w.

Research data indicated that the total anthocyanins content (TAC) in ‘Orkan’ cultivar blackberry pomace was 15.76 and 13.96 mg 100 g⁻¹ d.w. higher than in ‘Brzezina’ and ‘Polar’, respectively. According to the literature, a similar amount of TAC was observed in ‘Chester Thornless’ and ‘Thornless’ blackberry cultivars pomace, respectively, 134.6 and 146.8 mg 100 g⁻¹ [10]. Other researchers present that TAC content varies in the blackberry pomace depending on the growing year. Total anthocyanin content in the ‘Polar’ cultivar blackberry pomace in 2012 and 2013 differed by 1.68. In 2012, it was 135.59 mg 100 g⁻¹, and in 2013, it was 80.77 mg 100 g⁻¹ [10].

Chemical composition parameters and total anthocyanin content significantly depend on the cultivar, as well as color. The color parameters of different blackberry pomace differed significantly, except for L* values in ‘Orkan’ and ‘Polar’ varieties and h° (hue angle) in ‘Orkan’ and ‘Brzezina’ varieties (Table 2). The hue angle ranged from 0° to 90°, representing the red (−0°) and orange/yellow (90°) colors (

Table 3. The color parameters of blackberry pomace, NBS units, °.

Blackberry Cultivar	L*	a*	b*	C	h°
‘Polar’	33.72 ± 1.16 a	27.95 ± 0.62 b	10.3 ± 1.7 a	29.78 ± 1.4 b	20.22 ± 0.32 a
‘Orkan’	33.87 ± 0.24 a	28.96 ± 0.3 a	9.54 ± 0.41 b	30.49 ± 1.2 a	18.23 ± 0.21 b
‘Brzezina’	26.56 ± 0.44 b	25.49 ± 0.37 c	8.74 ± 0.26 c	26.95 ± 1.1 c	18.92 ± 0.92 b

* Data expressed as means ± standard deviation. Different letters in the columns indicate significant differences between the mean values (p ≤ 0.05).

).

Color is an important quality parameter, as it can determine the acceptability of consumers. The ‘Orkan’ cultivar pomace was the lightest and the reddest, respectively, 33.87 and 28.96 NBS units, while the ‘Brzezina’ cultivar pomace was the darkest (26.56 NBS) and the bluest (8.74 NBS). A correlation analysis between color parameters and total anthocyanins content showed that with increased total anthocyanins content the pomace redness was more intensive (r = 0.783, p ≤ 0.05). The hue and chroma values of the blackberry pomace range from 26.95 to 30.49 NBS and from 18.23 to 20.22°, respectively. Blackberry pomaces are located in a red hue area (positive values of a* and b*) corresponding to the reddish side, a*b* plane, with angles around 18–21°. Chroma (C) showed higher values for ‘Orkan’ blackberry pomace, which could be due to the higher concentrations of TAC in ‘Orkan’ blackberry pomace—129.58 mg 100 g⁻¹ d.w. A positive correlation between total anthocyanin content and chroma (r = 0.697, p ≤ 0.05) was determined. Scientific data also reveal that higher C values are related to higher concentrations of anthocyanins [15]. The data of the other researchers show that dried blackberry pomace color parameters were similar to our findings (L*—31.35; a*—23.22; b*—11.68 NBS units) [24].

The direct usage of agro-food byproducts is one of the most sustainable manners. To facilitate berry pomace application in foods, detailed knowledge of its composition and physicochemical properties is essential [18]. Physicochemical properties influence the characteristics of the final product, water holding capacity is important and plays a huge role in determining a product’s food texture, and oil absorption is important for product consistency and bulking [25]. Moreover, blackberry pomace functional properties are closely related to pomace drying processes, because they replace the structure of the pomace with its solubility, bulk density, porosity, and color [25].

Functional properties like swelling and water holding capacity are important to understand how fiber can retain water. The highest number of seeds was determined in the pomace of ‘Orkan’ cultivar blackberries, while the least—in ‘Polar’. It was observed that increasing the number of seeds had a negative effect on pomace oil holding capacity, but the effect of NDF, proteins, and fats was the opposite (Table 3 and

Table 4. Correlation coefficients between chemical content of pomace and physicochemical properties.

Parameter	Oil Holding Capacity (g/g)	Water Holding Capacity (g/g)	Swelling Capacity (mL/g)
Dry matter	0.066	−0.722 *	0.821 *
Protein	0.832 *	0.013	0.164
Fat	0.735 *	−0.408	0.793 *
Ash	−0.725 *	−0.418	0.138
ADF	0.499	0.660	−0.399
NDF	0.714 *	−0.464	0.811 *
Lignin	−0.249	0.158	−0.069
WSCs	0.018	0.184	0.074
Cellulose	0.614	0.496	−0.318
Hemicellulose	0.527	−0.666	0.917 *
Seed content	−0.865 *	−0.276	0.037

* Significant at p ≤ 0.05.

). The highest water holding capacity was of the ‘Brzezina’ cultivar blackberry pomace while between the ‘Orkan’ and ‘Polar’ pomace difference was not significant. Water holding capacity negatively correlated with the amount of dry matter (r = −0.722, p ≤ 0.05) (Table 4). The ‘Polar’ blackberry cultivar pomace showed the highest swelling capacity. A correlation analysis between swelling capacity and pomace chemical content showed that increasing the level of hemicellulose and NDF in pomace leads to higher swelling capacity. The dry matter and fat content also positively correlated with swelling capacity (r = 0.821, p ≤ 0.05) (Table 4). All these properties may be related to the particle size, absorption surface, protein structure, fiber and oil content, rheological characteristics, and compatibility with other food components [48]. Blackberry pomace physicochemical properties values are lower than those from other researchers where different berry’s pomace (chokeberry, bilberry, and elderberry) was analyzed and had a water holding capacity ranging from 2.38 to 3.10 g/g, a SC ranging from 5.08 to 10.16 mL/g, and an oil holding capacity ranging from 1.74 to 2.24 g/g d.w. [49]. According to the literature, the chokeberry, blackcurrant, redcurrant, gooseberry, and rowanberry pomace water holding capacity ranged from 3.20 to 4.74 g/g, swelling capacity ranged from 5.50 to 7.09 mL/g, oil holding capacity ranged from 1.91 to 2.27 g/g, and seed content ranged from 22.1% (chokeberry) to 61.0% (blackcurrant) [18]. Other researchers used cellulose as a nutritional and filler ingredient, which also improves the water vapor barrier [50] and may be related to the water holding capacity parameter; however, we did not find a correlation between cellulose and water holding capacity in our study. Wang et al. (2023) described the functional properties of blackberry pomace seeds and seed protein structure. Blackberry seeds contain bioactive components, such as carbohydrates, polyphenols, flavonoids, triterpenoids, pectins, and proteins. Researchers determined that blackberry pomace contains a lot of seeds, and from these they obtained protein isolates, albumin, globulin, glutelin, and prolamin [51]. They found that albumin and globulin from blackberry seeds showed good oil holding capacity [51]. In this study, we also determined a strong positive correlation (r = 0.832, p ≤ 0.05) between the number of proteins and oil holding capacity (Table 4).

4. Conclusions

In this study, the chemical content and physicochemical properties of blackberries were assessed. The proximate content of several chemical components in different cultivars of blackberry pomace varied. The main differences were observed in the content of protein, as well as in hemicellulose and total anthocyanins content. Blackberry pomace is obtained as a by-product from juice processing and is rich in fiber and can be a source of natural dyes because is an anthocyanin-rich (from 113.82 to 129.58 mg 100 g⁻¹ d.w.) by-product in the form of red-colored powder. The color parameters of different blackberry pomaces differed significantly, but all cultivar pomaces are located in a red hue area (angles around 18–21°). Fiber-rich blackberry pomace can be used as a functional food ingredient and assists in the texture and stability of food products. Fat and NDF content showed a strong positive correlation with such physicochemical properties such as oil holding capacity and swelling capacity. Therefore, one of the most important things is to avoid food waste and seek a new possibility to use agro-food byproducts for the fortification and enrichment of the food in order to find new alternatives to return them to the food chain.