Carrot Pomace Characterization for Application in Cereal-Based Products

Abstract

Carrot is one of the most consumed vegetables worldwide and the production of juices generates high amounts of valuable by-products such as pomace. In order to minimize the environmental effects and to optimize the production costs, carrot pomace can be considered as an ingredient in various food products. The aim of this study was to characterize carrot pomace powders from four varieties (Baltimore, Niagara, Belgrado, and Sirkana) and, from a chemical, functional, chromatic, microstructural, and molecular point of view, highlight the possibility of using them as food ingredients. The results obtained showed that the chemical composition, functional properties, color, and molecular structures of carrot pomace powders depend on the variety. Carrot pomace powders had high contents of fibers (20.09–33.34%), carbohydrates (46.55–58.95%), ash (5.29–5.89%), and proteins (6.87–9.14%), with the Belgrado variety being the richest in fibers and ash, while the Sirkana variety had the greatest protein and the smallest carbohydrate content. With respect to the functional properties, significant differences among the samples were recorded for water absorption and retention capacities, with the Baltimore carrot pomace presenting the highest values (16.99% and 7.64 g/g, respectively). All of the samples exhibited high foaming stability (FS > 94%), with the hydration capacity being higher than 57.96%, the oil absorption capacity being greater than 34.33%, and the bulk density comprised between 0.45 and 0.56 g/cm³. The highest luminosity was obtained for the Baltimore sample (73.30), while the Niagara variety exhibited the most yellowish (19.61), reddish (13.05), and intense (23.55) color. The microstructure of all the samples were compact, while the FT-IR spectra depicted the presence of beta carotene, fibers, carbohydrates, lipids, and proteins. These results could be helpful for processors and researchers interested in reducing their carbon foot print in the fruit processing industry and/or in creating food products with enriched nutritional and functional values.

1. Introduction

The food industry is constantly evolving, as evidenced by the appearance on the market of new products, enriched with ingredients that bring benefits to the health of consumers. The addition of various by-products in foods can provide both a viable economic solution through their use, and a substantial health aid through their nutritional and functional value. During carrot juice production, up to 50% of the roots result in pomace which is usually employed as feed or manure [1].

Medical studies have shown that the consumption of both fruits and vegetables brings important benefits to the health of consumers by reducing the risk of coronary heart disease and heart attacks, but also various types of cancer [2]. In addition to dietary fiber, organic micronutrients such as carotenoids, polyphenols, tocopherols, vitamin C, and many other vitamins also add value to food products which can contribute to human health [2]. The carrot (Daucus carota) is a root vegetable consumed worldwide, its color varying from orange, red, purple, white, and yellow. It is an important source of bioactive compounds such as dietary fibers and carotenoids, but also other functional groups wherein significant health benefits are to be found. One of the most important bioactive compounds is represented by β-carotene and vitamins (thiamine, riboflavin, folic acid, and vitamin B-complex) and minerals (calcium, copper, magnesium, potassium, phosphorus, and iron) [3].

A significant number of by-products is produced in the food industry, and their correct disposal is crucial in order to reduce environmental pollution. On the other hand, these residual components contain significant amounts of polysaccharides, polyphenols, carotenoids, and other functional components that could be retrieved and then reused in the production of functional foods [4]. Some data reported in the literature on the composition of trace elements in dried pomace revealed that carrot pomace contains the following trace elements (mg/kg): sodium (3.2), potassium (18.6), phosphorous (1.8), calcium (3.0), magnesium (1.1), copper (4.0), manganese (10.8), iron (30.5), and zinc (29.4) [5]. Nawirska and Kwasniewska [6] found that the main types of fiber found in the composition of carrot pomace are pectin (3.88%), hemicellulose (12.3%), cellulose (51.6%), and lignin (32.1%). Thus, the carrot by-product after juice extraction resulted in a promising source of phytochemicals with many health benefits that could be considered in the development of vegetal ingredients for the food industry and for dietary supplements [7]. Adding value to by-products helps to lower the price of the main product, thus leading to a direct profit for processors and consumers.

The proximate composition, physical properties, and functional characteristics of carrot pomace are influenced by the processing methods used. The chemical composition, color parameters, and water-holding capacity of carrot pulp were affected by blanching according to the data reported by Bao and Chang [8]. Carrot pomace dried convectively was recommended by Alam et al. [3] since the quality attributes recorded greater fiber, total carotenoids, β-carotene contents, and low modifications in color parameters compared to other treatments. The content of protein, reducing sugars, minerals, and fibers of carrot pomace vary from 4–5%, 8–9%, 5–6%, and 37–48%, respectively, and its use in food product fortification led to increases in dietary fiber [1].

The papers found in the literature revealed the possibility to valorize carrot pomace in different ways. Tańska et al. [5] demonstrated that carrot pomace can be incorporated into wheat bread by replacing wheat flour up to 5% when the final product presented the best quality parameters. Singh et al. [9] showed that carrot pomace can be used to prepare a carrot-based condensed milk product called “gazrella” which kept reasonable overall acceptability scores even after 6 months of depositing at room temperature. Kırbaş et al. [10] obtained gluten-free cake with enhanced fiber content by adding carrot pomace, with the final product presenting acceptable sensory characteristics. Another study conducted by Shiraz et al. [11] revealed that carrot pomace can be employed in the production of high fiber ready-to-eat expanded snacks from barley flour, with up to 10% addition being the optimum dose recommended by the authors.

The aim of the present study was to investigate four varieties of carrot pomace flours in terms of functionality, chemical composition, and microstructural and molecular characteristics. For this purpose, the proximate composition of flours was determined along with the molecular conformations, functional properties, color, and microstructure in order to highlight some possible uses of carrot pomace in order to create value-added products.

2. Materials and Methods

2.1. Materials

Four varieties of carrots (Niagara, Belgrado, Sirkana, and Baltimore) were purchased from a farmer in Bacau, Romania. The carrot pomace was obtained by extracting the carrot juice with a Bosch MES3500 (Philips Consumer Lifestyle B.V., Drachten, Holland) device. The drying treatment of carrot pomace was performed in a convector with hot air at a temperature of 60 °C for 24 h and a layer thickness of 0.5 cm. After drying, the resulting carrot pomace was ground using a grinding machine for 30 s. In order to obtain a particle size smaller than 200 μm, the whole carrot flour was sieved in a Retsch Vibratory Sieve Shaker AS 200 basic (Retsch GmbH, Haan, Germany) device. Carrot flours were kept in dark glass bottles until analysis.

2.2. Chemical Properties

The chemical properties (moisture, protein, fat, and ash) of carrot pomace powder were analyzed using International Association for Cereal Chemistry (ICC) methods: moisture (101/1), fat (104/1), protein (105/2), and ash (105/1). The amount of total dietary fiber was evaluated by using a Megazyme kit K-TDFR-200a 04/17 (Megazyme Ltd., County Wicklow, Ireland) in agreement with the American Association of Cereal Chemists (AACC) 32-05.01 protocol. The carbohydrate content was calculated by difference, by applying the equation (Equation (1)) used by Coţovanu et al. [12]. The determinations were made in duplicate (n = 2).

$$\mathrm{Carbohydrates} (\%)=100-\left(\mathrm{protein}+\mathrm{fat}+\mathrm{ash}+\mathrm{fiber}+\mathrm{moisture}\right)$$

(1)

The energetic value (kcal/100 g) of the samples was also calculated by multiplying the nutrient’s values by their corresponding conversion coefficients Equation (2):

$$\mathrm{Energy} \left(\mathrm{kcal}/100 \mathrm{g}\right)=\left(4\times \mathrm{protein}\right)+\left(9\times \mathrm{fat}\right)+\left(4\times \mathrm{carbohydrates}\right)+\left(2\times \mathrm{fiber}\right)$$

(2)

2.3. Functional Properties of Carrot Pomace Powder

2.3.1. Hydration Capacity (HC)

The hydration capacity was determined in duplicate (n = 2), in agreement with the protocol proposed by Bordei et al. [13] with modifications. An amount of 2.5 g of the sample was taken for analysis and placed in a 50 mL tube, where 15 mL of water was added. Within 1 h, the sample was mixed with a rod for 30 s every 10 min. The stem was washed with 10 mL of water and the resulting suspension was centrifuged for 20 min at 3000 rpm. After removing the supernatant, the sample was kept at a temperature of 50 °C for 25 min and after cooling it was weighed. The hydration capacity was calculated using the Equation (3):

$$\mathrm{HC} (\%)=\frac{\left(m_2-m_o\right)-m_1}{m_1}\times 100$$

(3)

where:

m_o—weight of the tube;

m₁—weight of sample taken into analysis;

m₂—weight of sample which absorbed water.

2.3.2. Water Absorption Capacity (WAC)

The water absorption capacity was determined (n = 2) by the method proposed by Oladiran and Emmambux [14] with modifications. The sample (1 g) was placed in a centrifuge tube with 10 mL of distilled water. The sample was kept in a water bath with continuous mixing for 30 min at 30 °C and then centrifuged for 15 min at 3500 rpm. The supernatant was removed and the residue was weighed. The results were calculated using the Equation (4):

$$\mathrm{WAC} (\%)=\frac{m_1}{m_o}\times 100$$

(4)

where:

m_o—weight of sample taken into analysis;

m₁—weight of sample after supernatant removal.

2.3.3. Oil Absorption Capacity (OAC)

Oil absorption capacity was determined in duplicate (n = 2) according to the method proposed by Elkhalifa and Bernhardt [15] with modifications. The sample of carrot pomace powder in a quantity of 1 g was placed in a centrifuge tube with 10 mL of sunflower oil. The sample taken for analysis was stirred for 1 min every 10 min for 30 min. After centrifugation at 3000 rpm for 15 min, the supernatant was decanted and the tubes were allowed to drain for 5 min, and then the residue was weighed. The result was calculated by using the Equation (5):

$$\mathrm{OAC} (\%)=\frac{m_1}{m_o}\times 100$$

(5)

where:

m_o—weight of sample taken into analysis;

m₁—weight of sample after supernatant removal.

2.3.4. Swelling Capacity (SC)

Swelling capacity was determined (n = 2) using the method of Raghavendra et al. [16] with modifications. For this purpose, 25 mL of deionized water put in a 50 mL graduated cylinder, which was covered with aluminum foil to prevent evaporation, was added to the sample of carrot pomace powder (1 g). The sample was stored at room temperature for 24 h. After 24 h, the sample volume was measured and expressed as mL of water on the carrot pomace powder Equation (6).

$$\mathrm{SC} \left(\frac{\mathrm{mL}}{\mathrm{g}}\right)=\frac{Volume occupied by sample}{Original sample weight}$$

(6)

2.3.5. Water Retention Capacity (WRC)

Water retention capacity (WRC) was determined in duplicate (n = 2) according to the method proposed by Raghavendra et al. [16] with modifications. An amount of 1 g of carrot pomace powder was placed in a centrifuge tube with 30 mL of distilled water. After 24 h, the sample was centrifuged at 3000 rpm for 20 min and the supernatant was removed. The sample was dried for 2 h at 105 °C in a convection oven. The results expressed as an average of two determinations were calculated with Equation (7):

$$\mathrm{WRC} \left(\mathrm{g}/\mathrm{g}\right)=\frac{m_1-m_2}{m_2}$$

(7)

where:

m₁—residue hydrated weight;

m₂—residue dry weight.

2.3.6. Foaming Capacity (FC) and Foaming Stability (FS)

Foaming capacity and stability were determined (n = 2) according to the methods proposed by Elkhalifa and Bernhardt [15]. For this purpose, 2 g of sample and 100 mL of distilled water were placed in a 500 mL beaker, the suspension was mixed with a blender at room temperature for 1 min. The contents were immediately moved to a 250 mL graduated cylinder and the foam volume was measured. The results were calculated using the (formula Equation (8)):

$$\mathrm{FC} (\%)=\frac{volume after whipping-volume before whipping}{volume before whipping}\times 100$$

(8)

Foam stability was determined by following the decrease in foam volume every 10 min for 1 h and using the Equation (9):

$$\mathrm{FS} (\%)=\frac{Foam volume after set of time}{Initial foam volume}\times 100$$

(9)

2.3.7. Bulk Density (BD)

Bulk density was measured (n = 2) according to the procedure presented by Okaka and Potter [17] with modification. The carrot pomace powder (5 g) was put into a 50 mL graded cylinder and tapped 20–30 times. The bulk density was calculated as weight per unit volume of sample.

2.4. FT-IR Spectra

FT-IR spectra used for the molecular characterization of carrot pomace flours were collected three times (n = 3) for each sample in the range of 650 to 4000 cm⁻¹ by using a Thermo Scientific Nicolet iS20 (Waltham, MA, USA) apparatus at a resolution of 4 cm⁻¹ by 32 scans. Average spectra were obtained on the Omnic software.

2.5. SEM Micrographs

SEM micrographs of carrot pomace flours were obtained by using a VEGA II LSH scanning electronic microscope (Tescan, Brno, Czech Republic). The acceleration tension used in the experiments was 30 kV and the magnifications were 100×, 500×, and 1000×. Carbon adhesive bands were used to fix the powders.

2.6. Carrot Pomace Powder Color

The color parameters of carrot pomace powder were measured (n = 3) by reflectance, in the CIE Lab system on a Konica Minolta CR-400 (Konica Minolta, Tokyo, Japan) device. Triplicate determinations were performed.

2.7. Statistics

All of the measurements were performed at least in duplicate (n ≥ 2). Statistical processing of data was performed on XLSTAT for Excel 2021 version (Addinsoft, New York, NY, USA) software. One-Way ANOVA with Tukey test was used to evaluate the differences among samples, the confidence level was considered, being 95%.

Principal Component Analysis (PCA) was applied to investigate the relationships between variables. The number of factors was established at 2, with a varimax rotation method and n data standardization being applied.

3. Results

3.1. Carrot Pomace Powder of Different Varieties Chemical Properties

The chemical composition of carrot pomace powders is presented in

Table 1. Chemical composition of carrot pomace powders.

Variety	Protein (%)	Fat (%)	Ash (%)	Fiber (%)	Moisture (%)	Carbohydrates (%)	Energetic Value (kcal/100 g)
Baltimore	6.87 ± 0.06 c	1.00 ± 0.02 b	5.29 ± 0.04 c	28.69 ± 0.58 c	4.04 ± 0.02 b	54.13 ± 0.52 b	339.40 ± 40.18 b
Belgrado	8.01 ± 0.06 b	1.01 ± 0.03 b	5.89 ± 0.02 a	33.34 ± 0.25 a	3.78 ± 0.01 b	48.00 ± 0.24 c	333.96 ± 47.87 b
Niagara	8.84 ± 0.12 a	0.70 ± 0.02 c	5.56 ± 0.03 b	20.09 ± 0.08 d	5.88 ± 0.46 a	58.95 ± 0.65 a	343.32 ± 34.64 a
Sirkana	9.14 ± 0.06 a	1.13 ± 0.03 a	5.89 ± 0.01 a	31.40 ± 0.70 b	5.91 ± 0.15 a	46.55 ± 0.64 c	332.00 ± 35.81 b

Mean values (n = 2) followed by different superscripts in the same column are significantly different between varieties (p < 0.05).

. Significant differences (p < 0.05) between the analyzed carrot pomace varieties were observed regarding the fat, ash, fiber, and carbohydrates values.

The Niagara variety presented the highest content of carbohydrates and the lowest fat and fiber content compared to the other varieties. The Belgrado carrot pomace showed the greatest fiber content and the smallest moisture. The richest in fat, protein, and ash contents was the Sirkana carrot pomace with this variety having the lowest carbohydrates content. The Baltimore variety presented the lowest ash content. With respect to the energetic value, only Niagara exhibited a significantly higher value compared to the other varieties.

3.2. Carrot Pomace Powder of Different Varieties Functional Properties and Color

The functional properties of carrot pomace powders varied slightly depending on the variety (

Table 2. Functional properties of carrot pomace powders.

Variety	HC (%)	WAC (%)	OAC (%)	WRC (g/g)	FC (%)	FS (%)	SC (mL/g)	BD (g/cm³)
Baltimore	67.94 ± 2.67 a	16.99 ± 0.24 a	37.31 ± 0.32 a	7.64 ± 0.03 a	5.00 ± 0.00 b	96.00 ± 0.00 a	25.95 ± 0.01 b	0.56 ± 0.00 a
Belgrado	66.81 ± 2.24 a	15.96 ± 0.44 ab	34.72 ± 0.85 c	5.33 ± 0.05 c	7.00 ± 0.00 a	94.00 ± 0.00 b	25.96 ± 0.01 b	0.46 ± 0.00 b
Niagara	57.96 ± 0.78 b	11.59 ± 0.01 c	34.33 ± 0.25 c	4.76 ± 0.01 d	7.00 ± 0.00 a	94.00 ± 0.00 b	27.22 ± 0.00 a	0.45 ± 0.00 b
Sirkana	68.26 ± 4.51 a	15.15 ± 0.37 b	35.29 ± 1.68 b	6.10 ± 0.00 b	5.00 ± 0.00 b	96.00 ± 0.00 a	27.20 ± 0.01 a	0.56 ± 0.00 a

HC—hydration capacity, WAC—water absorption capacity, OAC—oil absorption capacity, WRC—water retention capacity, FC—foaming capacity, FS—foaming stability, SC—swelling capacity, and BD—bulk density. Mean values (n = 2) followed by different superscripts in the same column are significantly different between varieties (p < 0.05).

). No significant differences (p > 0.05) among samples were obtained for HC, except for the Niagara sample which was different from the other samples, while Baltimore and Sirkana showed significant differences (p < 0.05). Regarding OAC, Baltimore registered the highest OAC. Regarding WAC, the values varied from 11.59% for Niagara to 16.99% for the Baltimore pomace, while the WRC comprised between 4.76 g/g for Niagara and 7.62 g/g for the Baltimore sample. The Baltimore and Sirkana carrot pomaces had the lowest FC compared to the other varieties, but the stability was superior. The Baltimore and Sirkana samples exhibited the highest BD, while Niagara had the biggest SC.

The color parameters of carrot pomace varied in function of variety, especially the luminosity (L*), the red nuance suggested by the positive values of a*, and the color intensity (C *)as is shown in

Table 3. Color CIE Lab parameters of carrot pomace powders.

Variety	L* (Adim.)	a* (Adim.)	b* (Adim.)	C* (Adim.)
Baltimore	73.30 ± 0.15 a	8.61 ± 1.68 b	18.85 ± 0.16 b	20.77 ± 0.62 c
Belgrado	71.30 ± 0.09 b	10.21 ± 0.15 b	19.47 ± 0.05 a	21.98 ± 0.10 b
Niagara	66.02 ± 0.08 d	13.05 ± 0.02 a	19.61 ± 0.06 a	23.55 ± 0.04 a
Sirkana	69.44 ± 0.01 c	9.25 ± 0.06 b	19.56 ± 0.04 a	21.63 ± 0.05 a

Means (n = 3) followed by different superscripts in the same column are significantly different between varieties (p < 0.05).

. The luminosity varied from 66.02 for the Niagara sample to 73.30 for the Baltimore sample. The most pronounced red nuance was observed in the case of the Niagara variety, while Baltimore presented the lowest value for a*. All of the studied samples had a yellow nuance because the values of b* parameters were positive, but no significant differences (p > 0.05) were observed between varieties, except for Baltimore which had the lowest value. The highest color intensity was obtained for the Niagara sample, while Baltimore had the smallest value.

3.3. Carrot Pomace Powder of Different Varieties Micrographs

The microstructure of carrot pomace powders at different magnifications is presented in Figure 1. SEM micrographs of carrot pomace from different varieties exhibited regular compact cellular network. Similar structure of carrot tissues was reported in previous works [18,19]. Fibrous structures can be depicted for all the analyzed samples.

3.4. Carrot Pomace Powder of Different Varieties FT-IR Spectra

FT-IR spectra of carrot pomace powders revealed the presence of bioactive compounds, with some differences regarding peak intensities being observed among the samples (Figure 2). The highest absorbances were obtained for the Niagara sample, followed in decreasing order by Sirkana, Baltimore, and Belgrado, except in the regions 1510–2325 cm⁻¹ and 2898–2939 cm⁻¹. The Niagara and Baltimore varieties presented the highest peaks at 1736 cm⁻¹ which may be associated with the presence of beta-carotene [20], while in the region 1550–1650 cm⁻¹, which could depict the presence of pectin [21], Niagara recorded higher intensities. The presence of galacturonic acid in all of the analyzed samples was suggested by the appearance of peaks at 2898 and 1606 cm⁻¹, with the Niagara variety exhibiting different peaks in the region 2898–2938 cm⁻¹ compared to the other samples. The peaks found at 1421, 1367, 1104, and 1032 cm⁻¹ could be related to cellulose [22], with the Niagara sample showing the biggest intensities, while the lowest were observed for the Belgrado variety. The peaks at 1649 and 1557 cm⁻¹ can be attributed to the presence of proteins in the carrot pomace powders.

3.5. Relationships between Characteristics

Principal Component Analysis (PCA) (Figure 3) allowed for the interpretation of the relationships between variables, based on correlations. The first principal component (PC1) explained 45.91% of the total variance, while the second one (PC2) explained 38.38% of the data variance. The highest contributions on PC1 were observed for protein (9.68%), ash (6.53%), b* (11,44%), SC (5.40%), and moisture (4.26%). Other parameters that contribute to PC1 were OAC (10.70%) and WRC (10.05%) which were in opposition to the protein content and b* parameter. Regarding PC2, it was observed that fat (12.69%), fiber (11.61%), carbohydrates (13.31%), energetic value (13.33%), and HC (10.30%) had a high contribution. The PC1 highlights an opposition between fat, HC and carbohydrates, energetic value, and between ash and FC, C*. PC2 distinguished between WAC and FC, fiber and a*, BD and a*, while L* was in opposition with FC and C*, and OAC was opposed to SC and moisture (Figure 3). The Sirkana and Belgrado samples were associated with PC2, with an opposition between these two varieties with Niagara being observed. PC2 clearly distinguished between the Niagara and Baltimore varieties, with Baltimore being associated with the OAC and WRC.

The fat content was significantly correlated (p < 0.05, r = 0.96) with HC, while the moisture content was strongly correlated (p < 0.05, r = 0.99) to SC. The energetic value was positively correlated (p < 0.05, r = 0.99) with the carbohydrates content. Significant negative correlation was observed between HC and a* (p < 0.05, r = −0.97), while WAC was positively correlated with L* (p < 0.05, r = 0.98) and negatively with C* (p < 0.05, r = −0.96). A strong and positive relationship was obtained for OAC with WRC (p < 0.05, r = 0.99) and negative with b* parameter (p < 0.05, r = −0.95). FC and FS were significantly (p < 0.05, r = −0.99, and r = 0.99, respectively) correlated with BD.

4. Discussion

The results obtained for the chemical composition of carrot pomaces demonstrated that they are an important source of fibers and carbohydrates, also providing an intake of proteins and minerals. The higher intake of fiber and total minerals would be given by the consumption of the Belgrado carrot pomace, while the Sirkana pomace presents the greatest protein level and the lowest carbohydrate content (Table 1). Kumari and Grewal [23] also reported the high amounts of ash and dietary fibers of carrot pomace used as an ingredient in biscuits, which resulted in the improvement of the final product’s mineral and fiber profile. The literature stated that carrot pomace may contain between 4% and 5% protein, 5% and 6% minerals, and 37% to 48% total dietary fiber, which is in agreement with the results obtained in the present study (Table 1). Fibers are considered complex carbohydrates present in the structural components of plants that cannot be soaked up by the body and have many health benefits such as prevention of constipation, control of blood sugar, heart disease prevention, and the inhibition of certain types of cancers [1]. The main components of total fibers in carrot pomace are represented by pectin, cellulose, lignin, and hemicellulose [1]. Tańska et al. [5] demonstrated that the dried carrot pomace is a rich source of organic compounds, mainly polysaccharides. The authors reported a total carbohydrates content higher than 50% which was in agreement with our results (Table 1), affirming at the same time that high amounts of monosaccharides could have positive effects on bread made with wheat flour with low amylase activity because they represent an important source of carbon for yeast multiplication [5]. The content of lipids considered as natural solvents for carotenoids and the fount of some important unsaturated fatty acids was reported as being 6.0% [5], which was higher than the results of the present study (0.70–1.13%). The same authors stated that the dried carrot pomace also presented 5.5% mineral components, which can improve and supplement wheat bread mineral content [5].

The functional properties of carrot pomaces recorded some differences among samples, depending on the variety. The presence of lipids and dietary fiber has an essential role in determining carrot pomace hydration characteristics such as water-holding, water retention, and swelling capacities [16]. These statements are also supported by the high correlation obtained between HC and fat content. In agreement with the data presented in Table 2, carrot pomace powders had high SC (25.95–27.22 mL/g), comparable to those reported by Raghavendra et al. [16] for coconut residue, highlighting that carrot pomace has a great ability to swell, this being the most desirable property for the physical functionality of dietary fiber. According to the data reported by Amin et al. [24], the SC of carrot waste was 29.23 mL/g which was close to the values obtained in the present study (25.95–27.22 mL/g, Table 2). SC is directly influenced by the fiber content and soluble dietary fiber which plays an essential role in the functionality of the material because pectin and gums have a greater water-holding capacity than cellulose fibers [25]. Water retention capacity (WRC) is defined as the “ability of a matrix of molecules, usually macromolecules at low concentrations, to physically entrap certain amounts of water under the application of an external or gravitational force” [24,26]. WRC depends on the fiber dimension, being known that grinding can damage the fiber structure and lower its ability to trap water [24]. The porous matrix composed of polysaccharide chains in plants holds high amounts of water by means of hydrogen bonds, thereby offering beneficial functionality to vegetal materials [25]. The main factors influencing the functionality of these polysaccharide chains are the proportion of insoluble to soluble dietary fiber and the dimension of product fraction [27]. Carrots are an important source of soluble fibers such as pectin, which have a higher WRC than insoluble fibers, and could explain the high WRC in carrot fibers. The dietary fiber content of coconut by-products after extraction of coconut milk was reported as being 60.21%, which was higher than that of the carrot pomace powders in the present study (20.09–33.34%), but was comparable with those reported for orange by-product (20.01%) [16]. However, WRC of coconut pomace (5.4 g/g) was close to those obtained in the present study (4.76–7.64 g/g, Table 2) according to the data presented by Raghavendra et al. [16]. The WRC of coconut pomace was greater than that of other dietary fiber wastes such as potato, pea, and wheat bran fibers [16]. These results suggest that the carrot pomace could provide benefits similar to those of coconut pomace, which would be superior to potato, pea, or wheat bran fiber. Carrot pomace OAC was comprised between 34.33% and 37.31% with small differences among varieties. The OAC depends on many factors such as plant polysaccharides, density, hydrophobic particle character, particle size, and the amount of insoluble dietary fiber [25]. Fibers present in carrot pomace could have the ability to stabilize food emulsions with a great fat content [24], which supports the results of the present study. SC is defined as “the ratio of the volume occupied when the sample is immersed in excess water after reaching equilibrium to the initial sample weight” [16,24]. A sample with high SC can be beneficial for gastrointestinal motility and defecation and contribute to the prevention of constipation. Carrot pomace powders presented relatively low foaming capacities (<7%, Table 2) but with good stability. FC and FS are due to the presence of proteins, which form an uninterrupted cohesive film around the air cells in the foam, reducing the surface tension at the air–water interface, therefore providing the foaming capacity [28]. Negi and Vaidya [29] also reported low FC for apple pomace powder (2%) while Grover et al. [30] obtained a value of 7% FC for unsieved apple pomace and 11.00% for particle size < 300 μm. The bulk densities of carrot pomace powders varied between 0.45 g/cm³ and 0.56 g/cm³ (Table 2) with these values being close to those reported by Michalska et al. [31] for blackcurrant pomace powders (0.45–0.42 g/cm³). Particle density is affected mostly by the solids content which is quite great in fruit by-products such as pomace [31].

The color of carrot pomace is mainly due to carotenes which are partly transformed into vitamin A [8]. Alam et al. [3] reported values of 65.0 for L*, 8.6 for a*, and 20.6 for b* parameters for carrot pomace convective dried and without any pretreatment, which was close to the results of the present study (Table 3). The color of carrot roots depends on the variety and ranges from orange to purple, depending on the chemical compounds contained [32]. For example, purple carrot color is mainly due to the presence of anthocyanins, while orange color varieties is due to the presence of carotenoids [32]. Niagara carrot pomace powder exhibited the highest color intensity which may be related to the beta carotene content, a fact also supported by the FT-IR spectra which revealed the highest intensity of the peak at 1736 cm⁻¹ associated with this compound. Generally, food carotenoids are classified into carotenes and xanthophylls, which are responsible for the red or yellow color of the product [1].

The microstructures of carrot pomaces studied in this paper showed compact fibrous structures. Sucheta et al. [19] reported the intact cellular structure of black carrots that could be related to the filled polymer network and also to the strong linkages of pectin molecules with the pigments. Plant cell walls are formed of complex polysaccharide networks with diverse structural and physiological importance, with pectins being the components that, together with other polysaccharides paste neighboring cells and strengthen them firmly [33]. The main components of the carrot cell wall are represented by pectin (galacturonans, rhamnogalacturonans, arabinans, galactans, and arabinogalactans-1), cellulose (β-4, D-glucan), lignin (trans-coniferyl alcohol, trans-sinapyl alcohol, and trans-p-coumaryl alcohol), and hemicellulose (xylans, glucuronoxylans β-D-glucans, and xyloglucans) [1].

A comparison of FT-IR absorption bands between the results obtained in the present study and those found in the literature are listed in

Table 4. Comparison of FT-IR absorption bands with previous results reported in the literature [19,22,35].

Measured Wavenumber (cm−1)	Wavenumber from the Literature (cm−1)	Assignment	Origin
3324	3000–3600	O–H and N–H stretch C–H	Water, alcohols, phenols, carbohydrates, peroxides polysaccharides, lipids, and carbohydrates
2898	2891	–CH stretching vibrations	Galacturonic acid
1717, 1736	1700–1799	C=O	Lipids, beta carotene
1649	1600–1706	Amide I of proteins, C–O, C–N, CNN	Proteins
1606	1600–1630	COO- antisymmetric stretching	Polygalacturonic acid, carboxylate (pectin ester group)
1557	1460–1590	Amide II of proteins, N–H, C–N	Proteins
1421	1421–1428	CH3 symmetric bending	Cellulose
1367	1370	CH2 bending	Xyloglucan, Cellulose
1329	1320–1330	Ring vibration	Pectin
1247	1243	C–O stretching	Pectin
1147	1147	O–C–O asymmetric stretching	Xyloglucan (glycosidic link)
1104	1103–1115	C–O stretching, C–C stretching	Cellulose (C2-O2)
1032	1030	C–O stretching, C–C stretching	Cellulose (C6-H2-O6)

. The peak at 1736 cm⁻¹ due to C=O stretching can be led to the bonds present in β-carotene [34]. The peak at 1456 cm⁻¹ is related to scissoring (CH₂) bending, while the peaks found at 1421 cm⁻¹ and 1367 cm⁻¹ are assigned to (CH₃) and (CH₂) bending, respectively. [20]. The bands observed between 1550–1650 cm⁻¹ in FT-IR spectrum of carrot pomace (Figure 2b) are the indicators of the C=C stretches in the pectin fractions [21]. The presence of the -OH groups of water was identified between 3000 and 3600 cm⁻¹ as a broad band. The peaks at 3324 cm⁻¹ given by the –OH stretching vibrations also led to the H-bonded hydroxyl of polysaccharides or polyphenols [19]. The peaks at around 2898 and 1606 cm⁻¹ can be associated with the –CH stretching vibrations and the appearance of free ionic non-esterified carboxyl (–COO) molecules of galacturonic acid [19]. The presence of cellulose in carrot pomace powders was suggested by the absorption bands found at 1421, 1367, 1104, and 1032 cm⁻¹ [22]. The peaks at 1649 and 1557 cm⁻¹ given by the C–O, C–N, CNN (Amide I), and N–H, C–N (Amide II) [35] vibrations, respectively, can be related to the presence of proteins in the studied samples. These results were in agreement with those obtained for the chemical composition of carrot pomace powders which showed high content of fibers and important amounts of proteins.

The results obtained in the present study confirm the possibility of using carrot pomace in the production of value-added food, with low costs and with many benefits for consumer health. Some possible applications of carrot pomace powders would be wheat bread, gluten-free bread based on pseudo-cereals, fitness bars, biscuits, cakes, pasta, etc. Carrot pomace could bring an important intake of nutrients, especially fibers, depending on the amount added to the final product. The results regarding the functional properties of carrot pomace flour are important for choosing the type of product and the dose that can be incorporated in order to achieve the desired quality and maximum nutritional benefits, it being known that fiber-rich ingredients such as carrot pomace could impact dough or mass behavior, depending on the particle size and dose.

5. Conclusions

The chemical composition, functional properties, and molecular structures of carrot pomace powders investigated depended on the variety. The results obtained showed that carrot pomace is a rich source of fibers, carbohydrates, and minerals, which suggested its capacity to improve the nutritional value of food products into which it can be incorporated. On the other hand, the functional properties in terms of water absorption and retention capacities, swelling capacity, bulk density, and foaming properties differed between carrot varieties, with the Baltimore sample exhibiting the highest water absorption capacity, water retention, foaming stability, and bulk density. The color also depended on the carrot variety, the most luminous being the Baltimore sample, the most reddish, yellowish, and intense color being obtained for the Niagara variety. SEM micrographs revealed a compact structure of carrot pomace powder, while FT-IR spectra revealed the presence of beta carotene, pectin, cellulose, proteins, and carbohydrates in the analyzed samples. Further research on the bioactive compounds quantification in carrot pomace would be necessary to better highlight the benefits of using it to create novel, value-added products.