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Article

Effect of Heat Treatment Methods on Color, Bioactive Compound Content, and Antioxidant Capacity of Carrot Root

by
Agnieszka Narwojsz
1,
Tomasz Sawicki
1,
Beata Piłat
2 and
Małgorzata Tańska
2,*
1
Department of Human Nutrition, Faculty of Food Science, University of Warmia and Mazury in Olsztyn, Słoneczna 45F, 10-718 Olsztyn, Poland
2
Department of Food Plant Chemistry and Processing, Faculty of Food Science, University of Warmia and Mazury in Olsztyn, Pl. Cieszyński 1, 10-726 Olsztyn, Poland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(1), 254; https://doi.org/10.3390/app15010254
Submission received: 7 November 2024 / Revised: 20 December 2024 / Accepted: 28 December 2024 / Published: 30 December 2024
(This article belongs to the Section Food Science and Technology)
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Abstract

:
Carrot (Daucus carota L.) is a globally consumed root vegetable, enjoyed both raw and after thermal processing. This study aimed to evaluate the effect of different heat treatment methods (traditional boiling in water, steaming in a steel pot, steaming in a combi oven, baking in a combi oven, and the sous-vide technique) on carrot color, total phenolic and flavonoid content, phenolic and carotenoid compound profiles, and antioxidant capacity. It was found that heat treatments resulted in significant (p ≤ 0.05) changes in carrot color, with reductions in lightness (L* decreased by 19–24%), redness (a* decreased by 52–67%), and yellowness (b* decreased by 15–25%). Interestingly, processed carrots showed an increase in total phenolics (by 25–133%), total flavonoids (by 60–126%), and total carotenoids levels (by 16–48%) compared to raw carrots. However, specific phenolic and carotenoid compounds showed notable reductions (p ≤ 0.05) after heat treatment, including vanillic acid and rutin (100% reduction after all treatments), α-carotene (up to 33.3% reduction after baking), zeaxanthin (up to 33.3% reduction after baking), and 13-cis-β-carotene (up to 40.7% reduction after steaming in a combi oven). In addition, heat treatment significantly (p ≤ 0.05) increased the antioxidant capacity of carrots, as determined by DPPH and ABTS assays, with increases up to 2.2-fold and 1.6-fold, respectively. The antioxidant properties of processed carrots were strongly correlated (p ≤ 0.05) with total phenolic content and the levels of chlorogenic acid, p-coumaric acid, and β-carotene (r = 0.86–0.96).

1. Introduction

Carrot (Daucus carota L.) is one of the most widely cultivated and consumed vegetables in the world, available in both raw and cooked forms. Global carrot production in 2021 reached approximately 42 million tons and has demonstrated a consistent upward trend over the past two decades [1]. Carrot roots are characterized by a wide range of colors, including white, yellow, orange, red, and purple [2]. They are a rich source of carotenoids, particularly β-carotene [3,4], as well as dietary fiber [5]. Additionally, carrots contain other bioactive compounds such as vitamin C [3], phenolic compounds [6], polyacetylenes [7], and various mineral components [8]. The bioactive compounds present in carrots contribute to numerous health-promoting properties, including anti-diabetic, cholesterol-lowering, cardioprotective, antihypertensive, hepatoprotective, renoprotective, and wound-healing effects [9,10]. Due to their high nutritional value and favorable storage characteristics, carrots are widely utilized in diverse culinary applications, including salads, cold dishes, cooked garnishes, and decorative elements in meals. Carrots also play an important role as an ingredient in vegetable broths and serve as a primary raw material for numerous processed products, such as frozen goods, juices, purées, dried powders, concentrates, canned foods, preserves, confections, and pickles. Furthermore, carrot pomace, which is notably rich in β-carotene, is often used to fortify various food products, including cakes, breads, and biscuits [11].
The preparation of carrots typically involves various thermal processing techniques, including traditional boiling, steaming, baking, and sous-vide cooking [1]. These heat treatments have a significant influence on the nutritional composition and sensory attributes of carrots, such as color, texture, and flavor [12,13]. Importantly, the concentration and bioavailability of bioactive compounds in carrots are highly dependent on the specific cooking method used [12,14,15]. For example, boiling often results in the leaching of soluble cellular components into the cooking water, as well as the degradation of antioxidants. In contrast, alternative methods like steaming, which allows for more uniform heat transfer compared to boiling, can reduce nutrient losses and better preserve the functional and nutritional properties of carrots [16]. Sous-vide cooking, a relatively modern technique, involves vacuum-sealing food in heat-resistant plastic bags and cooking it at precisely controlled, low temperatures. This method has been shown to improve flavor, texture, and nutritional quality while also extending the shelf life of prepared foods [17,18].
Numerous studies have examined the effects of thermal processing on the carotenoid composition, total phenolic content, and antioxidant properties of carrots [19,20,21,22,23,24,25], with particular emphasis on boiling, steaming, microwave cooking, and frying. However, limited data specifically address the impact of sous-vide cooking on carrot color [20,22,26], total phenolic content [20,22,26], phenolic compound profiles [3], and antioxidant properties [4,20,22,27]. Despite growing interest in the effects of thermal processing on the bioactive compounds in carrots, research on the phenolic compound profile remains scarce and inconclusive, indicating variability in the presence and/or degree of degradation of phenolic acids during processing [4,28,29]. Additionally, studies on the levels of specific bioactive compounds often yield ambiguous conclusions, suggesting either their degradation or release as a result of thermal treatments. For example, Zavadlav et al. [17] demonstrated that phenolic compounds were better preserved in vegetables cooked sous-vide than in conventional methods such as boiling or steaming. In contrast, Stanikowski et al. [26] reported a slightly higher total phenolic content in steamed carrots compared to those cooked sous-vide, emphasizing the role of both the method and duration of thermal treatment. On the other hand, Bemben and Sadana [21] observed a significant increase in the total phenolic content of carrots processed by various methods, including boiling, steaming, pressure cooking, microwaving, and sautéing. However, in all cases this increase was accompanied by a decrease in total flavonoid content. Variations in carotenoid levels were also observed. Chiavaro et al. [4] reported that both steam cooking and sous-vide processing induced significant changes in carotenoid profiles compared to raw samples, generally resulting in an increase in all carotenoids, except lutein, which exhibited similar levels in sous-vide and raw carrots. In contrast, Lim et al. [30] documented significant losses of α-carotene and β-carotene in carrots subjected to various cooking methods, including boiling, sautéing, pressure cooking, and microwaving. Interestingly, lutein content in their study increased slightly after boiling in water containing 1% NaCl but decreased when other home-cooking methods were applied. Importantly, no studies to date have directly compared the impact of traditional steaming in a steel pot with steaming in a combi oven on the chemical composition of carrot roots. Furthermore, most research has focused on carrot roots that were peeled and cut into cylindrical specimens [4,26,28,29], cubes [21,22], or slices [20,24] prior to processing. This approach may result in different quality attributes compared to those observed in whole carrot roots, which remain underexplored.
The objective of the present study was to evaluate the effects of different heat treatment methods on whole, unpeeled carrot roots, focusing on their color, total phenolic content, total flavonoid content, phenolic compound and carotenoid profiles, and antioxidant capacity.

2. Materials and Methods

2.1. Chemicals

6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox); 2,2-diphenyl-1-picrylhydrazyl (DPPH); 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS); HPLC-grade solvents; carotenoid standards; phenolic compound standards; and reagents such as acetonitrile, ammonium formate, formic acid, n-hexane, methyl tert-butyl ether (MTBE), methanol, and potassium acetate were purchased from Sigma Aldrich (Poznań, Poland). Analytical-grade reagents such as acetone, aluminum chloride, ethanol, Folin–Ciocalteu reagent, methanol, potassium hydroxide, sodium carbonate, sodium sulfate, and toluene were supplied by Chempur (Piekary Śląskie, Poland).

2.2. Research Materials

The research materials comprised the fresh roots of carrots (Daucus carota L. var. Berlikumer 2–Perfekcja) sourced from the Educational and Experimental Facility of the Faculty of Agriculture and Forestry at the University of Warmia and Mazury in Olsztyn (Poland). Prior to processing, the carrots were thoroughly washed, dried with paper towels, and subsequently subjected to various heat treatments.
The boiling process involved immersing carrots in a steel pot filled with boiling tap water, with a raw carrot-to-water mass ratio of 1:4 and a cooking duration of 38 min.
For the steaming process, two methods were employed: steaming in a steel pot with a perforated insert (50 min) and in a combi oven (Retigo B623i, Rožnov pod Radhoštěm, Czech Republic) utilizing steam for 55 min.
The baking process involved wrapping the carrot roots in aluminum foil and baking them in a combi oven (Retigo B623i) at 180 °C for 46 min.
The sous-vide process consisted of two stages. The carrots were first vacuum-sealed in PA/PE bags (15 µm polyamide/60 µm polyethylene; thermal resistance −20 °C to +110 °C; Hendi, Lamprechtshausen, Austria) using a chamber vacuum sealer (Edesa VAC-20 DT, Barcelona, Spain). They were then cooked in a water bath with a circulator equipped with a temperature sensor (Diamond Z, Julabo GmbH, Seelbach, Germany) at 85 °C for 105 min.
A control sample of raw, untreated carrots was also included. Thermal processing parameters were determined experimentally, and all treatments were conducted until a uniform softness level was achieved across samples. Following thermal processing, the carrots were cooled, sliced, freeze-dried, pulverized, and stored at −24 °C until analysis, but not longer than 2 weeks. The heat treatments applied to the carrots were performed in triplicate for each condition.

2.3. Color Analysis

Color measurements were conducted following the method outlined by Karafyllaki et al. [31]. A Konica Minolta CR-400 colorimeter (Konica Minolta, Sensing Inc., Osaka, Japan) with a standard 2° observer and D65 illumination was employed to determine the color parameters at 20 ± 1 °C. A calibration was performed using a white reference tile prior to measurement. The results of color were represented in the CIE L*a*b* color space, where the L* value indicates the lightness (ranging from 0 for black to 100 for white), a* value indicates the green–red spectrum (negative values representing green and positive values representing red), and the b* value indicates the blue–yellow spectrum (negative values for blue and positive values for yellow). Chroma (C*, representing color saturation) was calculated using the following Formula (1):
C* = √(a*)2 + (b*)2
Additionally, the total color difference (ΔE*), calculated to assess the color deviation of processed samples compared to that of the control sample, was determined using the following Formula (2):
ΔE = √(ΔL*)2 + (Δa*)2 + (Δb*)2
where ΔL*, Δa*, and Δb* are differences in L*, a*, and b* between the control sample and the processed sample.

2.4. Determination of Phenolic Compounds

2.4.1. Phenolic Extract Preparation

Extraction of phenolic compounds from carrot samples was carried out using a water/methanol mixture (20:80, v/v). Samples were vortexed for 30 s with 1 mL of the solvent, followed by 30 s of sonication, additional vortexing, and subsequent centrifugation (Micro star 30R, VWR, Radnor, PA, USA) at 14,000 rpm for 10 min at 4 °C. The resulting supernatants were collected into 5 mL flasks. The procedure was repeated five times using 1 mL of the solvent for each extraction cycle.

2.4.2. Total Phenolic Content (TPC) Analysis

The TPC was determined using the Folin–Ciocalteu phenol reagent, as described by Horszwald and Andlauer [32]. The absorbance of the colored solutions was measured at 765 nm using a FLUOstar Omega microplate reader (BMG LABTECH, Ortenberg, Germany). Results were expressed as milligrams of gallic acid equivalents (GAEs) per gram of dry weight (mg GAE/g dw). The calibration curve showed linearity in the range of 0.062–0.50 mg/mL (R2 = 0.999).

2.4.3. Total Flavonoid Content (TFC) Analysis

The TFC was analyzed following the procedure described by Horszwald and Andlauer [32]. The absorbances of the colored solutions was measured at 415 nm using a FLUOstar Omega microplate reader. Results are expressed as milligrams of quercetin equivalents (QEs) per gram of dw. The calibration curve showed linearity in the range of 0.02–0.20 mg/mL (R2 = 0.999).

2.4.4. Phenolic Profile Analysis by UHPLC-DAD-MS

The analysis of phenolic compounds was performed using the methodology described by Sawicki et al. [33]. Qualitative and quantitative assessments were conducted using a UHPLC system (Nexera XR, Shimadzu, Kyoto, Japan) equipped with a diode array detector (DAD) and a mass spectrometer (LCMS-2020, Shimadzu, Japan). Separation of phenolic compounds was performed on a C18 BEH column (1.7 μm particle size, 100 × 2.1 mm; Waters, Warsaw, Poland) at 50 °C oven temperature. The mobile phase consisted of 0.01% formic acid in water with 2 mM ammonium formate (eluent A) and 0.01% formic acid in a 95% acetonitrile solution with 2 mM ammonium formate (eluent B), and the flow rate was 0.15 mL/min. The analysis was performed in Selected Ion Monitoring (SIM) mode. Scanning was performed in negative ionization mode. Phenolic compounds were identified based on specific qualitative ions, retention times, and λmax values compared to previously published data [33,34]. Quantification of phenolic compounds was achieved by comparing UHPLC-DAD-MS peak areas with those of commercially available standards.

2.5. Determination of Carotenoids

2.5.1. Carotenoid Extraction

Carotenoid extraction was carried out following the procedure described by Dąbrowski et al. [35]. Ground carrot samples were mixed with a solvent mixture of n-hexane, acetone, ethanol, and toluene (10:7:6:7, v/v/v/v) and saponified by shaking with 40% KOH solution in methanol in the dark at room temperature for 16 h. Subsequently, carotenoids were extracted from the samples multiple times using n-hexane, with the addition of 10% sodium sulfate to facilitate phase separation. The collected n-hexane extracts were evaporated at 45 °C using an R-210 rotary vacuum evaporator (Büchi, Flawil, Switzerland), and the residues were dissolved in the methanol/dichloromethane mixture (45:55 v/v).

2.5.2. Carotenoid Profile Analysis by RP-HPLC

The carotenoid profile was analyzed using reversed-phase high-performance liquid chromatography (RP-HPLC) as described Dąbrowski et al. [35]. Chromatographic separation was performed at 30 °C on a YMC-C30 150 × 4.6 mm, 5 μm column (YMC-Europe GmbH, Dinslaken, Germany) using a 1200 series liquid chromatograph (Agilent Technologies, Palo Alto, CA, USA) equipped with a diode array detector (DAD). A methanol-methyl tert-butyl ether (MTBE) gradient applied as the mobile phase (0–5 min, 95% methanol, 1 mL/min; 25 min, 72% methanol, 1.25 mL/min; 33 min, 5% methanol, 1.25 mL/min; 40–60 min, 95% methanol, 1 mL/min). Carotenoids were identified by comparing their retention times with those of standards and their UV–visible absorption spectra. Quantitative analysis of carotenoids was performed using a β-carotene standard external calibration curve (linearity in the range of 1–150 μg/mL (R2 ≥ 0.9982); limit of quantification was 0.05 μg/g of sample dw).

2.6. Determination of Antioxidant Capacity

2.6.1. DPPH Assay

The antioxidant capacity was performed using the DPPH assay as described by Horszwald and Andlauer [32]. Mixtures of DPPH solutions with extracts or Trolox solutions were incubated in the dark at room temperature for 30 min. The reduction in absorbance was measured at 517 nm using a FLUOstar Omega microplate reader (BMG LABTECH, Ortenberg, Germany). A standard curve was constructed using Trolox at concentrations ranging from 0.01 to 2.0 mM, obtaining a linear response (R2 = 0.998). Results were expressed as micromoles of Trolox equivalents (μmol TE) per gram of dw.

2.6.2. ABTS Assay

The ABTS assay was carried out according to the method described by Horszwald and Andlauer [32]. Mixtures of ABTS+ solution with extracts, Trolox or blank (80% methanol), were prepared, and absorbance was measured at 734 nm after 6 min incubation at 30 °C using a FLUOstar Omega microplate reader. A standard curve was constructed using Trolox at concentrations ranging from 0.01 to 2.0 mM, demonstrating a linear response (R2 = 0.999). Results were expressed as μmol TE/g of dw.

2.7. Statistical Analysis

The data obtained from six parallel repetitions were statistically analyzed using Statistica 13.3 (Tibco Software Inc., Tulsa, OK, USA). Differences between mean values were assessed through analysis of variance (ANOVA) followed by Tukey’s post hoc test (p ≤ 0.05). Additionally, variabilities in sample properties and sample types were assayed using principal component analysis (PCA) with significance at p ≤ 0.05. Correlation coefficients (r) were calculated to determine the relationships between antioxidant capacity, color parameters, and the content of bioactive compounds (p ≤ 0.05).

3. Results and Discussion

3.1. Color Parameters

The color of food products has a great influence on its acceptability to the consumer [36]. The orange color of carrots depends mainly on carotenes, which are influenced by variety, maturity, and growing conditions [22]. The effect of heat treatments on carrot root color was observed in all parameters of the CIEL*a*b* model (Table 1). The L* parameter, representing brightness, ranged from 40.74 to 53.35 across the analyzed carrot samples. The highest L* value was recorded for the raw sample. Among the processed samples, the highest L* value (43.17) was recorded for the carrot root steamed in the combi oven. Boiling and sous-vide also had the strongest effect on the L* value, reducing it by about 24% compared to that of the control sample. The a* values were positive, indicating a color shift towards red, and ranged from 8.12 to 24.80. The lowest values were observed in the carrot roots subjected to sous-vide and steaming in combi oven processes, while the highest values were found in the raw sample. The b* values, reflecting color shifts between blue and yellow, ranged from 22.00 for sous-vide carrot samples to 29.28 for raw carrot samples. All heat treatments resulted in a decrease in color saturation (C*), with the lowest value for the sous-vide process, indicating a paler, more grayish color. The lowest changes in C* were caused by the baking process, which resulted in a decrease of approximately 29% compared to that of the control sample.
The total color differences ΔE of the processed carrot samples compared to those of the raw carrot sample were in the range of 17.40–22.09. The values indicate a very distinct (ΔE > 3) color deviation, which will be noticeable to a consumer. Differences in the color of carrot roots can also be seen in Figure 1. Clear differences can be seen in the inner and outer parts of the carrot root cross-section.
The decrease in color parameters occurring in carrot root slices as an effect of heat treatments has also been observed, e.g., by Zielinska and Markowski [37] during spout-fluidized bed drying at 60–90 °C; by Bao et al. [38] during cooking treatments (steaming, boiling, stir-frying, and frying); and by Salehi [39] during frying at 130–190 °C. Furthermore, Koç et al. [22] reported the same values of ΔE in carrot samples subjected to different cooking methods, i.e., sous-vide, cook-vide, and traditional cooking. They also observed that the ΔE value increases during cooking at lower temperatures over extended durations, which may explain the greater differences observed between the sous-vide and baking methods in the present study. Chiavaro et al. [4] hypothesized that the observed color changes could be due to the release of α- and β-carotenes under low-temperature, and vacuum conditions. Similarly, Chen et al. [40] emphasized that the color of carrots can change during cooking as a result of the cis-isomerization of both α- and β-carotenoids. Furthermore, Ashour and El-Hamzy [29] showed differences in color changes during boiling, steaming, and frying both in the internal and external surfaces of carrots. Interestingly, although the color parameters decreased due to heat treatment, C* decreased on the internal surface, while the opposite relationship was found on the external surface. In contrast, Islam et al. [41] found no significant color differences observed in carrot slices subjected to long periods (3–12 h) of moderate heating (75–95 °C), with or without low hydrostatic pressure.

3.2. Total Phenolic and Total Flavonoid Contents

The content of phenolic compounds in raw carrots was 0.81 mg GAE/g dw (Table 2). Stanikowski et al. [26] determined a higher content of these compounds in carrots, forming 94.74 mg GAE/100 g dw. Chatatikun and Chiabchalard [42] reported that the content of phenolic compounds in the carrots they studied was 30.7 mg GAE/g of dry plant material. The content of phenolic compounds in carrots depends on variety, origin [6], climatic conditions [43], farming system [44], type of fertilization (chemical and organic fertilizers) [45], and storage conditions [46].
Heat-treated carrots had a higher concentration of phenolic compounds compared to that of raw carrots. Among the heat-treated samples, sous-vide-cooked carrots had the lowest TPC value (1.01 mg GAE/g dw). This sample was not significantly different from raw carrots. On the other hand, the highest TPC values (1.89 mg GAE/g dw) were determined in carrots cooked by steaming in a steel pot. An increase in phenolic compounds in carrots when cooked in water, steam, and the sous-vide method for 10, 20, and 30 min compared to raw carrots was also observed by Stanikowski et al. [26]. The authors explain this fact by saying that this may have been related to the more severe thermally induced damage to the cell walls and thus more efficient release of phenolic compounds. Razzak et al. [47] report that carrots cooked in water, steam, and a microwave contained more phenolic compounds than those of raw carrots. Bembem and Sadana [21] observed a significant increase in phenolic compounds in carrots subjected to cooking (in water, steam, a microwave, and pressure) and frying, with the greatest increase in the fried and microwaved samples. According to Thanuja et al. [23], cooking carrots in water had no significant effect on the content of phenolic compounds, while microwave cooking and stir-frying resulted in a significant reduction in the content of these compounds, with stir-fried carrots containing significantly less phenolic compounds than those cooked in water or a microwave. Koç et al. [22] reported that the degradation of phenolic compounds during the sous-vide cooking of carrots ranged from 8.94 to 20.41%, cook-vide from 4.38 to 19.33% (depending on the temperature and duration of the process), and traditional cooking from 16.30 to 22.88% depending on the cooking time. According to Sultana et al. [19], cooking in water, microwaving, and frying increased the content of phenolic compounds in carrots. A study by Stanikowski et al. [26] showed an increase in the content of phenolic compounds in carrots, regardless of the cooking method used (sous-vide temperatures of 80 and 90 °C, in steam and in water) and the process time (10, 20, and 30 min) compared to in raw carrots.
The TFC of raw carrots was 0.43 mg QE/g dw (Table 2). Chatatikun and Chiabchalard [42] determined the flavonoid content of the carrots they studied to be 20.4 mg GAE/g of dry plant material. In the present study, as in the case of the TPC, heat-treated carrots, regardless of the treatment method used, had a higher flavonoid content than that of raw carrots. In the heat-treated samples, the flavonoid content ranged from 0.69 (steam-cooked carrots in a combi oven) to 0.97 mg QE/g dw (water-cooked carrots and baked carrots). Razzak et al. [47] found lower flavonoid content in water-cooked, steamed, and microwaved carrots than in raw carrots by 4.27%, 11.32%, and 22.28%, respectively. Bembem and Sadana [21] report that flavonoid content decreased in carrots cooked in water, steam, a microwave, and pressure cooking by 6.3, 8.6, 21.1, and 15.4%, respectively, and increased by 30.2% during frying (sautéing). Thanuja et al. [23] reported that cooking carrots in water had no significant effect on flavonoid content, while microwave cooking significantly increased the amount of these compounds. Stir-fried carrots showed significantly lower flavonoid content than that of carrots cooked in water or microwave.

3.3. Phenolic Compound Profile

Seven phenolic compounds were identified in raw carrots (Table 3): six phenolic acids (caffeic, chlorogenic, ferulic, m-coumaric, p-coumaric, and vanillic acids) and one flavonoid (rutin). Among these, chlorogenic acid was the most abundant (1026.10 µg/g dw), constituting 58.4% of all detected phenolic compounds. Miglio et al. [28] and Ashour and El-Hamzy [29] identified only three phenolic acids in raw carrots: chlorogenic, caffeic, and p-coumaric acids, with chlorogenic acid being the most abundant. Chiavaro et al. [4] reported the presence of five phenolic acids (caffeic, p-coumaric, sinapic, chlorogenic, and ferulic acids) and three flavonoids (quercetin, kaempferol, and luteolin) in raw carrots, with p-coumaric acid as the dominant compound, accounting for 33.7% of the total phenolic content.
In our study, all phenolic acids present in raw carrots, except for vanillic acid, were detected in heat-treated samples. Among the flavonoids, quercetin-3-O-glucoside was identified in all heat-treated carrot samples, whereas quercetin was only found in carrots boiled in water. Quercetin is a flavonoid commonly found in plants in glycosylated forms, such as quercetin 3-O-glucoside (Q3G), where it is bound to sugar molecules [48,49]. Heat treatment, such as boiling, facilitates the hydrolysis of these glycosidic bonds, leading to the release of quercetin [50]. The high temperatures disrupt the bonds between the sugar moiety and the quercetin aglycone, increasing the concentration of free quercetin [51]. Moreover, heat can also break down more complex flavonoids or polyphenols, converting them into simpler molecule forms, such as quercetin [52]. In raw plant tissues, glycosylated forms like Q3G are often sequestered within the cellular matrix, making them difficult to extract or detect analytically [53]. Treatments such as boiling breakdown cell walls and the surrounding matrix release these compounds into an extractable form [54]. Unlike free quercetin, which can be degraded by prolonged or intense heating, glycosylated forms are more stable during intermediate heat treatments due to the protective effect of sugar moiety on the core structure of the flavonoid [55,56]. Chlorogenic acid remained the predominant phenolic compound in heat-treated carrots, ranging from 52.6% in sous-vide samples to 70.2% in carrots steamed in a steel pot. Miglio et al. [28] and Ashour and El-Hamzy [29] identified three phenolic acids—chlorogenic, caffeic, and p-coumaric—in steamed and fried carrots, with caffeic acid predominating while no phenolic acids were detected in boiled carrots. Chiavaro et al. [4] detected five phenolic acids (caffeic, p-coumaric, sinapic, chlorogenic, and ferulic) and three flavonoids (quercetin, kaempferol, and luteolin) in carrots steamed in a convection-steam oven, with p-coumaric acid as the most abundant.
Our results indicate a general increase in the individual phenolic acid content after the heat treatment of carrots. The total phenolic acid content in raw carrots was 1718.18 µg/g dw, compared to 1744.68 µg/g dw in sous-vide-treated carrots, with no statistically significant difference between these samples. However, the phenolic acid content of carrots steamed in a combi oven, baked, steamed in a steel pot, and boiled in water was 2320.66 µg/g dw, 2845.88 µg/g dw, 3021.11 µg/g dw, and 3573.25 µg/g dw, respectively, significantly higher than in raw carrots. This study also observed a significant increase in the total flavonoid content after heat treatment, with the highest concentration found in traditionally boiled carrots, approximately 7.5 times higher than in raw carrots. No significant difference in flavonoid content was observed between carrots cooked using sous-vide (143.75 µg/g dw) and those steamed in a steel pot (143.85 µg/g dw), nor between samples steamed in a combi oven (145.48 µg/g dw) and baked (145.54 µg/g dw). However, losses of specific phenolic compounds such as vanillic acid and rutin were noted in all heat-treated samples. Chiavaro et al. [4] reported a decrease in the content of caffeic acid, p-coumaric acid, chlorogenic acid, ferulic acid, quercetin, and kaempferol as a result of steaming carrots, while the levels of sinapic acid and luteolin increased after this process. Similarly, Miglio et al. [28] found that boiling carrots led to a complete loss of chlorogenic acid, caffeic acid, and p-coumaric acid due to their diffusion into the cooking water. The authors also observed a decrease in chlorogenic acid content and an increase in caffeic acid content when carrots were steamed or fried compared to raw samples. This increase in caffeic acid could be attributed to the hydrolysis of chlorogenic acid into caffeic and quinic acids, explaining the significant increase in caffeic acid observed with these cooking methods. Additionally, polyphenol losses may be due to covalent bonds between oxidized phenols and proteins or amino acids, as well as the polymerization of oxidized phenols [28].
Analyzing the total phenolic compounds detected by UHPLC-DAD-MS, the phenolic content in the carrot samples increased in the following order: raw sample < sous-vide < steaming (combi oven) < baking < steaming (steel pot) < boiling. The increase in phenolic compounds observed during cooking can be explained by their localization and structural association within plant tissues. Phenolic compounds are typically stored in vacuoles and the apoplast, while others are bound to cell wall components as insoluble phenolic compounds. Cooking processes, particularly those involving heat and moisture, disrupt cellular structures such as membranes and cell walls. This breakdown facilitates the release of bound phenolic compounds into a soluble and extractable form, thereby increasing their detectable concentration in cooked samples [4,55].

3.4. Carotenoid Profile

Carotenoids are pigment compounds responsible for the characteristic orange color of carrots. The primary carotenoids identified in the analyzed samples included lutein, zeaxanthin, β-cryptoxanthin, various isomers of β-carotene, and α-carotene (Table 4). The total carotenoid content in raw carrot was 314.07 µg/g dw, and this amount increased in all heat-treated samples. The most substantial increases (over 47%) were observed in carrots after boiling and baking, with total carotenoid contents reaching 462.35 and 463.83 µg/g dw, respectively. In contrast, the sous-vide method had the smallest impact on the total carotenoid content, resulting in an increase of only 16% compared to that of the raw sample. In all carrot samples analyzed, β-carotene was the dominant carotenoid, accounting for 48–59% of the total carotenoid content. In raw carrots, β-carotene was present at 152.29 µg/g dw, and after heat treatment, its content increased by approximately 25% (steaming in a combi oven) to about 79% (baking). Lutein was the second most abundant carotenoid, although its concentration was more than four times lower than that of β-carotene. Notably, the changes in lutein content due to heat treatment were, in most cases, greater than those observed for β-carotene. The highest lutein content (53.15 µg/g dw) was found in carrots subjected to steaming in a steel pot. Heat treatment also had a positive effect on the levels of β-cryptoxanthin and 15-cis-β-carotene, with concentrations ranging from 26.36 to 50.94 µg/g dw across the samples. In contrast, no significant changes or degradation were observed for zeaxanthin, 13-cis-β-carotene, or α-carotene. However, a greater decrease in the content of these carotenoids (approximately 30% from the raw sample) was observed in carrots subjected to boiling and baking.
Changes in carotenoid content have also been noted by other researchers. For example, Ashour and El-Hamzy [29] found that cooking had a small but significant effect on these compounds, with boiling increasing the initial carotenoid content by about 15.1%, but steaming caused a slight decrease in them. The cited authors, as in the present study, noted a decrease in a-carotene content and an increase in lutein content due to boiling. An increase in the contents of total carotenoids and β-carotene after boiling and steaming was also shown by Bemben and Sadana [21] and Miglio et al. [28], with the changes being much greater after boiling, which was also confirmed in the present study. In contrast, Chiavaro et al. [4] showed a significantly higher increase in carotenoid content with the sous-vide method than with steaming. Buratti et al. [24] and Stanikowski et al. [26] reported that changes in carrots depend not only on the processing method, but also on its duration. In contrast, Lim et al. [30] showed that thermal processing leads to carotene loss, whereas lutein content can be increased by boiling or decreased by baking. Higher carotenoid content in heat-treated carrots is likely the result of the increased release of these compounds from cell structures and their higher extraction with solvent, as temperatures ranging from 65 to 95 °C disrupt the organelle membrane structure and/or protein–carotenoid interactions [57]. Hornero-Méndez and Mínguez-Mosquera [58] found that even though cooking heat treatment can have a negative effect on carotenoid content, it has a positive effect on the micellization of carotenes and thus increases their bioavailability.

3.5. Antioxidant Capacity

The results of the antioxidant capacity of the tested carrot samples are shown in Figure 2. Analysis of the DPPH radical scavenging test showed a significant increase (p < 0.05) in scavenging activity following the heat treatment of carrots. The baseline DPPH radical scavenging activity for raw carrot samples was 4.89 µmol TE/g dw. The antioxidant capacity of raw carrots determined by the ABTS radical assay was 5.53 µmol TE/g dw, while for heat-treated samples it ranged from 8.31 µmol TE/g dw (sous-vide-cooked carrots) to 14.57 µmol TE/g dw (traditionally cooked carrots in water). Among the samples analyzed, only steamed carrots in a steel pot and baked carrots did not differ significantly (p ≤ 0.05) in terms of antioxidant capacity.
The antioxidant properties in raw carrots are influenced by factors such as variety, growing season, location of cultivation [59], farming system (organic vs. conventional) [25], and storage conditions [60,61]. Among the thermally processed samples, the lowest DPPH radical scavenging activity was observed in sous-vide-cooked carrots (8.01 µmol TE/g dw), while conventionally boiled carrots demonstrated the highest activity, approximately 3.3 times greater than that of raw carrots. The highest antioxidant capacity observed in carrots prepared by boiling may be attributed to their elevated levels of phenolic compounds (Table 3) and carotenoids (Table 4). Additionally, the presence of quercetin in the sample (Table 3), a compound characterized by its potent antioxidant activity [62], likely contributes to this enhanced antioxidant capacity. Similarly, Razzak et al. [47] reported increases in DPPH scavenging activity in carrots cooked by boiling, steaming, and microwaving, showing activity levels elevated by 17.52%, 30.84%, and 26.07% compared to in raw carrots. Bembem and Sadana [21] observed the highest DPPH activity in microwave-cooked samples (13.75%) compared to in pressure-cooked (13.35%), fried (13.20%), steamed (17.4%), and boiled (13.0%) ones, with raw carrots demonstrating the lowest activity (11.20%).
Thanuja et al. [23] reported no change in DPPH scavenging activity with stir-frying, whereas microwave cooking and boiling significantly reduced DPPH activity. Jiménez-Monreal et al. [63] noted increases in ABTS radical anion scavenging after boiling (66.7%), pressure cooking (79.8%), baking (111.1%), microwaving (142.2%), griddling (191.1%), and frying (191.2%). Enhanced antioxidant properties following thermal processing may result from the release of antioxidants due to cell wall breakdown, the formation of thermally generated radical-scavenging compounds, the inhibition of oxidative enzymes, and the formation of new antioxidant compounds such as Maillard reaction products [63]. Kosewski et al. [27] observed a significant decrease in DPPH activity in carrots boiled in water, while sous-vide treatment resulted in a notable increase. For certain vegetables, sous-vide processing has demonstrated a higher antioxidant potential compared to that of conventional cooking. This effect may be due to reduced cell wall degradation and nutrient leaching in sous-vide cooking due to lower temperatures and vacuum-sealing, which help to preserve antioxidant compounds, including vitamins and minerals [27].
Table 5 shows the correlation coefficients (r) between antioxidant capacity and color and content of bioactive compounds. The obtained values indicate that the antioxidant capacity of carrot samples was positively correlated with the TPC and the content of selected phenolic acids and carotenoids. It seems that the contents of chlorogenic acid, p-coumaric acid, lutein, and β-carotene are of great importance (statistically significant, p ≤ 0.05) for the antioxidant capacity of carrot root (r > 0.86). The effect of color parameters and other compounds analyzed on the antioxidant capacity was not statistically significant, although most of the r values indicated moderate or strong correlations. It was noted that there were some strong negative correlations between antioxidant capacity and color parameters as well as vanillic acid, rutin, zeaxanthin, 13-cis-β-carotene, and α-carotene (r ranging from −0.58 to −0.80). The strong positive correlations were observed between antioxidant capacity and FC, caffeic acid, quercetin, quercetin-3-O-glucoside, and 15-cis-β-carotene, while ferulic acid and β-cryptoxanthin were moderately correlated with antioxidant capacity. In turn, m-coumaric acid and 9-cis-β-carotene were not affected by antioxidant capacity.
Positive correlations between total phenolic content and antioxidant properties in carrot samples, as confirmed in this study, have also been documented by other researchers using DPPH [6,61,64,65] and ABTS [59] assays. However, Jacobo-Velázquez and Cisneros-Zevallos [64] emphasized that this relationship may not accurately represent the antioxidant properties of individual phenolic compounds. Evidence from the literature suggests that the antioxidant efficacy of a specific phenolic compound is influenced by various factors, including the number of hydroxyl groups in its chemical structure. Furthermore, the proximity of the carboxylate group and hydroxyl groups on the phenolic ring in hydroxybenzoic acids negatively impacts their proton-donating capacity. Consequently, hydroxycinnamic acids generally exhibit higher antioxidant activity compared to that of their hydroxybenzoic counterparts [62,66]. The strong correlation coefficients (r values) observed in this study between the DPPH assay results and the concentrations of p-coumaric, caffeic, chlorogenic, and ferulic acids seem to support this conclusion. Moreover, phenolic compounds can also interact synergistically, additively, or antagonistically with other bioactive compounds, which consequently affects the total antioxidant capacity [65,66]. Consistent with the findings of the present study, Bozalan and Karadeniz [59] reported strong positive correlation coefficients (ranging from 0.61 to 0.97) between antioxidant activity and total carotenoid content. Furthermore, they observed a significant correlation between antioxidant activity and lutein content, a result also noted in the present study. However, Bozalan and Karadeniz [59] found no significant correlation between antioxidant activity and the β-carotene or α-carotene content in carrot samples.

3.6. Multivariate Analysis (PCA)

To present the variation in physico-chemical characteristics among carrot samples, a principal component analysis (PCA) was applied (Figure 3). It was found that the first two principal components (PC 1 and PC 2) accounted for 80.8% of the variation in the original data. The PCA analysis showed the grouping of heat-treated carrot samples, while the raw carrot was clearly distinguished from each other. The raw carrot was generally characterized by a lighter color with a higher proportion of both yellow and red tones, as well as the highest content of 13-cis-β-carotene, and the presence vanillic acid and rutin. Steamed in a combi oven and sous-vide-cooked carrots were distinguished by their higher content of ferulic acids, but the content of some phenolic compounds (chlorogenic and p-coumaric acids) and carotenoids (β-carotene, lutein, and 15-cis-β-carotene) as well as antioxidant capacity (determined by both assays) in these samples showed high similarity to those in boiled carrots. In contrast, carrot samples prepared by steaming in a combi oven and sous-vide were distinguished by the content of m-coumaric acid and 9-cis-β-carotene.

4. Conclusions

In summary, this study demonstrated the different effects of thermal processing methods (boiling in water, steaming in a pot, steaming in a combi oven, baking, and sous-vide cooking) on the color, phenolic compound content and profile, carotenoid profile, and antioxidant capacity of whole carrot roots. Regardless of the processing method applied to carrot roots, an increase in the content of bioactive compounds and antioxidant capacity (measured by DPPH and ABTS assays) was found. The sous-vide technique resulted in the smallest changes in phenolic compound and carotenoid contents, as well as antioxidant capacity, compared to those of raw carrot roots. However, significant losses of specific phenolic compounds (vanillic acid and rutin) and carotenoids (α-carotene, zeaxanthin, and 13-cis-β-carotene) were observed after processing.
This study provides valuable insights for both industrial processors and consumers, enabling informed choices to balance carrot quality with practical processing and cooking considerations. The results indicate that heat treatment of whole, unpeeled roots using traditional techniques, such as boiling or baking, significantly enhances the release of phenolic compounds and carotenoids, which positively impact the antioxidant capacity of processed carrots. This presents an opportunity for producers to improve the nutritional value of carrot-based products. While many researchers highlight the advantages of the sous-vide technique over traditional cooking methods, our study demonstrated that steaming in the oven may be a more attractive option for consumers. This method not only improves the bioavailability of bioactive compounds (particularly phenolic compounds) to a greater extent than sous-vide but also minimally alters the characteristic orange hue of carrots compared to all the other heat treatments applied.
Future research could expand on these findings by investigating the effects of different pre-treatment methods for carrots, such as peeling versus non-peeling, slicing versus whole processing, and variations in slicing techniques. Such investigations could provide valuable insight into how surface exposure, internal structure, and tissue integrity influence the retention or degradation of key nutrients, antioxidants, and other bioactive compounds during heat treatment. Moreover, the role of processing parameters, including cooking time, temperature, and their interactions with pre-treatment methods, warrants further exploration. For example, studies could examine how variations in sous-vide temperature or steaming time affect bioactive compound profiles and sensory characteristics. Investigating the combined effects of pre-treatment and specific cooking techniques on nutrient retention, antioxidant capacity, and sensory properties may facilitate the optimization of thermal processing to preserve the nutritional value and health-promoting properties of carrots.

Author Contributions

Conceptualization, A.N.; methodology, A.N., T.S., B.P. and M.T.; formal analysis, A.N., T.S., B.P. and M.T.; investigation, A.N., T.S., B.P. and M.T.; resources, A.N.; data curation, A.N., T.S. and M.T.; writing—original draft preparation, A.N., T.S., B.P. and M.T.; writing—review and editing, A.N. and M.T.; visualization, A.N. and M.T.; supervision, A.N. and T.S.; project administration, A.N.; funding acquisition, A.N. and T.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Images of carrot root cross-sections: raw sample (A) and processed by boiling (B), steaming in steel pot (C), steaming in combi oven (D), baking (E), and sous-vide (F).
Figure 1. Images of carrot root cross-sections: raw sample (A) and processed by boiling (B), steaming in steel pot (C), steaming in combi oven (D), baking (E), and sous-vide (F).
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Figure 2. Antioxidant capacity of carrot root before and after different heat treatments. Data are expressed as mean value ± standard deviation (n = 3). Different letters within the DPPH and ABTS assays indicate statistically significant differences (p ≤ 0.05).
Figure 2. Antioxidant capacity of carrot root before and after different heat treatments. Data are expressed as mean value ± standard deviation (n = 3). Different letters within the DPPH and ABTS assays indicate statistically significant differences (p ≤ 0.05).
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Figure 3. PCA plot defined by the first two principal components (PC 1 and PC 2), illustrating the relationships among the analyzed carrot samples and the identified similarity groups (a), as well as the relationships among the analyzed physical and chemical properties (b).
Figure 3. PCA plot defined by the first two principal components (PC 1 and PC 2), illustrating the relationships among the analyzed carrot samples and the identified similarity groups (a), as well as the relationships among the analyzed physical and chemical properties (b).
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Table 1. Color parameters of carrot before and after different heat treatments.
Table 1. Color parameters of carrot before and after different heat treatments.
Method of Heat TreatmentL*a*b*C*ΔE
Raw sample53.35 ± 1.41 c24.80 ± 2.46 d29.28 ± 1.05 c38.39 ± 2.25 c-
Boiling40.74 ± 2.75 a10.66 ± 1.59 bc22.40 ± 2.60 a24.81 ± 3.02 a20.16
Steaming
in steel pot		41.58 ± 1.03 ab10.09 ± 1.62 abc23.40 ± 0.84 ab25.54 ± 0.74 ab19.74
Steaming
in combi oven		43.17 ± 1.44 b8.99 ± 0.90 ab24.92 ± 1.29 b26.50 ± 1.44 b19.30
Baking42.72 ± 0.50 ab11.99 ± 2.22 c24.23 ± 0.34 b27.10 ± 1.04 b17.40
Sous-vide40.83 ± 1.93 a8.12 ± 1.41 a22.00 ± 1.12 a23.47 ± 1.50 a22.09
Data are expressed as mean value ± standard deviation (n = 6). Values in the same column with different superscript letters are significantly different (p ≤ 0.05).
Table 2. Total phenolic compound (TPC) and total flavonoid (TFC) contents of carrot roots before and after different heat treatments.
Table 2. Total phenolic compound (TPC) and total flavonoid (TFC) contents of carrot roots before and after different heat treatments.
Method of Heat TreatmentTPC
[mg GAE/g dw]		TFC
[mg QE/g dw]
Raw sample0.81 ± 0.06 a0.43 ± 0.01 a
Boiling1.75 ± 0.10 cd 0.97 ± 0.02 d
Steaming in steel pot1.89 ± 0.11 d0.83 ± 0.01 c
Steaming in combi oven1.33 ± 0.05 b0.69 ± 0.02 b
Baking1.68 ± 0.09 c0.97 ± 0.02 d
Sous-vide1.01 ± 0.04 a0.93 ± 0.02 d
Data are expressed as mean value ± standard deviation (n = 3). Values in the same column with different superscript letters are significantly different (p ≤ 0.05).
Table 3. Phenolic profile and content (µg/g dw) of carrot root before and after different heat treatments.
Table 3. Phenolic profile and content (µg/g dw) of carrot root before and after different heat treatments.
Phenolic CompoundMethod of Heat Treatment
Raw SampleBoilingSteaming in Steel PotSteaming in Combi OvenBakingSous-Vide
Caffeic acid253.30 ± 0.03 a460.60 ± 5.73 f354.21 ± 0.83 c424.21 ± 1.06 e404.16 ± 3.79 d327.62 ± 1.39 b
Chlorogenic acid1026.10 ± 16.28 a2674.49 ± 26.55 e2223.27 ± 8.60 d1473.49 ± 19.01 b2002.19 ± 0.63 c992.40 ± 1.64 a
Ferulic acid162.56 ± 0.11 b163.93 ± 0.11 b177.15 ± 1.28 c154.75 ± 1.76 a172.75 ± 1.85 c160.11 ± 1.49 b
m-Coumaric acid183.83 ± 0.00 a192.15 ± 0.84 d185.75 ± 0.02 b192.06 ± 0.67 d183.83 ± 0.00 a190.00 ± 0.35 c
p-Coumaric acid71.80 ± 0.01 a82.08 ± 0.21 c80.74 ± 0.93 c76.13 ± 1.07 b82.95 ± 0.11 c74.54 ± 0.05 b
Vanillic acid20.59 ± 0.000.00 ± 0.000.00 ± 0.000.00 ± 0.000.00 ± 0.000.00 ± 0.00
Sum of phenolic acids1718.18 ± 16.16 a3573.25 ± 31.12 e3021.11 ± 9.75 d2320.66 ± 20.04 b2845.88 ± 4.91 c1744.68 ± 4.22 a
Quercetin0.00 ± 0.00 a144.71 ± 0.07 b0.00 ± 0.00 a0.00 ± 0.00 a0.00 ± 0.00 a0.00 ± 0.00 a
Quercetin-3-O-glucoside0.00 ± 0.00 a145.60 ± 0.21 c143.85 ± 0.05 b145.48 ± 0.31 c145.54 ± 0.07 c143.75 ± 0.04 b
Rutin38.73 ± 0.05 a0.00 ± 0.00 b0.00 ± 0.00 b0.00 ± 0.00 b0.00 ± 0.00 b0.00 ± 0.00 b
Sum of flavonoids38.73 ± 0.05 a290.31 ± 0.14 d143.85 ± 0.05 b145.48 ± 0.31 c145.54 ± 0.07 c143.75 ± 0.04 b
Sum of phenolic compounds1756.91 ± 16.21 a3863.57 ± 31.26 f3164.97 ± 9.80 e2466.13 ± 20.35 c2991.42 ± 4.97 d1888.42 ± 4.25 b
Data are expressed as mean value ± standard deviation (n = 3). Values in the same line with different superscript letters are significantly different (p ≤ 0.05).
Table 4. Content of major carotenoids (µg/g dw) in carrot root before and after different heat treatments.
Table 4. Content of major carotenoids (µg/g dw) in carrot root before and after different heat treatments.
CarotenoidMethod of Heat Treatment
Raw SampleBoilingSteaming in Steel PotSteaming in Combi OvenBakingSous-Vide
Lutein29.87 ± 2.50 a51.03 ± 0.13 c53.15 ± 1.09 c43.59 ± 1.74 b49.84 ± 0.43 c40.58 ± 0.19 b
Zeaxanthin20.60 ± 0.64 c14.70 ± 1.58 ab14.69 ± 0.91 ab21.55 ± 0.51 c13.74 ± 0.11 a18.08 ± 1.33 bc
β-cryptoxanthin24.46 ± 0.32 a27.37 ± 0.54 ab32.33 ± 0.13 c32.87 ± 1.06 c28.25 ± 1.36 b26.36 ± 0.73 ab
15-cis-β-carotene24.86 ± 0.33 a45.99 ± 0.18 d30.41 ± 0.81 b37.81 ± 0.74 c50.94 ± 1.38 e26.46 ± 1.11 a
13-cis-β-carotene21.13 ± 0.01 b13.84 ± 0.23 a16.60 ± 0.57 ab12.53 ± 2.44 a14.60 ± 0.85 a20.05 ± 1.54 b
α-carotene20.14 ± 0.51 bc15.94 ± 1.88 a14.97 ± 1.14 a21.40 ± 0.44 c13.40 ± 0.42 a17.24 ± 0.43 ab
β-carotene152.29 ± 4.10 a270.08 ± 6.72 d218.01 ± 3.99 c190.05 ± 7.13 b272.22 ± 5.33 d193.09 ± 5.90 b
9-cis-β-carotene20.71 ± 0.12 a23.40 ± 1.43 ab20.19 ± 0.62 a24.69 ± 0.37 b20.84 ± 0.68 a23.09 ± 1.60 ab
Sum of carotenoids314.07 ± 5.96 a462.35 ± 0.76 d400.34 ± 6.81 c384.50 ± 11.57 bc463.83 ± 5.38 d364.95 ± 0.22 b
Data are expressed as mean value ± standard deviation (n = 6). Values in the same line with different superscript letters are significantly different (p ≤ 0.05).
Table 5. Pearson correlation coefficients (r) showing the relationships between antioxidant capacity and color parameters and the content of bioactive compounds.
Table 5. Pearson correlation coefficients (r) showing the relationships between antioxidant capacity and color parameters and the content of bioactive compounds.
Color Parameter/Content of Bioactive CompoundsAntioxidant Capacity
DPPH AssayABTS Assay
L* parameter−0.73−0.75
a* parameter−0.58−0.61
b* parameter−0.68−0.68
TPC0.96 *0.95 *
TFC0.740.78
Caffeic acid0.780.84 *
Chlorogenic acid0.96 *0.95 *
Ferulic acid0.530.48
m-Coumaric acid0.250.27
p-Coumaric acid0.93 *0.96 *
Vanillic acid−0.70−0.74
Sum of phenolic acids0.97 *0.96 *
Quercetin0.610.59
Quercetin-3-O-glucoside0.700.75
Rutin−0.70−0.74
Sum of flavonoids0.83 *0.84 *
Lutein0.95 *0.95 *
Zeaxanthin−0.80−0.80
β-cryptoxanthin0.440.44
15-cis-β-carotene0.660.76
13-cis-β-carotene−0.67−0.74
α-carotene−0.68−0.69
β-carotene0.86 *0.92 *
9-cis-β-carotene0.000.06
Sum of carotenoids0.88 *0.94 *
* Correlation coefficient statistically significant (p ≤ 0.05); TPC—total phenolic content; TFC—total flavonoid content.
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Narwojsz, A.; Sawicki, T.; Piłat, B.; Tańska, M. Effect of Heat Treatment Methods on Color, Bioactive Compound Content, and Antioxidant Capacity of Carrot Root. Appl. Sci. 2025, 15, 254. https://doi.org/10.3390/app15010254

AMA Style

Narwojsz A, Sawicki T, Piłat B, Tańska M. Effect of Heat Treatment Methods on Color, Bioactive Compound Content, and Antioxidant Capacity of Carrot Root. Applied Sciences. 2025; 15(1):254. https://doi.org/10.3390/app15010254

Chicago/Turabian Style

Narwojsz, Agnieszka, Tomasz Sawicki, Beata Piłat, and Małgorzata Tańska. 2025. "Effect of Heat Treatment Methods on Color, Bioactive Compound Content, and Antioxidant Capacity of Carrot Root" Applied Sciences 15, no. 1: 254. https://doi.org/10.3390/app15010254

APA Style

Narwojsz, A., Sawicki, T., Piłat, B., & Tańska, M. (2025). Effect of Heat Treatment Methods on Color, Bioactive Compound Content, and Antioxidant Capacity of Carrot Root. Applied Sciences, 15(1), 254. https://doi.org/10.3390/app15010254

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