Comparison of Antioxidant Activity of Commercial Beetroot (Beta vulgaris) Supplements and Beverages Available on the Polish Market

Abstract

Background: Due to its richness in bioactive compounds and health-promoting properties, beetroot is widely used in dietary supplements available in the form of powder, tablets, capsules, as well as in the form of beetroot juice and beetroot kvass. Methods: In this study, the antioxidant potential of selected beetroot supplements in solid form and beetroot drinks available on the Polish market was compared using ABTS⁺ and DPPH radical scavenging assays. Total polyphenol content was also determined using the Folin–Ciocalteu colorimetric method. The study material included two products each in powder, capsule, and tablet form, as well as three beetroot juices and three beetroot sourdoughs. Results: Among solid supplements, powders had the highest polyphenol content (up to 12.9 mg GAE/g) and the highest antioxidant potential, while the lowest values were recorded in tablets (4.20 mg GAE/g). When calculated per recommended dose, these differences were even more pronounced (129 mg GAE/dose for powders vs. 0.67 mg GAE/dose for tablets). In the liquid product group, beetroot juices contained significantly more polyphenols than sourdoughs (up to 2828 vs. 230 mg GAE/100 mL) and showed higher antioxidant activity, especially in the DPPH test. Conclusions: Based on the results obtained, it was found that among solid supplements, powders had the highest polyphenol content and the highest antioxidant potential, especially when calculated per recommended dose. In the group of liquid products, juices showed higher antioxidant activity, especially in the DPPH test, compared to beetroot leaven.

1. Introduction

Beetroot (Beta vulgaris L. var. rubra L.) is a root vegetable belonging to the Chenopodiaceae family [1]. Its root has a wide range of culinary uses—it is eaten boiled, baked, and as an ingredient in juices and beetroot kvass. In the food industry, beetroot is used to produce natural colorings, such as betanin (E162), which give products an intense red color. Due to its high nutritional value and potential health benefits, beetroot has gained the status of a functional food and is available in various forms of dietary supplements, including powdered concentrate, freeze-dried juice, and beetroot leaven, offered in tablets, capsules, powder, or liquids [2,3].

The root of red beet is a rich source of bioactive compounds, including vitamins (C, A, E, K, and B), minerals (potassium, sodium, phosphorus, magnesium, calcium, iron, zinc, selenium), nitrates, and phenolic compounds. Particularly important are the betalains present in beetroot—pigments with strong antioxidant and anti-inflammatory properties [4]. In addition, beetroot contains other compounds with antioxidant potential, such as carotenoids, flavonoids (e.g., astragalin, tiliroside, ramnocitrin, kaempferol, ramnetin), coumarins, triterpenes, and sesquiterpenoids [1,2,3].

The antioxidant effect of beetroot is based on the neutralization of reactive oxygen species (ROS), which helps protect cells from oxidative stress [5,6]—a condition associated with the development of many chronic diseases, such as atherosclerosis, cardiovascular diseases, type 2 diabetes, neurodegenerative diseases (e.g., Alzheimer’s and Parkinson’s disease), and cancer. The phytochemical diversity of red beetroot also determines its immune-stimulating, gastric mucosa-protective, antiseptic, antipyretic, choleretic, antimicrobial, and anti-inflammatory properties, as well as its ability to influence the composition and activity of the gut microbiome [3]. There are numerous dietary supplements containing red beet extracts available on the market, offered in various forms, such as powder, tablets, capsules, or liquids [2,7]. The content and bioavailability of bioactive ingredients in these preparations may vary depending on the production technology used and the degree of processing of the raw material [3]. Regular supplementation with beetroot-based products may support the body in fighting oxidative stress and inflammation, but its effectiveness depends on the quality and composition of the specific preparation.

This study compared the antioxidant potential of selected beetroot supplements available on the Polish market in solid form and in the form of beetroot drinks. The aim of the study was not to provide a detailed phytochemical characterization of beetroot, but rather to perform a comparative assessment of the antioxidant potential of commercially available beetroot products representing different technological forms, with particular emphasis on their antioxidant activity per recommended daily dose.

2. Materials and Methods

2.1. Research Material

The research material came from Polish producers and included two types of powders containing dried beetroot (numbers: 1, 2), two types of capsules containing beetroot extract (numbers: 3, 4), two types of tablets, one containing beetroot extract and the other dried beetroot juice (numbers: 5, 6), three natural beetroot juices without additives (numbers: 7, 8, 9) and two natural beetroot kvasses (numbers: 10, 11). The products were purchased in health food stores, pharmacies, and herbal shops. One of the leavens was made by one of the researchers (number: 12). Sample No. 12 was prepared using spontaneous fermentation, without the addition of any commercial or defined starter cultures. The tests were carried out immediately after the date of purchase, and the products did not exceed their expiry date. The leaven was analyzed after 5 days of fermentation. Natural sediment was observed in beetroot juices and beetroot kvass, which is typical for these products; however, this sediment was not collected for analysis, and only the clear liquid fraction was used for further determinations. The remaining samples did not exhibit visible turbidity or sediment. Blank samples were prepared for each extract to correct for the potential influence of intense color on absorbance measurements. The characteristics of the tested products and their dosages are presented in

Table 1. Characteristics of the tested supplements, juices, and beetroot leavens.

Product Number	Product Category	Product Form	Processing Method	Extract Content/Declared Composition	Dosage	Auxiliary Substances/Additives (Declared by the Manufacturer)
1	Dietary supplements	Dried beetroot powder	Drying	Whole beetroot, dried	10.0 g/day	no additives, preservatives or colorings
2	Dietary supplements	Freeze-dried beetroot powder	Freeze-drying (lyophilization)	Whole beetroot, freeze-dried	10.0 g/day	no additives, preservatives or colorings
3	Dietary supplements	Capsules containing beetroot extract	Extraction and encapsulation	Beetroot extract 10:1 (300 mg per capsule)	2 capsules/day	no additives, capsule shell: vegetable cellulose
4	Dietary supplements	Capsules containing beetroot extract	Extraction and encapsulation	Beetroot extract (500 mg per capsule)	1 capsule/day	no additives capsule shell: gelatin
5	Dietary supplements	Tablets containing beetroot extract	Extraction and tableting	Beetroot extract 20:1 (80 mg per tablet)	1–2 tablets/day	binding agent—dicalcium phosphate, emulsifier—microcrystalline cellulose, stabiliser—magnesium salts of fatty acids
6	Dietary supplements	Tablets containing dried beetroot juice	Juice drying and tableting	Dried beetroot juice (500 mg per tablet)	3–6 tablets/day	anti-caking agents: magnesium salts of fatty acids and silicon dioxide
7	Juices	Beetroot juice (100%)	Juice pressing	100% beetroot juice	250 mL/day	no additives
8	Juices	Juice from concentrated (99.3%)	Juice pressing and concentration	Juice from concentrated beetroot juice (99.3%)	250 mL/day	salt
9	Juices	Beetroot juice (100%)	Juice pressing	100% beetroot juice	250 mL/day	no additives
10	Fermented beetroot beverages (kvass)	Commercial beetroot kvass (Producer A)	Commercial fermentation	Beetroot kvass	250 mL/day	organic garlic 1%, Kłodawa salt 1%
11	Fermented beetroot beverages (kvass)	Commercial beetroot kvass (Producer B)	Commercial fermentation	Beetroot kvass	250 mL/day	English herbs, bay leaf, pepper, garlic, water, Kłodawa rock salt
12	Fermented beetroot beverages (kvass)	Beetroot kvass prepared by spontaneous fermentation (laboratory sample)	Spontaneous fermentation (laboratory conditions)	Beetroot kvass	250 mL/day	garlic 1%, salt 1%

.

Information on product composition, including the presence of excipients, was obtained from manufacturers’ declarations provided on product labels and official websites; however, in some cases, detailed information on excipients was incomplete or unavailable.

2.2. Test Methodology

2.2.1. Extraction

Phenolic compounds were extracted by weighing 1.0 g of the tested powders, crushed tablets, or capsule contents. The weighed products were transferred to test tubes, and 10 mL of 80% acidified methanol (0.1% HCl) was added. The test tubes were closed and mixed for 30 s, then placed in an ultrasonic bath for 3 min at a temperature of 30 ± 5 °C. The samples were then centrifuged at 3000 rpm for 10 min at a temperature of 25 °C. After centrifugation, the supernatant was collected, and the solid residue was subjected to a second extraction. Finally, both supernatants were combined, and the prepared samples were subjected to further analysis. Samples for juice and acid analysis were taken from the original packaging without prior extraction. It should be noted that liquid beetroot products were analyzed without prior extraction, which may result in partial overlap of naturally occurring pigments with the absorbance wavelengths used in spectrophotometric assays. Therefore, the results obtained for juices and beetroot kvass should be interpreted with appropriate caution.

2.2.2. Determination of Total Polyphenols

The total polyphenol content was determined using the Folin–Ciocalteu colorimetric method. To 0.2 mL of extract or 0.01 mL of juice, 0.2 mL of Folin–Ciocalteu reagent was added. After waiting 1 min, 0.4 mL of sodium carbonate was added, and the volume was made up to 2.0 mL with distilled water. After 90 min of incubation in the dark, the absorbance was measured at a wavelength of 760 nm using a UV-Vis spectrophotometer (UV-1500; Analytik, Jena, Germany). The results were expressed as the amount of gallic acid equivalents (GAL) per unit of mass or volume. For beetroot powders, capsules, and tablets, the results were additionally expressed per recommended dose in order to reflect actual dietary intake. The calibration curve (y = 0.5837x + 0.0096) was obtained from measurements of the absorbance of a standard solution of gallic acid (0.2 g/L).

2.2.3. Determination of Antioxidant Activity Using the ABTS⁺

The degree of ABTS⁺ free radical scavenging was determined using a spectrophotometric method based on the ability of substances contained in extracts or juices to neutralize the cation radical generated under the influence of potassium persulfate [8]. To 44.0 mL of phosphate buffer with a pH of 7.4, 0.5 mL of ABTS⁺ solution was added. Then, 2.0 mL of the mixture was transferred to test tubes, and 40.0 μL of juice or 20.0 μL of extract was added. The absorbance was measured at a wavelength of 734 nm. The antioxidant content was expressed as the amount of Trolox equivalents per unit of mass or volume.

2.2.4. Determination of Antioxidant Activity Using the DPPH Radical

The antioxidant activity of juices and extracts was also determined by spectrophotometry using a DPPH solution, based on the ability to neutralize the DPPH radical [9]. A 0.1 mM DPPH solution was prepared in methanol. Then, 2.0 mL of the DPPH solution was added to 10.0 μL of the extract and 20.0 μL of the juice. The mixture was stirred in a vortex mixer. The samples were left in the dark for 30 min. The absorbance was measured at a wavelength of 517 nm. The results were converted according to the Trolox standard curve.

2.2.5. Statistical Analysis

Statistical analysis was performed using PQStat Software (2024) v.1.8.6.120. Poznan, Poland. Descriptive statistics were used for the initial analysis. The Shapiro-Wilk test was used to check the normality of the distribution. For the comparative analysis of polyphenol content and ABTS⁺ and DPPH radical scavenging capacity between individual groups of preparations, the Student’s t-test, Mann–Whitney U test, ANOVA for independent groups, or Kruskal–Wallis ANOVA were used. In addition, the Dunn Benjamin-Hochberg or Fisher post hoc test was also performed. All results were subjected to statistical analysis with a significance level of α = 0.05.

3. Results

3.1. Antioxidant Potential of the Tested Products

The polyphenol content and ABTS⁺ and DPPH radical scavenging abilities of beetroot products are presented in

Table 2. Polyphenol content, ABTS⁺ and DPPH radical scavenging capacity in the analyzed beetroot powders, capsules and tablets.

Product Groups	Formulation	Polyphenol Content (mg GAL/g)	Ability to Remove ABTS Radicals (μM Trolox/g)	Ability to Remove DPPH Radicals (μM Trolox/1 g)
		X ± SD	X ± SD	X ± SD
I	(1)	12.9 ± 0.70 D	487 ± 21.5 A,B	5978 ± 50.1 A,B
	(2)	9.63 ± 0.48 C	582 ± 26.2 A,B	6193 ± 52.5 B
	p-value	0.0027	0.0084	0.0068
II	(3)	9.17 ± 0.57 C	1212 ± 32.5 B	6049 ± 34.9 A,B
	(4)	9.89 ± 0.18 C	564 ± 9.64 A,B	5533 ± 68.6 A
	p-value	0.1824	0.0495	0.0003
III	(5)	4.20 ± 0.38 A	93.2 ± 11.1 A	6084 ± 25.5 A,B
	(6)	5.71 ± 0.35 B	508 ± 31.4 A,B	6032 ± 96.8 A,B
	p-value	0.0076	0.0495	0.4193

X—mean, SD—standard deviation, I—beetroot powder, II—beetroot capsules, III—beetroot tablets; A, B, C, D—uppercase letters indicate statistically significant differences between all analyzed products regardless of group, based on ANOVA and post hoc tests; values sharing the same letter do not differ significantly (α = 0.05).

and

Table 3. Polyphenol content, ABTS⁺, and DPPH radical scavenging capacity in analyzed juices and ferments from red beetroot.

Product Groups	Formulation	Polyphenol Content (mg GAL/g)	Ability to Remove ABTS Radicals (μM Trolox/g)	Ability to Remove DPPH Radicals (μM Trolox/1 g)
		X ± SD	X ± SD	X ± SD
IV	(7)	1204 ± 154 a/B	9.77 ± 0.06 b a/A	27.2 ± 0.77 b/E
	(8)	2160 ± 80.9 b/D	9.91 ± 0.02 b/B	22.7 ± 0.41 a/C
	(9)	2828 ± 114 c/E	9.93 ± 0.08 b/B	28.9 ± 0.55 c/F
	p-value	<0.0001	0.0251	<0.0001
V	(10)	230 ± 17.5 a/A	9.92 ± 0.10 a/B	16.2 ± 0.24 a/A
	(11)	2331 ± 34.0 c/D	9.92 ± 0.04 a/B	25.3 ± 1.63 c/D
	(12)	1469 ± 51.9 b/C	9.93 ± 0.11 a/B	18.4 ± 0.23 b/B
	p-value	0.0273	0.9904	0.0001
All products statistical significance (p-value)		<0.0001	<0.0001	<0.0001

X—mean, SD—standard deviation, IV—beet juice, V—beet leaven; a, b, c—lowercase letters indicate statistically significant differences within the same product group based on ANOVA for independent samples followed by post hoc tests (Dunn or Fisher); A, B, C, D, E, F—uppercase letters indicate statistically significant differences between all analyzed products regardless of group, based on ANOVA and post hoc tests; values sharing the same letter do not differ significantly (α = 0.05).

.

3.1.1. Polyphenol Content in Beetroot Products

In the analyzed preparations in the form of powders, tablets, and capsules, the polyphenol content differed significantly when considering all preparations (p < 0.0001). Differences were also found within the group of tested powders (p = 0.0027) and tablets (p = 0.0076), while no differences were found in the capsule group. Only the polyphenol content in powder No. 2 and capsules No. 3 and 4 did not differ significantly. The highest polyphenol content was found in powder No. 1 (12.9 ± 0.70 mg GAE/g), while the lowest was found in tablet No. 5 (4.20 ± 0.38 mg GAE/g) (Table 2).

The analyzed beet juices and leavens also differed significantly in terms of polyphenol content, both in terms of the form of administration (juices vs. leavens) and in terms of all preparations in liquid form (p < 0.05), with the exception of preparations 8 and 11, which did not differ from each other. The lowest polyphenol content was found in leaven No. 10 (230 ± 17.5 mg GAL/100 mL), while the highest polyphenol content was found in juice No. 9 (2828 ± 114 mg GAL/100 mL), significantly exceeding the polyphenol content in beetroot kvasses (Table 3).

3.1.2. ABTS⁺ Radical Scavenging Capacity in Beetroot Products

The ability to scavenge ABTS⁺ radicals differed significantly within the groups of analyzed products (powders, capsules, tablets), depending on the manufacturer (p < 0.05). However, taking into account all analyzed products, a significant difference was found only between preparation No. 5 (tablet), which had the lowest ability to remove ABTS radicals (93.2 ± 11.1 µM Trolox/g), and preparation No. 3 with the highest ability to remove ABTS⁺ radicals (capsules) (1212 ± 32.5 µM Trolox/g). The differences between the other preparations were insignificant (Table 2).

The antioxidant activity measured by the ABTS method for juices ranged from 9.77 to 9.93 mM Trolox/100 mL (p = 0.0251), while for acidules it was similar (9.92–9.93 mM, p = 0.9904). Taking into account all the analyzed products, only the antioxidant activity measured by the ABTS method for juice No. 7 differed significantly from the others (Table 3).

3.1.3. DPPH Radical Scavenging Capacity in Beetroot Products

Antioxidant activity measured by the DPPH method differed between groups for the analyzed powders and capsules, while no significant differences were found between the analyzed tablets in this respect (p = 0.4193). Taking into account all analyzed supplements, a significant difference was found only between preparation No. 4 with the lowest DPPH radical scavenging capacity (5533 ± 68.6 μM Trolox/g) and preparation No. 2 with the highest antioxidant activity measured by the DPPH method (6193 ± 52.5 μM Trolox/g).

The ability to remove DPPH radicals varied both when considering all preparations in liquid form (p < 0.0001) and separately juices and ferments within groups (p < 0.05). The lowest DPPH radical scavenging capacity was found in acid no. 10 (16.2 ± 0.24 mM Trolox/100 mL), and the highest in juice No. 9 (28.9 ± 0.55 mM Trolox/100 mL).

3.2. Polyphenol Content and Antioxidant Potential of the Tested Products Depending on the Dose

The polyphenol content and ABTS⁺ and DPPH radical scavenging capacity in red beetroot products, depending on the dose, are presented in

Table 4. Polyphenol content, ABTS⁺ and DPPH radical scavenging capacity in analyzed beetroot powders, capsules, and tablets per dose.

Formulation		Extract Content (mg per Daily Dose)	Recommended Daily Dose/Recommended Intake	Polyphenol Content (mg GAL per Dose or per 250 mL)	ABTS Radical Scavenging Capacity (µM Trolox per Dose or per 250 mL)	DPPH Radical Scavenging Capacity (µM Trolox per Dose or per 250 mL)
I	(1)	Data not available	10.0 g	129 ± 7.01 C	4874 ± 218 B,C	59781 ± 498 B,C
	(2)	Data not available	10.0 g	96 ± 4.77 B,C	5820 ± 262 C	61934 ± 528 C
p-value				0.0027	0.0086	0.0068
II	(3)	600	2 capsules	5.50 ± 0.44 A,B,C	727 ±19.7 A,B,C	3629 ± 20.7 A,B,C
	(4)	450	1 capsule	4.45 ± 0.08 A,B	253 ± 4.33 A,B	2490 ± 30.9 A,B
p-value				0.0160	<0.0001	<0.0001
III	(5)	160	2 tablets	0.67 ± 0.06 A	14.9 ± 1.78 A	973 ± 4.14 A
	(6)	3000	6 tablets	17.1 ± 1.07 A,B,C	1524 ± 94.1 A,B,C	18095 ± 291 A,B,C
p-value				0.0014	0.0013	0.0001
All products statistical significance (p-value)				0.0054	0.0054	0.0054

I—beetroot powder, II—beetroot capsules, III—beetroot tablets; A, B, C—uppercase letters indicate statistically significant differences between all analyzed products regardless of group, based on ANOVA and post hoc tests; values sharing the same letter do not differ significantly (α = 0.05).

and

Table 5. Polyphenol content, ABTS⁺, and DPPH radical scavenging capacity in analyzed juices and ferments from red beetroot depending on the dose.

Formulation		Extract Content (mg per Daily Dose)	Recommended Daily Dose/Recommended Intake	Polyphenol Content (mg GAL per Dose or per 250 mL)	ABTS Radical Scavenging Capacity (µM Trolox per Dose or per 250 mL)	DPPH Radical Scavenging Capacity (µM Trolox per Dose or per 250 mL)
IV	(7)	Data not available	250 mL	3011 ± 385 a/B	24.4 ± 0.15 a/A	68.0 ± 1.92 b/E
	(8)	Data not available	250 mL	5399 ± 202 b/D	24.8 ± 0.05 b/B	56.9 ± 1.03 a/C
	(9)	Data not available	250 mL	7070 ± 285 c/E	24.8 ± 0.18 b/B	72.3 ± 1.37 c/F
p-value				<0.0001	0.0272	<0.0001
V	(10)	Data not available	250 mL	574 ± 42.8 a/A	24.8 ± 0.25 a/B	40.5 ± 0.62 a/A
	(11)	Data not available	250 mL	5328 ± 85.7 b/D	24.8 ± 0.11 a/B	63.2 ± 4.07 c/D
	(12)	Data not available	250 mL	3672 ± 131 a,b/C	24.8 ± 0.27 a/B	45.9 ± 0.57 b/B
p-value				0.0273	nn	<0.0001
All products statistical significance (p-value)				<0.0001	0.1511	<0.0001

IV—beetroot juice, V—beetroot leaven; a, b, c—lowercase letters indicate statistically significant differences within the same product group based on ANOVA for independent samples followed by post hoc tests (Dunn or Fisher); A, B, C, D, E, F—uppercase letters indicate statistically significant differences between all analyzed products regardless of group, based on ANOVA and post hoc tests; values sharing the same letter do not differ significantly (α = 0.05).

.

In all tested groups of beet supplements, significant differences were found in terms of polyphenol content and ABTS and DPPH radical scavenging capacity per manufacturer’s recommended dose (p < 0.05). The highest polyphenol content in beet supplements in solid form per dose was found in beet powders (powder no. 1, 129 ± 7.01 mg GAL/dose), and the lowest in tablet no. 5 (0.67 ± 0.06 mg GAL/dose). The powders also had the highest ability to scavenge ABTS and DPPH radicals (powder no. 2, 5820 ± 262 µM Trolox/dose and 61,934 ± 528 µM Trolox/dose, respectively), and tablets no. 5 had the lowest (14.9 ± 1.78 µM Trolox/dose and 973 ± 4.14 µM Trolox/dose, respectively). In the group of liquid products, beetroot juices were a better source of polyphenols than beetroot leavens. They also had a higher DPPH radical scavenging capacity per dose compared to leavens. However, no differences were found in the ability to remove ABTS radicals at the same dose of juices and leavens (p = 0.1511).

For beetroot powders, capsules, and tablets, the results were expressed per recommended dose in order to reflect actual dietary intake.

4. Discussion

The study showed significant differences in polyphenol content and antioxidant activity between the analyzed beetroot products in the form of supplements (powders, capsules, tablets) and liquid products (juices, leavens). These results are consistent with previous reports indicating high variability in the content of bioactive compounds in processed plant products resulting, among other things, from varietal differences, the form of the preparation, the processing technologies used, and the degree of standardization [10,11,12].

Among solid dietary supplements, powdered preparations had the highest total polyphenol content and the highest free radical scavenging capacity (both DPPH and ABTS⁺). Significantly lower values were observed in capsules and tablets, despite the declared high concentration of active ingredients. Although the literature on the effect of tableting and encapsulation processes on the polyphenol content in beetroot is limited, there are indications that intensive technological processing may lead to the degradation of phenolic compounds. While the drying process does not adversely affect the polyphenol content [13] and may even increase it by breaking down cell structures and releasing bioactive compounds [14], other processes, especially high-temperature ones, can cause significant losses [13,15], which may have been the case in the production of tablets or capsules. Another factor explaining the low phenolic compound content in tablets and capsules could also be excessive storage time and improper storage conditions [16,17]. These differences are reflected in the results presented in Table 4.

The polyphenol content in the powders analyzed in our study exceeded their content in beet powder tested by Farhan et al. [18] and in dried beet [19]. The tablets contained a similar amount of polyphenols to the results of Farhan et al. [18], while all analyzed preparations exceeded beetroot powder in terms of polyphenol content [19].

Similar to the study by Brzezińska-Rojek et al. [20], in our study, powders also showed higher antioxidant activity than capsules and tablets. The antioxidant activity of the preparations measured by the ABTS⁺ and DPPH methods differed significantly between products, which was consistent with the differences in polyphenol content, but, interestingly, was not strictly correlated with them in all cases. The presence of excipients in capsule and tablet formulations may represent an additional factor influencing the observed antioxidant activity of these products and should be considered when interpreting the results. For example, capsules No. 3, despite their lower polyphenol content, had the highest ABTS activity, tablets No. 6 showed a high ability to scavenge ABTS radicals despite the lowest polyphenol content. A similar phenomenon was observed in the DPPH method—tablets No. 5 and 6 showed relatively high activity despite low polyphenol content. This may indicate that not only the quantity, but also the quality, chemical profile, and bioavailability of polyphenols play an important role in determining their antioxidant activity. The observed discrepancies between total polyphenol content and antioxidant activity may also be related to the presence of other bioactive compounds characteristic of beetroot [21]. In particular, betalains, including betacyanins such as betanin, are considered key components responsible for the antioxidant potential of red beetroot [10,22,23].

It should also be noted that the Folin–Ciocalteu method used in this study is a non-specific test and may react with other reducing substances naturally present in beetroot, such as ascorbic acid or reducing sugars. Therefore, the total polyphenol content determined by this method should be interpreted as an indicator of overall reducing capacity rather than a precise measurement of phenolic compounds alone. The lack of a strict correlation between polyphenol content and ABTS⁺ or DPPH scavenging activity observed in this study probably reflects the combined and synergistic effects of different classes of bioactive compounds present in beetroot products. Due to the high heterogeneity of the analyzed products, including differences in matrices, product forms, and recommended doses, a direct correlation analysis between total polyphenol content and antioxidant activity could lead to overinterpretation of the results. Therefore, relationships between these parameters were discussed in a descriptive manner. It should be noted that dry matter content may influence the observed antioxidant activity; however, this parameter was not determined in the present study and therefore was not included in the analysis.

As in the case of polyphenols, the antioxidant activity of beetroot can also be modified by the processing technology used [19,22]. In addition, the form of the preparation may affect the stability, solubility, and bioavailability of active compounds—e.g., capsules may contain additional ingredients that affect the stability or solubility of active substances.

In the present study, fermented beetroot products were referred to as beetroot kvass, obtained either by commercial fermentation or spontaneous fermentation, depending on the sample.

Although microorganisms involved in fermentation may contribute to the formation of biologically active compounds, detailed information on microbial strains or enzymatic activity was not available and therefore was beyond the scope of this study. Significant differences in polyphenol content were also observed in the group of liquid products. These differences may be associated with variations in raw material quality, cultivation, and storage conditions [24], as well as differences in production technology. In several cases, as in the study conducted by Wruss et al. [10], the antioxidant capacity of beetroot juice was related to the concentration of polyphenolic compounds, but not always. In fermented beetroot products, fermentation-related processes may additionally influence the polyphenolic profile through both the release of polyphenolic compounds from the plant matrix and their potential degradation [25]. Our study indicates that beetroot juice was a better source of polyphenols than beetroot kvass. Despite differences in polyphenol content, the juices and leavens analyzed in this study contained higher concentrations than commercial beetroot juice tested by Wołosiak and Chedę [13]. In addition, juices No. 8 and 9 and leaven No. 11 had higher concentrations of phenolic compounds (calculated as mg GAE/L) than apple and blackberry juices and apple and chokeberry juices analyzed by Pyryt [14]. Only juice No. 7 had a lower phenol content than all the juices analyzed by Pyryt. These observations are consistent with the data presented in Table 5.

The ability to scavenge ABTS radicals also showed significant differences between liquid beet products. Interestingly, beet ferments showed high homogeneity in terms of antioxidant activity, and their effectiveness was comparable to some juices (No. 8 and 9), which may indicate a similar profile of bioactive compounds responsible for antioxidant activity. The ability to scavenge ABTS radicals in the analyzed juices was slightly lower, and in leavens comparable to the activity in commercial juice analyzed by Wołosiak and Cheda [13], but significantly higher than in juices from 14 beet varieties tested by Gościnna et al. [26].

In turn, the antioxidant activity against the DPPH radical showed greater variation, both within the entire group of liquid products and between juices and leavens. This may indicate that the DPPH test is more sensitive to subtle differences in the composition of antioxidants. The lowest activity was found in leaven No. 10, which may be related to the lower content of reducing compounds, including polyphenols. The highest values were observed for juice No. 9, which may result from the good quality of the raw material, the lower degree of processing, and the presence of strong antioxidants, such as betalains, which are found in the highest amounts in fresh beetroot and its unfermented products [19]. Although fermentation can increase the content of free phenolic acids and thus antioxidant activity, too long a fermentation process can lead to an overall decrease in the level of phenolic compounds [27].

Currently, the health food market is seeing growing popularity of products containing beetroot, due to its well-documented cardioprotective and antioxidant properties [28,29]. However, in order for a product of this type to contribute to improving health, it must not only be safe and effective, but also contain a standardized, repeatable, and controlled amount of bioactive ingredients to ensure a therapeutic effect [29,30].

In the products analyzed in this study, information on dosage or recommended intake was only available for supplements in capsule and tablet form. The manufacturers of the other preparations (powders, juices, leavens) did not provide such information. Therefore, for the purposes of the analysis, reference values were adopted: for juices and beetroot kvasses—250 mL (the volume of one glass), and for powders—10 g, in accordance with the recommendations for their use as a food supplement.

Due to the lack of uniform data on dosage, it is not possible to clearly determine which of the tested products provides the greatest health benefits, depending on the dose. However, considering the recommended or accepted doses, powders showed the highest content of polyphenolic compounds and the greatest ability to scavenge free radicals, while tablets showed the lowest. These results indicate that the form of the preparation and the dose are crucial in assessing its potential health-promoting properties.

Importantly, when calculated per analyzed dose, no significant differences in ABTS⁺ radical scavenging capacity were found between juices and ferments, which may suggest comparable efficacy of these two forms in this respect. In the DPPH test, juices showed higher antioxidant activity than vinegars. This may be related to the greater stability of betacyanins in an acidic environment or differences resulting from production technologies, such as heat treatment or fermentation.

A limitation of this study was the analysis of only selected batches of commercial products, which does not allow for a complete generalization of the results to the entire category of beetroot supplements and food products. Furthermore, only the total content of polyphenolic compounds was assessed, without identifying their quality profile. The content of other bioactive compounds that may contribute to antioxidant activity, including betalains, ascorbic acid, and flavonoids, was not analyzed. An additional limitation was the necessity to apply indicative, consumer-oriented reference portions (10 g for powders and 250 mL for juices and beetroot kvass), resulting from the lack of uniform manufacturer recommendations for different product forms, which limits the full comparability of results between supplements and liquid products. In future studies, it would be advisable to extend the analysis to include a qualitative and quantitative assessment of individual bioactive compounds, including polyphenols and betalains, taking into account their bioavailability and stability. It would also be important to consider the influence of technological parameters (e.g., freeze-drying, convection drying, presence of excipients) on the content and activity of antioxidant compounds, which could help optimize beet processing and improve the quality of final products. The interpretation of the results was limited by the lack of detailed compositional data, including dry matter content and information on fermentation microbiota, which were not within the scope of the present study.

5. Conclusions

The form of the product proved to be an important factor influencing its health-promoting properties. The highest content of phenolic compounds and the strongest antioxidant properties, especially when calculated per recommended dose, were found in powdered products. Among liquid products, higher activity, especially in the DPPH test, was observed in juices compared to ferments.

At the same time, it was found that antioxidant activity did not always correlate directly with the polyphenol content, suggesting a significant contribution of other bioactive compounds present in red beetroot. The varied activity between the analyzed products may also have resulted from different processing technologies, such as drying or pasteurization, and storage conditions. This is an interesting direction for further research, including the qualitative identification of the phenolic compounds and betalains present. The results of the study also highlight the need for greater standardization of beetroot dietary supplements, as the declared content of active ingredients does not always translate into actual biological effects. The lack of clear information on the composition makes it difficult to assess the effectiveness of the preparations and for consumers to use them consciously, which may lead to ineffective supplementation.