The Effect of the Addition of Powdered Sumac (Rhus coriaria L.) and Cold Plasma Treatment on the Quality of Carrot Juice

Abstract

The aim of the study was to investigate the effect of cold atmospheric plasma (CAP) and sumac powder (Rhus coriaria L.) on the pH, total soluble solids, color, content of phytochemicals (carotenoids and polyphenols), and microbiological quality of freshly pressed carrot juice. Experiments were carried out with sumac powder concentrations of 0.5 and 3%, which were added before or after 20 min plasma treatment using a gliding arc reactor. The combination of CAP and 3% sumac powder resulted in very effective microbial reduction (to an undetectable level on each day of testing). These juices were characterized by an extended microbiological shelf life of up to 72 h. Additionally, the juice which was first enriched with 3% sumac and then treated with cold plasma, even on the last day of testing, contained 34.36 mg/100 mL of polyphenols and 3.49 mg/100 g more carotenoids than the control samples. The total effect of the application of these method is highly important for the improvement of the quality and safety of carrot juice.

1. Introduction

The greatest risk associated with the possibility of microbiological contamination of juices is due to the lack of thermal processing. They are usually pasteurized [1,2,3]. However, in recent decades, the possibility of applying cold atmospheric pressure plasma—CAP (a mixture of electrons and ions, positively and negatively charged atoms and molecules, generated during an electric discharge at atmospheric pressure)—for food treatment has been investigated [4,5,6]. From the microbial inactivation point of view, the hydroxyl group (OH•) plays the most important role. It attracts H⁺ ions from the structural proteins of a bacterium’s cell wall [7]. Plasma also leads to the degradation of microbial DNA. Ultraviolet rays, also generated during an electric discharge, are characterized by a high energy value and a high degree of absorbance by DNA and RNA molecules, which leads to the formation of thymine dimers and fragmentation of the nucleoid [8,9,10,11,12,13].

From the point of view of promoting a healthy lifestyle, an important issue is the availability of food containing phytochemicals, i.e., substances with biological activity (clean label products) [14]. The spice prepared from the fruit of a shrub plant belonging to the genus Rhus coriaria L. has strong antioxidative and antibacterial properties. It contains flavonoids such as gallic acid, methyl gallate, kaempferol, fustine, fisetin, sulfuretin, butein, quercitin and myrcetin. Sumac also contains mainly monounsaturated oleic acid (omega-9) and polyunsaturated linolenic acid (omega-6). Micronutrients include certain amounts of vitamins C, B₁, B₂ and B₆, as well as potassium, calcium, magnesium, iron, zinc, manganese and copper [15,16,17,18,19]. This combination of nutrients could have beneficial properties supporting the defense against free radicals, which, according to the published literature, are partly responsible for formation of diseases such as cancer, diabetes or heart problems [20]. Consuming this oriental spice ensures proper blood sugar levels and regulates cholesterol levels [21]. Sumac fruit is also used as a natural diuretic, which helps in the proper elimination of toxins and cleansing the whole body [22,23]. Several positive effects of using sumac in meat dishes, fish, cooking oils or dairy products have been described in the literature [24,25,26,27,28].

In this study, the addition of sumac powder combined with cold plasma treatment was used for juice products for the first time. The aim of the study was to investigate the effect of using this type of treatment on the number of microorganisms and the nutritional value of carrot juice during refrigerated storage.

2. Materials and Methods

2.1. Equipment and Materials

Fresh carrots (Daucus carota) of the variety Nerac, from the spring harvest of 2023, and tannery sumac (Rhus coriaria L.) were obtained from a local supermarket (Lublin, Poland). PCA (plate count agar) media and nutrient agar media with chloramphenicol were obtained from BIOMAXIMA (Lublin, Poland). Chemical reagents for juice qualitative analysis were purchased from POCH (Gliwice, Poland) and STANLAB (Lublin, Poland). The following reagents were used: acetone with 0.2% BHT, ethanol and hexane to determine the total content of carotenoids. To determine the total polyphenol content, the Folin–Ciocalteu phenol reagent and sodium carbonate were used. A cold atmospheric plasma (CAP), as shown in Figure 1, was used to treat carrot juice.

2.2. Carrot Juice Preparation, CAP Application and Sumac Powder Addition

Freshly pressed carrot juice was prepared in a laboratory using a slow juicer (Sana EUJ-707, Omega Products, České Budějovice, Czech Republic). Then, the juice was enriched with powdered Rhus coriaria L. sumac fruit with a maximum granularity of 0.5 mm in the selected order (before or after plasma treatment) and at the amount shown in

Table 1. The method of sample preparation and time of treatment in gliding arc reactor (V = 3.8 kV, f = 50 Hz).

Probe Code	Plasma Treatment Time (min)	Sumac Powder: Quantity (%) and Order of Addition into the Juice
C	0	0
S05	0	0.5
S3	0	3.0
P	20	0
SP05	20	0.5 (before plasma treatment)
SP3	20	3.0 (before plasma treatment)
P+05S	20	0.5 (after plasma treatment)
P+3S	20	3.0 (after plasma treatment)

. The samples were exposed to plasma-treated gas. Air at 440 NL/h was used as a substrate gas for the two-electrode AC gliding arc plasma reactor [29], which operated at a mean power of 40 W. Furthermore, 25 mL of the juice sample was placed in a sterile glass container positioned beneath GAD electrodes at a 1 cm distance between the electrodes and the liquid surface. The samples were mixed with a magnetic stirrer at 100 rpm speed. The maximum temperature of the samples were measured using the DT-847U meter (Yu Ching Technology, Taipei City, Taiwan) with a K-type thermocouple ranged 35 °C. The evaluation of the quality of the prepared juices was carried out after 24, 48 and 72 h of refrigerated storage at 6 °C.

2.3. Microbiological Analysis—Methodology

Aerobic mesophilic microorganisms were measured according to the following Polish Standard PN-EN ISO 4833–2 [30] spread plate method. Moreover, 50 μL of inoculum was placed on each agar plate. The plates were incubated at 30 °C for 72 h after adding the juice samples into the plate count agar media. Yeasts and mold counts (PN-ISO 21527–2 [31]) were determined by adding the juice sample into sabouraud dextrose with chloramphenicol agar and incubating the plates at 25 °C for 5 days. Serial dilutions were made, and colonies were counted for the dilution, on which several or a dozen colonies grew, and the result was presented in log CFUs (colony-forming units) per mL of juice. If nothing grew in the sample in several repetitions, the number of microorganisms was assumed to be below the limit of detection (1 log₁₀ CFU/mL). The shelf life of the juice enriched with sumac was determined after 24, 48 and 72 h on the basis of the Regulation of the Minister of Health of 13 January 2003 (Poland) [32] with later amendments, which establishes the maximum levels of chemical and biological contaminants that may be present in food ingredients, permitted additives, processing aids or on the surface of food.

2.4. Juice Qualitative Analysis

2.4.1. pH and Total Soluble Solids Measurement

The pH was determined using the digital 780 pH Meter Metrohm (Herisau, Switzerland) at 25 ± 1 °C. A hand refractometer of LLG-uniREFRACTO (Meckenheim, Germany) was used to measure the total soluble solids in the juices (°Brix) at 25 ± 1 °C.

2.4.2. Determination of Color Attributes

The color attributes were calculated using the spectrophotometer SF80 (3Color, Marcq-en-Barœul, France). Following the CIE (color space defined by the International Commission on Illumination) recommendations, illuminant D65 (daylight source) and a 10° standard observer (perception of a human observer) were used. Color values were expressed as L* (lightness or darkness), a* (redness/greenness) and b* (yellowness/blueness). Total color difference (ΔE) was evaluated as follows:

$$\Delta \mathit{E}=\sqrt{{({\mathit{L}}^{\mathit{*}}-{\mathit{L}}_{\mathbf{0}})}^{\mathbf{2}}+{({\mathit{a}}^{\mathit{*}}-{\mathit{a}}_{\mathbf{0}})}^{\mathbf{2}}+{({\mathit{b}}^{\mathit{*}}-{\mathit{b}}_{\mathbf{0}})}^{\mathbf{2}}}$$

(1)

where L₀*, a₀*, b₀* are the control juice (C) values.

2.4.3. Determination of Phytochemicals

The total phenolic compounds were determined using the Folin–Ciocalteau reagent [33]. Moreover, 5 mL of juice and 5 mL of 80% methanol were shaken for 5 min using the orbital shaker S-3.02 20M (ELMI Ltd., Riga, Latvia) at 250 rpm. Furthermore, 100 µL of this blend was mixed with 2.0 mL of water and subsequently with 200 µL of the Folin–Ciocalteau reagent. After that, 1 mL of sodium carbonate (20%) was added and the reaction started. The absorbance was measured after 60 min of reaction at 765 nm on a UV–VIS spectrophotometer (Helios Omega, Waltham, MA, USA). A blank sample was also prepared using water instead of juice. A calibration curve was prepared with standard solutions of gallic acid, following the same colorimetric method.

The total carotenoid content was determined using the method described by Canan et al. [34]. This method is based on extracting carotenoids from the test sample with a mixture of ethanol, acetone and hexane (1:1:2) and on their spectrophotometric determination at a wavelength of 450 nm using the Thermo Scientific UV–VIS Helios Omega 3 spectrophotometer (MA, USA). A calibration curve was prepared with standard solutions of β-carotene.

2.5. Microscopic Analysis

The juice uniformity and morphology was observed with the KEYENCE VHX-5000 digital microscope (Osaka, Japan). The control juice and plasma-treated juice samples were kept refrigerated at 6 °C for 1 h in closed sterile containers. Then, each sample was manually mixed for 30 s, and a 2 mL drop of the juice was collected from the container using an automatic pipette and placed on the microscopic slide. In order to achieve the most beneficial conditions for the observation of the sample, several conditions for the microscope settings were tested and the option of transmitted light and 1000× magnification was selected.

2.6. Statistical Analysis

Measurements of pH, soluble solids and phytochemicals were performed in 3 replicates and microbiological analyzes in 4 replicates. Obtained data were presented as the mean value ± standard deviation (SD). Significant differences between mean values were determined via the Tukey test (analysis of variance ANOVA) at a p-value ≤ 0.05. Statistical analyses were determined using the Statistica software package (Version 10, StatSoft Inc., Tulsa, OK, USA).

3. Results and Discussion

3.1. Reduction in Microbial Counts and Shelf Life of Juice

The average levels of contamination of fresh samples of carrot juice with aerobic mesophilic microorganisms and yeast were 3.6 and 0.73 log₁₀ CFU/mL, respectively. In the present study, the shelf life of juices after 24, 48, and 72 h was determined on the basis of the criterion of the permissible content of mesophilic aerobic microorganisms in pasteurized fruit and vegetable juices, as specified in the Regulation of the Polish Minister of Health of 13 January 2003 [32]. In accordance with the Regulation, the allowable number of mesophilic aerobic microorganisms should be lower than or equal to 3.0 log₁₀ CFU/mL and in the range of 3.0–4.0 log₁₀ CFU/mL in a maximum of two out of five samples from one batch. A microbial count exceeding 4.0 log₁₀ CFU/mL disqualifies the entire batch of the product. It is also assumed that the allowable yeast and mold content in pasteurized juices can be equal to or lower than 1 log₁₀ CFU/mL.

The results of the microbiological analyses of cold-stored fresh carrot juice treated with cold atmospheric plasma and/or supplemented with sumac powder are shown in

Table 2. Evaluation of the total number of microorganisms and yeasts of control carrot juice and juice samples treated with cold atmospheric plasma and/or supplemented with sumac after 24, 48, and 72 h of refrigerated storage (6 °C).

		Time Storage (h)
Quality Parameters	Juice Sample Codes	24	48	72
Total mesophilic aerobic microorganisms (log10 CFU/mL)	C	5.27 ± 0.16 A c	6.45 ± 0.24 B f	7.36 ± 0.22 C d
	S05	5.13 ± 0.05 A bc	5.43 ± 0.10 B e	6.24 ± 0.12 C c
	S3	4.62 ± 0.20 A bc	4.32 ± 0.15 A c	4.58 ± 0.08 A b
	P	4.46 ± 0.26 A b	4.70 ± 0.05 A d	4.35 ± 0.22 A b
	SP05	2.69 ± 0.58 A a	2.64 ± 0.09 A b	2.60 ± 0.07 A a
	SP3	ND	ND	ND
	P+05S	2.79 ± 0.40 B a	2.25 ± 0.11 A a	2.36 ± 0.15 AB a
	P+3S	ND	ND	ND
Yeast and molds (log10 CFU/mL)	C	2.19 ± 0.07 A c	4.30 ± 0.13 B d	5.34 ± 0.13 C d
	S05	1.88 ± 0.06 A b	3.54 ± 0.27 B c	4.21 ± 0.09 C c
	S3	1.68 ± 0.22 A b	2.27 ± 0.15 B b	2.54 ± 0.06 B b
	P	1.36 ± 0.11 AB a	1.50 ± 0.14 B a	1.17 ± 0.06 A a
	SP05	1.13 ± 0.04 a	ND	ND
	SP3	ND	ND	ND
	P+05S	1.14 ± 0.07 a	ND	ND
	P+3S	ND	ND	ND

The results are expressed as a mean ± standard deviation, ND—not detected; different letters mean statistically significant differences (p ≤ 0.05); ^A,B,C—effect of storage time, ^a,b,c,d,e,f—effect of treatment.

.

The comparison of the results of microbiological cultures with the permissible levels specified in the legal regulations on the microbiological quality of pasteurized juices indicates that the total number of aerobic microorganisms in the fresh carrot juice was exceeded at 24 h after pressing. A further increase in the number of microorganisms was observed during the subsequent hours of storage; therefore, the analyzed carrot juice was unsuitable for consumption [32].

The addition of sumac powder and the plasma treatment of the freshly squeezed juice samples proved to be effective in limiting microbial growth, but this effect was clearly dependent on the sumac concentration and plasma treatment time.

The analyses showed that the supplementation of the carrot juice with 0.5% and 3.0% of sumac powder and the plasma treatment reduced the number of microorganisms. The total number of aerobic microorganisms in juice samples S05 and S3 detected at the specified time points decreased on average by 0.14–2.78 log₁₀ CFU/mL in comparison with the corresponding control samples. The number of bacteria in the plasma treatment variant (sample code P) decreased on average by 0.81–3.01 log₁₀ CFU/mL. In turn, the amount of yeasts decreased by a maximum of 1.11 log₁₀ CFU/mL in sample S05, 2.80 log₁₀ CFU/mL in sample S3, and 4.17 log₁₀ CFU/mL after the plasma treatment. The largest decrease was observed after 72 h of refrigerated storage. The data shown in Table 2 indicated a high level of significant (according to the statistical test) reduction in the microbial count induced by the experimental treatments. However, these juices did not meet the requirements specified in the Polish Minister’s Regulation [32].

The supplementation of the juice with 0.5% of sumac powder and the plasma treatment (SP05) or the use of the additive after the plasma exposure yielded in better results (2.58–4.76 log reduction in aerobic mesophilic microorganisms), although they were not satisfactory in terms of extending the microbiological shelf life of the juice at 24 h after pressing, due to the presence of yeast above 1 log₁₀ CFU/mL [32]. What is noteworthy is that given the microbial growth in the control samples during storage and the inhibition of the growth of microorganisms in the plasma-treated samples (before or after the sumac powder addition), the greatest reduction in the number of microorganisms was recorded after 72 h of storage. Compared to the control, the total number of aerobic microorganisms decreased in samples SP05 and P+05S by 4.76 and 5.00 log₁₀ CFU/mL, respectively, and the yeast count after this storage time was reduced below the limit of detection.

The application of the higher amount of sumac powder in the SP3 and P+3S combinations extended the microbiological shelf life of the unpasteurized carrot juice to 72 h. The total number of microorganisms and yeasts after 24, 48 and 72 h of refrigerated storage was below the limit of detection (1 log₁₀ CFU/mL).

The present results clearly indicate that the cold plasma treatment and the natural sumac powder addition have a decontaminating effect on the microbial load of carrot juice. Similar research results reporting the ability of cold plasma to inactivate harmful microorganisms in beverages have been described in many publications [12,35,36,37,38]. In the Starek et al. [12] publication, 5 minutes of plasma treatment generated in the GlidArc reactor (where the process gas was air) enabled 3.45, 3.55 log and 3.32 log₁₀ CFU/mL reductions just after the treatment for the total aerobic mesophilic bacteria colonies, yeast and molds, respectively. It has also been proved that sumac (Rhus coriaria L.) fruit extract has inhibitory activity against the growth of food spoilage and/or pathogenic bacteria, especially Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, Penicillium sp., and Aspergillus niger [39,40,41,42]. Sumac can be considered a natural antimicrobial protectant against a number of microorganisms found in food. Mardoukhi and Alizadeh [43] used aqueous sumac extracts to improve the microbiological quality of silver carp fillets. After 18 days of refrigerated storage, they observed a decrease in the amount of total viable organism from 9.01 to 7.34 log₁₀ CFU/g and total psychrophilic count from 8.97 to 7.21 log₁₀ CFU/g in products treated with 5% sumac extract in comparison with control samples. Carrot juice supplementation with ground sumac in amounts of 0.5, 1.5 and 3 g/100 mL caused (at 72 h of testing) a reduction in the total number of microorganisms by 1.7, 2.9 and 3.1 log₁₀ CFU/g, respectively, compared to the control [44].

The quality of juice during storage can be improved with methods based on the use of more than one preserving factor: acidification with sonication, pulsed electric field with sonication, sonication with high-voltage cold plasma treatment, and pulsed electric field combined with temperature and natural preservatives [45,46,47,48].

Importantly, the combination of plasma treatment with the sumac powder addition to the freshly pressed carrot juice was analyzed here for the first time and yielded high-quality products that were suitable for consumption (from the microbial load point of view), even after 72 h refrigerated storage.

3.2. The Acidity (pH) and Total Soluble Solids Values (°Brix)

The active acidity of the carrot juices ranged from 6.33 to 4.21. The analyses carried out after 24 h revealed that the sumac powder addition and the cold plasma treatment increased the acidity of the juices in comparison with the control sample. The lowest pH was exhibited by samples supplemented with 3% of sumac powder. Sumac is rich in organic acids [49]; hence, the supplementation increased the acidity of the product. The time-point of the addition of sumac powder (before or after the cold plasma treatment) had no impact on the pH value. The lowest reduction in this parameter in relation to the control sample was observed in the plasma-treated juice without the sumac supplementation (P); in this case, an increase by approximately 0.6 units was observed. These changes are comparable with observations reported by other authors who found only a slight decrease in the pH of cold plasma-treated juices [50,51]. This was probably associated with the generation of a small amount of acidogenic radicals during the cold plasma treatment.

A statistically significant decrease in the pH value during storage was observed in the control sample. After 72 h, the value of this parameter decreased by 0.4, which could be related to the growth and acidifying effect of the juice microflora (

Table 3. Effect of sumac supplementation and plasma treatment on the pH and total soluble solid values of carrot juice stored in a refrigerator for 72 h.

		Time Storage (hours)
Quality Parameters	Juice Sample Codes	24	48	72
Acidity (pH)	C	6.32 ± 0.01 C e	6.25 ± 0.03 B e	5.92 ± 0.01 A d
	S05	5.41 ± 0.01 B c	5.22 ± 0.02 A c	5.35 ± 0.05 B c
	S3	4.24 ± 0.01 A a	4.23 ± 0.01 A a	4.23 ± 0.01 A a
	P	5.76 ± 0.06 A d	5.86 ± 0.06 A d	5.91 ± 0.01 A d
	SP05	5.14 ± 0.00 A b	5.14 ± 0.01 A b	5.15 ± 0.01 A b
	SP3	4.21 ± 0.00 A a	4.22 ± 0.01 A a	4.22 ± 0.00 A a
	P+05S	5.20 ± 0.00 A b	5.35 ± 0.30 A c	5.19 ± 0.00 A b
	P+3S	4.37 ± 0.01 A a	4.37 ± 0.02 A a	4.38 ± 0.00 A a
Total soluble solids (°Brix)	C	8.40 ± 0.17 A a	8.43 ± 0.06 A a	8.37 ± 0.12 A a
	S05	8.30 ± 0.26 A a	8.75 ± 0.21 A a	8.75 ± 0.07 A ab
	S3	8.73 ± 0.06 A a	8.90 ± 0.00 B ab	9.45 ± 0.21 B b
	P	8.27 ± 0.06 A a	8.70 ± 0.14 B a	8.85 ± 0.07 B ab
	SP05	10.33 ± 0.06 A c	10.67 ± 0.21 B d	10.37 ± 0.15 B c
	SP3	11.13 ± 0.25 A d	11.20 ± 0.17 A d	11.50 ± 0.26 A d
	P+05S	9.17 ± 0.15 A b	9.40 ± 0.17 A bc	9.40 ± 0.17 A bc
	P+3S	9.63 ± 0.23 A b	9.80 ± 0.20 A c	9.90 ± 0.26 A c

The results are expressed as the mean ± standard deviation; different letters mean statistically significant differences (p ≤ 0.05); ^A,B,C—effect of storage time, ^a,b,c,d,e—effect of treatment.

) [52].

The Brix degree (°Brix) is traditionally used in vegetable and fruit industries. After 24 h of storage, the mean value of this index was 8.40 for the unprocessed carrot juices and 8.27–8.73 for the CAP-treated products (P) or samples supplemented with the sumac powder (S05 and S3). Higher indices of total soluble solids were observed in samples P+05S and P+3S. The addition of 0.5% of sumac powder combined with the plasma treatment proved to be a significant factor, as it contributed to an increase in the parameter on average to 10.33 °Brix. The highest value of total soluble solids, which was 25% higher than that in the control (C), was obtained in the variant supplemented with the maximum sumac powder concentration combined with the CAP treatment (SP3). The increase in total soluble solids may be due to the dissolution of compounds from sumac and probably the hydrolysis of insoluble compounds under the influence of energy supplied during processing. In general, the storage time did not exert a significant effect on this parameter (in most cases). Many researchers have reported a similar insignificant change in the level of total soluble solids in response to the cold plasma treatment of orange or apple juices [50,53,54]. As reported by Liao et al. [53], soluble solids present in juices are mainly composed of carbohydrates, and it is difficult for active molecules produced in the plasma to reach these macromolecules within their short lifetime. In contrast to the above results, a significant increase in total soluble solids was noted in samples of freshly cut pears treated with plasma-activated water (PAW), where the increase was related to the conversion of starches to sugars [54]. In turn, Ma et al. [55] reported a decrease in total soluble solids in PAW-treated Chinese blueberries.

3.3. Color

Color is a visual attribute that consumers use to evaluate a product before making a purchase decision, as it can help determine such qualities as freshness. The presence of natural pigments and the apparent chemical reactions during processing are significant factors of the notable color appearance of fruits and vegetables. As shown in

Table 4. Effect of sumac supplementation and plasma treatment on the color parameters of carrot juice stored in a refrigerator for 72 h.

Parameters	Juice Samples Code	Time Storage (hours)
		24	48	72
L*	C	39.91 ± 0.18 B e	38.86 ± 0.23 A cd	38.49 ± 0.05 A cd
	S05	39.58 ± 0.56 A e	38.68 ± 0.12 A cd	39.26 ± 0.12 A d
	S3	39.78 ± 0.08 A e	39.55 ± 0.01 A d	39.38 ± 0.03 A d
	P	39.29 ± 0.83 A de	38.76 ± 0.03 A cd	39.23 ± 0.08 A d
	SP05	38.30 ± 0.04 B bc	38.06 ± 0.01 A bc	38.22 ± 0.01 B c
	SP3	36.28 ± 0.02 B a	35.58 ± 0.10 B a	34.33 ± 0.21 A a
	P+05S	38.80 ± 0.04 B cd	38.19 ± 0.02 B c	37.16 ± 0.11 A b
	P+3S	37.85 ± 0.16 C b	37.18 ± 0.01 A b	37.22 ± 0.02 B b
a*	C	15.87 ± 0.17 B c	15.30 ± 0.25 A c	15.18 ± 0.08 A cd
	S05	15.73 ± 0.59 A c	15.69 ± 0.03 A c	16.26 ± 0.08 A d
	S3	15.74 ± 0.17 A c	15.65 ± 0.30 A c	15.46 ± 0.02 A cd
	P	14.72 ± 0.11 B bc	14.37 ± 0.05 A bc	14.56 ± 0.04 A cd
	SP05	14.86 ± 0.10 B bc	14.23 ± 0.01 A bc	14.19 ± 0.05 A c
	SP3	12.35 ± 0.00 C a	10.76 ± 0.05 B a	8.65 ± 0.11 A a
	P+05S	14.38 ± 0.06 C bc	14.57 ± 0.03 B bc	12.06 ± 0.04 A b
	P+3S	13.60 ± 0.42 A ab	12.72 ± 0.02 A b	14.04 ± 2.07 A c
b*	C	20.58 ± 0.20 C e	19.53 ± 0.30 B e	18.96 ± 0.07 A f
	S05	21.26 ± 0.16 C f	19.54 ± 0.08 B e	20.09 ± 0.15 A g
	S3	19.78 ± 0.18 B d	19.73 ± 0.16 B e	19.12 ± 0.01 A ef
	P	19.09 ± 0.16 B c	18.81 ± 0.05 A d	18.72 ± 0.06 A e
	SP05	18.96 ± 0.08 C c	18.06 ± 0.00 B c	17.81 ± 0.04 A d
	SP3	14.96 ± 0.08 C a	12.82 ± 0.08 B a	10.13 ± 0.16 A a
	P+05S	18.54 ± 0.01 C c	18.29 ± 0.04 B cd	15.05 ± 0.11 A b
	P+3S	16.98 ± 0.40 C b	16.11 ± 0.01 B b	15.95 ± 0.01 A c
ΔE	S05	1.64 ± 0.09	0.48 ± 0.15	1.74 ± 0.08
	S3	0.86 ± 0.45	0.89 ± 0.50	0.95 ± 0.05
	P	2.04 ± 0.14	1.19 ± 0.33	1.00 ± 0.06
	SP05	2.51 ± 0.43	3.06 ± 0.63	1.55 ± 0.17
	SP3	7.56 ± 0.43	8.75 ± 0.32	11.75 ±0.14
	P+05S	2.76 ± 0.32	1.59 ± 0.48	5.18 ± 0.01
	P+3S	4.74 ± 0.89	4.60 ± 0.46	3.75 ± 0.71

The results are expressed as the mean ± standard deviation; different letters mean statistically significant differences (p ≤ 0.05); ^A,B,C—effect of storage time, ^{a,b,c,d,e,f,g}—effect of treatment.

, the highest mean values of the L* parameter (after 24 h of storage), thus the lightest colors, were determined in the control carrot juice (39.91), in the samples enriched with higher or lower sumac powder concentrations (39.28 and 39.78, respectively), and in the cold plasma-treated juice, without sumac powder addition (39.29). In turn, the lowest values of the parameter and hence the darkest color were observed in products supplemented with 3% of sumac powder before or after the plasma treatment (36.28 and 37.85, respectively). The storage time induced only slight changes in this parameter. The value of the L* parameter in the control juice (C) after 72 h decreased to 38.48, i.e., by 4% of the value noted three days before. A difference in the L* values was also observed during the storage of the SP3 sample, i.e., the values decreased from 36.28 (after 24 h) to 34.33 (after 72 h). The other products did not exhibit such significant changes in the lightness parameter during storage.

The low values of the a* parameter determined in the sumac powder-supplemented and CAP-treated juice (SP3) indicate a lower proportion of redness. In comparison with the control product (15.89), the value of this parameter declined to 12.35 and continued to decrease, as evidenced by the a* value of 8.65 after 72 h of storage. The b* parameter also changed after the cold plasma treatment and supplementation of the carrot juice with the sumac powder. On the first day of the study (24 h), the supplementation of the juice with sumac combined with the CAP treatment (SP3) reduced the yellow color factor by approximately 27%, compared to the control product (C). At 72 h of refrigerated storage, the chromaticity parameter b* in this treatment variant had the lowest value (10.13), compared with the value recorded after 24 h (14.96). The total color difference (ΔE) describes the color distance in the three-dimensional color space and refers to the difference between the color parameters of the control juice and the juice treated with cold plasma and/or supplemented with sumac powder. Depending on the value of ΔE, differences in perceivable color can be analytically classified as very distinct (ΔE > 3), distinct (1.5 < ΔE < 3), and small difference (ΔE < 1.5). Throughout the study period, the treatment of the carrot juice with cold plasma (P) or the supplementation with sumac powder (S05 and S3) resulted in inconsiderable or distinct visual differences in the color, compared with the control sample (C). After 72 h of storage, distinct or highly distinct changes in the color compared with the control sample (C) were observed in the juice samples supplemented with the sumac powder and exposed to the cold plasma treatment (SP05; P+05S; SP3; P+3S). Ali et al. [56] observed that, after plasma treatment, tomato juice samples turned slightly yellow, which was observed by changes in the hue angle. They found that this change occurred due to the breakdown of carotenoid pigments by the plasma species. The application of sumac extract to bread resulted in a decrease in the L* parameter value by approximately 21%, the a* parameter by approximately 33%, and the b* value by almost 55%. The authors of these studies [57,58] attributed the changes in the color to the content of phenolic pigments, mainly anthocyanins, in sumac.

3.4. Characteristics of Phytochemicals

The total content of polyphenols in the control carrot juice ranged from 11.18 mg/100 mL to 13.46 mg/100 mL. The sumac powder supplementation clearly increased the content of these bioactive compounds in the juice. Sumac fruits are rich sources of polyphenols [59,60]; hence, they can be an attractive additive for the enrichment of juices with these pro-health ingredients. The total content of polyphenols in the cold plasma-treated carrot juice (P) was only slightly lower than that in the control sample. The greatest difference (2.24 mg/100 mL) was noted after 72 h, but it was not statistically significant. The effect of cold plasma on the content of polyphenols is not clear-cut. Their amount may decrease due to the degradation process accompanying the exposure of the product to reactive radicals released during plasma generation. In turn, the action of charged particles and UV radiation may result in a more intense rupture of raw material tissues as well as the disintegration and disruption of cell membranes, which facilitates the extraction of phenolic compounds [61]. This dual effect of cold plasma treatment was evidenced by the present results. The cold plasma treatment of carrot juice supplemented with 0.5% of sumac contributed to an increase in the total content of polyphenols, whereas a decline in the content was observed in juice samples enriched with 3% of the additive (

Table 5. Effect of sumac supplementation and plasma treatment on the phytochemicals content of carrot juice stored in a refrigerator for 72 h.

		Time Storage (hours)
Phytochemicals	Juice Sample Codes	24	48	72
Total polyphenol content (mg/100 mL)	C	13.40 ± 0.42 B a	11.18 ± 0.26 A a	13.46 ± 0.20 B a
	S05	30.71 ± 0.41 B c	27.55 ± 0.33 B c	25.50 ± 0.26 A c
	S3	103.16 ± 2.04 C g	85.49 ± 0.73 B f	66.98 ± 0.79 A f
	P	11.40 ± 0.28 A a	10.41 ± 0.46 A a	11.22 ± 0.46 A a
	SP05	35.78 ± 1.38 C d	23.22 ± 0.33 B b	18.29 ± 0.46 A b
	SP3	74.74 ± 1.79 C f	57.54 ± 0.20 B e	47.82 ± 0.53 A e
	P+05S	18.34 ± 0.26 A b	23.45 ± 0.26 B b	18.29 ± 0.20 A b
	P+3S	58.14 ± 1.50 C e	48.33 ± 0.95 B d	42.05 ± 0.35 A d
Total carotenoids content (mg/100 g)	C	15.84 ± 0.05 C b	15.55 ± 0.05 B c	11.13 ± 0.02 A a
	S05	15.89 ± 0.15 A b	17.70 ± 0.04 B e	17.99 ± 0.01 C f
	S3	18.25± 0.05 B e	17.98 ± 0.04 A f	18.90 ± 0.28 C g
	P	15.15 ± 0.05 B a	15.06 ± 0.14 B b	14.76 ± 0.05 A c
	SP05	16.01 ± 0.10 B b	15.11 ± 0.04 A b	14.84 ± 0.04 bA c
	SP3	17.60 ± 0.08 B d	17.16 ± 0.02 A d	17.16 ± 0.02 A e
	P+05S	16.28 ± 0.11 B c	15.57 ± 0.02 A c	15.57 ± 0.02 A d
	P+3S	16.32 ± 0.02 B c	14.62 ± 0.02 A a	14.62 ± 0.02 A b

The results are expressed as the mean ± standard deviation; different letters mean statistically significant differences (p ≤ 0.05); ^A,B,C—effect of storage time, ^{a,b,c,d,e,f,g}—effect of treatment.

). Carotenoids are important components of all orange/red fruits and vegetables, as they are responsible for the attractive color and pro-health properties. Some of these natural antioxidants are used for the synthesis of vitamin A in the human organism. Therefore, the content of carotenoids should be taken into account while processing carotenoid-rich raw materials. The total content of carotenoids in the analyzed carrot juices ranged from 11.13 mg/100 g to 18.90 mg/100 g. After 24 h, it was observed that the 3% addition of sumac powder resulted in a 15% increase in the content of these pigments. After 24 h, it was observed that the 3% addition of sumac powder increased the content of these pigments by 2.41 mg/100 g. In turn, the cold plasma treatment of carrot juice samples resulted in a significant decrease in the content of carotenoids compared to the untreated samples (by 0.74 mg/100 g in the sample without added sumac and by 0.65 mg/100 g in the variant with the 3% addition) (Table 5).

As shown in the other studies of the effect of cold plasma on juices, the content of carotenoids increased in some cases. The use of a dielectric barrier discharge (DBD) plasma reactor at a voltage of 70 kV for 4 min allowed an increase in the amount of carotenoids in carrot juice compared to the control sample [47]. Also, cold plasma treatment carried out using the laboratory PE-100 plasma system (with nitrogen as the process gas) using an electric field with a frequency of 80 kHz resulted in an increase in the content of these compounds in acerola juice. The greatest increase in carotenoids was observed at a gas flow rate of 10 mL/min and a treatment duration of 10 min [62]. The increase in the content of these bioactive compounds through the action of cold plasma can be explained by the increased extraction thereof from the juice matrix. The bioavailability of some compounds in cold plasma-treated juices may be increased as a result of cell disruption as well as the dissociation of aggregates and association of bioactive substances with the cell wall [61]. During the storage of the carrot juices, the greatest losses in the total content of carotenoids were detected in the control sample. After 72 h, their content was approximately 30% lower than in the juice analyzed after 24 h.

3.5. Description of the Juice Microstructure

Rheological properties and the structure of carrot juice without (Figure 2) and with added sumac (Figure 3) were observed using a digital microscope. As presented in Figure 2, the aggregation of solid fractions in carrot juice was visible. It was also observed that cold plasma treatment resulted in the homogenization of the juice.

The structure of sumac microparticles distributed in carrot juice can be clearly distinguished (Figure 3). As in the case of juice without the addition of sumac, plasma treatment resulted in slight homogenization. However, plasma impact on the sumac particles was negligible. This kind of treatment can be considered as mild in the terms of its influence on the juice morphology.

4. Conclusions

In the present study, it was demonstrated that both CAP and sumac (Rhus coriaria L.) fruit powder have high potential to ensure microbiological safety and desirable physicochemical properties of carrot juice.

The data obtained in this study clearly indicate that the total effect of the innovative SP3 method’s application is highly important for improvement of the quality and safety of Nerac carrot juice, and the technique has the potential for practical application in the industrial production of juices and other beverages. It has been proved that this type of treatment reduces the content of mesophilic aerobic microorganisms and increases the stability of carrot juice, which additionally has a very good nutritional value (exceeding the value of the control juice).

Such treatments are effective in eliminating natural microbiological contamination of carrot juice and allow us to obtain an unpasteurized food product with an extended shelf life and increased nutritional value.