Figure 1 shows the types of analyzed juices: SBH (sea buckthorn with honey), SB (sea buckthorn), AH (aronia with honey), A (aronia), BCH (black currant with honey), SBA (50% sea buckthorn and 50% aronia). The juices were not dried, in all analyses they were used in their natural liquid state. These juices are concentrated juices, without water addition, being made up only of the fruit juice and the rapeseed honey which has not changed the natural flavor of the fruit. Each of the juices was processed in an appropriate environment to preserve product quality and prevent contamination, and after packaging were stored at refrigeration temperatures until the analysis were performed. The fruits were picked at the end of summer and the beginning of autumn, when they are fully ripe, having a high content of vitamin C and nutrients. The fruits were washed under cold water to remove any impurities, dried and cleaned, removing the leaves and impurities. The fruits were crushed into a pulp using a commercial fruit pulper (Linxiao Juicer Model X20, Linxiao Machinery Co., Ltd., Taizhou, China) operating at 850 rpm rotational speed and equipped with a 0.5 mm stainless steel sieve to remove skins and seeds. The juice was filtered through a fine sieve, mixed with honey and homogenized until the honey completely dissolves. The obtained juices were packed in plastic containers and kept under refrigeration at 0–4 ⁰C for analysis performing.

A quantity of 100 mg of juices from six different samples was measured and introduced into a special crucible in the derivatograph SDTQ600 (TA Instruments, New Castle, DE, United States). The curves of thermogravimetry (TG) and differential thermal analysis (DTA) were recorded. The registration of these curves was carried out by a SDT Q600 (TA Instruments, New Castle, DE, United States) instrument in air up to 600 °C with a speed of 5 °C/min heating rate using alumina standards.

The sensory analysis of the juices was performed according to the scoring quality assessment method (Dippong, 2017). The analysis was carried out by a group of 10 taster volunteers (five women and five men) aged between 20 and 30 years. The tasters examined the characteristics of the six juices by comparison with the scoring scale of 20 cumulated points for six juices according to the sensory analysis standards (Dippong, 2017). The juices were evaluated for appearance (using scores ranging from 0 (very poor) to five (excellent)), color (0-3), smell (0-3), taste (0-7) and foreign bodies (0-2).

Total sugar content was determined by a digital refractometer (PAL-RI, Tokyo, Japan) with the following technical characteristics: range of use 1.3306–1.5284, resolution of 0.0001, accuracy of 0.0003, measuring temperature between 5°C–45°C (with 1°C resolution), measuring time of 3 s, in accordance with the requirements of the EMC directive 93/68/EEC. The refractometer is calibrated with distilled water, after which 2 drops of the sample are placed on the optical prism and the sugar content is displayed in Brix degrees.

Determination of carbohydrates from juices was analyzed by UHPLC (1,260 Infinity II), which contains a quaternary pump (Agilent Technologies, G7111B, 1,260 Infinity II, Santa Clara, CA, United States), an Agilent Autosampler with an injection valve fitted with a 10 µL sample loop. The separation was performed on a 2.5 µm Polaris NH₂ 250 μm × 4.6 mm (Agilent Technologies, Santa Clara, CA, United States). All the samples were filtered through a 0.45 µM PTFE filter for LC analysis.

The dry matter (DM) content was determined by the air oven method after drying 2 g sample at 105°C in a Universal Oven ULE 500 (Memmert GmbH + Co. KG, Schwabach, Germany) to a constant weight. The titrable acidity (TA) was measured by titrating 10 g of juice that had been homogenized with 100 mL distilled water. The initial pH of the samples was recorded before titration with 0.1 N NaOH. The acidity was expressed as the percentage of citric acid equivalent to the quantity of NaOH used for the titration (Jakobek et al., 2007).

Vitamin C content was determined by spectrophotometric method using a UV-VIS spectrophotometer Perkin-Elmer Lambda 25 (Perkin-Elmer Lambda 25, United States, 2015).

10 g of sample was homogenized with 50 mL of 5% metaphosphoric acid and 10% acetic acid solution, then was transferred into a 100 mL volumetric flask and gently stirred until homogenized. It was diluted to the mark with 10% acetic acid and 5% metaphosphoric acid solution. The solution was filtered, and the obtained filtrate was collected for the determination of vitamin C. Bromine water was added to the filtrate to oxidize ascorbic acid into dehydroascorbic acid. A few drops of thiourea were added to remove excess bromine, thus obtaining a clear solution. The standard solution of ascorbic acid was introduced, and then 1 mL of 2,4-dinitrophenylhydrazine solution. The obtained mixture was maintained for 3 h at a temperature of 30 °C in a water bath. After incubation, the mixture was cooled in an ice bath, treated with 5 mL H₂SO₄ 85% solution, and constantly stirred. The absorbance was recorded at 254 nm, and results were expressed as milligrams per 100 mL of juice based on a standard calibration curve of ascorbic acid (0–50 mg/L).

To perform the determination, the samples were diluted with water, in a proportion of 1:1, 50% water and 50% juice. The pH was determined with an HI98161 pH meter (Hanna Instruments, Bucharest, Romania). For electrical conductivity and dissolved oxygen, a HI6522 Modular Multiparameter was used (Hanna Instruments, Bucharest, Romania). The pH electrode used was thoroughly cleaned after the analysis and stored in a KCl solution. Buffer solutions were used to calibrate the pH-meter before each series of measurements.

For microbiological analysis, the juice samples were evaluated immediately after opening and at 7-day intervals until day 56 during storage at 4 °C. The total number of viable aerobic mesophilic bacteria, yeasts and molds, as well as Enterobacteriaceae and Staphylococcus sp., was determined to monitor the microbiological changes that occur during storage. Each sample was analyzed in triplicate (3 technical replicates). The samples were serially diluted with 0.85% NaCl solution and 1 mL of each dilution was inoculated into Petri dishes with the corresponding culture medium. To control for potential contamination, uninoculated plates were used as negative controls. The developed colonies were counted, and the results were expressed as colony-forming units per milliliter (log CFU/mL).

Statgraphic XVIII programme was used to performe correlation analysis and Principal component analysis of the data aiming to find the similarities between the juice assortments and to reduce the dimensionality of the data set. All experiments were conducted in triplicate. The data were presented as the mean ± standard deviation. Data were analyzed via factorial ANOVA using the General Linear Model in Minitab 19.1.1 (LEAD Technologies, Inc., Charlotte, NC, United States). Tukey’s honest significance test was carried out at a 95% confidence level (p < 0.05).

The thermal behavior of SBH, SB, AH, A, BCH and SBA juices is presented through TG and DTA diagrams in Figure 2, where is shown the decomposition up to 600 ^oC. SBH (sea buckthorn with honey) and SB (sea buckthorn) juices, presented four stages: (i) the endothermic effect at 86–97 ^oC, with a mass loss of 52% (SBH had lower water loss, due to the honey content which did not decompose at this temperature) and 83% (SB had the highest weight loss due to higher water content) which corresponded to drying of juices and desorption of physically absorbed water molecules (at these temperature values, the heating of the shell can be related to moisture and water linked with the structure evaporation phenomenon (Melnikova et al., 2023)); (ii) the exothermic effect at 222–256 ^oC, with a mass loss of 7%–22% (SBH contained more volatile compounds and sugars than SB which was a watery juice) is attributed to the decomposition of flavor substances, polyphenols and sugars; (iii) the exothermic effect at 331–353 ^oC, with a mass loss of 6%–15% corresponded to the breakdown of fatty acids (saturated, monounsaturated, polyunsaturated), amino acids, proteins and carbohydrate (dextrose, sucrose, starch); (iv) the exothermic effect at 476–485 ^oC, with a mass loss of 4%–13%, corresponded to the decomposition of cellulose, hemicellulose and lignin (on the DTA diagram, a sharp peak was observed and on either side of this peak there were shoulders, the explanation lies in the separate decomposition of cellulose, hemicellulose and lignin in this type of juice) (Cai et al., 2019; Dippong et al., 2022; Dippong et al., 2023; Liu et al., 2024; Tian et al., 2016). Hemicellulose, a compound that possesses a lower degree of polymerization, is a mixture of various polymerized monosaccharides (mannose, xylose, galactose, glucose, and arabinose). At the same time, cellulose is a high-molecular-weight compound consisting of a long linear chain of D-glucosyl groups (Cai et al., 2019).

AH (aronia with honey), A (aronia), BCH (black currant with honey) and SBA (50% sea buckthorn and 50% aronia) juices, showed five corresponding effects on the DTA curves: (i) the endothermic effect from 90–125 ^oC, with a mass loss of 53%, corresponded to drying of juices and could be related to humidity and evaporation (SBA and A juices contained the highest amount with a mass loss of 83%–86%); (ii) the exothermic effect from 204–227 ^oC, with a mass loss of 4%–20% (the higher mass loss for AH and BC was due to the decomposition of honey in this temperature range) was attributed to the decomposition of flavor substances, polyphenols and the pectic polysaccharides; (iii) the exothermic effect at 227–391 ^oC, with a mass loss of 5%–12% corresponded to the decomposition of lipids (fatty acids) (saturated, monounsaturated, polyunsaturated), amino acids, proteins and carbohydrate breakdown; (iv) the broad exothermic effect at 423–488 ^oC (just in the case of AH, A and SBA), with a mass loss of 3%–4%, corresponded to the decomposition of cellulose; (v) the exothermic effect at 523–590 ^oC, with a mass loss of 5%–15%, corresponded to the decomposition of hemicellulose and lignin (in the case of AH, A and BCH, a broad exothermic effect was observed due to the decomposition of hemicellulose and lignin, while in SBA, the decomposition of hemicellulose and lignin was observed in two stages, clearly evident by the exothermic effects from 564 ^oC to 590 ^oC (Cai et al., 2019; Dippong et al., 2021; Dippong et al., 2022; Liu et al., 2024; Tian et al., 2016). The crystalline structure of cellulose renders its thermal degradation more difficult than that of hemicellulose. In addition, on account of the complex composition, the degradation of lignin and macromolecular substances was also more strenuous than that of hemicellulose (Cai et al., 2019).

In juices that do not contain honey, a highest water loss of 83%–86% was observed, up to 125 ^oC, while in honey juices in the temperature range of 120–227 ^oC, a mass loss of 18%–20% occurs. If we compare the results with juices without honey, a mass loss of 4%–7% was observed in the range of 120–227 ^oC, it can be assumed by the difference that the decomposition of bee honey was carried out in this temperature range and could be 13%–16%.

The total mass loss was 100% in all cases, this means that all organic compounds decomposed up to 600 ^oC without remaining carbonized residues and did not contain mineral compounds. The activation energy necessary for the thermal decomposition of a mixture of components depends on the energy barrier for the individual constituents and is influenced by the chemical composition of studied juices (Sunooj et al., 2011).

The sensory analysis was performed on juices: SBH (sea buckthorn with honey), SB (sea buckthorn with honey), AH (aronia with honey), A (aronia), BCH (blackcurrant with honey), SBA (50% sea buckthorn and 50% aronia). The juices had an intense orange color (those made from sea buckthorn or with sea buckthorn) or dark blue, a slightly viscous consistency, a sweet taste (those with added honey) or sour (those unsweetened), and a flavor specific to the fruits from which they were prepared. The appearance was analyzed in terms of uniformity, homogeneity, opacity, watery consistency or degree of concentration, by awarding a score from 5 (very good) to 0 points (altered). The color was analyzed according to intensity, degree of shine, uniformity, by awarding a score from 3-0 points. For the smell, between three and 0 points were awarded and was observed whether it was specific to the assortment, well specified, characteristic to the natural smell of the fruit, without foreign odors or other nuances and without astringent tints. The taste was analyzed from the perspective of the specificity of the fruit variety, well-pronounced, pleasant, specific to the natural fruit from which it comes, without the presence of other foreign taste nuances, awarded between 7-0 points. Foreign bodies were analyzed from the perspective of the absence of foreign bodies, without a gelatinous or watery appearance (2 points), the presence of foreign bodies (0 points) (Dippong, 2017). Juices with added honey had higher scores for all sensory characteristics. Honey improved the taste of the fruit juice, making it more pleasant to the taste. The highest total score was for aronia with honey juice (AH), and the lowest score was for SBA juice (50% sea buckthorn and 50% aronia), probably due to the lack of appropriate mixing from a sensory point of view. The preference series of the 10 tasters was: AH > BCH > SBH > SB > A > SBA (Table 1).

According to Table 2, the samples with added honey showed a higher content of total sugar compared to the plain samples. The addition of honey in the case of sea buckthorn juice led to a 4 times higher sugar content compared to simple juice and for aronia juice 2.3 times higher. Honey brings to fruit juice an important supply of fructose and glucose easily assimilated by the body, while sugar contains sucrose that must be metabolized to be assimilated (Li et al., 2023; Feszterová et al., 2023). Sugars are polyhydroxyaldehydes or ketones and their derivatives or condensations. Depending on the number of molecules that form monosaccharides, they can be classified into three types: monosaccharides (such as glucose and fructose), oligosaccharides (such as sucrose and maltose), and polysaccharides (such as starch and cellulose) (Li et al., 2023). The dry matter content of the samples ranged from 14.5% to 19.3%. The highest value was determined for sea buckthorn with honey juice. Acidity is given by the content of organic acids in the product. A higher value of acidity was determined for the juice samples with the addition of honey. The highest titratable acidity was found for sea buckthorn with honey sample (3.86%), whereas the lowest was observed for the mixture 50% sea buckthorn and 50% aronia sample (2.63%) (Table 1). Denev et al., 2018, reported titratable acidity in the range of 0.89%–1.06% as citric acid in chokeberry juices from different growing seasons. Xia et al., 2023, have documented the nutritional profile of SB juice, which encompasses the following measurements: total soluble solids at 2.63% ± 0.06%, total acidity at 6.34% ± 0.07%, total sugar at 1.87% ± 0.00%, vitamin C at 356.90 ± 8.13 mg/100 mL, total phenols at 382.23 ± 2.58 mg GAE/100 mL, and total carotenoids at 0.36 ± 0.00 mg/100 mL.

Insoluble dietary fiber is a complex of polysaccharides, including cellulose, hemicellulose, and lignin. These components serve as the primary building blocks of cell microfibrils. The presence of insoluble dietary fiber in juices can enhance nutritional value and provide various health benefits, such as: digestive health, increased satiety, glycemic control, and cancer prevention (Liu et al., 2024). Honey juices had a higher carbohydrate content AH (5.12%), BCH (5.65%), found mainly in the form of sugar and fiber. The exact proportion of carbohydrates in juices varies depending on the processed fruit, processing methods, and added ingredients (Liu et al., 2024).

Previous research indicated that the concentration of soluble solids in black chokeberry juices varied between 18.15% and 25.61% across different growing seasons (Denev et al., 2018), while other studies reported levels of 13.30%–20.99% (Sidor and Gramza-Michałowska, 2019) or 12.50%–20.10% in commercially available juices sourced solely from black chokeberry (Veberic et al., 2015).

All the samples were acidic, the pH varied between 2.78 and 3.75. A high conductivity was found in all juices, which showed that these samples were dense, had a high viscosity and were rich in minerals and ionized organic acids. The pH values were low, being influenced of the degree of ripeness of the fruit. The pH values and fluctuations found during juice analyses may be impacted by the region’s predominant soil type and the buildup of organic matter (Adesakin et al., 2020). In chokeberry juice (A) the electrical conductivity was the highest (3.62 ms/cm), and the lowest value of conductivity was found for chokeberry juice with honey (AH), with a value of 1.77 ms/cm. Dissolved oxygen values were low in most cases, except for chokeberry juice (8.57 mg/L), which had the greatest exposure to the attack of microorganisms. Blackcurrant juice with honey (BCH) had the lowest concentration of dissolved oxygen (4.81 mg/L), followed by SBH (6.32 mg/L) and SB (6.75 mg/L), being the least exposed product to the action of microorganisms.

The physico-chemical characteristics of juices samples, namely, total sugar content (TSC), titrable acidity (TA), dry matter content (DMC), pH, carbohydrate content (Carb), electrical conductivity (EC), dissolved oxygen (DO), vitamin C content, scavenging capacity of DPPH (SC-DPPH), lycopene (Lyc), β-carotene (β-car) and total polyphenol content (T-polyph) that were shown in Tables 2,3 were statistically analyzed using correlation analysis and Principal component analysis to reduce the variability of data.

The correlation analysis of data (Table 4) showed high positive correlations between β-carotene and lycopene, titratable acidity and vitamin C, EC and vitamin C, carbohydrate and total sugar content, dry matter content and vitamin C, while other variables showed negative high correlations: EC and total sugar content, EC and vitamin C, carbohydrate and EC.

The results of principal component analysis are shown in Figures 3. Principal component analysis was conducted aiming to obtain a small number of liniar combinations of the variables considered (12 physico-chemical characteristics of the juices samples) which account for most of the variability in the data.

Figure 3 (left) depicted the eingenvalue of the components extracted by linear combination of the 12 variables The principal component analysis showed three components extracted that present eigenvalues higher than or equal to 1.0: component one (eigenvalue of 5.55) account for 46.23% of the variability in the original data, component 2 (eigenvalue of 3.88) which account for 32.32% and component 3 (1.53) which account for 12.76% (Figure 3) (left), while component 4 with an eigenvalue of 0.96 account for 7.96% of the variability (Figure 3) (left). The first two principal components which account were choosen to represent the juices samples (Figure 3) (right). The total percentage of the first three principal components together accounted for 91.31% of the variability in the original data. The first two principal components PC1 and PC 2 were used to represent the juice samples (Figure 3) (right) with the aim of finding possible similarities.

The juice samples (observations) were represented in two dimensions diagram shown in Figure 3 (right) where the axes are component 1 and component 2. The honey juices formed a distinct group in the diagram, while the juices without honey are also grouped due to their similarity considering their lower dry matter, lower carbohydrate concentrations, higher titratable acidity and lower value of pH.

The principal component analysis showed that honey addition to juices modify the properties of juices by increasing their carbohydrate content, total sugar content and decreased their EC values and total polyphenol concentrations as well as their vitamin C concentrations.

Natural juices are extremely vulnerable to spoilage by microorganisms (Xia et al., 2023), especially yeasts and molds could grow exponentially in fruit and vegetable juice at room temperature (McKay et al., 2011). The source of fresh fruit juices contamination comes from the microflora that is normally present on the surface of the fruit, from the air and soil. The results of the microbiological analysis on the variants of juices based on sea buckthorn, aronia and black currants can be seen in Table 5. This analysis was necessary to determine the validity period of the analyzed samples from the moment the sample was opened up to 56 days, during which the juices were kept under appropriate conditions, following the process of contamination and multiplication of microorganisms. With the extension of the storage period at 4 ^oC, the microbial load increases variably depending on the variety. Upon opening, no degree of contamination was observed, and with the passage of time, a progressive increase in CFU/mL was observed.

The limited number of juice variants (n = 6) is due to the fact that this study was designed as an initial exploratory investigation. Although the results provide valuable insights into microbial stability and the antimicrobial effect of honey in fruit juices, they should be regarded as a solid foundation for potential future research expansion. Future studies that involve biological replicates and a broader variety of formulations would help validate and expand these findings.

The microbiological evolution during storage revealed that, under refrigeration at 4 °C, the microbial load increased progressively over time, with variation depending on the juice composition.

In the case of the analyzed juice samples, the number of microorganisms (bacteria, yeasts, molds) registered a progressive increase, and reached a high quantitative level at 56 days of refrigerated storage (Table 5). This was also reported in other studies (Iqbal et al., 2015; Yi et al., 2022; Xia et al., 2023) whose results showed that unpasteurized fruit juices were highly contaminated, especially after 4 weeks of refrigerated storage. The monitoring of the general state of contamination for sea buckthorn, aronia and blackcurrant juices, plain and with the addition of honey, with aerobic mesophilic bacteria, yeasts and molds, enterobacteria, indicated differences depending on time and the variety of fruit.

The initial results, upon opening the samples, showed the absence of any microorganism in all analyzed samples, which suggested proper hygiene during the preparation and packaging of the product. After the first 7 days of storage, the results showed a development of aerobic mesophilic bacteria to 1.19 ± 0.14 log CFU/mL in sea buckthorn juice, and to 1.37 ± 0.14 log CFU/mL in aronia juice; while yeasts, molds and enterobacteria were absent (Table 5). After 14 days, there was an increase in aerobic mesophilic bacteria in a proportion of 47.9% for sea buckthorn with honey, 49.63% for blackcurrant juice with honey, 50% for aronia juices with honey, 50.8% for sea buckthorn, 52.94% for sea buckthorn and aronia 1:1, and 59.85% for aronia juices without honey.

After 21, respectively 28 days, the values regarding aerobic mesophilic bacteria presented in fruit juices were maintained within the accepted limits <4 log CFU/mL (Gulf Standards. 2000; Codex Stan., 2005), but an increase was observed in sea buckthorn juice and aronia juice 50% of each fruit (3.30 ± 0.06 log CFU/mL) and aronia (3.52 ± 0.06 log CFU/mL) juice without added honey. These data are in accordance with other findings (Tasnim et al., 2010; Rahman et al., 2011; Ndife et al., 2022) who reported the number of bacteria in fruit juices within the standard limits, but some situations were reported where the microbial load was above the standard consumption limit (Bagde and Tumane, 2011; Rashed et al., 2013; Yi et al., 2022; Xia et al., 2023). After 56 days of storage, a significant deterioration of the juices was observed, with microbial counts exceeding five log CFU/mL, thereby surpassing the maximum limits established by relevant food safety standards (Gulf Standards, 2000, Codex Stan. 2005), which generally recommend a threshold of <4 log CFU/mL. This was especially evident in samples containing aronia and a mixture of aronia and sea buckthorn without honey. Therefore, at the end of the storage period at 4°C, the degree of contamination of the analyzed juices is presented in the following increasing order: SBH →SB → BCH → AH → SBA → A. The addition of honey to juices, through a possible synergistic effect with bioactive compounds in the fruits, such as vitamin C, polyphenols, and organic acids, can enhance the preservative action of the juices, thereby contributing to the slowing of microbial growth and the extension of the shelf life.

Yeasts and molds were counted in fruit juices at 14 daysof storage, with values between 1.29 ± 0.20 and 1.61 ± 0.18 log CFU/mL, with a higher degree of contamination in aronia varieties without added honey (A). It follows an increase of yeasts and molds of over 50% on the 21st day of determinations for all samples, with values between 2.53 ± 0.05 and 2.83 ± 0.11 log CFU/mL. The results were above compliance, according to the legislation in force (Commission Regulation (EC) 2073/2005). According to de (Correa et al., 2024), juices should present yeasts and molds in a maximum number of 10² CFU/mL, i.e., < 2 log CFU/mL. After 28 days, were recorded values of 3.16 ± 0.04 log CFU/mL for SBH, and of 3.25 ± 0.02 log CFU/mL for A, but after 56 days values were >5 log CFU/mL for all juice samples. The degree of contamination is presented in the following ascending order: SBH → SB → AH → BCH →SBA → A. In terms of fungal contamination, the juices can be consumed within the first 14 days after opening by keeping them at refrigeration temperature (4 ⁰C). Over this time interval (at 21, 28, respectively 56 days), the juices were no longer safe to drink, and the obtained results confirm their inappropriateness from a microbiological point of view.

Enterobacteriaceae contamination of juice samples was not detected in the first 28 days after opening, only after 56 days in aronia samples A (1.41 ± 0.27 log CFU/mL), respectively sea buckthorn juice and aronia juice 50% of each fruit (0.99 ± 0.16 log CFU/mL) SBA sample. Enterobacteriaceae were absent in the samples with added honey. Usually, Enterobacteriaceae are sensitive in acidic environments (Sawada and Yamada, 2024), in the three varieties of juice where the acidity had the highest values were not detected throughout the monitored period.

In the case of Staphylococcus detection, the values reported as ≤ 10 CFU/mL correspond to the detection limit of the method and do not reflect an exact number of microorganisms. It rather indicates a very low presence or absence, below the quantifiable threshold. In all analyzed samples, Staphylococcus sp. was either not detected or was present at levels ≤10 CFU/mL, remaining within the permitted limits by food safety regulations (Commission Regulation (EC) No 2073/2005). These findings support the hypothesis of an antimicrobial effect exerted by the bioactive compounds naturally present in berry juices. The content of major bioactive components in sea buckthorn, chokeberry, and blackcurrant berries makes them true resources against infectious agents. Similar results regarding the antimicrobial properties of berries against potentially pathogenic bacteria such as Staphylococcus sp were also reported (Criste et al., 2020; Daoutidou et al., 2021; Ren et al., 2022; Trajković et al., 2023).

Although the Fisher LSD test allowed for the comparison of average microbial values between juice variants at each time point, it did not capture the overall dynamics of microbial growth during storage. To better understand the microbial evolution over time, linear regression models were applied to the microbial load data over the 56-day storage period, as presented in Figure 4.

The validity of fruit juices also varies depending on the assortment, because some fruits are used both for consumption and for the natural antimicrobial agents they contain. Their microbiological quality can be improved by honey addition, which exhibits antimicrobial activity and helps preserve the drinks (Gomashe et al., 2014). In general, sea buckthorn berries (Hippophae rhamnoides L.) retain their nutritional value and medicinal efficacy in juice (Abliz et al., 2021), maintaining the natural taste described as sour and astringent (Ma et al., 2017). The sugar content of sea buckthorn fruits was quite low, which makes the acidity more obvious, the source of the acidity is due to the high organic acid content (Liu et al., 2022). This is also evident in the case of the pH of the natural juice subjected to research, both plain (pH = 2.78) and with the addition of honey (pH = 2.86), which allows for a higher degree of preservation than for the other varieties of juice. The total number of aerobic mesophilic bacteria, yeasts and molds in sea buckthorn juice with honey compared to the other varieties of juice, Enterobacteriaceae and Staphylococcus sp. were not detected during the entire monitored period.

Black aronia fruits (Aronia melanocarpa L.) are notable for high levels of phenolic compounds, with strong antioxidant properties and other functional attributes beneficial to human health (Bontsidis et al., 2021; Bontsidis et al., 2024), but they may have different antimicrobial effects (Denev et al., 2019). This could also be observed in the case of the analyzed juice samples through an increase in the number of microorganisms, with higher values than in other types of juice for aerobic mesophilic bacteria, as well as for yeasts, molds and Enterobacteriaceae. The added honey showed a beneficial effect of inhibiting bacterial growth compared to the simple aronia juice, where microbial growth was recorded due to the high content of dissolved oxygen (8.57 mg/L). Blackcurrant berries (Ribes nigrum L.) are characterized by a high content of sugar, acids and pectin (Laaksonen et al., 2014), the juice with the added honey had a good storage capacity over time. The number of microorganisms falls within the intermediate values ​​of buckthorn juice, respectively aronia, throughout the monitored period. Honey added to fruit juice contributed to improving the antibacterial properties and helped to remove contaminants, a fact also proven in the research conducted by (Iqbal et al., 2015).