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Article

The Effect of Thymus serpyllum L. and Its Preparations on Reduction of L. monocytogenes and S. aureus in Kombucha Fresh Cheese

by
Vladimir Vukić
*,
Jovana Degenek
,
Katarina Kanurić
,
Dajana Vukić
,
Branimir Pavlić
,
Mirela Iličić
,
Sunčica Kocić-Tanackov
,
Živan Mrkonjić
,
Sandra Bulut
and
Zoran Zeković
Faculty of Technology Novi Sad, University of Novi Sad, Bulevar Cara Lazara 1, 21000 Novi Sad, Serbia
*
Author to whom correspondence should be addressed.
Processes 2024, 12(6), 1187; https://doi.org/10.3390/pr12061187
Submission received: 24 May 2024 / Revised: 6 June 2024 / Accepted: 7 June 2024 / Published: 9 June 2024
(This article belongs to the Special Issue Emerging Technologies in Sustainable Dairy Processing)
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Versions Notes

Abstract

:
Fresh cheese is characterized by a limited shelf life, which represents a major challenge in its production. Wild thyme (Thymus serpyllum L.) has an antimicrobial capacity demonstrated in numerous studies. The utilisation of its by-product obtained in the production of filter tea could improve fresh cheese technology by obtaining a product with additional functional value and protecting the environment by reducing industrial waste. Our study sought to explore how incorporating wild thyme, in the form of dry extract, supercritical fluid extract, and herbal ground, affects the microbiological composition of fresh cheese made with kombucha inoculum as the starter culture over a 30-day storage period. To assess antimicrobial efficacy, we deliberately exposed the samples we produced to common foodborne pathogens, namely Listeria monocytogenes and Staphylococcus aureus. The results showed that the total number of L. monocytogenes and S. aureus in each sample (produced with dry extract, supercritical fluid extract, and herbal ground) decreased significantly during the storage period. The decrease in L. monocytogenes count varied from 0.6 to 1.7 log CFU/g. The results suggest that a by-product from the production of wild thyme filter tea is suitable for the production of fresh cheese to improve its antimicrobial properties against L. monocytogenes and S. aureus.

Graphical Abstract

1. Introduction

Fresh cheese belongs to a broad group of nutritious cheeses where ripening is not part of the production process. They are characterized by a sour-milky or very mildly sour taste, homogeneous and spreadable consistency [1]. Because of its pH value of over 5 and high aw value, fresh cheese is particularly susceptible to microbial contamination after the manufacturing process [2]. Bacterial growth can seriously affect the quality and safety of cheeses, as pathogenic microorganisms including Staphylococcus aureus and Listeria monocytogenes increase the risk of poisoning [3].
The most commonly used starter culture in the production of fresh cheese is a conventional mesophilic starter culture, which is responsible for the lactose decomposition into lactic acid [1] (p. 1). The use of kombucha inoculum as an unconventional starter culture in dairy technology has shown a significant impact on the duration of the fermentation process as well as on the microbiological quality, especially in fresh cheese production [4,5]. Kombucha is a symbiotic association of the yeasts (Pichia, Zygosaccharomyces, Saccharomyces, Schizosaccharomyces, Saccharomycodes, Brettanomyces, Torulaspora and Candida) and the acetic acid bacteria (Acetobacter and Gluconobacter), which has been applied for a fermentation of sweetened black or green tea (Camellia sinensis) for centuries [6,7,8]. Besides refreshment effect, due to products of metabolitic activity, kombucha beverage has a wide range of prophylactic and therapeutic properties. Kombucha is used to treat headache, arteriosclerosis, reuma, problems with metabolism and immune system, burns, skin injuries, etc. [9]. The fermentation process induced by kombucha produces several bioactive compounds that possess antimicrobial characteristics, which makes it a promising avenue for investigating alternative sources of antimicrobial agents to address the growing concern about antibiotic resistance [10]. Extensive research has demonstrated the therapeutic effect of kombucha, which has been confirmed by preventing infections caused by the activity of bacteria such as Listeria monocytogenes, Staphylococcus aureus and etc. [11,12]. The interaction of different species in the microbiota of kombucha could be the main cause of its antimicrobial activity, leading to production of compounds including acetic acid and diverse polyphenols possessing antimicrobial attributes [10].
Due to its high water content, fresh cheese is certainly a more than suitable substrate for the growth and development of various types of microorganisms. Enrichment with medicinal herbs, essential oils and herbal extracts extends its shelf life and improves the biological potential, sensory and antioxidant properties of the products and provides protection against pathogenic microorganisms [13,14]. One of the most recent possibilities is the utilisation of wild thyme (Thymus serpyllum L.), so-called herbal dust (ground), which is residual product from the filter tea production and whose products could be used in various forms as functional additives to fresh cheese [15].
Wild thyme (T. serpyllum L.) represents an aromatic plant that belongs to the Lamiaceae family and is considered a valuable raw material for the production of numerous formulations in the chemical, cosmetic and food industries [16]. The ultimate reason for this is certainly the numerous beneficial properties including antiseptic, analgesic, antibacterial, diuretic, etc. [17,18]. Wild thyme has been thoroughly researched for its antioxidant properties, which are closely linked to its abundance of polyphenolic compounds [19]. Moreover, the substantial presence of thymol and carvacrol in the essential oils significantly contributes to its antimicrobial potency [20]. Literature provides data on the utilization of thyme as an additive in specific dairy products like yogurt [21], fresh cheese [22] and traditional Pecorino Romano, sheep’s milk cheese [23]. Previous studies have demonstrated the effect of added thyme extracts and essential oils on improving the antimicrobial activity of fresh cheeses against bacteria such as L. monocytogenes and S. aureus and etc. [24,25]. However, the same results specifically related to the usage of wild thyme (T. serpyllum L.) in combination with kombucha in the role of non-conventional starter culture for the production of fresh cheese are not found in the available literature, which represents a research opportunity.
In our previous study, we successfully produced kombucha fresh cheese enriched with wild thyme and its extracts and evaluated its technological characteristics [26]. Our study revealed that wild thyme preparations are suitable for the production of the kombucha fresh cheese. The obtained results have shown good technological parameters and sensory characterists of the produced cheese. As a continuation of this research and with a detailed analysis of the previously presented facts, this study aimed to determine the influence of the incorporation of wild thyme (T. serpyllum L.) as a dry extract, supercritical fluid extract and herbal ground on the microbiological profile of fresh cheese manufactured by kombucha inoculum as an unconventional starter culture during a 30-day storage period.

2. Materials and Methods

2.1. Herb Material

The herbal ground of wild thyme (T. serpyllum L.) was obtained from the commercial tea factory. This plant material was collected as a residual product in the production of filter tea. It was used both as a raw material for subsequent extractions and as ground herbs (G) for immediate application.

2.1.1. Manufacturing the Dry Extract

The wild thyme liquid extract utilized for spray drying was prepared following the method outlined in our previous research [15] (p. 2). In brief, spray drying was conducted using a system from APV Anhydro AS, located in Søborg, Denmark. Maltodextrin (20%) was applied as a carrier, achieved through continuous mixing at 40 °C. During the spray drying process, the inlet temperature ranged from 140 °C to 150 °C, while the outlet temperature was consistently held at 80 °C. The resulting dry extract (DE) was then stored and safeguarded against exposure to air and moisture. The characterization of the dry extracts, including the determination of total phenolic content and in vitro antioxidant activity via DPPH, FRAP, and ABTS assays, was conducted using spectrophotometric methods as detailed elsewhere [27].

2.1.2. Extraction Using Supercritical Fluid

Extraction using supercritical fluid (SFE) was conducted utilizing a high-pressure extraction system comprising essential components such as a CO2 gas cylinder, a diaphragm compressor capable of reaching pressures up to 1000 bar, a 200 mL extraction vessel, a separator, temperature and pressure control systems, and control valves. The extraction of the sample was occurring for 3 h, maintaining a temperature of 50 °C, a pressure of 350 bar, and a CO2 flow rate of 0.3 kg/h. The collected extract was stored under refrigeration (4 °C) for subsequent analysis.

2.1.3. GC–MS and GC-FID Analysis

The volatile compounds in the lipid extract obtained from the herbal dust of wild thyme were identified by GC–MS analysis (7890A, Agilent Technologies, Santa Clara, California, USA) coupled with MS detector (5975C, Agilent Technologies, Santa Clara, California, USA) and capillary column (30 m 0.25 mm, 0.25 µm; 19091S-433UI HP-5MSUI, Agilent Technologies, Santa Clara, California, USA) as previously described in Šojić et al. (2023) [28]. The prevailing lipid extract constituents in wild thyme were identified by analyzing solutions containing standard compounds at varying concentrations (1–500 μg/mL), with methylene chloride employed as the solvent. This analysis aimed to establish the correlation between peak area and concentration, ensuring a high coefficient of determination (R2 > 0.99). The analysis was performed in triplicates and the results are presented as a mean value. The obtained results were quantified expressed as mg per g of extract (mg/g).

2.2. Fresh Cheese Sample Production

The Kombucha fresh cheese was manufactured under controlled conditions from pasteurised milk (in a regime of 30 s at 75 °C) containing 2.8% milk fat. Three batches of milk were used for the production of three cheese batches. All produced cheese samples produced in one replication were made from one batch of milk.
Kombucha inoculum was used as a starter culture for the kombucha fresh cheese production. The preparation of kombucha inoculum has been published previously [29]. The inoculum was ready for use after seven days of incubation at a temperature of 25 °C. At the end of the incubation period, the pH of the kombucha inoculum dropped to a value of 3.25. The prepared kombucha inoculum was used for milk fermentation which had previously been used for production of fermented milk products [30].
To initiate coagulation of the milk, the commercial enzyme (CHY-MAX®Powder Extra NB) was applied in accordance to the manufacturer’s instructions (1 g of freeze-dried enzyme in 200 mL of water and 5 mL of this solution in 1L of milk at 35 °C).
Fermentation of the kombucha fresh cheese was performed at the temperature of 35 °C (in a GFL incubation/inactivation water bath 1005, Lab Logistics Group, Meckenheim, Germany) and continued until a pH of 4.6 was established. Immediately after the fermentation process was stopped, the resulting coagulum was cut and pasteurised for 5 min at 60 °C. The produced cheese was drained through a sterile gauze. After production, the final fresh cheese samples were packaged in 400 g cups, covered with lids, and refrigerated at 4 °C until subsequent investigation. Figure 1 depicts the process of fresh cheese production.
To improve the antimicrobial properties of the produced kombucha fresh cheese samples (Kombucha C), they were enriched with wild thyme herbal ground (G), dry extract (DE) and supercritical fluid extract (SFE) (Table 1). The added concentrations were calculated so that all samples received the same amount of calculated initial plant source material. The resulting samples were homogenised and yielded four different samples for analysis: Kombucha C, Kombucha G, Kombucha DE and Kombucha SFE, all prepared in triplicate. All samples (Kombucha C, Kombucha G, Kombucha DE and Kombucha SFE) from one replicate were prepared from a single batch of cheese, presented in Figure 2.

2.3. Analysis of Physico-Chemical Characteristics

Physico-chemical characteristics, that have a major influence on the growth of applied microorganisms, have been investigated. The pH values were measured at 25 °C using a pH Spear pH meter (OAKTON Instruments, Vernon Hills, Illinois, USA), while the aw (water activity) values were measured utilizing a LabSwift-aw device (Novasina AG, Lachen, Switzerland).

2.4. Microbiological Analysis

To investigate the effect of T. serpyllum L. and its preparations on the reduction of L. monocytogenes and S. aureus in contaminated kombucha fresh cheese, each sample was intentionally contaminated with L monocytogenes ATCC 13932 and S. aureus ATCC 6538 strains. The procedure of contamination and quantification of the microorganisms in the final products is described in our previous research [31].

2.5. Total Phenols Content

The Folin-Ciocalteu spectrophotometric method was applied to determine the total phenol content of the produced kombucha fresh cheese samples [32]. A range of gallic acid concentrations were used to prepare the calibration curve for standardization, and spectrophotometric analysis was performed (750 nm). The overall phenolic content was measured and reported as milligrams of gallic acid equivalents (GAE) per gram of fresh cheese sample (mg GAE/g).

2.6. Analysis of Statistical Parameters

All experiments and measurements were performed in three replications and the results were presented as mean value ± standard deviation. To assess significant differences between the tested variables, an ANOVA test (analysis of variance), correlation analysis, and Duncan multiple range test were conducted using “Statistica 13.5.0.17” software using the parameters described in Vukić et al. (2023) [31]. Statistical significance among the tested parameters was determined at a threshold of p < 0.05. Moreover, response surface methodology, coupled with the desirability function, was employed to ascertain the optimal conditions [33]. This function indicates the desirable ranges for each response variable, with values ranging from zero to one (least to most desirable).

3. Results

The kombucha fresh cheese was successfully produced according to the procedures described in the Section 2. The lactic fermentation was followed until reaching a pH of 4.6, which took 14 h.
Microbiological analysis of milk and kombucha inoculum used as starter culture was performed to investigate their viability. The milk exhibited a total count of aerobic mesophilic bacteria (MAB) at 4.3 log CFU/g. In the kombucha inoculum, aerobic mesophilic bacteria were present at 7.1 log CFU/g, alongside lactic acid bacteria at 6.2 log CFU/g. Neither L. monocytogenes nor S. aureus was detected in the analysed milk or the kombucha starter culture. The results obtained showed that the used milk and the kombucha starter culture had an appropriate microbiological profile for further preparation of the samples. To explore the antimicrobial capabilities of kombucha fresh cheese and assess the impact of wild thyme (T. serpyllum L.) herbal ground, as well as its DE and SFE, the prepared cheese samples were deliberately contaminated with typical pathogens present in cheese: L. monocytogenes and S. aureus. There was a significant reduction in total counts of L. monocytogenes and S. aureus in all samples throughout the 30-day storage period (p < 0.05) (Table 2). The number of L. monocytogenes in Kombucha C decreased by 0.6 log CFU/g after the 30 days of storage, while S. aureus decreased by 0.9 log CFU/g. These results revealed that S. aureus had the highest decrease in total count.
The physico-chemical properties that have a major influence on the growth and survival of pathogenic microorganisms were investigated. According to the obtained results (Table S1), there were no differences in the aw value between the prepared samples throughout the 30-day storage period. Also, the changes in pH in the fresh cheese samples during storage were not high enough to cause changes in the growth and survival of the microorganisms studied. These results indicate that changes in the total number of microorganisms analysed were triggered by the content of bioactive compounds.
The yield of total phenols and the antioxidant activity of the extract obtained by ultrasound-assisted extraction and the dry extract were determined by DPPH, FRAP and ABTS assays (Table 3).
The content of the main terpenoid compounds of T. serpyllum L. supercritical fluid extract is shown on Figure 3.
The growth of L. monocytogenes and S. aureus was significantly influenced by the analysed parameters (sample and day of storage) (p < 0.05), as shown by the ANOVA analysis in Table 4. In addition, a significant decrease in the number of examined pathogens (p < 0.05) was observed throughout the entire storage period (Figure S1). The interaction of the analysed parameters Sample*Day of storage has also exerted a notable impact on microbial proliferation (p < 0.05).
The desirability of the examined parameters has been presented through a response surface plot (Figure 4).

4. Discussion

The observed decrease in the total number of pathogens tested in kombucha fresh cheese could explain the antimicrobial activity of the kombucha beverage and is in line with our previously published results [12] (p. 2). The antibacterial activities of kombucha cultured with black and green tea has been investigated [34]. These authors found that kombucha cultivated with black tea was characterized by 55.69% higher content of total phenols (1.09 mg GAE/mL) than kombucha cultivated with green tea (0.70 mg GAE/mL). In their research, kombucha cultured on green tea was responsible for inhibiting the growth of the tested bacteria (E. coli, L. monocytogenes, and S. aureus) at a MIC (Minimum Inhibitory Concentration) of 250 μL/mL, whereas kombucha cultured on black tea inhibited the growth of S. aureus and L. monocytogenes (with a MIC of 250 μL/mL). In addition, the authors above reported that kombucha cultured on green tea inhibited a higher number of pathogenic bacterial strains than kombucha cultured on black tea. These results may be because green tea kombucha beverage represents a rich source of catechins, which have been shown to have an antibacterial effect, while their content determined in the black tea kombucha beverage is significantly lower. Kombucha beverage also contains a high concentration of phenolic compounds with antiproliferative and bacteriostatic effects [35,36,37]. This assertion was validated through the examination of total phenols, revealing that the Kombucha C sample exhibited a notable total phenol content—1.38 ± 0.05 mg GAE/g. This observation may be ascribed to the existence of phenols inherent in the native kombucha inoculum. Moreover, the metabolic activity of kombucha during the process of fermentation could produce phenols, leading to an increase in content of the total phenols throughout the storage period, as shown by the value of 1.77 ± 0.08 mg GAE/g. Previous studies have reported an increase in total phenolic content (up to threefold) during the fermentation of milk with kombucha inoculum, which is consistent with our results [38].
Previously, wild thyme extract revealed significant antimicrobial activity [39]. Hence, we explored avenues to enhance the antimicrobial efficacy of the resulting kombucha fresh cheese by incorporating ground wild thyme, its DE, and SFE. The findings, detailed in Table 2 and statistically analyzed, are illustrated in Figure S1, revealing a notable decrease in the targeted pathogenic microorganisms.
In comparison with the control sample (Kombucha C) (Table 2), the addition of wild thyme herbal dust (Kombucha G sample), dry extract (Kombucha DE) and supercritical fluid extract (Kombucha SFE) in kombucha fresh cheese led to an increase in antimicrobial activity against L. monocytogenes. In addition, although the reduction in the total number of S. aureus was recorded in all samples, compared with control sample, the activity is increased only in the Kombucha G sample. In the Kombucha G sample, the total count of L. monocytogenes decreased by 1.7 log CFU/g, while S. aureus decreased by 1.3 log CFU/g, indicating an increase in antimicrobial activity in comparison with the Kombucha C sample. Although the herbal dust from wild thyme is considered a by-product, this plant matrix is nevertheless characterised by a significant amount of polyphenols and terpenoids [15,40] (p. 2).
The analysis of the total phenolic content in the examined cheese samples revealed significant differences in the control sample (Kombucha C = 1.38 ± 0.05 mg GAE/g) compared to the samples that contained wild thyme ground and dry extract of wild thyme (Kombucha G = 1.56 ± 0.05 mg GAE/g; Kombucha DE = 1.86 ± 0.06 mg GAE/g), while there were no differences compared to the supercritical fluid extract (Kombucha SFE = 1.30 ± 0.07 mg GAE/g). The higher polyphenol concentration found in the Kombucha G sample was consistent with its stronger antimicrobial effectiveness against the studied pathogens. In contrast, the antimicrobial properties of the Kombucha SFE sample can be ascribed to the presence of oxygenated monoterpenes, specifically carvacrol (63.25 mg/g), thymol (19.64 mg/g) and α-terpineol (77.47 mg/g), which constitute the main constituents of the wild thyme SFE used in this study and are known to possess antimicrobial properties (Figure 3) [41,42,43].
The addition of dry extract (Kombucha DE) led to the same decrease in the total number of L. monocytogenes and S. aureus (0.8 log CFU/g). The increased antimicrobial activity against L. monocytogenes could be due to the present polyphenolic compounds with proven antimicrobial activity such as p-coumaric acid, quercetin and luteolin [44,45,46].
Desirability increased with increasing storage time and increasing total phenols content, with total phenols content being favorable for reducing the number of studied pathogens. During storage, total phenols content increased due to the metabolic activity of the kombucha inoculum, affecting the reduction of the total bacterial count [38] (p. 11).
Our results suggest that industrial leftovers generated as a by-product in the manufacture of wild thyme filter tea can effectively find use in fresh cheese production process to improve its antimicrobial properties against L. monocytogenes and S. aureus.

5. Conclusions

The results obtained showcased a robust antimicrobial activity in the prepared kombucha fresh cheese samples. Utilizing kombucha as a non-traditional starter culture effectively shielded the fresh cheese samples against contamination by L. monocytogenes and S. aureus. Incorporating wild thyme in the form of ground, dry extract, and supercritical fluid extract increased the antimicrobial activity towards L. monocytogenes in kombucha fresh cheese. The added wild thyme ground increased the antimicrobial effectiveness of kombucha fresh cheese towards S. aureus, while dry extract and supercritical fluid extract showed no effect. The demonstrated antimicrobial effectiveness against prevalent pathogens holds significant value in prolonging the somewhat restricted shelf life of fresh cheese. This underscores the recommendation for incorporating kombucha inoculum and preparations of wild thyme (T. serpyllum L.) in fresh cheese production. The use of the wild thyme dust fraction, which is a by-product in the production of filter tea, therefore has a high potential for the preservation of fresh cheese against typical foodborne pathogens such as L. monocytogenes and S. aureus and offers a double benefit: waste recovery and food preservation.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/pr12061187/s1, Figure S1: Influence of the day of storage on the growth of the examined pathogens. Vertical bars denote 0.95 confidence intervals; Table S1: pH and aw values of fresh cheese with the addition of wild thyme during the 30 days of storage.

Author Contributions

Conceptualization, V.V.; methodology, J.D. and D.V.; software, V.V., J.D., D.V.; validation, V.V., J.D. and D.V.; formal analysis, B.P., S.K.-T., S.B. and Ž.M.; investigation, J.D., D.V., B.P. and S.K.-T.; resources, K.K.; data curation, V.V., J.D. and D.V.; writing—original draft preparation, V.V.; writing—review and editing, J.D., K.K., D.V., B.P., M.I., S.K.-T., S.B., Ž.M. and Z.Z.; visualization, V.V., J.D. and D.V.; supervision, V.V., M.I., S.K.-T. and Z.Z.; funding acquisition, K.K., V.V. and D.V. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Ministry of Science, Technological Development and Innovations of the Republic of Serbia, grant numbers 451-03-66/2024-03/200134 and 451-03-65/2024-03/200134.

Data Availability Statement

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

Acknowledgments

The authors would like to thank the Faculty of Technology Novi Sad for providing laboratory space and the necessary equipment.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Processes 12 01187 g001
Figure 1. Kombucha fresh cheese manufacturing process.
Figure 1. Kombucha fresh cheese manufacturing process.
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Figure 2. Samples of fresh kombucha cheese with added wild thyme, where are (a) Kombucha C; (b) Kombucha G; (c) Kombucha SFE; (d) Kombucha DE.
Figure 2. Samples of fresh kombucha cheese with added wild thyme, where are (a) Kombucha C; (b) Kombucha G; (c) Kombucha SFE; (d) Kombucha DE.
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Figure 3. Content of the main terpenoid compounds of T. serpyllum L. SFE extract.
Figure 3. Content of the main terpenoid compounds of T. serpyllum L. SFE extract.
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Figure 4. Quadratic fit surface plot illustrating the desirability of day of storage and content of total phenols on reduction of total count of the examined pathogens.
Figure 4. Quadratic fit surface plot illustrating the desirability of day of storage and content of total phenols on reduction of total count of the examined pathogens.
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Table 1. Produced samples and contents of wild thyme.
Table 1. Produced samples and contents of wild thyme.
SampleForm of Wild ThymeConcentration (g/100 g)
Kombucha GGround2.1
Kombucha DEDry extract0.62
Kombucha SFESupercritical fluid extract0.025
Table 2. Microbiological analysis of the produced kombucha cheese samples with the addition of three forms of wild thyme—dry extract, supercritical fluid extract and herbal ground—during 30-day storage (log CFU/g).
Table 2. Microbiological analysis of the produced kombucha cheese samples with the addition of three forms of wild thyme—dry extract, supercritical fluid extract and herbal ground—during 30-day storage (log CFU/g).
Day of
Storage		Kombucha CKombucha GKombucha DEKombucha SFE
MABL. monocytogenesS. aureusMABL. monocytogenesS. aureusMABL. monocytogenesS. aureusMABL. monocytogenesS. aureus
09.0 *a ± 0.23.8 a ± 0.14.1 a ± 0.09.0 a ± 0.04.0 a ± 0.14.0 a ± 0.18.8 a ± 0.43.6 a ± 0.03.7 a ± 0.28.9 a ± 0.04.1 a ± 0.24.2 a ± 0.0
108.7 b ± 0.03.4 b ± 0.13.4 b ± 0.08.8 a ± 0.23.5 b ± 0.13.8 a ± 0.18.9 a ± 0.13.6 ab ± 0.03.7 a ± 0.18.7 b ± 0.13.7 b ± 0.03.9 ab ± 0.0
208.4 b ± 0.13.2 b ± 0.03.2 c ± 0.08.8 a ± 0.13.1 c ± 0.23.2 b ± 0.08.7 a ± 0.13.5 b ± 0.13.5 a ± 0.08.8 ab ± 0.03.5 bc ± 0.13.5 b ± 0.3
308.6 b ± 0.03.2 b ± 0.23.2 c ± 0.08.6 a ± 0.02.3 d ± 0.02.7 c ± 0.28.7 a ± 0.12.8 c ± 0.02.9 b ± 0.18.8 ab ± 0.03.3 c ± 0.13.5 b ± 0.2
* Values denoted by different letters (a–d) within each parameter in the same column exhibit significant differences (p < 0.05).
Table 3. Total phenol content (TP) and antioxidant activity of the extract obtained by ultrasound-assisted extraction (UAE) and dry extract.
Table 3. Total phenol content (TP) and antioxidant activity of the extract obtained by ultrasound-assisted extraction (UAE) and dry extract.
SampleTP [g GAE/100 g]DPPH [mM TE/g]FRAP [mM Fe2+/g]ABTS [mM TE/g]
UAE *4.39 ± 0.10430.25 ± 0.00210.77 ± 0.02100.52 ± 0.0095
Dry extract2.05 ± 0.05890.94 ± 0.01034.56 ± 0.04925.53 ± 0.0566
* [11].
Table 4. Multivariate Tests of Significance of examined factors on the count of investigated microorganisms.
Table 4. Multivariate Tests of Significance of examined factors on the count of investigated microorganisms.
Wilks’ LambdaFEffect DFError DFp
Thyme addition0.0000748053.57964130.0000
Day of storage0.050656.034349251234.68626970.00001
Sample * Day of storage0.01259612.21083781234.68626970.0000
* A p-value < 0.05 indicates a noteworthy impact of the factor on the abundance of the examined microorganisms.
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MDPI and ACS Style

Vukić, V.; Degenek, J.; Kanurić, K.; Vukić, D.; Pavlić, B.; Iličić, M.; Kocić-Tanackov, S.; Mrkonjić, Ž.; Bulut, S.; Zeković, Z. The Effect of Thymus serpyllum L. and Its Preparations on Reduction of L. monocytogenes and S. aureus in Kombucha Fresh Cheese. Processes 2024, 12, 1187. https://doi.org/10.3390/pr12061187

AMA Style

Vukić V, Degenek J, Kanurić K, Vukić D, Pavlić B, Iličić M, Kocić-Tanackov S, Mrkonjić Ž, Bulut S, Zeković Z. The Effect of Thymus serpyllum L. and Its Preparations on Reduction of L. monocytogenes and S. aureus in Kombucha Fresh Cheese. Processes. 2024; 12(6):1187. https://doi.org/10.3390/pr12061187

Chicago/Turabian Style

Vukić, Vladimir, Jovana Degenek, Katarina Kanurić, Dajana Vukić, Branimir Pavlić, Mirela Iličić, Sunčica Kocić-Tanackov, Živan Mrkonjić, Sandra Bulut, and Zoran Zeković. 2024. "The Effect of Thymus serpyllum L. and Its Preparations on Reduction of L. monocytogenes and S. aureus in Kombucha Fresh Cheese" Processes 12, no. 6: 1187. https://doi.org/10.3390/pr12061187

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