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Article

Valorization on the Antioxidant Potential of Volatile Oils of Lavandula angustifolia Mill., Mentha piperita L. and Foeniculum vulgare L. in the Production of Kefir

by
Ovidiu Tița
1,*,
Maria Adelina Constantinescu
1,
Mihaela Adriana Tița
1,
Tiberius Ilie Opruța
1,
Adriana Dabija
2 and
Cecilia Georgescu
1,*
1
Department of Agricultural Sciences and Food Engineering, Lucian Blaga University of Sibiu, Doctor Ion Rațiu No. 7, 550012 Sibiu, Romania
2
Faculty of Food Engineering, Stefan cel Mare University of Suceava, 720229 Suceava, Romania
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2022, 12(20), 10287; https://0-doi-org.brum.beds.ac.uk/10.3390/app122010287
Submission received: 9 September 2022 / Revised: 8 October 2022 / Accepted: 10 October 2022 / Published: 13 October 2022
(This article belongs to the Special Issue Unconventional Raw Materials for Food Products)
Browse Figures
Versions Notes

Abstract

:
(1) Background: Natural antioxidants are health products found in many plants and may have a therapeutic effect on various diseases caused by oxidative stress. The purpose of this research is the antioxidant analysis of some kefir samples enriched with volatile oils extracted from three aromatic plants; (2) Methods: The volatile oils were extracted from lavender, fennel and mint. Four samples of kefir were made: kefir enriched with encapsulated lavender volatile oil, kefir enriched with encapsulated mint volatile oil, kefir enriched with encapsulated fennel volatile oil and a control sample without volatile oils. The analysis took place in three periods of storage: on the first day, on the 10th day and the 20th day; (3) Results: The antioxidant activity of kefir samples had decreased during the storage. The kefir sample with fennel and lavender volatile oil had the highest antioxidant activity, while the control sample had the lowest activity; (4) Conclusions: We can conclude that the volatile oils add value to the finished product.

1. Introduction

Stress is a response to environmental stressors that affect the lives of individuals, and relationships with other people. Stress can cause social, physical and mental problems. People may experience many symptoms, such as irritability, difficulty concentrating, sleep disturbances, diarrhea, fatigue, anger, palpitations, frequent urination, constipation and headaches [1]. Long periods of stress lead to reduced cell proliferation and neurogenesis, thus playing a significant role in depression and Alzheimer’s disease (AD). Environmental stressors cause immune system symptoms and hormonal effects, neuroplastic changes that result in neurogenesis and impaired neurotransmission. Eventually, this can lead to neurodegenerative changes, dementia, and cognitive decline [2,3].
At high levels, oxidative stress could degrade lipids, proteins and deoxyribonucleic acid (DNA). This leads to inflammation and cell death. It also has an important role in many cardiovascular diseases, such as heart failure, cardiac arrhythmia, atherosclerosis and ischemia-reperfusion injury [4,5,6,7]. It can influence the development of leukemia [8] and can harm male fertility [9].
Antioxidants are health care products that can be sold worldwide without a prescription. Many types of research show the benefits of antioxidants, but only a few mention their possible harmful effects. The balance between free radicals and antioxidants in the human body is offset when any of these predominate [10].
Plants activate antioxidant defense mechanisms under abiotic stress, which helps maintain the integrity of cellular components and attenuates oxidative damage [11]. Important compounds with antioxidant properties found in medicinal and aromatic plants include polyphenols, stilbene, flavonoids, chalcone, capsaicinoids and casinoids, lignans and curcuminoids, carotenoids, isothiocyanates and catechins. Thus, natural antioxidants have therapeutic potential for many diseases caused by stress [12].
The antioxidant activity of plants is the result of their phenolic compounds. Phenolic compounds are functional compounds synthesized by plants. They play an important role in human nutrition for a healthy life, and mint is an important source [13]. Mint (Mentha piperita L.) is a medicinal and aromatic plant used in traditional medicine and drugs for its antimicrobial and antioxidant properties [14]. The antioxidant activity of mint prevents oxidative stress at the cellular level by its chemical composition [15]. Mint-derived secondary metabolites are antioxidants that have immunostimulatory, cardio-tonic and antiviral properties [16]. Mint contains volatile components, flavonoids, organic acids, and quinones, necessary for the digestive system, central nervous system, and respiratory system. It has antioxidant, antimicrobial, anti-inflammatory and anesthetic properties [14,17,18,19]. The most important components of volatile oil are menthol, menthone, menthofuran, isomenthone, caryophyllene, eucalyptol, linalool, limonene, carvone, pulegone and α-terpinol [20]. In the study conducted by Bleiziffer et al., in 2017, it was observed that mint and sage oil are the freest amino acids (>4 mg·g−1) [21]. In 2013, Tsai et al., demonstrated that the most important compound of mint essential oil is menthol and it has a high antimicrobial activity against Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli. Antioxidant activity has been demonstrated using the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) method and the β-Carovtene-linoleic acid test [14]. Brahmi et al., in 2018 demonstrated that mint essential oil is a good source of compounds with antioxidant, cytoprotective and immunomodulatory properties [22]. In 2019, Park et al., using high-performance liquid chromatography (HPLC) analysis demonstrated that the mint flower has a higher level of phenolic compounds, flavonoids and anthocyanins that offer antimicrobial and antioxidant effects compared to the stem and leaves [23]. Two other studies conducted in 2019 and 2021 by Wu et al., and Hejna et al., respectively, demonstrated the antioxidant activity using the Trolox equivalent antioxidant capacity test and the DPPH method [24,25].
Fennel (Foeniculum vulgare L.) is part of the family Apiaceae Lindl. [26]. It is a medicinal plant used as an analgesic, diuretic, anti-inflammatory and antispasmodic [27,28,29]. The essential oil is used as a component in cosmetics, pharmaceuticals and flavoring agents in different food products. Fennel essential oils have hepatoprotective and antispasmodic effects. It is also known for its diuretic, analgesic, anti-inflammatory and antioxidant properties [26,27,30]. The most important components of the essential oil are α-pinene [31], estragol, trans-anethole, a-phellandrene and fenchone [27]. Numerous studies have shown its antioxidant, anti-inflammatory and antimicrobial action [28,30,32,33,34,35,36]. In 2021, Korinek et al., showed that volatile fennel oil had a positive effect on human neutrophils [37] and Mazandrani et al., in 2015 studied the antioxidant and antimicrobial effects during the storage of silver carp fillet [38].
Lavender (Lavandula angustifolia Mill.) belongs to the Lamiaceae Martinov family [39] and is used as a culinary herb and medicine for burns, skin wounds, headaches, digestive problems, insect bites [40], analgesic, antiseptic, sedative and urinary tract improvement [41,42]. Lavender is rich in essential oil, and studies have concluded that it has antimicrobial, antioxidant, insecticidal and anticholinesterase inhibitory activities [39,40]. The essential oil contains many compounds such as borneol, fenchon cineole, terpineol, camphor [41], linalool, linalyl acetate and β-ocimene [43]. Research has concluded that the essential oil has antimicrobial, antioxidant, anti-inflammatory and antiseptic properties due to its high content of flavonoids and polyphenols [39,40,44,45,46,47,48]. In 2017, Küçükyilmaz et al., concluded that supplementing levels of 24 to 48 mg/kg of lavender essential oil is effective in exerting antioxidant and growth-promoting activities [49]. In 2021, Adaszynska-Skwirzynska et al., showed that by adding it as an additive to the drinking water of broilers it can become an excellent alternative to banned antibiotics to stimulate growth [50]. In a study performed on mice by Kozics et al., in 2017, it was concluded that cell death mediated by oxidative stress in liver tissue can be prevented by treatment with lavender essential oil [51].
Kefir is an acidic fermented milk drink with a creamy consistency produced by bacteria through the alcoholic and lactic fermentation of kefir grains. Kefir is a milk-based drink with antioxidant properties and benefits, such as reduced symptoms of lactose intolerance, immune system stimulation, lower cholesterol, and antimutagenic and anticancer activity. The health benefits have been attributed to various bioactive compounds such as vitamins, minerals, lipids, proteins, amino acids and trace elements [52,53,54,55,56,57]. The antioxidant and anti-inflammatory properties of kefir have been demonstrated in numerous studies [58,59,60,61,62,63]. Sabokbar et al., in 2014 and 2015 made drinks based on kefir and added apple and pomegranate juice, and the results obtained showed a high antioxidant activity [64,65,66].
Current studies targeting the use of encapsulated volatile oils in foods are limited [67]. The encapsulation of oils is used especially for their antimicrobial effect to inhibit certain pathogenic microorganisms that can develop in food products [68,69,70,71].
In the present research, we propose the antioxidant analysis of some kefir samples enriched with volatile oils extracted from aromatic plants. The volatile oils were extracted from lavender, fennel and mint, and due to their sensitivity to external factors, it was decided to encapsulate them. Four types of kefir were made: kefir enriched with encapsulated mint volatile oil, kefir enriched with encapsulated lavender volatile oil and kefir enriched with encapsulated fennel volatile oil and a control sample in which no volatile oils were added. The samples were made in the laboratories of the Faculty of Agricultural Sciences, Food Industry and Environmental Protection in Sibiu, Romania. To ensure that these products are accepted by consumers, we initially tested the sensory acceptance and texture of these kefir samples [72].

2. Materials and Methods

2.1. Extraction of Volatile Oils

For the extraction were used dried and crushed lavender (Lavandula angustifolia Mill.), mint (Mentha piperita L.) and fennel (Foeniculum vulgare L.) seeds. For the extraction, the Neo-Clevenger apparatus modified by Moritz with water vapor was used. This method was used according to the Romanian Pharmacopoeia edition X [73]. Table 1 presents the volatile oil extraction efficiency. The highest extraction efficiency was obtained in the case of fennel due to the use of seeds. For volatile oils extracted from the herb, the mint had the highest efficiency and lavender had the lowest.
The volatile oils obtained had a pale yellow to greenish yellow color—for mint—and a characteristic odor, the strongest being that of fennel, followed by lavender and mint. All the plants used came from authorized plantations in Sibiu, Romania [72].

2.2. Encapsulation of Volatile Oils

To protect the volatile oils from environmental factors, we encapsulated them in sodium alginate. Three types of oils were used to make the capsules with volatile oils: mint, fennel and lavender. 30 μL of each volatile oil in 10 mL of 2% sodium alginate solution was added [72].
The 2% sodium alginate solution was prepared the day before forming the capsules, this was necessary for it to clear.
After mixing the volatile oil with the sodium alginate, we proceeded to the formation of the capsules. The solution was pipetted dropwise into 250 mL of 2% calcium chloride in an ultrasonic water bath (manufacturer Bandelin Sonorex) at 25 °C. After pipetting the entire solution of sodium alginate with volatile oil, solution was held in the water bath for another 10 min. A solution of calcium chloride and capsules with volatile oils was filtered with the help of a muslin cloth. The capsules were washed with distilled water, after which they were left to dry at room temperature for 10 min. The procedure was identical for each type of volatile oil.
The structure of a capsule was gelatinous and the size was 240 μm. They had an opalescent white color and a characteristic odor of the plant [72].

2.3. Obtaining Samples of Kefir with Volatile Oils Encapsulated

The pasteurization of raw milk was made for 25 min at 85–90 °C. The starter culture of 0.15 g:2 L of milk and pre-mixed powder milk of 150 g:2 L of milk were added after cooling the milk to 20 °C. The capsules were added at 1 g for every 100 g of kefir. Afterwards the milk was placed into plastic containers to a final weight of 250 g. The thermostat had two stages: the first thermostat at 18 °C for 10 h, and the second thermostat at 10 °C for 8 h. The glasses with samples were covered with cling film and stored at 4 °C. Raw milk came from healthy animals from an authorized farm in Vulpăr village, Sibiu, Romania. The starter culture was a mix of LYOFAST cultures, MS 059 DT, manufacturer SACCO [72].

2.4. Extraction of Compounds to Determine Antioxidant Capacity

For the extraction of compounds the method adapted from Patel et al. (2016) was used [74]. 0.5 g of the sample was extracted with 10 mL solvent containing methanol, water and hydrochloric acid 0.12 M = 70:29:1 (v/v/v) for 24 h at room temperature. For 30 min the mixture was kept in the ultrasonic bath (manufacturer Bandelin Sonorex) at 25 °C, then it was centrifuged at 8000 rpm for 10 min, and the supernatant was collected. The second extraction was performed exactly like the first, except the time spent in the ultrasonic bath was 15 min. The total quantity of supernatant was evaporated using the rotary evaporator (manufacturer Hei-VAP Precision). After evaporation the residue was taken up with 10 mL of methanol and then the mixture was filtered and filled with methanol to a total volume of 10 mL [75].

2.5. Determination of Antioxidant Activity

To determine the antioxidant activity a method adapted from Tylkowski et al. (2011) was used [76]. A DPPH solution with a concentration of 25 µg/mL was prepared by solubilizing a quantity of DPPH in absolute methanol. To complete the solubilization, the mixture was prepared in advance for 2 h. Seven DPPH solutions made from methanol in the range of 0.1–1 µg/mL were prepared for plotting the calibration curve, starting from a stock DPPH solution. 970 µL of a 25 µg/mL DPPH solution was added into 30 µL od methanol extract, obtained using the extraction described above. Absorbance was measured at 515 nm using a spectrophotometer (manufacturer Shimadzu 1900 UV-VIS), and an absorbance graph was plotted as a function of concentration [75].
The concentration of the solutions was calculated with Formula (1):
C = A − i . c . c s . c . c .
where:
C—the concentration of the DPPH solution (µg/mL);
A—sample absorbance;
i.c.c.—the intercept of the calibration curve;
s.c.c.—the slope of the calibration curve.
The antioxidant activity expressed as a DPPH radical inhibition process was calculated according to Formula (2):
AA = C 0 − C 1 C 0   ·   100
where:
AA—antioxidant activity (%);
C0—the concentration of the blank solution (DPPH solution in methanol without sample);
C1—the remaining concentration of DPPH in the sample [76].
For each sample, three repeats were performed, and the analysis took place at three periods of storage: on the first day, on the 10th day and the 20th day.

2.6. Statistical Analysis

All results obtained from the determination of the antioxidant activity were expressed according to the following statistical indicators: mean value, standard error of the mean (SEM), median, standard deviation (SD), maximum value, minimum value, skewness. Statistical significance was determined using correlation analysis of data obtained using the Pearson correlation. Thus, we correlated the data obtained for the samples with volatile oils with those of the control sample [77]. All statistical analyses were performed using Minitab version 14 and p < 0.05 was considered significant.

3. Results

3.1. Realization of the Calibration Curve to Determine the Antioxidant Activity

To achieve the calibration curve, we prepared seven DPPH solutions made from methanol in the range of 0.1–1.0 µg/mL starting from a stock solution of DPPH.
According to Figure 1, the slope of the calibration curve is 0.0411, and the intercept of the calibration curve is 0.0349. The absorbance at which the measurements were made is equal to 515 nm. Depending on the absorbance of each sample, we determined the concentration of the solutions, and then the antioxidant activity.

3.2. Determination of Antioxidant Activity for Volatile Oil Samples

Figure 2 shows the antioxidant activity for the three assortments of volatile oils used in encapsulation. Fennel volatile oil has a mean value of 30.623 ± 0.012. The median is 30.63 and the histogram is tilted to the left, the skewness being −1.73. The mean value for the antioxidant activity of lavender volatile oil is 12,757 and the standard deviation is 0.015. The skewness is −0.9, the histogram is tilted to the left, and the median value is 12.76. The mean antioxidant activity for mint volatile oil is 25.62 and the standard deviation is 0.01. The median is 25.62 and the histogram is perfectly symmetric because the skewness is 0.

3.3. Determination of Antioxidant Activity for Kefir Samples Enriched with Encapsulated Volatile Oils

Figure 3 shows the comparative variation of antioxidant activity in the kefir sample with lavender volatile oil and the control sample. On the first day of storage, the antioxidant activity mean value for the sample of kefir with lavender volatile oil is 65.39, and the standard deviation is 0.021. The median value is 65.38, and the skewness is 1.29, so the histogram is oriented to the right. In the case of the control sample, the mean value of the antioxidant activity is 59.96 and the standard deviation is 0.006. The median value is 59.96, and the skewness is −1.73, the histogram is oriented to the left. On the 10th day, the kefir with lavender volatile oil has an antioxidant activity mean value of 59.78, and the standard deviation is 0.006. The median value is 59.78, and the skewness is 1.73, with the histogram being oriented to the right. For the control sample, the mean value of the antioxidant activity is 35.05 and the standard deviation is 0.01, the median value is 35.05 and the histogram is perfectly symmetrical because the skewness is 0. On the 20th day, the kefir with lavender volatile oil has an antioxidant activity mean value of 13.71 ± 0.01, the median value is 13.71 and the histogram is perfectly symmetrical because the skewness is 0. In the case of the control sample, the mean value of the antioxidant activity is 10.95 and the standard deviation is 0.012. The median value is 10.94 and the skewness is 1.73, the histogram is oriented to the right. On the first day, the Pearson correlation coefficient between the control sample and the kefir with lavender volatile oil is 0.693, which indicates a strong positive association between the two variables. On the 10th and 20th days, the correlation coefficient between the two samples is 0.177, the association being weakly positive.
Figure 4 shows the comparative variation of the antioxidant activity in the kefir sample with mint volatile oil and the control sample. On day 1, the kefir with mint volatile oil has an average antioxidant activity value of 72.47 and the standard deviation is 0.006. The median value is 72.47 and the skewness is −1.73, the histogram is oriented to the left. The mean value of the antioxidant activity for the control sample is 59.96 and the standard deviation is 0.006. The median value is 59.96, and the skewness is −1.73, the histogram is oriented to the left. On day 10 of storage, the antioxidant activity mean value for the kefir sample with mint volatile oil is 41.15 and the standard deviation is 0.01. The value of the median is 41.15, and the histogram is perfectly symmetrical because the skewness is 0. For the control sample, the mean value of the antioxidant activity is 35.05 and the standard deviation is 0.01, the median value is 35.05 and the histogram is perfectly symmetrical because the skewness is 0. On the 20th day of storage, the antioxidant activity mean value for the kefir sample with volatile mint oil is 11.64 ± 0.012. The median value is 11.65 and the skewness is −1.73, the histogram is oriented to the left. The mean value of the antioxidant activity for the control sample is 10.95 and the standard deviation is 0.012. The median value is 10.94 and the skewness is 1.73, the histogram is oriented to the right. For the correlation between the kefir sample with mint volatile oil and the control sample, the Pearson coefficient from day 1 is 1, the association being strongly positive. On day 10 the coefficient is equal to −0.5, the association between the two variables being moderately negative, and on day 20 the coefficient is equal to 0.5, the association between the two variables being moderately positive.
Figure 5 shows the comparative variation of antioxidant activity in the kefir with fennel volatile oil and the control sample. On the first day of storage, the kefir sample with fennel volatile oil has an antioxidant activity mean value of 78.59 ± 0.006. The median is 78.59, and the skewness is −1.73, the histogram being oriented to the left. The mean value of the antioxidant activity for the control sample is 59.96 and the standard deviation is 0.006. The median value is 59.96, and the skewness is −1.73, the histogram being oriented to the left. On the 10th day, the kefir with fennel volatile oil has an antioxidant activity mean value of 41.32 ± 0.017. The median is 41.33, and the skewness is −1.73, the histogram being oriented to the left. For the control sample, the mean value of the antioxidant activity is 35.05 and the standard deviation is 0.01, the median value is 35.05 and the histogram is perfectly symmetrical because the skewness is 0. On the 20th day, the mean value of the antioxidant activity for the kefir sample with fennel volatile oil is 12.59 ± 0.012, and the skewness is −1.73, the histogram being oriented to the left. The mean value of the antioxidant activity for the control sample is 10.95 and the standard deviation is 0.012. The median value is 10.94 and the skewness is 1.73, the histogram being oriented to the right. In the case of the kefir with fennel volatile oil and the control sample, the Pearson coefficient is 1 on the first day, the association being strongly positive. On the 10th day, the correlation coefficient is 0.866, the association being strongly positive, and on the 20th day, the correlation coefficient is 0.5, the association being moderately positive between the two variables.
Figure 6 shows the decline in antioxidant activity on day 10 and day 20 of storage compared to day 1 of storage for kefir samples. For the kefir sample with fennel volatile oil, the decline on day 10 compared to day 1 has a mean value of 8.75%, and that on day 20 is 79.03% compared to day 1. For the kefir sample with lavender volatile oil, the decline on day 10 compared to day 1 is 43.22%, and that on day 20 is 83.93%. For the kefir sample with mint volatile oil, the decline on day 10 is 47.42% and on day 20 it is 83.98%. The control sample has a decline in antioxidant activity on day 10 compared to day 1 of 41.54%, and on day 20 has a decline of 81.74%. We can conclude that the kefir with fennel volatile oil is the most stable in terms of antioxidant activity because it has the lowest value of decline compared to day 1. In the case of the other three kefir samples, the value of the decline on day 10 is approximately equal. The largest decrease is recorded between day 10 and day 20 of storage, this being visible by the high value of the decline on day 20 compared to day 1 for all four kefir samples.

4. Discussion

Stress is one of the factors that can affect people’s mental health. Long-term stress leads to various cellular and neuronal disorders, playing a significant role in the onset of depression and Alzheimer’s disease [1,2,3].
Oxidative stress influences physiological and pathological conditions leading to the appearance of various cardiovascular and neuronal diseases. To avoid and reduce the effects of stress on the human body, studies recommend the external intake of antioxidants. Medicinal and aromatic plants have been excellent sources of antioxidants. Creating food products that meet certain food needs, but also contribute to health [78] is a growing interest for many processors in the food industry.
The antioxidant character of the three plants used in this study is given by their different compounds. The main compound in fennel volatile oil is α-pinene [31]. α-pinene is a natural and active monoterpene that is very often used as a flavoring or pharmaceutical agent [79]. This compound is known to have notable antioxidant activity [80]. The antioxidant character of the volatile mint oil is given by menthone, caryophyllene and linalool [20]. Menthone is generally used in the flavoring industry. It is very often found in combination with menthol in various types of volatile oil. This compound has antimicrobial and antioxidant properties, its insecticidal potential has been proven in rice control [81]. Caryophyllene is a sesquiterpene found in reasonable amounts in the volatile oils of many plants [82]. Following studies, it has been shown that caryophyllene gives volatile oil antioxidant and antimicrobial properties [83]. Linalool is a linear monoterpene alcohol [81] that has been shown to have antimicrobial and antioxidant activity [84]. The compounds present in lavender volatile oil that give it antioxidant properties are linalool [43] and terpineol [41]. Terpineol is a monoterpene that has a wide range of properties: antimicrobial [85], antioxidant, anti-inflammatory, anticancer, and insecticidal [81]. The mechanism of action may be due to cytoplasmic membrane compromise or organic membrane penetration that induces deformation, damage and ultimately death of microbial cells [86].
In 2019 we started the study of the antioxidant activity of various yoghurt samples enriched with encapsulated volatile oils, and due to the positive results obtained we decided to test these effects on other dairy products. We chose kefir because of its notoriety and the benefits it brings to consumers’ health. Before the antioxidant analysis, we analyzed consumer acceptance of the new kefir assortments through sensory and textural analysis.
The purpose of this study was to produce a dairy product with high nutritional properties. Thus, three types of kefir with volatile oils were made: lavender, mint and fennel. The volatile oils are sensitive to various external factors, and they were encapsulated and introduced as spherical capsules into the dairy product. According to studies, these volatile oils have a high antimicrobial and antioxidant capacity.
Initially, we tested the antioxidant activity of the volatile oils obtained from their extraction from plants harvested from authorized crops in Sibiu, Romania. The highest value of the antioxidant activity of pure volatile oils belongs to the volatile oil of fennel, followed by the volatile oil of mint, and the lowest value belongs to the volatile oil of lavender. Three spectrophotometer readings were taken for each volatile oil.
The antioxidant activity of kefir samples decreased during the twenty days of storage. The highest values of antioxidant activity were obtained on the first day of storage, and the lowest values were obtained on the 20th day of storage. The largest decrease was recorded between day 10 and day 20 of storage for all kefir samples. The highest antioxidant activity for the entire storage period was the kefir sample with fennel volatile oil. This was followed by the kefir with mint volatile oil, and then the lavender volatile oil sample. The control sample showed the lowest values over the entire storage period.
Compared to the study carried out in 2019, the antioxidant activity of kefir samples was higher. The fennel volatile oil brought a significant contribution to both types of dairy products; both the kefir and yogurt samples obtained the highest values during the entire analysis period. In the current study, kefir samples with lavender volatile oil had the lowest antioxidant activity, and in the 2019 study, the yogurt sample with mint volatile oil had the lowest antioxidant activity. In both cases, the volatile oils used added value to the dairy product, giving it a superior antioxidant capacity.

5. Conclusions

We can conclude that volatile oils add value to the finished product. All three samples with volatile oils have good results compared to the control sample for the entire analysis period. The use of medicinal and aromatic plants in the preparation of food is an excellent alternative due to their antioxidant properties.
All these aspects show that the obtained products are an important source of antioxidant compounds that can bring benefits to the health of consumers and can also increase the shelf life of the product due to the incorporation of bioactive compounds.

Author Contributions

Conceptualization, O.T., M.A.C. and A.D.; methodology, M.A.T., T.I.O. and C.G.; software, M.A.C.; validation, O.T., M.A.T. and C.G.; formal analysis, O.T. and T.I.O.; investigation, M.A.C. and A.D.; resources, C.G. and A.D.; data curation, M.A.C. and T.I.O.; writing—original draft preparation, O.T., M.A.C. and A.D.; writing—review and editing, M.A.T., T.I.O. and C.G.; visualization, O.T., M.A.T. and C.G.; supervision, O.T.; project administration, O.T.; funding acquisition, O.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Lucian Blaga University of Sibiu and Hasso Plattner Foundation, grant number LBUS-IRG-2021-07/No. 2946—26 July 2021.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

We would like to express our sincere gratitude to the Research Center in Biotechnology and Food Engineering (C.C.B.I.A.), the Lucian Blaga University of Sibiu and the Hasso Plattner Foundation for their support provided throughout the research period. We also appreciate the editor and the anonymous reviewers for their constructive comments and insightful suggestions on the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 12 10287 g001 550
Figure 1. Calibration curve with DPPH to determine antioxidant activity.
Figure 1. Calibration curve with DPPH to determine antioxidant activity.
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Figure 2. Antioxidant activity for the three assortments of volatile oils used in encapsulation.
Figure 2. Antioxidant activity for the three assortments of volatile oils used in encapsulation.
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Figure 3. Comparative variation of antioxidant activity in kefir sample enriched with encapsulated lavender volatile oil and control sample.
Figure 3. Comparative variation of antioxidant activity in kefir sample enriched with encapsulated lavender volatile oil and control sample.
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Figure 4. Comparative variation of antioxidant activity in kefir sample enriched with encapsulated mint volatile oil and control sample.
Figure 4. Comparative variation of antioxidant activity in kefir sample enriched with encapsulated mint volatile oil and control sample.
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Figure 5. Comparative variation of antioxidant activity in kefir sample enriched with encapsulated fennel volatile oil and control sample.
Figure 5. Comparative variation of antioxidant activity in kefir sample enriched with encapsulated fennel volatile oil and control sample.
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Figure 6. The decline in antioxidant activity on day 10 and day 20 of storage compared to day 1 of storage for kefir samples.
Figure 6. The decline in antioxidant activity on day 10 and day 20 of storage compared to day 1 of storage for kefir samples.
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Table
Table 1. Volatile oil extraction efficiency.
Table 1. Volatile oil extraction efficiency.
Aromatic PlantEfficiency [%]
Mint (herb)2.93
Fennel (seeds)5.17
Lavender (herb)1.21
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Tița, O.; Constantinescu, M.A.; Tița, M.A.; Opruța, T.I.; Dabija, A.; Georgescu, C. Valorization on the Antioxidant Potential of Volatile Oils of Lavandula angustifolia Mill., Mentha piperita L. and Foeniculum vulgare L. in the Production of Kefir. Appl. Sci. 2022, 12, 10287. https://0-doi-org.brum.beds.ac.uk/10.3390/app122010287

AMA Style

Tița O, Constantinescu MA, Tița MA, Opruța TI, Dabija A, Georgescu C. Valorization on the Antioxidant Potential of Volatile Oils of Lavandula angustifolia Mill., Mentha piperita L. and Foeniculum vulgare L. in the Production of Kefir. Applied Sciences. 2022; 12(20):10287. https://0-doi-org.brum.beds.ac.uk/10.3390/app122010287

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Tița, Ovidiu, Maria Adelina Constantinescu, Mihaela Adriana Tița, Tiberius Ilie Opruța, Adriana Dabija, and Cecilia Georgescu. 2022. "Valorization on the Antioxidant Potential of Volatile Oils of Lavandula angustifolia Mill., Mentha piperita L. and Foeniculum vulgare L. in the Production of Kefir" Applied Sciences 12, no. 20: 10287. https://0-doi-org.brum.beds.ac.uk/10.3390/app122010287

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