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Article

Red Pepper Fermentation with Geothermal Mineral Water: Impact on Nutritional Profile and Quality Characteristics

by
Anna Wrzodak
,
Justyna Szwejda-Grzybowska
,
Wioletta Popińska
and
Monika Mieszczakowska-Frąc
*
Fruit and Vegetable Storage and Processing Department, The National Institute of Horticultural Research, Konstytucji 3 Maja 1/3, 96-100 Skierniewice, Poland
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(10), 2279; https://doi.org/10.3390/agronomy15102279
Submission received: 29 August 2025 / Revised: 19 September 2025 / Accepted: 24 September 2025 / Published: 26 September 2025
(This article belongs to the Section Plant-Crop Biology and Biochemistry)
Browse Figure
Versions Notes

Abstract

Red bell pepper (Capsicum annuum L.) is a valuable source of health-promoting phytochemicals and essential minerals. This study investigated the impact of using geothermal mineral water versus tap water as the fermentation medium on the nutritional, physicochemical, and sensory properties of two red bell peppers (cultivars ‘Yecla F1’ and ‘Salomon F1’). The results showed that fermentation caused a significant decrease in the content of L-ascorbic acid (by 30–50%), carotenoids (~30%) and polyphenols (by 25–30%), with lower nutrient losses observed in peppers fermented with geothermal water. In addition, fermentation with geothermal water increased the calcium, magnesium, and potassium contents of the peppers compared to tap water. Sensory analysis showed that the pepper cultivars had a greater impact on the overall sensory quality than the fermentation medium or the evaluation time, although geothermal water had a positive effect on the texture of the fermented peppers. These results suggest that geothermal water may be a beneficial alternative to traditional water sources in vegetable fermentation, improving both the nutritional and sensory properties of the final product.

1. Introduction

Red bell pepper (Capsicum annuum L.) is one of the most widely consumed vegetables in the world due to its high nutritional value, health-promoting properties, and distinct sensory characteristics. Pepper fruits are a rich source of antioxidant compounds, including polyphenols, vitamin C, flavonoids, and carotenoids (e.g., capsanthin, which are capable of neutralizing free radicals and inhibiting oxidative processes in the human body) [1,2,3] The regular consumption of these substances has been associated with the prevention of various non-communicable diseases, such as certain types of cancer, atherosclerosis, and cardiovascular disease [4,5].
The distinctive pungency and aroma of the red bell pepper, along with its broad spectrum of colors (green, yellow, orange, red, purple), shapes, and sizes [6], have contributed to its popularity in numerous food products. The red bell pepper is widely used in the production of dried spices, fermented and marinated products, and pastes and as an ingredient in salads and pizzas.
Vegetable fermentation is a traditional food preservation method with a long history across various cultures, particularly in Asia, Africa, and Central and Eastern Europe [7,8]. In Poland, cucumbers and cabbage are traditionally fermented, although fermented red beet, cauliflower, and broccoli are becoming more common. Fermented red bell pepper, despite being popular in Chinese cuisine, is not a customary part of Polish culinary practices. Fermentation is a natural biochemical process in which microorganisms, such as lactic acid bacteria, convert carbohydrates into alcohol, carbon dioxide, and/or organic acids to obtain energy. The fermentation process leads to changes in the flavor and texture of fermented products, results in increased acidity, promotes the proliferation of beneficial bacteria, improves the digestibility of proteins and carbohydrates, and enhances the bioavailability of selected vitamins and minerals [9,10,11,12,13]. There are three main types of vegetable fermentation: spontaneous fermentation (driven by the native microbiota of the raw material), controlled fermentation (using introduced starter cultures), and directed fermentation (performed after pasteurization with added microbial cultures) [14,15,16,17]. During fermentation, the sugars present in vegetables are significantly reduced as they are metabolized by microorganisms to produce lactic acid. This acidification leads to a reduction in the environmental pH, inhibiting the growth of spoilage microorganisms [18]. Additionally, fermentation contributes not only to food preservation and sensory enhancement but also significantly improves the nutritional profile of vegetables. One of the key benefits is the increased bioavailability of essential minerals such as calcium (Ca), zinc (Zn), and iron (Fe), which may become more easily absorbed due to microbiological and biochemical transformations during the process [19,20]. Fermented red bell pepper, in particular, is known to be a rich source of several nutrient compounds, including vitamin C, B-group vitamins, phenolic compounds, carotenoids, and minerals such as potassium, sodium, magnesium, calcium, and phosphorus [21,22].
These compositional improvements, resulting from fermentation, enhance the overall nutritional value of the product and contribute to a healthier diet. Moreover, fermented foods are widely regarded as good carriers of lactic acid bacteria (LAB), which may possess probiotic properties and support good health [23,24]. Fermentation also results in desirable modifications in taste, texture, and sometimes color. The final product often differs significantly from the raw material. These changes are driven by the activity of various microorganisms—including lactic acid bacteria, yeasts, and filamentous fungi—which also contribute to improved food safety and sensory quality [25,26]. Furthermore, fermentation may contribute to the reduction of undesirable substances such as heavy metals in food [27,28,29]. Fermentation also leads to the partial dehydration of plant tissues, which results in a higher concentration of nutrients and increased production of lactic acid—a compound that may help stabilize the gastrointestinal environment [30].
One of the key factors determining the proper course of fermentation is the quality of the water used in the process. According to the Polish Standard PN-A-77701:1997 [31], relevant to the production of fermented cucumbers, water intended for fermentation must be clean, sourced from a safe and controlled supply, and contain very low levels of free chlorine—below 0.1 mg·L−1. Additionally, the total hardness of water should not exceed 0.1 g CaO/L. These parameters are critical, as deviations may disrupt the natural fermentation microflora and negatively affect the structural integrity of the fermented product.
Another essential component of the fermentation process is sodium chloride (NaCl), which plays a crucial role in establishing the appropriate osmotic pressure within the fermentation environment. The presence of salt creates a concentration gradient between the plant cells and the brine, facilitating the bidirectional transport of nutrients and metabolic substrates. This exchange continues until osmotic equilibrium is reached, thereby ensuring optimal conditions for microbial activity and contributing to both the microbiological safety and the sensory quality of the final product [32].
Our previous studies have demonstrated that the application of geothermal mineral water as a fermentation medium for red beet significantly enhances both the sensory attributes and the concentration of bioactive compounds in the final product [33]. The research involved the controlled lactic acid fermentation of red beet roots (Beta vulgaris L.) using brine prepared with geothermal water sourced from the Uniejów geothermal field in central Poland. Based on [33], the use of geothermal water in vegetable fermentation may serve not only as a functional medium improving the taste and texture, but also as a natural means to enrich fermented foods with minerals and health-promoting substances.
The objective of this study was to comprehensively assess the effects of different water sources on the fermentation of red bell pepper (Capsicum annuum L.) fruits, using cultivars ‘Yecla F1’ and ‘Salomon F1’. Specifically, the research aimed to investigate the influence of mineral water derived from a geothermal source in Uniejów (central Poland, 51°58′12″ N 18°48′01″ E) versus tap water from Skierniewice (central Poland, 51°57′10″ N 20°08′30″ E) on the contents of selected bioactive compounds and the profile of the mineral components in fermented bell peppers of both cultivars.
This approach is intended to deliver relevant insights for optimizing the quality and nutritional value of fermented vegetables in the context of agricultural production and food processing.

2. Materials and Methods

2.1. Plant Material

Red fruits of the bell pepper cultivars ‘Salomon F1’ and ‘Yekla F1’, sourced from a producer in Potworów, Poland (51°30′30″ N 20°43′19″ E), were used for the study. The fruits were thoroughly washed and quartered, and seeds were removed. The pepper pieces were placed into sterile 1300 mL glass jars along with a standard set of fermentation spices: 3 cloves of garlic, 2 slices of horseradish, and 1 umbel of dill. Two types of brine were prepared: tap water from Skierniewice, to which ‘Kłodawa’ salt was added at a concentration of a 3.5% NaCl solution, and geothermal water from Uniejów, which naturally contained approximately 0.6% NaCl (Table 1). For the geothermal water, additional ‘Kłodawa’ salt was added to the brine to reach a total NaCl concentration of 3.5%. After adding the spices and preparing the brine, the jars were tightly sealed. This methodology was developed according to scientific standards for vegetable fermentation, allowing the precise replication of experimental conditions and comprehensive monitoring of the fermentation process.
The geothermal water used in the study was extracted from a depth exceeding 2000 m (Uniejów GT-1 borehole) and emerges at a temperature of 67–70 °C. It is characterized by high mineralization, with a total dissolved solid content of approximately 8 g·L−1, and belongs to the chloride-sodium type (Cl–Na) [34].
Geothermal water from Uniejów is characterized by a significantly higher concentration of mineral components such as sodium (Na+), chloride (Cl−), calcium (Ca2+), magnesium (Mg2+), sulfates (SO42−), and iron (Fe2+/3+) compared to tap water from Skierniewice. Tap water is characterized by a low mineral content, typical for water intended for consumption, with lower concentrations of mineral ions and microelements (Table 1).
These differences confirm the unique nature of geothermal water from Uniejów, which, due to its high mineralization, exhibits potential therapeutic and healing properties, whereas tap water from Skierniewice meets drinking water quality standards for everyday consumption. By decision of the State Sanitary Inspectorate in Skierniewice of 27 December 2024, it is declared that the water from the Skierniewice intake is fit for consumption.

2.2. Fermentation, Pasteurization, and Storage Process

Fermentation experiments were conducted based on two variants, differing by the type of water used: one process utilized geothermal water from the Uniejów source, while the other used standard tap water from Skierniewice. The pepper fermentation proceeded spontaneously and naturally, without the addition of bacterial starters, for 7 days at a constant temperature of 20 °C. After fermentation, all samples were pasteurized through immersion in boiling water for 3 min, counted from the moment the water reached boiling. After pasteurization, some samples were stored with refrigeration at 5 °C for further analyses.
Physicochemical analyses, as well as macro- and microelement determinations, were performed on fresh pepper fruits, as well as after the completion of fermentation and pasteurization and following a 2-month refrigerated storage period. Sensory evaluations were conducted after 10 days and after 2 months of storage following fermentation and pasteurization.
Early sensory analysis (after 10 days) allowed us to capture the organoleptic characteristics of the product at the initial stage of fermentation, while repeating the sensory analysis and physicochemical tests two months later reflected the stability and final quality of the product, which is key from a consumer and food safety perspective.

2.3. Analitycal Methods

For the chemical analysis, pepper fruits were finely sliced and frozen at −20 °C and then ground in dry ice. The following chemical analyses of fruits of the pepper were carried out. Dry matter was determined using the weight-drying method following PN-90/A-75101/03 [35]. The samples were dried at 70 °C under a vacuum (3 kPa) to a constant weight. The results are expressed in %. Active acidity (pH) was determined according to the PN-EN-12147:2000 standard [36], using an automatic titrator (TitroLine® 7000, SI Analytics, Weilheim, Germany).
The analysis of the total sugar content of pepper fruits was determined via high-performance liquid chromatography (Agilent Technologies, Waldbronn, Germany), equipped with a differential refractometric detector. The separation of sugars was carried out using an Aminex HPX-87C (300 mm × 7.5 mm) column (Bio-Rad Laboratories, Hercules, CA, USA) with a precolumn according to European Standard UNE EN 12630:1999 [37]. The elution conditions were as follows: isocratic flow 0.6 mL·min−1, temperature 80 °C, mobile phase—edetate calcium disodium (Ca-EDTA, Sigma-Aldrich Chemie GmbH, Steinheim, Germany). Samples of peppers for sugar determinations were dissolved in redistilled water, homogenized, and purified on a Waters SepPak PLUS C18 filter (Waters, Milford, MA, USA). The sugars were quantified based on a calibration curve for sucrose, glucose, and fructose, and the results were expressed as g·100 g−1.
The content of L-ascorbic acid in pepper fruits was determined via high-performance liquid chromatography (Agilent Technologies, Waldbronn, Germany), equipped with a DAD detector. Separation was performed using a Supelco LC-18 column (250 mm × 4.6 mm; 5 µm) (Sigma-Aldrich Chemie GmbH, Darmstadt, Germany) with a precolumn according to IFU procedures; 1% phosphate-buffered solution KH2PO4, pH 2.5 (potassium phosphate, monobasic, JT Baker Chemicals, Phillipsburg, NJ, USA), was used as the mobile phase. The isocratic flow was 0.8 mL min−1, with a temperature of 30 °C. The detection of L-ascorbic acid was based on the absorbance at 244 nm. The samples of pepper fruits were dissolved in 6% HPO3 (meta-phosphoric acid, Sigma-Aldrich Chemie GmbH, Steinheim, Germany, homogenized, and filtered. The acid was quantified using a calibration curve for the L-ascorbic acid standard (Sigma-Aldrich Chemie GmbH, Steinheim, Germany). The results were expressed as mg·kg−1.
The total carotenoid content was determined using the method according to [38]. The sample of pepper fruits was homogenized in the extraction solution (hexane:acetone, 6:4) (JT Baker Chemicals, Phillipsburg, NJ, USA) with the addition of magnesium carbonate (Chempur, Piekary Śląskie, Poland). The solution was filtered through a Büchner funnel under reduced pressure. The extract was transferred to a separatory funnel with water added and shaken. After phase separation, the water–acetone phase was discarded. The residue on the filter was washed with a small amount of extracting solution. The extract was then poured into a separating funnel, and water was added, shaken, and allowed to separate. The lower water–acetone phase was poured off and discarded. The acetone washing process was repeated four times until the lower phase contained no acetone. The hexane phase containing carotenoids was then filtered through a filter paper containing anhydrous Na2SO4 into a volumetric flask. After filtration, the Na2SO4 (sodium sulphate, Chempur, Piekary Śląskie, Poland) remaining on the filter was rinsed with a small amount of hexane and topped up with hexane. The content of total carotenoids was determined based on the spectrophotometric method, using a spectrophotometer UviLine 9400 (SI Analytics, Hofheim am Taunus, Germany) at a wavelength of 451 nm [39]. The calculations were made according to a standard curve for the β-carotene standard (Sigma-Aldrich Chemie GmbH, Darmstadt, Germany). The carotenoid content was expressed in mg·kg−1.
The content of total polyphenolic compounds was determined using a spectrophotometric method [40] using the Folin-Ciocalteu reagent (Sigma-Aldrich Chemie GmbH, Darmstadt, Germany). The fruits of the pepper were homogenized with 80% ethanol. Next, the homogenate was centrifuged for 10 min at 20,000 rpm. The prepared solution was filtered under reduced pressure through a Buchner funnel filter. Then, 0.75 mL of the extract was transferred to a 25 mL volumetric flask, and 10 mL of distilled water, 1.25 mL of Folin–Ciocalteu reagent, and 2.5 mL of 20% NaCO3 solution were added and mixed. After incubation for 60 min at an ambient temperature and in darkness, the absorbance was read against the prepared blank at 750 nm using a UviLine 9400 spectrophotometer (SI Analytics, Hofheim am Taunus, Germany). The total polyphenol content was expressed as mg of catechin (Sigma-Aldrich Chemie GmbH, Darmstadt, Germany) equivalents in mg·kg−1.
The mineral contents, macronutrients (Ca, K, Mg, P, Na), and micronutrients (Zn, Mn, Cu, Fe, As, Cd, Pb) were determined in fermented peppers after wet dissolution of the sample using 5 mL of 65% HNO3 (nitric acid, Merck KGaA, Darmstadt, Germany) in a microwave oven. The solution was quantitatively transferred to 50 mL falcons topped up with distilled water. The mineral content was determined using an inductively coupled plasma optical spectrometer (ICP-OES) from Thermo Scientific, type iCAP 6500 (Loughboroug, UK), according to the PN-EN 16943:2017 standard [41].
The level of cadmium, lead, and arsenic was determined using an inductively coupled plasma atomic spectrometer (ICP-MS) from Thermo Scientific, type Xseries 2 (Bremen, Germany), according to the PN-EN 15763:2010 standard [42]. The nitrate content was determined using a high-performance ion chromatograph HPLC/IC (Dionex, Sunnyvale, CA, USA)according to PN-EN 12014-2:2018-01 [43]. The mercury level was determined using the atomic absorption method (AAS) with the amalgamation technique. Water analysis was performed using an optical spectrometer (ICP-OES) according to PN-EN ISO 11885:2009 [44].
All presented physicochemical results were expressed as the fresh sample weight.

2.4. The Sensory Evaluation

The sensory quality of fermented fruits of the pepper was performed in a sensory laboratory by an expert panel consisting of 10 assessors, using the quantitative description analysis (QDA). Sensory evaluation of the fermented red peppers was performed after 10 days of fermentation and two months, using a 10-score scale, with respect to their smell and taste of the fermentation pepper, texture (hardness of flesh), basic taste (sweet, sour, bitter, salty), and overall quality. Each analysis was performed in two independent sessions. The ANALSENS version 7.0 (Caret Digital Systems and Software, Gdańsk, Poland) was used to perform the evaluation on the processed results. Sensory characteristics of the evaluated plant material were described using principal component analysis (PCA), based on a correlation matrix.

2.5. Statistical Analysis

Statistical analysis was performed with STATISTICA v.13 (StatSoft, 2011 Dell Inc. 2016) as one-way analysis of variance for fresh fruit cultivars and as one-way analysis for the type of water used, separately for each fermented cultivar. The significant differences between means were determined at p = 0.05 based on Tukey’s HSD test. The results are expressed as the means of three replicates.

3. Results and Discussion

3.1. Physicochemical Characteristics of Fresh and Fermented Pepper Fruits

The results of the chemical analysis of fresh peppers of the ‘Yecla F1’ and ‘Salomon F1’ varieties and those fermented in thermal water from Uniejów and in tap water from Skierniewice are presented in Table 2 and Table 3.
The pepper fruit consists of almost 90% water. The content of dry matter in the pepper varieties studied ranged from 8.34 to 9.59% and was significantly higher in the ‘Salomon F1’ cultivar than in the ‘Yecla F1’ (Table 2). These data are consistent with the results of other authors, who in their studies determined the dry matter content of pepper fruits at the level of 5.24–10.29% [45,46]. After the fermentation process, no significant difference was observed depending on the water used, and the dry matter content for the ‘Yecla F1’ and ‘Salamon F1’ varieties was 7.77–7.84% and 7.21–7.32%, respectively (Table 3).
There is no literature data on the effect of acidification with geothermal water on the chemical composition of peppers. Our studies found that the tested ‘Yecla F1’ and ‘Salomon F1’ pepper varieties differed significantly in the contents of individual components depending on the water used, but these changes were not always statistically significant.
The pH value is one of the most important parameters determining the high quality and storage durability of the product [47,48]. In our studies, the initial pH value of fresh bell pepper was 6.3–6.6, and after acidification for ‘Yecla F1’ and ‘Salomon F1’ pepper fruits, the pH decreased within the range of 4.30–4.40 and 4.35–4.45, respectively (Table 3). Such a pH value at this level effectively inhibits the growth of pathogenic microflora [49]. No significant difference was found for this parameter depending on the type of water used (thermal water from Uniejów, tap water from Skierniewice), for both varieties.
In the conducted studies, the content of total sugars in fresh fruits of both pepper varieties ranged from 5.64 to 5.80 g·100 g−1. The value of this component at this level met the quality requirements of the plant material that can be allowed for fermented products and is consistent with the results of other authors [50]. No significant difference was found in the content of total sugars after the fermentation process depending on the water used for both pepper varieties, ‘Yecla F1’ and ‘Salomon F1’ (Table 3). In our studies, it was observed that not all sugar was used in the fermentation process by lactic acid bacteria, independent of the water used. On the one hand, sugars are a nutrient for the bacteria; on the other hand, they pass into the brine via diffusion, which reduces their content in the product [51]. The decomposition of sugars during the fermentation process of peppers may also result from the fact that some bacteria consume other sugars during the fermentation process, e.g., pentose sugar over glucose (L. brevis) [52,53].

3.2. Bioactive Compounds of Fresh and Fermented Pepper Fruits

The pepper fruits are considered a vegetable of high nutritional value, rich in health-promoting compounds, including high levels of L-ascorbic acid, carotenoids, and polyphenols, with low levels of acids and sugars [54,55,56]. The literature data shows that the compositions and contents of bioactive compounds in fruits of pepper depend on the cultivar and phase of ripeness and are highest in fully colored fruits [57,58,59].

3.2.1. L-Ascorbic Acid

The fermentation process has a significant impact on changes in the contents of vitamins and other bioactive substances. Pepper fruits are a valuable source of L-ascorbic acid, the content of which depends on the variety, climatic conditions, the stage of fruit ripeness, and the harvest date and can vary widely [60,61]. The L-ascorbic acid is rapidly degraded under the influence of external factors such as light, temperature, oxygen, and pH. Its losses can also be caused by technological processes such as drying, salting, steaming, ultraviolet radiation, and the use of preservatives [62,63]. In the conducted studies, the content of L-ascorbic acid in the fresh pepper fruits ‘Yecla F1’ and ‘Salomon F1’ was, respectively, 1407 and 1506 mg·kg−1 (Table 2). After the fermentation process, a lower content of this compound was observed, by approximately 30–50%, depending on the cultivar, which was as follows: for the ‘Yecla F1’ variety, 907–954 mg·kg−1; ‘Salomon F1’, 709–745 mg·kg−1 (Table 3). The type of water used had a significant effect on the content of L-ascorbic acid in the pepper fruits in the case of both cultivars. The bell pepper fermented in geothermal water contains a significantly higher content of this compound compared to fruits fermented using tap water (Table 3). The losses in the content of L-ascorbic acid after the fermentation process may also be caused by the release and activation of the enzyme—ascorbate oxidase produced by microorganisms during the fermentation process. On the other hand, the low pH value contributes to the limitation of enzymatic processes, thanks to which a significant amount of L-ascorbic acid contained in them is preserved in vegetables subjected to the fermentation process [64,65,66]. Lower contents of L-ascorbic acid after the fermentation process are also confirmed by the results of the studies by [14,53], in which a decrease in its content by approx. 50% was observed.

3.2.2. Total Carotenoids

The content of total carotenoids in fresh pepper fruits significantly differed between varieties. The higher content of these compounds was noted in the ‘Salomon F1’ variety—96.5 mg·kg−1 compared to ‘Yecla F1’—87.3 mg·kg−1 (Table 2). The level of these compounds in pepper fruits depends on the variety, which is confirmed by literature data and may fluctuate within a wide range [58,61,67]. In the presented studies, after the fermentation process, a lower content of total carotenoids, by approximately 30%, was observed for both varieties, depending on the type of water used. Significantly lower losses in the content of these compounds were noted after using Uniejów water for acidification than tap water from Skierniewice (Table 3). The content of carotenoids during fermentation may vary depending on the plant material and the technological process conditions. In addition, carotenoids are degraded during vegetable processing and are sensitive to pH changes, which is confirmed by studies [14,53]. The decrease or increase in the content of various carotenoids during the fermentation process may also depend on the variety and degree of ripeness of peppers that were used during the fermentation process [68]. In addition, the increase in carotenoid content in pepper after fermentation may be related to the breakdown of tissue cells in which these carotenoids may be placed [69]. Also, in our studies, the degradation of these bioactive compounds could be partially caused by bacterial metabolism and environmental conditions, such as the type of water used, temperature, pH, and sugar content.

3.2.3. Total Polyphenols

The content of total polyphenols ranged from 1369 to 1483 mg·kg−1 and significantly depended on the cultivars (Table 2). The literature indicates that the content of total polyphenols in pepper fruits is very diverse, and the cultivar may be a decisive factor determining the level of these compounds [60,61,70,71]. After the fermentation process, a lower content of these compounds was observed by approximately ~30% for the Yecla F1 cultivar (955–996 mg·kg−1) and approximately ~25% for the Salomon F1 cultivar (1077–1191 mg·kg−1). The decrease in the content of these compounds may be caused by the migration of these compounds to the brine and their use by lactic acid bacteria during the fermentation process. Significantly lower losses in the contents of these compounds were observed after using geothermal water Uniejów for acidification than tap water, for both cultivars (Table 3). Also, in the studies of the acidification of beetroot [33], a higher level of total polyphenol content was observed after using water from a Uniejów borehole.

3.3. Mineral Composition

Much the same as the contents of bioactive compounds, the mineral composition of bell peppers varies depending on the cultivars, maturity, place of production, and many environmental factors [72,73], as evidenced by the values presented in Table 4. The following literature data (Table 4) presents the values of mineral components for fresh peppers from two regions of the world: Poland (Europe) and the United States (North America).
The fermentation process is accompanied by a multidirectional modification of the basic chemical composition of processed raw materials, even in terms of the contents of mineral components. Fermentation can also affect the contents of minerals, as presented in Table 5 and Table 6 below. Vegetable processing, including microbial fermentation, reduces or neutralizes tannins and phytins, which results in greater bioavailability of minerals, among others [28,76].
Fermented peppers are characterized by a high potassium content. Potassium and sodium play an important role in maintaining the homeostasis of cellular osmotic pressure. This is the basic active transport mechanism (so-called sodium-potassium pump) that maintains the correct electrochemical balance in each cell, pumping sodium out and potassium into the cell [77]. In the fermentation process, these activities are disturbed by the use of brine/brine as one of the ingredients to initiate the fermentation process.
In the studied pepper varieties, differences in potassium contents were observed, from 106.4 mg to 120.8 mg per 100 g, and in sodium, from 587.6 to 654.3 mg per 100 g, in fermented pepper. High Na levels found in fermented vegetables are associated with the use of salt in the fermentation process [78,79]. However, peppers fermented in geothermal water have higher sodium values. Such high salt contents in fermented vegetables may constitute a certain limitation to their consumption by humans [80]. According to the Food and Agriculture Organization and the World Health Organization (FAO/WHO), the total NaCl intake should not exceed 5 g/day for an adult [81]. On the other hand, salt enhances the taste, which translates into the palatability of meals in the human diet [82]. Apart from its role in relation to sensory value, a high concentration of Na+ ions increases the transport of active substances and nutrients, accelerating and optimizing the fermentation process [83].
Minerals, mainly Ca2+, Mg2+, Fe2+, Na+, or Zn2+, are essential for the proper course of the fermentation process [84]. In particular, Fe2+ and Ca2+ ions are coagulants needed for the agglomeration and multiplication of anaerobic microorganisms in the fermentation process. Ca2+ ions play a biocatalytic role for microorganisms, accelerating the biodegradation process. On the other hand, an excessive concentration of these ions can inhibit the growth of lactic acid bacteria by dehydrating their cells. And magnesium ions in fermented vegetables act as mediators and support the use of substrates to optimize the bacterial metabolic pathway [85]. There were noticeable losses of minerals (such as K, Mg, Zn, and Cu) during the fermentation process (Table 5) compared to fresh peppers (Table 4), similar to the studies by [20,76]. This may be related to the nutritional needs of growing lactic acid bacteria to meet their metabolic requirements when the fermented plant material becomes a medium for these microorganisms [86]. The authors [14,87] reported that the fermentation process had an impact on the reduction of calcium, magnesium, and phosphorus contents compared to fresh raw material, while our study confirmed this thesis concerning magnesium and phosphorus. We did not observe a decrease in the calcium content in peppers after the fermentation process compared to fresh peppers. The Ca level of fermented peppers ranged from 14.7 to 18.7 mg∙100 g−1. However, not every fermented product behaves similarly, as can be seen in the studies of [76]. Different species of vegetables subjected to fermentation showed increased or decreased contents of minerals (Ca, Mg, Fe, Zn) in relation to vegetables before fermentation. A similar observation was made by [88] in legumes, where he obtained a higher content of Fe and Zn in the fermented product. It is worth emphasizing that fermented peppers, regardless of the variety, using geothermal water for fermentation, were characterized by higher values for macroelements (Ca, Mg, K, P) (Table 5). However, in the case of microelements (Cu, Fe, Mn, Zn), the situation was not so clear-cut. It is difficult to find similarities in changes in microelements. This may be due to the mutual dependence between elements and the use of different waters for the fermentation.
Recently, there has been a noticeable approach to analyzing the interactions between elements. This shows the overall principles of the diet, when the appropriate nutrient ratio is more important than its individual components (single element) [89,90]. For example the Ca/P ratio is important for the human diet. Excessive P intake can be harmful to bones through increased parathyroid gland section, but the adverse effect on bone mass increases when Ca intake in the diet is too low [73,91]. In many countries, P intake is high, while Ca intake does not meet nutritional recommendations, so it is difficult to achieve an optimal Ca/P ratio in the diet [88]. In our experiment, in fresh peppers, this ratio was at the level of (0.41), and similar values for peppers were obtained by [92] (0.51, 0.52). During the fermentation process, beneficial changes occur in relation to elements. In fermented peppers, in our own studies, this ratio ranges from 1.12 to 1.35 Ca/P, which indicates a favorable ratio of elements for the human body. The fermentation process improves the bioavailability of ingredients for the human body [19,20].
However, there may also be a negative interaction of ions that causes low bioavailability of these nutrients. These include sodium–potassium, calcium–magnesium, manganese–iron, iron–copper and zinc–copper. These interactions become potentially significant when the first metal of each pair mentioned above is in excess and the second is at a lower level of requirement. Zn–Cu is one of the most important in human nutrition due to the negative effect of excess Zn on the bioavailability of Cu, i.e., when the first metal of each pair is in excess, the second is less bioavailable [93]. In our case, fermentation caused the ratio of Fe to Cu and Zn to Cu to be much higher than these ratios in fresh peppers. High Fe values in products may interfere with Cu absorption [94]. An impaired balance between Fe/Cu and Zn/Cu may indicate the blocking of copper uptake by the body [95,96,97].
Considering the level of contaminants such as cadmium and lead (Table 6), the levels determined for the metals do not pose a risk to the health of the consumer. Lower values for lead were recorded in peppers fermented using geothermal water. There are reports in the literature [14,98] that vegetable fermentation contributed to a reduction in the level of some heavy metals such as Cu, Pb, and Cd. Bacteria of the genus Bacillus are effective in binding the above-mentioned elements. As shown by [27], bacteria fermenting carrot pulp were very effective in binding Pb, Ni, Zn, and Fe. This phenomenon was explained as a result of metal binding to the cell walls of fermenting bacteria and fungi. Carboxyl, amino, hydroxyl, phosphate, and sulfhydryl groups present in the external structures of microorganisms participate in the chelation of heavy metals [99]. This process has been known for years; ref. [100] showed that most often, heavy metal ions are adsorbed and combine to form a complex with negatively charged reaction sites on the cell surface. These metals are relatively difficult to remove from plant material through culinary processing. However, it should be emphasized that the determined levels for the heavy metals cadmium and lead (Table 6) are significantly below the maximum levels (MRLs) according to the [101] Commission Regulation (EU) 202/915 of 25 April 2023, which for cadmium are 0.02 mg∙kg−1 for fruit vegetables and 0.050 mg∙kg−1 for lead. The results obtained in the experiment were similar to those obtained by other authors [102].

3.4. Sensory Evaluation

The PCA graphical projection (Figure 1) shows the sensory quality of the fermented pepper in the two principal components system (as coefficients). The statistically analyzed fermented bell pepper objects are distributed throughout the graph, indicating large differences in their sensory notes. The vector of the overall quality score is closely correlated with the vectors of fermented pepper flavor, fermented aroma, and sweet taste (the vectors are oriented in the same direction). The best result of the overall quality was found for the pepper cultivar ‘Yekla F1’ fermented with geothermal water after 10 days of analysis (the object located nearest to the vector of the overall quality assessment). Moreover, after 10 days of fermentation, no differences were found between bell peppers fermented using tap water or geothermal water, regardless of the cultivars. Analyzing the results obtained, it is possible to conclude that the effect of the cultivar of bell pepper, rather than the type of brine or the date of analysis, on the sensory quality of the fermented pepper is more significant. Sensory analysis confirms the better sensory quality of the fermented pepper of the ‘Yekla F1’ cultivar than of the ‘Salomon F1’ after 2 months of storage. The effect of the geothermal water used for fermentation on the firmness of the fermented peppers was noted. The authors [33] found the same effect in the study on the fermentation of red beets using geothermal water from Uniejów, where the application of mineral water as a fermentation medium significantly improved the firmness and hardness of the beet flesh. Furthermore, according to research on the effect of various salt solutions on pickled cucumbers [103], the mineral profile of the brine solution, and especially the presence of calcium ions, favorably affects the sensory quality and firmness of the pickled cucumbers. They observed that the presence of calcium salt at higher pH levels promotes the formation of calcium pectinates, which strengthen the integrity of the cell wall. The geothermal water used in our study has twice the level of Ca2+ ions as tap water (Table 1), so this may explain the higher firmness of the fermented red bell pepper in geothermal brine. Additionally, samples of both pepper varieties fermented in geothermal water demonstrated higher firmness after two months. In summary, the results of the PCA analysis indicate that selecting the appropriate pepper cultivar is crucial for achieving high sensory quality of the fermented product, and the use of geothermal water may positively affect the product’s texture.

4. Conclusions

To our knowledge, this is the first report describing the effect of geothermal water with a unique mineral composition on spontaneous fermentation and on selected mineral and chemical compounds and the sensory quality of fermented red peppers. The fermentation of ‘Yecla F1’ and ‘Salomon F1’ pepper varieties in a brine based on geothermal water from Uniejów significantly increased the contents of biologically active compounds, such as L-ascorbic acid, polyphenols, and carotenoids, compared to fermentation in a traditional control brine from Skierniewice. The values of these compounds were statistically higher, indicating a positive effect of the physicochemical properties of geothermal water on the preservation and extraction of antioxidants during fermentation. The fermentation process was stable in terms of the pH, dry matter, and total sugar content, regardless of the brine used. The lactic fermentation process significantly affected the mineral content in the fruits of both pepper varieties. Compared to the control brine from Skierniewice, peppers fermented in geothermal water had higher levels of important macronutrients, such as phosphorus, potassium, magnesium, and calcium, which shows that the fruit was better enriched with nutrients. In terms of microelements (copper, iron, manganese, zinc), variable trends were observed—some of them were slightly higher in samples from Skierniewice, reflecting differences in the chemical compositions of both types of water and their impact on the accumulation of these elements. These differences were statistically significant, confirming that the type of water used for fermentation has a real impact on the mineral profile of the final product. In terms of food safety, the level of chemical contamination, i.e., heavy metals and nitrates, varied but was below the permissible standards set by applicable regulations. The results of the sensory analysis show some differentiation of the fermented peppers depending on the cultivar and water used for fermentation purposes. The use of mineral water from geothermal sources for the fermentation of red peppers resulted in fermented products characterized by high sensory quality, a unique mineral aftertaste, and high flesh firmness. The best overall quality results indicated that the ‘Yecla F1’ pepper variety fermented in geothermal water from Uniejów (regardless of the date of analysis) was rated the highest.

Author Contributions

Conceptualization, A.W.; methodology, A.W., J.S.-G., W.P., and M.M.-F.; software, A.W., J.S.-G., W.P., and M.M.-F.; validation, J.S.-G., W.P., and M.M.-F.; formal analysis, A.W., J.S.-G., and W.P.; investigation, A.W., J.S.-G., and W.P.; resources, A.W., J.S.-G., W.P., and M.M.-F.; data curation, A.W., J.S.-G., and W.P.; writing—original draft preparation, A.W., J.S.-G., and W.P.; writing—review and editing, A.W., J.S.-G., W.P., and M.M.-F.; visualization, A.W., W.P., and M.M.-F.; supervision, M.M.-F.; project administration, A.W.; funding acquisition, A.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Polish Ministry of Science and Higher Education, grant number 6.2.4: ‘The effect of fermentation and freeze-drying on the sensory quality of beetroot and pepper products’.

Data Availability Statement

Data supporting the results presented in this publication are available upon request from the corresponding author.

Acknowledgments

The authors thank the staff of the Fruit and Vegetable Storage and Processing Department for their support of this study.

Conflicts of Interest

The authors declare no conflicts of interest.

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Agronomy 15 02279 g001
Figure 1. Principal component analysis (PCA) of the sensory evaluation of fermented pepper. The chart shows the distribution of samples in the space of the first two principal components (PC1—48.47%, PC2—21.19%), highlighting the variability related to the smell and taste of fermented pepper, texture (hardness of flesh), basic taste (sweet, sour, bitter, salty), and overall quality. The samples are grouped by variety (Yekla F1, Salomon F1), different water sources for fermentation (TP—tap water from Skierniewice, GW—geothermal water from Uniejów), and fermentation times (10D—10 days, 2M—2 months). All samples are described in purple font.
Figure 1. Principal component analysis (PCA) of the sensory evaluation of fermented pepper. The chart shows the distribution of samples in the space of the first two principal components (PC1—48.47%, PC2—21.19%), highlighting the variability related to the smell and taste of fermented pepper, texture (hardness of flesh), basic taste (sweet, sour, bitter, salty), and overall quality. The samples are grouped by variety (Yekla F1, Salomon F1), different water sources for fermentation (TP—tap water from Skierniewice, GW—geothermal water from Uniejów), and fermentation times (10D—10 days, 2M—2 months). All samples are described in purple font.
Agronomy 15 02279 g001
Table 1. Content of chemical composition (mg·L−1) of geothermal water from the PIG/AGH-2 well in Uniejów (based on the PZH certificate) and tap water in Skierniewice (Laboratory for Quality Testing of Horticultural Products—The National Institute of Horticultural Research).
Table 1. Content of chemical composition (mg·L−1) of geothermal water from the PIG/AGH-2 well in Uniejów (based on the PZH certificate) and tap water in Skierniewice (Laboratory for Quality Testing of Horticultural Products—The National Institute of Horticultural Research).
ParameterGeothermal Water—UniejówTap Water—Skierniewice
Potassium K+19.03.24
Phosphorus P+0.010.02
Magnesium Mg+34.0314.5
Calcium Ca+140.377.6
Sodium Na+2290.08.66
Sulfur SO4−2127.624.6
Boron B+0.750.11
Copper Cu+0.040.01
Iron Fe2+/3+1.00.01
Manganese Mn2+0.0020.03
Zinc Zn2+0.01750.17
Chlorides Cl−3615.915.4
Content of Hg, As, Cd, Pb<0.001<0.001
Table 2. The chemical compositions of two cultivars of the fresh bell peppers ‘Yecla F1’ and ‘Salomon F1’ immediately after harvesting.
Table 2. The chemical compositions of two cultivars of the fresh bell peppers ‘Yecla F1’ and ‘Salomon F1’ immediately after harvesting.
CutivarDry Matter
[%]		pHTotal Sugars
[g·100 g−1]		Ascorbic Acid
[mg·kg−1]		Total Polyphenols
[mg·kg−1]		Total Carotenoids
[mg·kg−1]
‘Yecla F1’8.34 b6.34 b5.64 b1407 b1369 b87.3 b
‘Salomon F1’9.59 a6.62 a5.80 a1506 a1483 a96.5 a
Note: means in each column marked with the same letter are not different according to Tukey’s HSD test (p = 0.05).
Table 3. The chemical compositions of two cultivars of the fermented bell pepper ‘Yecla F1’ and ‘Salomon F1’ after two months of storage at 5 °C.
Table 3. The chemical compositions of two cultivars of the fermented bell pepper ‘Yecla F1’ and ‘Salomon F1’ after two months of storage at 5 °C.
Water
Used		Dry Matter
[%]		pHTotal Sugars
[g·100 g−1]		Ascorbic Acid
[mg·kg−1]		Total Polyphenols
[mg·kg−1]		Total Carotenoids
[mg·kg−1]
‘Yecla F1’
Geothermal water 7.84 a4.40 a1.52 a954 a996 a72.6 a
Tap water7.77 a4.30 a1.60 a907 b955 b66.4 b
‘Salomon F1’
Geothermal water 7.32 a4.45 a1.36 a745 a1191 a78.5 a
Tap water7.21 a4.35 a1.32 a709 b1077 b71.8 b
Note: means in the column for each cultivar marked with the same letter are not different according to Tukey’s HSD test (p = 0.05).
Table 4. Characteristics of selected mineral components in fresh peppers, mg·100 g−1. Data in the table are according to ‘Tables of composition and nutritional value of food’ [74] and USDA National Nutrient Database for Standard Reference [75].
Table 4. Characteristics of selected mineral components in fresh peppers, mg·100 g−1. Data in the table are according to ‘Tables of composition and nutritional value of food’ [74] and USDA National Nutrient Database for Standard Reference [75].
Mineral Compounds Poland USDA
[75]
([74])
Calcium (Ca)137
Iron (Fe)0.60.36
Magnesium (Mg)1110,3
Phosphorus (P)3125
Potassium (K)255197
Sodium (Na)3<2.5
Zinc (Zn)0.260.19
Copper (Cu)0.080.045
Manganese (Mn)0.10.142
Table 5. Characteristics of mineral components of two pepper varieties, ‘Yecla F1’ and ‘Salomon F1’, after the fermentation process in geothermal water from Uniejów and tap water from Skierniewice.
Table 5. Characteristics of mineral components of two pepper varieties, ‘Yecla F1’ and ‘Salomon F1’, after the fermentation process in geothermal water from Uniejów and tap water from Skierniewice.
Water UsedMinerals [mg∙100 g−1]
PKMgCaNaCuFeMnZn
‘Yecla F1’
Geothermal water 13.5 a 115.5 a 8.20 a 15.3 a607.9 a0.005 b0.217 b0.048 b0.066 b
Tap water13.1 a 111.1 b7.47 b 14.7 b587.6 b0.009 a0.233 a0.062 a 0.140 a
‘Salomon F1’
Geothermal water 13.9 a120.8 a8.25 a18.7 a639.4 b0.005 a0.223 a0.059 a0.084 b
Tap water13.0 a106.4 b7.15 b17.3 b654.3 a0.003 b0.204 b0.051 b0.107 a
Note: means in the column for each cultivars marked with the same letter are not different according to Tukey’s HSD test (p = 0.05).
Table 6. Characteristics of some components in fermented peppers of two cultivars: ‘Yecla F1’ and ‘Salomon F1’.
Table 6. Characteristics of some components in fermented peppers of two cultivars: ‘Yecla F1’ and ‘Salomon F1’.
Water UsedMinerals [mg∙kg−1]
NO3AsCdPb
‘Yecla F1’
Geothermal water 12.3 a0.003 a0.004 a0.002 b
Tap water8.84 b0.003 a0.004 a0.005 a
‘Salomon F1’
Geothermal water 5.41 b0.003 a0.003 b0.004 b
Tap water7.07 a0.003 a0.004 a0.006 a
Note: means in the column for each cultivars marked with the same letter are not different according to Tukey’s HSD test (p = 0.05).
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Wrzodak, A.; Szwejda-Grzybowska, J.; Popińska, W.; Mieszczakowska-Frąc, M. Red Pepper Fermentation with Geothermal Mineral Water: Impact on Nutritional Profile and Quality Characteristics. Agronomy 2025, 15, 2279. https://doi.org/10.3390/agronomy15102279

AMA Style

Wrzodak A, Szwejda-Grzybowska J, Popińska W, Mieszczakowska-Frąc M. Red Pepper Fermentation with Geothermal Mineral Water: Impact on Nutritional Profile and Quality Characteristics. Agronomy. 2025; 15(10):2279. https://doi.org/10.3390/agronomy15102279

Chicago/Turabian Style

Wrzodak, Anna, Justyna Szwejda-Grzybowska, Wioletta Popińska, and Monika Mieszczakowska-Frąc. 2025. "Red Pepper Fermentation with Geothermal Mineral Water: Impact on Nutritional Profile and Quality Characteristics" Agronomy 15, no. 10: 2279. https://doi.org/10.3390/agronomy15102279

APA Style

Wrzodak, A., Szwejda-Grzybowska, J., Popińska, W., & Mieszczakowska-Frąc, M. (2025). Red Pepper Fermentation with Geothermal Mineral Water: Impact on Nutritional Profile and Quality Characteristics. Agronomy, 15(10), 2279. https://doi.org/10.3390/agronomy15102279

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