Application of Mineral Water from Geothermal Source for Fermentation of Beetroot

Fermentation is one of the oldest technologies, which prolongs the shelf life of food products and increases their nutritional and organoleptic values (Kavitake et al. 2018). Nowadays, fermentation still plays a significant role in the preservation and maintenance of food safety. Properly fermented food containing lactobacilli and bifidobacteria remains the best proof of their safety and the storability (Bourdichon et al. 2012). Fermentation may be the most economical and straightforward way of improving nutritional value, sensory properties and functional qualities of food. Particularly, fermented vegetables are low-caloric food as they contain considerably lower quantities of sugars compared to raw vegetables. Lactic acid may also lower the gut pH, therefore inhibiting the development of putrefactive bacteria. In addition, fermented vegetables can be a source of lactic bacteria strains with probiotic features (Manning et al. 2004).

In recent years, roots of Beta vulgaris L. has attracted considerable attention as a functional health promoting food (Chhikara et al. 2019). It is a rich source of biologically active substances, such as carotenoids (Dias et al. 2009), glycine betaine (de Zwart et al. 2003), saponins (Atamanova et al. 2005), betacyanins, folates (Jastrebova et al. 2003), betanin, polyphenols and flavonoids (Váli et al. 2007), nitrates, ascorbic acid (Clifford et al. 2015) and minerals, such as potassium, sodium, phosphorus, magnesium etc. (Ormsbee et al. 2013). Betalains are classified as cationic antioxidants, possessing hydroxyl group (-OH) at the C₆ position and amino group (-NH) in the ring; therefore, they are good electron donors (Strack et al. 2003), and may act as scavengers of free radicals (Pedreño & Escribano 2000). Studies of Klewicka and Czyżowska (2011) were focused on the effect of low temperature storage and fermentation of beet juice on betalain profiles, and their biological stability.

Beetroot belongs to vegetables eaten in relatively large quantities throughout the year; it is cheap and easily available as fresh material on the Polish market. This raw material is mainly consumed after its processing, during which the structure of betalain dyes is destroyed and antioxidant properties of this raw material are reduced (Sawicki & Wiczkowski 2018).

Generally, in Poland, well, spring or tap water is used to fermentation of vegetables. Water hardness is of great importance in acidification. Due to the higher content of calcium salts, hard water has a positive effect on maintaining the favorable consistency of fermented products. Water used for making brine should contain not less than 0.1 g of CaO per liter of water. Sometimes, to reduce the risk of softening of cucumbers, 7.5 g·dm⁻³ calcium chloride or other calcium salt is added to the brine. The brine should contain up to 5–7% NaCl and must be clear and free of impurities (Elkner & Smolińska 2002). One of the studies have documented using of different types of salts containing of Ca²⁺ and Mg²⁺ in brine and the influence of these on the texture of fermented cucumbers (Yoo et al. 2006).

Geothermal water is used in heating households and providing hot water, as well as in balneal-therapeutic and recreational services, but also for the production of drinks. Poland, mainly the Polish lowlands, the Sudety and the Carpathian Mountains, possess huge potential and resources of geothermal energy. Underground water is mostly found at a depth of 3000–4000 m and temperature can be from 20 to 130 °C. The level of mineralization of geothermal water is diverse and ranges from 1 to 100 g·dm⁻³. According to Latour and Drobnik (2016), the analysis of chemical composition of water from 60 geothermal sources in different regions of Poland showed their possible usefulness for various purposes. It is assumed that the use of mineral water from geothermal sources in vegetable processing will result in a product with improved nutritional value, health and sensory quality. We propose the use of geothermal water from Uniejów that is a highly mineralized composition of chloride-sodium-calcium-magnesium, in the process of fermentation of vegetables, instead of tap water conventionally used for this purpose (Table 1).

There is no literature dealing with vegetable fermentation technology based on the use of geothermal water for brine. Therefore, the purpose of our research was to evaluate geothermal water from Uniejów for making brine used in the process of fermentation of beetroot with the aim to obtain product with increased nutritional and pro-health value.

It was found that the two tested cultivars of beetroot differed from each other in the content of individual components in fresh roots, but the differences were not always statistically significant. The significantly higher content of dry matter was found in roots of ‘Wodan F₁’ (16.5%) as compared with ‘Alto F₁’ (15.4%). In roots of ‘Wodan F₁’ also, higher content of extract, total sugars, total polyphenols and higher hardness were scored than in the beets of ‘Alto F₁’ (Table 2). There was no significant difference in the pH value and color coordinates. The content of betanin was higher in ‘Alto F₁’. After the fermentation process, the above characteristics (except for hardness) did not differ between the products fermented in brine made from water of various sources (Table 3). Hardness of the cubes was the only trait that was higher when fermented in geothermal water. The literature indicates that the content of dry matter in different cultivars of beetroots can range from 12 to 20%, including: 4–12% sugars, 1.5% protein, 0.1% fat, and 0.8% fiber (Janiszewska 2014; Biegańska-Marecik et al. 2007). Makowska (1991) found that the level of the extract depends on the root size: the smaller the root, the higher the content of the extract. In his studies, the content of total polyphenols depended on the cultivar and ranged between 659 and 756 mg·kg⁻¹. After the fermentation process, the content of this compounds ranged from 314 to 450 mg·kg⁻¹ FM.

In the studies of Wruss et al. (2015), the content of total polyphenols in beetroot juices ranged between 0.85–1.29 g·dm⁻³. In the studies of Kazimierczak et al. (2016), the level of these compounds in beetroot juice after fermentation process ranged between 37.3–123.3 mg·100 g⁻¹ and depended on the cultivation method. Czyżowska et al. (2020) found that the total phenolics content in the fermented beetroot of the cultivar ‘Wodan F₁’ ranged from 920 mg·kg⁻¹ after 7 months of cold storage and decreased to 570 mg·kg⁻¹ after 10 months of storage.

In our research, the level of betanin depended on the cultivar and was respectively: in ‘Wodan F₁’ beetroots – 0.11%, and in ‘Alto F₁’ – 0.17%. After the fermentation process, the content of betanin for both cultivars ranged from 0.042 to 0.048%. The type of used water had no significant impact on the level of betanin. The literature showed that the content of betanin in the beetroots depends on the cultivar and ranged between 0.1% to 0.25%. In the studies of Gościnna and Czapski (2013), the content of betanin in beetroot juice ranged from 1093 to 1890 mg·dm⁻³. According to other authors, the content of this compound in beetroots was between 750 and 1300 mg·kg⁻¹ (de Zwart et al. 2003, Petterson et al. 2008; Sawicki & Wiczkowski 2018). The big differences in the content of betalain dyes may depend on several factors: cultivar, size and shape of root, climatic and agro-technical conditions (Gościnna et al. 2012; Gościnna & Czapski 2017).

In our experiment, beetroots hardness depended on the cultivar and was higher in ‘Wodan F₁’ (89.3 N) than in ‘Alto F₁’ (70.2 N). Moreover, there was a significant difference in the hardness of beet cubes of both cultivars fermented with the use of geothermal water (Tables 2 & 3).

The sensory assessment of the fermented cubes showed significant differences between cultivars ‘Wodan F₁’ and ‘Alto F₁’ in the four descriptors of sensory quality – in beetroot smell and sweet smell and also in the taste, which made higher score of overall quality of ‘Wodan F₁’ (Table 4).

In juice, differences were only found in the overall quality and fermented beetroot smell, which were scored higher in ‘Wodan F₁’ (Table 5). The type of water had a significant effect on the perception of sour taste of juice of ‘Wodan F₁’ (Table 4). The differences in the other quality attributes resulting from water type were not significant (Tables 4, 5), except for the higher intensity of sweet smell in juice of cultivar ‘Wodan F₁’ obtained with the use of geothermal water (Table 5).

Results of the study showed some significant differences in physicochemical composition and sensory quality of the fermented beetroots products (cubes and juice), which depended mostly on the cultivar and only little on the water type used for making brine. A significantly higher content of analyzed compounds was found in the cultivar ‘Wodan F₁’ than in ‘Alto F₁’. Used water had influence only on the hardness, which was higher in cubes fermented in Uniejów water. The fermented beetroot cubes ‘Wodan F₁’ from the geothermal water was characterized by the best scores of overall quality due to the highest intensity of fermented beetroot taste and smell.