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. 2021 Nov 4:12:732019.
doi: 10.3389/fmicb.2021.732019. eCollection 2021.

Tradition as a Stepping Stone for a Microbial Defined Water Kefir Fermentation Process: Insights in Cell Growth, Bioflavoring, and Sensory Perception

Sarah Köhler  1 , Maximilian Schmacht  1   2 , Aktino H L Troubounis  1 , Marie Ludszuweit  1 , Nils Rettberg  3 , Martin Senz  1
Affiliations

Tradition as a Stepping Stone for a Microbial Defined Water Kefir Fermentation Process: Insights in Cell Growth, Bioflavoring, and Sensory Perception

Sarah Köhler et al. Front Microbiol. .

Abstract

A process development from a traditional grain-based fermentation to a defined water kefir fermentation using a co-culture of one lactic acid bacterium and one yeast was elaborated as a prerequisite for an industrially scalable, controllable, and reproducible process. Further, to meet a healthy lifestyle, a low ethanol-containing product was aimed for. Five microbial strains-Hanseniaspora valbyensis, Dekkera bruxellensis, Saccharomyces cerevisiae, Liquorilactobacillus nagelii, and Leuconostoc mesenteroides-were used in pairs in order to examine their influence on the fermentation progress and the properties of the resulting water kefir products against grains as a control. Thereby, the combination of H. valbyensis and L. mesenteroides provided the best-rated water kefir beverage in terms of taste and low ethanol concentrations at the same time. As a further contribution to harmonization and reduction of complexity, the usage of dried figs in the medium was replaced by fig syrup, which could have been proven as an adequate substitute. However, nutritional limitations were faced afterward, and thus, an appropriate supplementation strategy for yeast extract was established. Finally, comparative trials in 5-L scale applying grains as well as a defined microbial consortium showed both water kefir beverages characterized by a pH of 3.14, and lactic acid and aromatic sensory properties. The product resulting from co-culturing outperformed the grain-based one, as the ethanol level was considerably lower in favor of an increased amount of lactic acid. The possibility of achieving a water kefir product by using only two species shows high potential for further detailed research of microbial interactions and thus functionality of water kefir.

Keywords: bioflavoring; co-culture; lactic acid bacteria (LAB); process development; water kefir; yeast; yeast extract.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer SJ declared a shared affiliation with one of the authors MSc, to the handling editor at time of review.

Figures

FIGURE 1
FIGURE 1
Course of bacteria (A) and yeast (B) cell concentration and pH change (C) during WK fermentation with different starter culture combinations. Data are the mean value of biological duplicates (LAB–yeast combinations) or triplicates (grains). WK, water kefir; LAB, lactic acid bacteria.
FIGURE 2
FIGURE 2
Course of produced ethanol, lactic, and acetic acid and consumed sugar during the WK fermentations with different LAB–yeast combinations (A–F) and complex grains (G). Shown are the data of biological duplicates (LAB–yeast combinations) or biological triplicates (complex grains) and the corresponding trend lines. WK, water kefir; LAB, lactic acid bacteria.
FIGURE 3
FIGURE 3
Concentrations of different selected volatile components in the unfermented basis medium and beverages produced with different LAB–yeast combinations and WK grains after 7 and 4 days of fermentation, respectively. The quantified aroma-relevant analytes included higher aliphatic alcohols and esters (A,B), fatty acids (C), fatty acid ethyl esters (D), and thiols and other sulfur components (E,F). The detection limit is specified for the components for which no detection was possible. The analytes pentanoic acid, dodecanoic acid, ethyl hexanoate, and propane-1-thiol (all not shown) were not detected in any sample. Data of the fermented products are the mean value of biological duplicates ± mean deviation. WK, water kefir; LAB, lactic acid bacteria.
FIGURE 4
FIGURE 4
Sensory properties of products fermented with different LAB–yeast combinations after 7 days of fermentation. Shown are the mean data of two samples produced in biological duplicates. The rating scale of the descriptive analysis (A) ranges from 1 (imperceptible) to 5 (very pronounced). The overall rating of the taste (B) ranges from 1 (very good) to 5 (bad taste). LAB, lactic acid bacteria.
FIGURE 5
FIGURE 5
Course of cell concentrations (A,B), pH value (C), residual sugar (D), produced lactic acid (E), and ethanol (F) during the WK fermentation by Leu + Han with different types and concentrations of supplemented YE. Data are the mean value of biological duplicates. WK, water kefir; YE, yeast extract.
FIGURE 6
FIGURE 6
Concentrations of different volatile components in modified media (references) and in 7-day fermented beverages produced with the Leu + Han combination and different types and amounts of YE. The quantified aroma-relevant analytes included higher aliphatic alcohols and esters (A,B), fatty acids (C), fatty acid ethyl esters (D), and thiols and other sulfur components (E,F). The detection limit is specified for the components for which no detection was possible. The analytes pentanoic acid, dodecanoic acid, ethyl hexanoate, and propane-1-thiol (all not shown) were not detected in any sample. Data are the mean value of biological duplicates ± mean deviation. YE, yeast extract.
FIGURE 7
FIGURE 7
Sensory properties of the products fermented with the microbial combination Leu + Han under the investigation of 0, 0.2, and 1 g/L of two different YEs after 7 days of fermentation. Shown are the mean data of two samples produced in biological duplicates. The rating scale of the descriptive analysis (A) ranges from 1 (imperceptible) to 5 (very pronounced). The overall rating of the taste (B) ranges from 1 (very good) to 5 (bad taste). YE, yeast extract.
FIGURE 8
FIGURE 8
Off-line data of WK fermentations in 5-L bioreactors with grains (A,C) and the defined co-culture Leu + Han (B,D). Fermentations were conducted in biological triplicates. Data from identical sampling times are shown as the mean value of a triple (full-filled mark), double (half-filled mark), or single (unfilled mark) sampling. WK, water kefir.
FIGURE 9
FIGURE 9
Sensory properties (A) and rating (B) of products fermented with the combination of Leu + Han as well as WK grains in 5-L bioreactors. Shown are the mean data of biological triplicates at the best time of each single fermentation depending on the best achieved sensory properties: Leu + Han at 7 days of fermentations. Grain trial 1 (f1) at 3 days, trial 2 (f2) at 6 days, and trial 3 (f3) at 5 days of fermentation. The rating scale of the descriptive analysis (A) ranges from 1 (imperceptible) to 5 (very pronounced). The overall rating of the taste (B) ranges from 1 (very good) to 5 (bad taste). WK, water kefir.
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