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.
Highlights
Fermented beverages enjoy increasing popularity against the background of a conscious and healthy lifestyle (Kandylis et al, 2016)
5-L bioreactor fermentations applying the appropriate microorganism combination compared with fermentations with original water kefir (WK) grains were performed
The work presented described steps from a traditionally produced process to a defined water kefir fermentation process applying a co-culture of only one lactic acid bacteria (LAB) and one yeast, respectively
Summary
Fermented beverages enjoy increasing popularity against the background of a conscious and healthy lifestyle (Kandylis et al, 2016). The so-called cross-feeding occurs when LAB and yeast are fermented in co-culture meaning that both groups of organisms can profit from the metabolic products of one another (Bader et al, 2010; Smid and Lacroix, 2013; Stadie et al, 2013; Zhang et al, 2017). This is especially important in the case of WK, where the nutrients in general and nitrogen in particular are limited and may induce sulfurous off-flavors (Vardjan et al, 2013; Laureys et al, 2018). The mixture of the involved organisms results in a distinct profile of organic acids and exopolysaccharides that have an important influence on the sensory properties of the final beverage (Bader et al, 2010; Bertsch et al, 2019; Jin et al, 2019)
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