Interactions between Kazachstania humilis Yeast Species and Lactic Acid Bacteria in Sourdough

Abstract

Sourdoughs harbor simple microbial communities usually composed of a few prevailing lactic acid bacteria species (LAB) and yeast species. However, yeast and LAB found in sourdough have been described as highly diverse. Even if LAB and yeast associations have been widely documented, the nature of the interactions between them has been poorly described. These interactions define the composition and structure of sourdough communities, and therefore, the characteristics of the final bread product. In this study, the nature of the interactions between strains of two commonly found sourdough yeast species, Kazachstania humilis and Saccharomyces cerevisiae, and lactic acid bacteria isolated from sourdoughs has been analyzed. Population density analysis showed no evidence of positive interactions, but instead revealed neutral or negative asymmetric interaction outcomes. When in coculture, the yeasts´population size decreased in the presence of LAB regardless of the strain, while the LAB´s population size was rarely influenced by the presence of yeasts. However, a higher maltose depletion was shown in maltose-negative K. humilis and maltose-positive obligately heterofermentative LAB cocultures compared to monocultures. In addition, tested pairs of obligately heterofermentative LAB and K. humilis strains leavened dough as much as couples of LAB and S. cerevisiae strains, while K. humilis strains never leavened dough as much as S. cerevisiae when in monoculture. Taken together, our results demonstrate that even if higher fermentation levels with increased maltose depletion were detected for K. humilis and obligately heterofermentative LAB pairs, these interactions cannot be ecologically classified as positive, leading us to rethink the established hypothesis of coexistence by facilitation in sourdoughs.Sourdough is a mixture of flour and water where fermentation occurs, leading to the leavening of dough. A microbial community composed of lactic acid bacteria (LAB) and yeast is responsible for the fermentation process [5]. These microbial communities are quite simple, usually harboring one effective yeast species and two effective LAB species [6]. However, a rather high microbial diversity has been described when considering different sourdoughs all over the world; more than 60 LAB species and 30 yeast species have been described so far [7][8][9][10][11][12][13][14][15][16]. Most described LAB species belong to the genus Lactobacillus, and most yeast species to the genera Saccharomyces, Kazachstania, Wickerhamomyces, Torulaspora, and Pichia. The most commonly found Lactobacillus species is Lactobacillus sanfranciscensis (obligately heterofermentative), but many other Lactobacillus species were also detected, such as Lactobacillus brevis, Lactobacillus fermentum, Lactobacillus hammesii (obligately heterofermentative), Lactobacillus paralimentarius, Lactobacillus sakei, Lactobacillus kimchi, Lactobacillus pentosus, Lactobacillus curvatus Lactobacillus plantarum (facultatively heterofermentative), and less frequently Lactobacil...

Characterization and selection of functional yeast strains during sourdough fermentation of different cereal wholegrain flours

“…In particular, S. cerevisiae IMA D4Y, D17Y and D25Y showed a www.nature.com/scientificreports/ significant higher leavening performance than S. cerevisiae commercial baker's yeast in doughs obtained using wheat flours, highlighting their efficiency as leavening agents. Similar results were found by Carbonetto et al 39 , who reported that K. humilis strains never leavened dough as much as S. cerevisiae when singly inoculated in doughs. Moreover, our results showed that, contrary to S. cerevisiae commercial baker's yeast, 33% of strains were able to increase the volume of doughs made using barley, which is a cereal with a lesser ability to form a gluten complex than wheat, thus decreasing dough gas retention 40 .…”

“…Similar results were found by Carbonetto et al . 39 , who reported that K. humilis strains never leavened dough as much as S. cerevisiae when singly inoculated in doughs. Moreover, our results showed that, contrary to S. cerevisiae commercial baker’s yeast, 33% of strains were able to increase the volume of doughs made using barley, which is a cereal with a lesser ability to form a gluten complex than wheat, thus decreasing dough gas retention 40 .…”

Yeast Biodiversity in Fermented Doughs and Raw Cereal Matrices and the Study of Technological Traits of Selected Strains Isolated in Spain

“…Distinct microbial ecosystems are created in Type I sourdoughs. The metabolic diversity of two groups of microorganisms, yeasts and bacteria, enables a wide range of interactions and associations [ 5 , 6 ] that greatly affect the performance of the dough, the nutritional properties, and the overall quality of sourdough breads, including the microbial shelf life [ 7 , 8 ] and functional properties [ 9 , 10 ]. Sourdoughs are widely used to produce “slow breads” (long fermentation time) and “low FODMAP breads” (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols), which are increasingly appreciated by consumers due to their nutritional and sensory qualities and effect on human health [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ].…”

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“…In sourdough B, four strains belonged to the S. cerevisiae species, while the other strains belonged to K. humilis species (Table 1). These two species represent typical yeast interactions found in other traditional sourdoughs [12,14]. Furthermore, as demonstrated by Fujimoto et al [15], the reduced fermentation of sourdough could favor the dominance of S. cerevisiae, as happened in sourdough B.…”