Gluten hydrolysis and probiotic potential of lactic acid bacteria isolated from sourdough fermentation

Objective: While various fermented dairy products have been produced for many years, plant-based fermented products have gained more attention in recent years. The health benefits of plant-based fermented products and the trends in vegetarian diets have influenced changing consumer preferences. Sourdough fermentation based food products provide numerous benefits to the product and consumer health due to the activities of lactic acid bacteria (LAB) in the microflora. These microorganisms, with their probiotic potentials and gluten-degrading abilities, can be used to find new solutions for gluten sensitivity, which is an important health issue today. The aim of this thesis is to isolate lactic acid bacteria from sourdough, to screen their potential probiotic properties (low pH, bile tolerance, antibiotic susceptibility, gastric acid resistance, resistance to gastrointestinal conditions), to determine their gluten-degrading properties, and to present an innovative approach for developing food products suitable for consumption by individuals with gluten sensitivity. Materials and Methods: Six sourdough samples were used for the isolation of LAB. The isolates were purified by the streak plate method and preliminarily identified by Gram staining and catalase testing. The gluten hydrolysis potential of the selected isolates was then analyzed based on their ability to grow in gluten-containing media. The main probiotic properties of the isolates with gluten-degrading potential were determined by pH resistance, bile salt tolerance, simulated gastric and pancreatic juice tolerance, autoaggregation, coaggregation, hydrophobicity, antibiotic resistance, and antimicrobial activity tests. Finally, the species-level identification of the isolates was determined by 16S rRNA sequencing analysis. Results: At the end of the study, 44 isolates were purified and preliminarily identified as LAB. Sixteen of the isolates showed high growth potential in gluten-containing media. Eight of these isolates were selected due to their high gluten hydrolysis potential and significant viability at pH 2.5. Selected isolates highly tolerated bile salts. Autoaggregation values (1.93-31.72%), hydrophobicity (21.11-57.73%), and coaggregation properties (24.39-33.04%) were determined at varying levels. All isolates met the desired probiotic criterion with viability above 106 cfu/ml after simulated gastrointestinal passage. All pathogens were inhibited by the bacterial isolates, with the largest inhibition zones against Bacillus cereus. Most isolates were found to be resistant to vancomycin and streptomycin. Finally, eight isolates were identified as belonging to the genera Enterococcus, Levilactobacillus, and Lactiplantibacillus. Conclusion: LAB isolated from sourdough contain high probiotic potential and gluten-degrading bacteria. Isolates with high gluten hydrolysis, such as Enterococcus faecium coded as L11, Levilactobacillus spicheri coded as K26, and Lactiplantibacillus plantarum coded as K35, can be used in the future for the development of probiotic supplements or cereal-based probiotic beverages that consider gluten sensitivity. Keywords: Lactic acid bacteria, Sourdough, Gluten, Gluten sensitivity, Probiotic