Browsing by Subject "Saccharomyces boulardii"
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(2022)Saccharomyces boulardii is a probiotic yeast related to Saccharomyces cerevisiae but with distinct genetic, taxonomic, and metabolic properties. S. cerevisiae has been used extensively in biotechnological applications. Currently, many strains are available, and multiple genetic tools have been developed, which allow the expression of several exogenous proteins of interest with applications in the fields of medicine, biofuels, the food industry, and scientific research, among others. Although S. boulardii has been widely studied due to its probiotic properties against several gastrointestinal tract disorders, very few studies addressed the use of this yeast as a vector for expression of foreign genes of interest with biotechnological applications. I studied the previously constructed S. boulardii SAC12, which secretes the anti-listerial bacteriocin leucocin C originating from Leuconostoc carnosum 4010. The objective was to study if the bacteriocin leucocin C producing S. boulardii could produce leucocin C in beer fermentation and if leucocin C containing beer can be used as marinade to control Listeria monocytogenes in raw chicken breast strips. The results showed that SAC12 has good ability to secrete LecC, and thus it was used to brew anti-listerial beer. According to results, beer could maintain its anti-listerial activity for 38 days. The anti-listerial effect of the beer stored for different times was analyzed through marinating chicken breast strips (spiked with L. monocytogenes) with the beer for overnight. Results indicated a positive impact of anti-listerial beer in reduction of the viable cells of L. monocytogenes by about 1.6 log from (2.2 ± 0.6) × 10⁷ CFU/g (beer from day 24), and 2.2 log from (1.8 ± 0.3) × 10⁵ CFU/g (beer from day 38). To sum up, the S. boulardii SAC12 efficiently secreted the bacteriocin leucocin C. Brewing beer with S. boulardii SAC12 resulted in beer containing leucocin C. Such beer showed anti-listerial effect when used as marinade for chicken breast strips.
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(2020)Beer is the world´s most popular alcohol drink, with a long history. It is commonly made with baker’s yeast Saccharomyces cerevisiae. Yeast used for fermentation has an effect on the sensory properties of the product. Saccharomyces boulardii is a probiotic yeast. The objective of the thesis was to explore the use of probiotic yeast S. boulardii in wheat beer and develop it further with the help of sensory evaluations. S. boulardii is used to prevent travelers' diarrhea and as a help to many intestinal disorders. The use of probiotic yeast could make a new interesting product with functional properties. In the experimental part of the study beer was produced with two yeasts, S. cerevisieae and S. boulardii. The beer was matured in two different temperatures (20°C and 37°C). The four samples were compared to commercial reference product. One sample (C37) did not meet quality standards so it was left from sensory analysis. The sensory analysis was performed with 9 trained panelists by using generic descriptive analysis. Concentration for alcohol was measured with High Performance Liquid Chromatography (HPLC). Also pH value and the colour shade was measured. The samples were plated on agar plates to calculate colonies forming units (CFU) to test the yeast surviving in 1, 2 and 3 months time. Eight attributes were rated using visual analogue scales, anchored verbally at the end points. Sensory evaluation showed that the beer differed statistically significantly from each other in three attributes: appearance of foam, the mouthfeel of carbon dioxide and stale, musty smell. B37 was categorized in the same group in Tukey’s test with commercial product although the alc. vol.% was lower. The samples that were fermented in the room temperature had a musty smell and they had darker colour. pH values had only minor differences and the sourness did not have statistically significant differences in sensory analysis. Yeasty taste did not vary significantly between samples. B37 maintained colonies forming units better in the first month and B20 in the second and third measurement. B37 was the most similar to the commercial product, so further studies are encouraged to assess right fermentation conditions. The survival of the probiotic yeast was good, so the product has potential to the beer market.
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