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Browsing by Author "Yassami, Shiva"

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  • Analysis on Anti-listerial Properties of Beer Fermented by Bacteriocin Leucocin C Secreting Saccharomyces boulardii 
    Yassami, Shiva (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.
  • Monitoring of Acidification and Exopolysaccharide Production by Lactic Acid Bacteria Fermentation in Wheat Matrices 
    Yassami, Shiva (2016)
    Wheat bran is obtained after conventional milling of wheat grains for the production of white flour, which is an important source of dietary fiber, vitamins and minerals, but still remains underutilized in food manufacturing. In spite of the increasing evidence about the health effects of whole-meal and fiber-rich foods, refined white flour is still preferred. Bran also has a negative influence on dough rheology, texture and the sensory quality of bread, which limits its use in bran bread baking. The use of starter culture for sourdough fermentation can drive the fermentation process and confer specific changes on the matrix. Exopolysaccharides (EPS) produced by some lactic acid bacteria (LAB) are important due to their physicochemical properties affecting dough rheology and bread texture, as well as their health-promoting potential. The screening of EPS-producing strains has been carried out mostly on wheat and rye sourdough, and very few studies have considered different matrices. The objective of this work was to determine and compare whole-wheat flour and wheat bran fermentation by two strains of LAB (Leuconostoc spp. and Weissella spp.) in the presence of added sucrose and without, and to study the effect of sourdough obtained with a selected EPS-producing LAB strain on the quality of bread and its shelf-life. Sourdough quality was studied by means of microbiological, rheological and chemical analysis by comparing the growth and acidification performance in the different matrices, and by evaluating EPS production using viscosity measurements. The physical and mechanical properties of fresh bread made using the best EPS producer LAB were investigated to study the product shelf-life by using the seed replacement method and texture analysis test. The results showed that dough prepared with Weissella confusa with added sucrose had a positive impact on viscosity, as well as providing mild acidic sourdough leading to better bread quality properties, whereas in the presence of Leuconostoc pseudomesenteroides, no positive viscosity has observed in whole-wheat sourdough. Bran sourdough samples with Weissella confusa showed a higher volume, better color and shelf-life during storage than samples with un-soured bran, confirming the effect of sourdough and the positive role of EPS on the functional properties of high-fiber bread making.

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