TARRAH, ARMIN (2019) Characterization and Assessment of Health-related Probiotic Properties of Newly Isolated Lactic Acid Bacteria and Study of their Technological Potential by In-silico, In-vitro, and In-vivo Approaches. [Ph.D. thesis]
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Abstract (italian or english)
Lactic Acid Bacteria (LAB) are the most frequently probiotics used. Within this functional group, Streptococcus thermophilus is a thermophilic species widely used as a starter culture for a huge number of dairy products. Besides being rapid acidifiers, many S. thermophilus strains can produce and release folate during growth. S. macedonicus is another homofermentative lactic acid bacterium (LAB) which was first isolated from a typical Greek cheese obtained by natural fermentation in Macedonia. Some Streptococcus macedonicus strains have revealed some interesting properties, such as proteolytic activity, production of bacteriocins against food pathogens, production of exopolysaccharides and tolerance to stress associated with food processing. Lactobacilli also as a member of LAB identified as GRAS and used as a commercial starter in fermented dairy products or as probiotics related to human health. They can play significant roles in different ways such as inhibition of pathogens, anti-cancer activity and different vitamins production in human. Given this point, this thesis has aimed to identify and select some new potential probiotic-technological strains of LAB which recently were isolated from different sources through genomic and physiological studies to be used in human health and food industry. All the strains were evaluated for different technological aspects such as acidification activity and fermentation on different sugars. The genomes of strains were sequenced and applied for in-silico analysis to get enough information about their safety and application in technology and human health. On the other side, the interesting strains from technological part were selected to be evaluated for different in-vitro probiotic properties such as antibiotic susceptibility, hemolytic activity, resistance to simulated gastrointestinal conditions, bile salts hydrolysis activity, different vitamins production, adhesion to HT-29 human epithelial cell and anti-cancer activity against colorectal cancer cells (HT-29). Based on results from in-vitro probiotic characterization, strains Lactobacillus paracasei DTA81 and S. thermophilus TH982 were chosen for in-vivo experiments using the laboratory mice. The results of this study revealed that strain L. paracasei DTA81 was found to possess in-vitro and in-vivo probiotic properties besides lowering the blood cholesterol and Light Density Lipid (LDL) as well as Fasting Blood Sugar (FBS). Lactobacillus paracasei DTA81 had already indicated interesting technological traits such as growing on all different sugars including some prebiotics as well.
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