Improvement of probiotic properties in lactic acid bacteria strains by chemical and physical mutagenesis

Lactic acid bacteria (LAB) have a wide range of uses in the food industry as starter and probiotic cultures. In this respect, it is of great importance to develop the technological and probiotic properties of strains. Mutation practices play an active role in the development of strains. Within the scope of the thesis study, local LAB strains (Lb. brevis MF105, Lb. plantarum MF239, Lb. plantarum MF376, Lb. plantarum MF556, P. ethanolidurans MF229, P. ethanolidurans MF50) with weak probiotic properties (bile salt, pH 2.5 and proteolytic enzyme resistance) were enhanced by mutation using UV radiation, ethidium bromide (EtBr) and ethyl methane sulfonate (EMS). In order to determine the change in probiotic properties of LAB strains, properties such as pH 2.5 resistance, bile salt resistance, pepsin-pancreatin resistance, cholesterol assimilation, antibiotic resistance and surface hydrophobicity were determined as in Vitro. In addition, after the determination of probiotic properties, genomic DNAs of mutant LAB strains were examined by RAPD-PCR technique and genetic polymorphism was revealed. It was determined that the decrease in cell viability caused by EtBr mutations in mutations performed with EtBr, EMS and EtBr/EMS (Mix) in LAB strains was lower compared to EMS and Mix. In the preselection after mutations, 16 Lb. plantarum MF239 mutant strain, 2 Lb. plantarum MF376 mutant strain, 3 Lb. plantarum MF556 mutant strains, 16 P. ethanolidurans MF229 mutant strains and 7 P. ethanolidurans MF50 mutant strains were selected. In the probiotic properties of the selected mutant strains, the lowest viability loss in gastric pH resistance tests was measured in the MF239 Mix1 mutant strain, and an increase of 91.37% viability and +27,27-unit viability compared to the parent strain were achieved, respectively. The highest vitality increase in bile salt resistance was Lb. plantarum MF376 strain was measured in the MF376 Mix1 mutant and the main strain viability level was 51.55%, 76.62% in the mutant strain, resulting in a +25.07-viability increase. In terms of pancreatin enzyme resistance, the highest pancreatin enzyme resistance increase was obtained in the mutant MF50 Mix2 strain of P. ethanolidurans MF50 strain and a value of +14.07 was obtained. In chloramphenicol antibiotic resistance (C30), a complete resistance was observed in mutant strains MF239 KUV1 (0 mm zone) and MF239 EMS2 (0 mm zone) compared to the parent strain. The increases in cholesterol assimilation (MF239 UV5, MF229 Mix3) and surface hydrophobicity (MF229 EMS3, MF239 Mix3) values in some mutant strains were found to be statistically significant. Lb. plantarum MF239 Mix1 and Lb. plantarum MF376 Mix1 mutant strains differed in RAPD primary bands compared to the parent strain.