Browsing by Author "Okuklu, Burcu"

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Investigation of chromosomal and plasmid dna profiles of lactococcus lactics ssp. lactis
(Izmir Institute of Technology, 2005) Okuklu, Burcu; Güneş, Hatice
Lactic acid bacteria used in the manufacturing of cheese and other fermented milk products are known as starter cultures. Starters play an important role in the sensory properties of fermented milk products by lactic acid production which influences desirable quality characteristics. In dairy industry, diversity of starter strains of Lactococcus lactis is very limited. There is a considerable demand for novel starters with technologically desirable properties. Gene products responsible for lactose fermentation are encoded on plasmid DNA. Therefore, the plasmid stability of lactic acid bacteria is an important industrial property for starter culture. In the previous study, Lc. lactis ssp. lactis strains were isolated from an artisanal "comlek peyniri'" from Cappodocia and these strains were selected as good acid producers. The aim of this study was to investigate intraspecific diversity of 54 Lc. lactis ssp. lactis by choromosomal and plasmid profiling. In addition, the plasmid stability of 35 artisanal starters was determined by the examination -galactosidase activity. First of all, partial DNA sequencing of the 16S rRNA genes was carried out in order to confirm that the previously identified isolates were Lc. lactis ssp. lactis. The partial DNA sequencing and blast search results indicated that representative isolates showed 90 % homology with Lactococcus lactis. Based on chromosome and plasmid profiling results, 35 Lactococcus lactis artisanal starters exhibiting good acidifying activities were classified into ten different genotypes and nine plasmid groups. None of the reference strains of Lactococcus lactis ssp. lactis and Lc. lactis ssp. cremoris and Lc. lactis ssp. lactis biovar. diacetylactis were included into these genotypes and plasmid groups. The rest of the 17 isolates which were defined as low acid producers by technological methods were clustered into thirteen unique genotypes and seven plasmid groups. Only four of the isolates were found to contain the most stable plasmids by instability studies and these kept their lactase activities during prolonged subculturing. As a result, chromosome and plasmid DNA profiling allowed us to classify artisanal starter strains in certain groups. The strains with stable and instable plasmids will serve us to characterize and improve technological features of these artisanal starter strains in future studies.
Isolation, characterization, and screening probiotic properties of artisanal yoghurt starter strains from Urla Region
(Izmir Institute of Technology, 2014-07) Okuklu, Burcu; Harsa, Hayriye Şebnem; Yenidünya, A.Fazıl
Probiotics are bacteria that help to maintain the natural balance of microflora in the intestine. The largest group of probiotic bacteria in the intestine is lactic acid bacteria, found in yoghurt with live culture. In this study, 13 different artisanal yoghurt samples were collected from Urla region to isolate artisanal starter strains. These isolated strains were firstly identified and characterized by using basic biochemical, physiological and probiotic characterization methods. Among 453 LAB strains in total, 5 Streptecoccus thermophilus and 26 Lactobacillus delbrueckii ssp. bulgaricus isolates resulted as probiotic candidates. PCR-RFLP and PFGE-RFLP methods were used for the differentiation of probiotic candidates. Probiotic features of strains were screened by using bile salt tolerance, bile salt deconjugation, and cholesterol assimilation, transit tolerance to gastrointestinal tract, antibiotic resistances, autoaggregation, cell surface hydrophobicity, antimicrobial activities, adhesion abilities, and growth capacity with prebiotics. The results showed that, the isolated strains gave different properties against these tests; but all of them were acid and bile resistant, had ability to adhesion Caco-2 cell lines, and grown very well with prebiotic sources. They had also antimicrobial activity against Escherichia coli and Listeria innocua. Further studies were conducted; probiotic yoghurts were produced by using probiotic candidates. Sixteen starter combinations were made using the two cocci and eight bacilli isolates, and thus these yoghurt products were characterized by using physical, chemical, rheological, and organoleptic methods. Acetaldehyde content of yoghurt samples varied between 5.61 and 15.38 mg/L and apparent viscosity values ranged from 261 and 608 m Pa.s. Hardness value of samples ranged from 3.81 and 6.71 N. Yoghurt starter having probiotic features is an advantage for dairy industry to produce large amount of functional yoghurt. In this study, a good number of cocci and bacilli were paired as probiotic/starter strain combinations that could perfectly be used for the production of functional yoghurt for dairy industry.