Food Engineering / Gıda Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/12
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Article Citation - WoS: 34Citation - Scopus: 39High Genetic and Phenotypic Variability of Streptococcus Thermophilus Strains Isolated From Artisanal Yuruk Yoghurts(Academic Press Inc., 2014) Erkuş, Oylum; Okuklu, Burcu; Yenidünya, Ali Fazıl; Harsa, ŞebnemStreptococcus thermophilus is a commonly used starter bacterium in dairy industry. It reduces the pH of milk rapidly and equilibrates the medium for the growth of Lactobacillus delbrueckii subsp. bulgaricus during yoghurt fermentation. Efforts to increase the diversity of artisanal yoghurt starters are not only important to bring new strains with novel and desirable characteristics, but also for the preservation of natural diversity which diminishes with the overuse and spread of industrial starters to natural resources. In the present study, 14 artisanal yoghurt samples were processed for the isolation of promising strains for yoghurt starter culture production and 66 strains were subsequently characterized. They were all identified as S. thermophilus using species-specific PCR and 16S rRNA gene sequencing. Genotypic diversity at the strain level was investigated by pulsed field gel electrophoresis (PFGE), and 22 homology groups were obtained. Further phenotypic characterization unearthed a significant phenotypic heterogeneity within homology groups, mostly with atypical novel character. Only 7 out of 66 strains showed S. thermophilus type-strain like phenotypic traits. Majority of the isolates were determined to be protease positive and fast milk acidifier to be used as yoghurt starter culture.Article Citation - WoS: 48Citation - Scopus: 59Biochemical and Thermal Properties of Ss-Galactosidase Enzymes Produced by Artisanal Yoghurt Cultures(Elsevier Ltd., 2010) Üstok, Fatma Işık; Tarı, Canan; Harsa, Şebnemβ-Galactosidases, produced by pure and mixed cultures of Streptococcus thermophilus 95/2 (St 95/2) and Lactobacillus delbrueckii ssp bulgaricus 77 (Lb 77) isolated from the Toros mountain region of Turkey, were characterised with respect to their biochemical and thermal properties. Optimum pH and temperature for maximum activity were determined and these enzymes were stable in the pH range 7-9 and in the temperature range 20-37 °C, retaining 80-90% of their initial activities. The inactivation energies of β-galactosidase from Lb 77, St 95/2 and mixed culture (Lb 77 and St 95/2) were 51.3, 44.0 and 48.3 kcal mol-1, respectively. Moreover, thermodynamic (ΔG, ΔS, ΔH) and kinetic constants (Km and Vmax) were determined and effects of metal ions were investigated. As a result, these enzymes could be considered as potential candidates for lactose hydrolysis of milk and milk products. © 2009 Elsevier Ltd. All rights reserved.