Isolation, characterization, and screening probiotic properties of artisanal yoghurt starter strains from Urla Region

Abstract

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.