Determination of Some Technological Characteristics of Streptococcus thermophilus and Streptococcus macedonicus Isolated from Classical White Cheese Production Stages

Lactic acid bacteria (LAB) are classified within the taxonomic family Lactobacillaceae family and are renowned for their pivotal roles in food safety and public health. Additionally, they contribute to the formation of aroma, flavour and texture in fermented foods. Among LAB, Streptococcus spp. is considered at the generally recognized as safe (GRAS) level, particularly for use as starter cultures in the dairy industry. The aim of this study was to ascertain the technological properties of S. thermophilus BST2001-BST2007 (7) and S. macedonicus BSGM2471- BSGM2471 (2). These were isolated from samples obtained at various stages of classical white cheese production, including acid forming capacity, proteolytic activity, viability at different pH, temperature and salt concentrations, and diacetyl production. The findings of the study demonstrated that the acid forming capacities of all isolates were similar during the initial 6th hour. However, at the 12th hour, the S. thermophilus BST2006 and BST2007 isolates decreased the pH of the medium to 4.45 and 4.46, respectively, resulting in the formation of a clot. At the end of the 24-hour period, it was observed that all S. thermophilus isolates had formed clots, whereas the S. macedonicus isolates had demonstrated a markedly reduced capacity for acid production and did not form any clots. In contrast, both species showed high proteolytic activity (zone diameter >10 mm) and were able to growth within a temperature range of 15-45°C. Isolates of S. macedonicus were observed to be unable to grow at a salt concentration of 7%. Additionally, diacetyl production was observed in four S. thermophilus isolates and one S. macedonicus isolate. These results indicate that there may be significant differences in technological properties even among the same LAB species. This highlights the importance of researching and introducing new LAB species to the sector to develop products with specific, targeted properties in the fermented food industry, particularly in cheese production.