Determination of some physicochemical, microbiological, sensorial properties and vitamin B₁₂ contents in kefirs by using biopreservative cultures

In this study, the effect of the use of protective cultures in kefir production on kefir quality and vitamin B-12 formation was investigated. Kefirs were produced using lactic and propionic acid bacteria with natural bioprotective properties, namely Lactiplantibacillus plantarum, Lacticaseibacillus rhamnosus (CR) and Propionibacterium freudenreichii subsp. shermanii (CS). A comparison was made with a control group sample (CK) without adding any protective culture. While the use of protective cultures in kefir did not affect the dry matter, fat and protein contents, it affected the pH and titratable acidity (p < 0.05). High viscosity values were observed in the control sample during storage (595 - 1034 mPa.s), whereas the highest viscosity was observed in kefir containing P. shermanii at the end of storage (p < 0.05). Vitamin B-12 content ranged from 412 to 640 mu g/100 mL, with the highest amount found at the end of storage found in kefir containing P. shermanii. Microbiological viability remained above 6 log CFU/mL; however, the viability of L. plantarum and L. rhamnosus which can also be used as probiotics, decreased during storage but still remained above 6 log CFU/mL. Yeast counts increased to 6.5 log CFU/mL in the control group, while they remained below 5 log CFU/mL in the other treated groups. Due to the greater suppression of yeast counts in kefir containing P. shermanii, the lowest level observed was 3 log CFU/mL. Sensory evaluation revealed that all kefir samples received acceptable scores for consistency, odor, taste-aroma, and these scores were not affected by the use of different preservatives. Among all samples, kefir containing L. plantarum received the lowest sensory score when compared to the control sample. These findings emphasize that protective cultures can be an effective strategy for extending the shelf life of kefir and preventing the growth of undesirable microorganisms. They can also be applied in various combinations and at higher inoculation rates.