Determination of proteolytic activities of psychrotrophic bacteria isolated from raw milk

In this study, a total of 130 tanks and silos of raw milk from 10 different locations in Antalya and Burdur provinces were collected for 13 months and physicochemical, somatic cell count (SCC), microbiological and molecular biological analyses were carried out. Component, SCC, total aerobic mesophilic bacteria (TAMB) and total psychrotrophic aerobic bacteria (TPAB) contents of raw milk produced in Antalya and Burdur provinces, which have significant shares in the total raw milk production of Turkey, were determined throughout the year and proteolytic enzyme activity and deoxyribonucleic acid (DNA) sequence analyses of psychrotrophic bacteria isolated from raw milk were carried out. It is believed that this research may contribute to revealing the quality of raw milk in our country. The following analyses were carried out on the raw milk; pH, conductivity, %fat, %protein, %lactose, %dry matter, SCC, TAMB and TPAB. The pH value varied between 5.86-6.89, and the conductivity value changed between 5.02-6.34 µS/cm. The contents of fat, protein, lactose, and dry matter varied between 2.21-4.37%, between 2.36-3.50%, between 3.55-4.82%, and 10.29-12.55%, respectively. SCC ranged from 14000 to 706500 SCC/mL. TAMB count ranged from log 5.78 colony forming unit (cfu)/mL to log 8.55 cfu/mL, while TPAB count was in the range of log 5.18 cfu/mL-log 8.66 cfu/mL. Proteolytic enzyme activity and the Enzyme Index (EI) values of 26 psychrotrophic bacterial isolates, selected based on the differences in their morphological structures, were determined by incubation on Skim Milk Agar at 7°C and 37°C for 24-48 hours. The EI values of the psychrotrophic bacterial isolates were found to vary between 1.09 and 2.27 at 7°C and between 1.22 and 3.10 at 37°C. Nine separate psychrotrophic bacterial isolates with proteolytic enzyme activity were identified on a strain basis by DNA sequence analysis, of which 3 were Pseudomonas lundensis, 2 were Pseudomonas spp., 1 was Lactococcus spp., 1 was Rahnella sp., 1 was Carnobacterium maltaromaticum and 1 was identified as Chryseobacterium carnipullorum. As a result of the study, it was assessed that it is necessary to include the total number of psychrotrophic aerobic bacteria in raw milk as a criterion in the relevant legislation in order to improve the quality of raw milk in our country, to obtain higher quality dairy products and to prevent economic losses caused by low quality raw milk.