Extraction of free and capsular exopolysaccharides from lactic acid bacteria isolated from milk and dairy products: Determination of bioactivities and emulsion properties of EPS

Herein, a total of 242 lactic acid bacteria were isolated from 22 milk and fermented dairy products collected from different geographical locations and 51 isolates with high EPS production potential were selected from these isolates. Crude free EPS (fEPS) and capsular EPS (cEPS) were extracted from 51 isolates following determination of optimal EPS production and extraction conditions. The production yields, the total carbohydrate contents, the total protein contents and the total uronic acid contents of the crude EPSs were determined. The FTIR analysis for the determination of the functional groups of the EPSs and the TGA analysis for the determination of thermal stability were performed. Emulsion activities and stability of EPSs with high uronic acid content were evaluated. The antioxidant activities of EPS species were determined by DPPH and ABTS, and their antibacterial activities were determined by agar well diffusion and broth microdilution methods. The findings revealed that the incubation conditions for EPS production yield varied from strain to strain and between EPS types (fEPS and cEPS) for the same strain, while the use of ethanol at a ratio of 1:2 in EPS extraction resulted in higher EPS yields. The production yields of fEPS ranged from 0.04 g/L to 7.48 g/L, while the production yields of cEPS ranged from 0.02 g/L to 1.54 g/L. The chemical contents of the crude EPSs were determined as follows: total carbohydrate contents of fEPS: 0.58 - 13.49 g/L and cEPS: 0.19 - 1.07 g/L; total protein contents of fEPS: 0.02 - 1.21% (w/w) and cEPS: 0.10 - 7.0% (w/w) and total uronic acid contents of fEPS: 0.16 - 26.06% (w/w), cEPS: 0.02 - 3.0% (w/w). The protein content of 23 fEPSs and 22 cEPSs were below the detection limit of the Bradford method. Moreover, the uronic acid content of 21 cEPSs could not be determined since they were below the detection limit of the method used. FTIR analysis revealed the characteristic functional groups of crude EPS and elucidated the differences between EPS types. TGA analysis showed that M17 21.7 fEPS was thermostable below 210 °C. Among the EPSs whose emulsion activities and stability were determined, 5 fEPSs were found to exhibit emulsion stability ranging from 13.03 - 80.00% after 72 hours of incubation. Among these EPSs, M17 19.9 showed a higher emulsion stability than xanthan gum by maintaining 80% emulsion stability. M17-22.6 fEPS showed the highest antioxidant activity (30.58%) using the DPPH method, while MSE-19.4 fEPS showed the highest antimicrobial activity with 66% inhibition against B. cereus.