3 18ks centrifuge

The cell surface hydrophobicity was assessed with n-hexadecane and chloroform. Cells were suspended in 3 mL of 50 mM potassium phosphate buffer at pH 7.0 (28 (link), 29 (link)). The suspensions were centrifuged (3-18KS centrifuge, Sigma, Germany) at 10,000×g for 5 min at 4°C. Pellets were collected, washed twice, and then resuspended with the same buffer. Absorbance at 600 nm was measured and considered as A₀. One milliliter of the suspension was mixed with 200 μL of n-hexadecane and chloroform by vortexing for 120 s. The two phases were allowed to separate for 1 h at room temperature. The lower aqueous layer was cautiously shifted to hygienic tubes and absorbance was determined as A. Changes in the absorbance of probiotic bacterial suspension were recorded at 600 nm by a spectrophotometer.
Surface hydrophobicity (SHb%) was determined using the following formula:
Here, A₀ and A are the absorbances before and after extraction with chloroform and n-hexadecane, respectively. For statistical analysis, all SHb experiments were repeated three times.

Chitosan gels of different concentrations and molecular weights were produced: 2% MMW chitosan gel, 4% MMW chitosan gel, 2% HMW 80/1000 chitosan gel, and 2% HMW 80/3000 chitosan gel. For gel production, the required amount of chitosan powder was weighed and slowly added to a 3% acetic acid solution and stirred using a IKA EUROSTAR 200 digital stirrer set at 500 revolutions per minute (rpm) until a clear gel was formed. Since a large amount of air bubbles formed in the gel during stirring, the prepared gel was transferred to 50 mL centrifuge tubes and centrifuged for 2 min at 2000 rpm speed in a Sigma 3–18KS centrifuge to remove air bubbles from the gel.