Characterization of chitosan films incorporating thyme oil and its effect on black olives

This study purposed to determine the impacts of chitosan film (CF) (2%, w/v) coating combined with thyme oil (TO) (0.2%, 0.5%, 1%, (v/v)) on the quality properties of black olives during storage (3 months, +4 and 25 degrees C). In the study, film properties (color, elongation at break, tensile strength, Young's modulus, and scanning electron microscope (SEM)) were analyzed. In the second stage, table olive samples were assessed for physicochemical (% moisture, pH, titratable acidity, color (L*, a*, b* and triangle E*), and microbiological (yeast-mold and total viable count) properties. The average elongation at break, tensile strength, and Young's modulus values of the obtained film coating samples were 70.02%, 16.66 MPa, 24.05 MPa for the CF; 74.69%, 14.79 MPa, 19.65 MPa for the CF + 0.2% TO; 77.21%, 10.79 MPa, 13.94 MPa for CF + 0.5% TO and 83.78%, 10.40 MPa, 12.69 MPa for CF + 1.0% TO group, respectively. Chitosan film sample was determined the highest tensile strength value and the CF+1% TO sample group was detected with the highest elongation at break. It was determined that the increase in the concentration of TO in the film increased the elongation at break and decreased the Young's modulus value. Scanning electron microscope (SEM) surface images of group CF film have a homogeneous and uniform structure but added thyme oil occured a heterogeneous appearance. The L*, a*, b*, and triangle E* values increased with the addition of thyme oil and a statistically significant difference was found between samples (P < 0.05). The highest moisture loss was determined in the control (uncoated) group. The highest decrease in yeast-mold and total viable count value was found 4.89 log CFU/g CF + 0.2% TO and 5.21 log CFU/g in CF + 1.0% TO sample at the end of storage period at 4 degrees C in table olives.