Determination of antimicrobial efficiency and film properties of borax added thermoplastic starch films

In recent years, it is known that various substances with antimicrobial properties have been added to starch films to develop packaging materials with antibacterial and antifungal properties. In the studies, it has been determined that borax and boron derivatives have antimicrobial activities and it has been reported that they can be used in food packaging materials for this purpose. In addition, the antimicrobial properties of packaging and packaging products containing boron compounds in food packaging materials have been examined in previous studies and shown in the literature. In this thesis, in order to gain antimicrobial properties; 5%, 10% and 15% sodium tetraborate (borax) was added into packaging solution containing 8% thermoplastic starch (TPS) to produce packaging films by pouring method. In the determination of the antibacterial and antifungal properties of the produced TPS-boron films; E. coli ATCC 25922, E. coli O157: H7 NCTC 12900, Staphylococcus aureus ATCC 6538, Salmonella Typhi ATCC 14028, Schizosaccharomyces pombe, Candida albicans ATCC 10351, Saccharomyces cerevisiae, Aspergillus flavus diffusion method applied on. In addition, the optical properties, mechanical properties and water vapor permeability of the films were investigated. It is determined that all TPS-borax films tested in the study showed antibacterial activity against S. Typhi ATCC 14028. In addition, 10% and 15% borax concentration films showed antimicrobial activity on E. coli O157: H7 NCTC 12900, while no borax dose applied did not indicate an inhibitory effect on E. coli ATCC 25922 and S. aureus ATCC 6538. On the other hand, when the antifungal activities of the films are examined; It was determined that the films in which all borax doses (5%, 10%, 15%) were applied showed an inhibitory effect on S. pombe and C. albicans ATCC 10351. However, it was determined that no borax dose applied did not impart antifungal properties to TPS-borax films against S. cerevisiae, A. flavus and P. digitatum. It was determined that the inhibition effect of sodium tetraborate (borax) increased with increasing dose. Among the test microorganisms, it was determined that S. pombe was the most sensitive microorganism to the thermoplastic borax added films with a 52.19 mm inhibition zone. The thickness of the films produced decreased with the effect of the added borax mineral, and the thickness amount of 0.263 mm in the control group showed a decreasing trend up to the range of 0.203-0.205 mm in the 10% and 15% borax films as the boron concentration increased. While an increase was detected in the L* and b* color values, a decrease was observed in the a* value and it was determined that the films took on a yellowish color. The opacity value, which was 0.383 in the control groups, decreased significantly with the addition of boron, while the borax amount of the films was 15%, the opacity value decreased to 0.006. The process of adding boron mineral to the films decreased the water vapor permeability compared to the control group, increased the mechanical properties and increased the elasticity coefficient of the film by 20%. In conclusion, improvements in optical, mechanical and water vapor permeability properties were determined with boron salt added in TPS-borax added films. When these films are considered on the basis of both antimicrobial activity and film characterization properties, it is believed that TPS films containing 10% and 15% sodium tetraborate may be promising candidates as antimicrobial packaging materials. Boron mineral derivatives offer the opportunity to be cost-effective, reliable and effective agents for developing antimicrobial starch films. Keywords: Borax, thermoplastic starch, antimicrobial activity, active packaging, antimicrobial films.