Physical, mechanical properties and antifungal activity of bioactive film containing Williopsis saturnus var. saturnus antagonistic yeast

The mold growth leading physical, chemical and sensory changing in food products and carrying health risks with toxin production is a main problem in the food industry. In our study, as an alternative solution for this problem, bioactive packaging materials were developed by incorporating Williopsis saturnus var. saturnus at different concentrations (0; 3.2; 6.8 and 8.8 cfu/cm2) into whey protein concentrate (WPC) based edible films. Following packaging of the developed edible films with vacuum or non-vacuum packages they were stored at 25 °C for 28 days. Viability of W. saturnus var. saturnus and the number of total bacteria, lactic acid bacteria, mold and yeast in the films were investigated during the time of the storage. Moreover, the antifungal activity of the films incorporated with W. saturnus var. saturnus were also tested against Penicillium expansum and Aspergillus niger at two different pH values (4.5 and 5.2) by disk diffusion method. The effect of the antagonist yeast occurance in the film on physical properties (thickness, water vapor permeability, water solubility, water activity) and microstructural properties of the films were analyzed using Scanning Electron Microscope (SEM). The optical properties and the mechanical properties in terms of tensile strength and percent elongation at break of the film samples were also observed by L*, a*, b* color measurements and by using the Instron, respectively. The results showed that bioactive WPC films containing 6.8 and 8.8 log cfu/cm2 W. saturnus var. saturnus were able to maintain more than 36% and 60% of the initial antagonist yeast population, respectively. In addition, the developed films incorporated with the antagonist yeasts reduced mycelium growth of P. expansum and A. niger on the medium by more than 29% and 19% at pH 4.5, respectively. Incorporation of more than 3.2 log cfu/cm2 antagonist yeasts significantly increased water vapor permeability of the films (P<0.05). However, 28 days of storage has led to 9% improvement in the barrier properties of the films. Increased population of the yeasts also significantly increased percent water solubility of the films (P <0.05). Moreover, the distribution of the antagonistic yeasts in the films presented homogenous microstructure at SEM observation. Increasing concentration of the killer yeasts in the films presented a significant tendency to greenness and yellowness as well as lightness values (P<0.05). The concentrations more than 3.2 log cfu/cm2 of killer yeast population in the films significantly increased tensile strength but decreased percent elongation at break (P<0,05). In conclusion, this study showed that bioactive films by combination of edible films and bioactive agents in the concept of the hurdle technology have a coating potential on the food products to eliminate mold spoilage. Keywords: Edible film, biocontrol, killer yeast, antifungal