Investigation of antimicrobial and structural properties of edible films obtained by partial hydrolysis of food proteins and incorporation of active agents

Packaging is of great importance in order to prevent quality losses and to prevent microbiological contamination in food storage and transportation processes. Interest in edible films and coatings has increased in recent years due to their wide functionality and to reduce the damage caused by synthetic packaging to the nature as well. In this study, it was aimed to produce and characterize edible films and coatings with antimicrobial properties by the incorporation of marjoram (Origanum majorana) oil and thyme (Thymus vulgaris) juice using thermal denaturation and enzymatic hydrolysis methods from whey and soy proteins. The physical properties of the films and changes in protein structure were examined. Moisture loss in cheese samples were evaluated by texture analysis after coating of cheddar cheese. In addition, the antimicrobial activities of the films against Aspergillus niger were investigated. The originality of the study comes to the forefront with the creation of edible films from both animal and vegetable-based proteins, not heat treatment, which is often expressed in the literature, but by enzymatic hydrolysis. The protein solutions showed shear thinning fluid properties in the viscosity measurement performed after determination of appropriate compositions for film solutions. When protein compositions in solutions were examined using chromatography and spectroscopy, it was determined that glycerol and antimicrobial agents binded protein and caused changes in protein secondary structures. In the physical analysis of the edible films obtained, thickness and color measurements were made. As a result, the addition of antimicrobials had no effect on the film thickness, while the glycerol increased the thickness slightly. The highest color change and high yellowness index was observed in soy-based films, and the least color change was observed in WPI films. Depending on the texture analysis of the cheddar cheese applied to the coating, it has been observed that the marjoram oil hardened the film surface and thus caused excessive drying in the cheeses. The least loss of moisture was achieved in enzymatic hydrolysis. As a result of antimicrobial analysis, it has been observed that marjoram oil and thyme juice had no antimicrobial activity against A. niger, but could repress sporulation in some film formulations. With all these findings, it is necessary to conduct more detailed experiments and improve the properties of films and coatings.