Optimization of chitosan film and effect of mixing ratio in chitosan-polyvinyl alcohol coating on internal quality parameters of eggs

To optimize the chitosan film with level, molecular weight and solvent and then use it in the composite coating in the appropriate mixing ratio, in a completely random design using the 23 factorial methods with 3 factors, level (2 and 4 %), molecular weight (high and low) and solvent (acetic acid and citric acid), was carried out to investigate the physical and mechanical properties of chitosan film. Then the selected film was incorporated in the chitosan-polyvinyl alcohol composite coating, aiming of achieving the optimal mixing ratio and affecting the internal quality parameters of eggs, in a completely randomized design with 6 treatments including uncoated eggs (control), coated with a pure coating of chitosan and polyvinyl alcohol separately as well as composite coatings of chitosan: polyvinyl alcohol (25, 50 and 75% of each component). The results showed the highest tensile strength and Young's modulus (0.16 and 2.45 MPa, respectively) and water vapour impermeability (2.17.10-8 g/msPa) in 4% chitosan film with high molecular weight dissolved in acetic acid and the highest elongation at break (54.33%) was observed in chitosan film in citric acid (P<0.05). Also, eggs coated with chitosan-polyvinyl alcohol at 25:75 have the lowest weight loss (0.57%) and the highest values of Haugh unit (61.00) and yolk index (0.37) (P<0.05). Therefore, it is possible to use chitosan-polyvinyl alcohol composite coating in the optimal mixing ratio (25% chitosan: 75% polyvinyl alcohol) as a packaging material to extend the shelf life of eggs for at least 2 weeks at ambient temperature.