Vanillin as a natural cross-linking agent in chitosan-based films: Optimizing formulation by response surface methodology

Abstract One way of improving mechanical and water barrier properties of chitosan films is through cross-linking reactions. Cross-linking agents usually used for this purpose include glutaraldehyde, glyoxal, and formaldehyde, which may cause some undesirable side effects and are consider health hazards. Hence, the objective of this work was to optimize the formulation of chitosan (CH) films with vanillin as a natural antioxidant cross-linking agent, to simultaneously improve their physical, barrier, antioxidant and mechanical properties. Three parameters were studied at three levels: vanillin content (0, 25 and 50% w/w chitosan), glycerol content (30, 45 and 60% w/w chitosan) and drying temperature (35, 50 and 65 °C). Response surface methodology (RSM) and desirability function (D) were used to find the levels of each factor that simultaneously optimize different properties of the films: opacity value, total soluble matter (TSM), Young modulus (YM), T 0 and T max parameters (obtained from thermogravimetric analysis), water vapor permeability (WVP), total phenolic content (TPC) and antioxidant capacity by DPPH method. Fifteen formulations combining the studied factors were prepared according to a Box-Behnken design. An optimal chitosan film formulation was found, with vanillin content of 37.5% (w/w of CH), glycerol content of 45% (w/w of CH) and drying temperature of 57.5 °C. RSM approach using the desirability function was found to be an effective tool to investigate changes in films properties and to search for the optimal active chitosan film formulation with a natural cross-linking agent, such as vanillin.