Abstract
The aim of this work was to evaluate the release of Rosmarinic acid (RA) from pure pea starch (PS), pure chitosan (CH) and composite films (CH:PS) enriched with thyme extract in different food simulants. Moreover, the effect of the addition of Tannic acid (TA) on pure CH and composite films was studied. PS, high molecular weight CH films and PS:CH composite films (4:1 ratio) with and without TA (polymer:TA ratio, 1:0.04) were prepared by castingand keeping the total amount of polymer constant. Films were conditioned at 25ºC and 75% relative humidity and were evaluated in terms of optical properties, oxygen and water vapor permeability and moisture content. The release study of RA was studied at 20ºC after immersion of the different films during 24 hours in three different food simulants (water, 10% and 20% ethanol) by means of HPLC. Results showed that the addition of thyme extract and TA to films did not relevant change their barrier properties but films became less transparent and yellowness due to the incorporation of the phenolic compounds. The release of RA depended on both the film composition and the simulant. Thus, the highest amount of RA was released from pure PS films, because the matrix network became hydrated very fast, leading to a weakening structure which promotes a fast diffusion of RA. On the other hand, release of RA was inhibited in pure CH films while the composite films showed intermediate results. The increase of the RA release when the ethanol concentration rises in the food simulant agreed with the decrease in the solvent polarity and the subsequent increase of the chemical affinity and solubility of RA with the solvent. The tannic acid promoted a closer matrix structure, due to the cross-linking effect. These changes in the film structure affected the diffusion of the RA through the polymer matrix into the outer solution, which was diminished.
