Influence of storage conditions on functional properties of multilayer biopolymer films based on chitosan and furcellaran enriched with carp protein hydrolysate

In this paper, the impact of water activity regarding storage environment on mechanical and water properties is presented, as well as the structural and morphological features of triple-layered films. Furcellaran (FUR), chi-tosan (CHIT) and carp skin gelatin hydrolysates (HGEL) were used for the production of the film. The films were made using a casting method, in which three successive stages were applied. First stage: preparation (pouring onto the mould) of 1st layer - FUR + HGEL, second: 2nd layer preparation (pouring onto 1st layer) - FUR, and third: 3rd layer (pouring onto 1st layer) - CHIT + HGEL. The second and third steps began after gelation of the previously poured layer. The drying process of the film was carried out for 24 h under a fume hood at room temperature. The mechanical properties of control sample was: tensile strength The control sample has tensile strength 7.76 +/- 0.35 MPa, elongation at break - 3.69 +/- 0.33%, maximum breaking load - 15.86 +/- 0.58 N. Water properties of control sample - water absorption a solubility were 25.80 +/- 1.14% and 52.91 +/- 1.31%, respec-tively. Reducing the water content in the film increased its tensile strength (from 7.76 +/- 0.35 MPa for the control film to 14.36 +/- 0.07 MPa) and elongation at break (from 3.69 +/- 0.34% for the control film to 8.74 +/- 0.69%). Reducing water content in the film also decreased its ability to absorb water, which is crucial in the case of biodegradable films due to their hydrophilic nature. The multimolecular sorption of the films was described using the BET model. Structural and morphological changes observed on the basis of surface and cross-section photographs of the films confirm the negative impact of high water activity on the film and its mechanical parameters.