Delonix regia galactomannan-based edible films: Effect of molecular weight and k-carrageenan on physicochemical properties

Delonix regia galactomannan (DRGM) hydrolysates were blended with k-Carrageenan (k-Carr) to evaluate the DRGM molecular weight (M-w) reduction effect and the interaction between the polysaccharides on the properties of film forming solution (FFS) and edible films produced thereof. The DRGM M-w was enzymatically reduced obtaining 3 fractions: high (HMWH), medium (MMWH), and low (LMWH) M-w hydrolysates. The FFSs viscosity was lower as the DRGM M-w decreased. The addition of k-Carr to the DRGM showed evident interaction between them, since they formed gels at lower temperature than k-Carr. The MMWH FFS blend apparent viscosity (0.044 Pa s) was higher than the MMWH (0.029 Pa s) and k-Carr (0.023 Pa s) FFSs at 10 s(-1) shear rate. Moreover, the moduli, gelling and melting temperatures decreased compared with the k-Carr FFS gel. From the FFS, colorless and transparent galactomannan-based films were obtained that turned to a slightly yellow color when blended with k-Carr. The galactomannan interaction with k-Carr was identified by the shift on some FTIR bands. On other hand, the M-w reduction increases the films solubility from 69.10% to 76.08% and when blended with k-Carr the solubility reaches 100%. The water vapor permeability (WVP) of native DRGM film increased from 7.55 x 10(-11) g/(m*s*Pa) to 12.62 x 10(-11) g/(m*s*Pa) for HMMH and MMWH films, respectively, although the LMWH WVP decreases to 9.60 x 10(-11) g/(m*s*Pa). In all cases it was found that the k-Carr blended with the DRGM hydrolysates decrease the WVP of the films. Finally, although the FFSs rheological properties decreased by M-w, reduction, the films mechanical properties did not show significant changes.