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

Abstract

Delonix regia galactomannan (DRGM) hydrolysates were blended with k-Carrageenan (k-Carr) to evaluate the DRGM molecular weight (Mw) reduction effect and the interaction between the polysaccharides on the properties of film forming solution (FFS) and edible films produced thereof. The DRGM Mw was enzymatically reduced obtaining 3 fractions: high (HMWH), medium (MMWH), and low (LMWH) Mw hydrolysates. The FFSs viscosity was lower as the DRGM Mw 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 Mw 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 × 10−11 g/(m*s*Pa) to 12.62 × 10−11 g/(m*s*Pa) for HMMH and MMWH films, respectively, although the LMWH WVP decreases to 9.60 × 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 Mw reduction, the films mechanical properties did not show significant changes.