Structure and properties of hydroxypropyl methyl cellulose—Sodium caseinate film cross-linked by TGase

Abstract

• The number of entanglement within the films increased by increasing the protein concentration. • High concentration of HPMC were a limiting factor for protein–protein interaction. • Increasing HPMC concentration, increased the stiffness of the films and decreased the elongation at break. • The different ratio of HPMC/CS film did not affect the permeability to water vapour of the films. The objective of the present work was to study the influence of composition of hydroxypropyl methyl cellulose (HPMC)–sodium caseinate (SC) edible films cross-linked by transglutaminase enzyme (mTGase), on film structure and functional properties. To this end, SDS–PAGE, scanning electronic microscopy and mechanical analysis at low and at high deformation were performed. The thickness, solubility and water vapor permeability of films were also studied. Our results show that the enzyme mTGase allows the formation of a stiffer film, which behaves more like a solid material than does a film not cross linked with TGase. HPMC may well act as fillers of the protein network, affecting the mechanical spectra of the film as a function of the HPMC/SC ratio. In the presence of high HPMC concentrations the mechanical spectra of the blends may be similar to HPMC film. Only in the presence of high SC concentration does the order of relaxation ( α ) considerably increase from 0.0464 ± 0.002 to 0.111 ± 0.002 showing an increase in intermolecular cross-links. Mechanical properties measurement confirmed the positive influence of polysaccharides on protein film stiffness, and its negative effect on film extensibility. Different ratios of HPMC/SC did not affect film water vapor permeability.