Film-forming properties of guar gum, tara gum and locust bean gum

Galactomannan films have received great interests due to the sustainability, biodegradability and biocompatibility. Guar gum (GG), tara gum (TG) and locust bean gum (LBG), with a mannose/galactose (M/G) ratio of 2, 3 and 4, respectively, were systematically compared in their film-forming properties by characterizing the film-forming solutions and their resultant films. TG and LBG produced strong and flexible films with higher elastic modulus, tensile strength and elongation at break values than GG. These were caused by the bean-like morphology of GG film-forming solution due to the steric hindrance at lower M/G ratio (2), where polymer chains were hard to intertwine via inter-chain hydrogen bonding to form a strong network. Additionally, low-field nuclear magnetic resonance, fourier transform infrared spectroscopy, x-ray diffraction showed that increasing M/G ratio from 2 to 4 did not alter the basic chemical structure but led to the denser packing of polymer chains and lower crystallinity, as well as smoother and more compact morphology with fewer nodular structures in resultant films, which further verified the improvement in mechanical properties. These studies provide information on film-forming properties of galactomannans that guide reasonable selection of M/G ratio for special application as food packaging.