Insights into novel konjac glucomannan/zein/fatty acid composite films with excellent properties for food packaging

Conventional non-degradable petroleum-based packaging films cause serious food safety and white environment pollution problems. Thus, a series of novel konjac glucomannan (KGM)/zein (KZ) films with different chain lengths and concentrations of fatty acids were prepared using a solution casting method in this paper. Effects of stearic acid and lauric acid on the rheological properties of the film-forming solutions, structure, mechanical properties and water barrier abilities of KZ film were systematically studied. The apparent viscosities analysis indicated that all the film-forming solutions were typical non-Newtonian pseudoplastic fluids and KGM/Zein/fatty acid (KZ-FA) film solutions exhibited higher apparent viscosities than KZ film solution at the test FA concentration. Fourier transform infrared spectroscopy results confirmed that hydrogen bonds were the main intermolecular interactions among KGM, Zein and fatty acids. Differential scanning calorimetry and X-ray diffraction results demonstrated that the incorporation of fatty acids enhanced the thermal stabilities and crystallinities of KZ film. Scanning electron microscopy and atomic force microscope results revealed that the surface morphologies and roughness of KZ film were significantly affected after adding FAs. The rougher and more irregular surfaces were observed in the KZ films with stearic acid. Moreover, KZ film with 0.4% stearic acid exhibited higher surface hydrophobicity, mechanical, water resistance and water vapor barrier properties than other KGM-based films. These results suggested that KZ films with appropriate types and concentrations of fatty acids are promising food packaging films for the required properties.