Molecular Structure, Physicochemical Characterization, and in Vitro Degradation of Barley Protein Films

Barley protein films were prepared by thermopressing using glycerol as a plasticizer. The combined effects of heating temperature and amount of plasticizer interacted to determine protein conformation and, subsequently, the properties of the film matrix. The film barrier and mechanical properties were systematically investigated using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), SDS-PAGE, and protein solubility tests. These experiments demonstrated that heat treatment induced barley protein unfolding and then protein aggregation and the formation of covalent disulfide bonds to enhance film strength. Increasing the amount of plasticizer reduced protein denaturation and limited protein interactions, resulting in significantly improved film flexibility at the cost of reduced film moisture barrier property and tensile strength. In vitro degradation experiments demonstrated that barley films were resistant in gastric conditions, yet can still be completely degraded by intestinal enzymes, and they possess low cytotoxicity to Caco-2 cells. The prepared barley films have potential for development as delivery systems for gastric-sensitive bioactive compounds to the intestine for release.