Effects of combined pullulan polysaccharide, glycerol, and trehalose on the mechanical properties and the solubility of casted gelatin-soluble edible membranes

Protein-biodegradable edible membranes are environmentally friendly and economical to the food packaging industry compared with traditional packaging materials. In the present study, the mechanical properties (including flexibility index, viscosity index, brittleness index and texture comprehensive index) and solubility of casted gelatin-soluble edible membranes were investigated as functions of the contents of pullulan polysaccharide (0.0%, 0.5%, 2.5%, 5.0%, 7.5%), glycerol (0.0%, 0.5%, 2.5%, 5.0%, 7.5%), and trehalose (0.0%, 0.5%, 2.5%, 5.0%, 7.5%). The results indicated that the texture comprehensive index of the membrane increased from 4.65 ± 0.22 to 5.85 ± 0.10, while solubility decreased from 10 to 9.0 ± 0.20 as the pullulan polysaccharide's concentration increased (0%–2.5%), that it had an adverse effect on solubility. For the membrane with glycerol, the texture comprehensive index increased at a low glycerol concentration range (0%–2.5%), while decreased at a high concentration rage (2.5%–7.5%). Trehalose had similar effect to glycerol on the texture comprehensive index and a similar effect to pullulan polysaccharide on solubility. The resultant membranes with better flexibility, less brittleness, and greater solubility could be used to pack instant coffee, noodles, milk powder, and other food in food applications. Practical applications With the intensification of a series of pollution problems caused by plastic products and people's attention to food safety, various countries are striving to find a "green packaging material." In many "green packaging," the edible film attracts much attention. Are natural edible substances (such as polysaccharides, proteins, and lipids) as raw materials, added edible plasticizers, crosslinking agents, etc., through different molecular interactions, and wrapped, coated, micro-capsules and other forms cover the surface or inside of foods to block the penetration of moisture, oxygen, or various solutes to protect them. The current study is mostly a single base film with gelatin as the main body, and there are significant differences in their properties. For example, the protein film has poor water resistance, but the gas barrier property is relatively strong. The water resistance of the large polysaccharide film is not good, but there are some outstanding advantages. For example, its heat sealability and water solubility are better. Gelatin, glycerol, pullulan, and trehalose are compounded to make edible films. Their mechanical properties and water solubility are good. They are suitable for packing instant coffee, instant noodles, instant milk powder, and other food materials.