Preparation of Chitosan as Insoluble Edible Film

At present, China's food packaging is still generally used plastic bags, plastics are not only easy to produce harmful gases and odors, a certain degree of toxicity to the human body, and after use in the environment is not easy to decompose and cause environmental pollution.

Edible packaging materials, like synthetic packaging materials, can prevent foods from absorbing water or water, prevent oxidation and odor, and can also be used as carriers for food flavors, nutritional enhancers, and other ingredients. Edible packaging materials are receiving increasing attention.

However, due to the fact that edible films made of ordinary starch are water-soluble, the foods to be packaged are required to be dried beforehand, which affects the flavor and quality of foods; and films made of collagen have high manufacturing costs and are not ideal in appearance. Its application is limited.

As a natural polymer membrane material, chitosan can change the water insolubility of the membrane if starch is added, and it can be used as an edible packaging material with high mechanical strength.

The composite membrane synthesis process experimental results show that the higher the chitosan content, the better the tensile strength and water insolubility of the membrane. When the mixing ratio (W/W) of chitosan to water starch is less than 1:1, the mechanical strength and water insolubility of the film begin to decrease.

Above this ratio, the strength of the film does not change significantly, but as the starch content increases, the film strength decreases and the water solubility increases dramatically. When chitosan is mixed with starch, the higher the drying temperature, the higher the tensile strength of the film after water immersion, and therefore the drying temperature should exceed 80°C.

After the film is made, it is naturally dried or heat-dried, which affects the mechanical strength of the film. The chitosan membrane is water-absorptive, and there is a strong hydrogen bond in the crystal region of the chitosan molecular chain. The adsorption of water is mainly in the amorphous region. The heating of the membrane reduces the amount of adsorbed water in the membrane and increases the crystallinity of the membrane, so that the membrane strength increases.

Chitosan is a natural film-forming substance, the film is insoluble in water, and its content is increased, which is beneficial to improve the water-insolubility of the composite film. The problems related to the production process of composite membranes Chitosan is first dissolved in acetic acid and then mixed with starch. The concentration of chitosan prepared at this time should not exceed 5%. Otherwise, the viscosity of the solution may be too high, resulting in processing difficulties.

After the chitosan is formed into a film, HCl is present on the amino group. Treatment with alkali removes the HCl on the amino group to make it a free amino group, and the non-ionization of chitosan makes it lose its water solubility. Therefore, if the prepared chitosan-starch composite membrane is not subjected to lye treatment, the membrane swells very much in water and immediately loses strength after being wetted. Therefore, the film must be soaked in 4% dilute lye for a period of time.

The mechanical strength and water insolubility of the chitosan-starch composite membrane were affected by the ratio of chitosan and starch. The optimum mass ratio of the mixture was 1:1, and the drying temperature was above 80°C, which could significantly improve the mechanical strength; The sugar should be formulated into an acetic acid solution with a concentration of less than 5% and mixed with the starch; the alkali treatment process is finally required to prevent the expansion of the composite film in water.

The film thus obtained has high mechanical strength, water insolubility, and gas and moisture barrier properties. After being left in water for a long time, its performance does not change significantly. Even if it is heated in boiling water for a while, its water solubility does not change significantly. .