1. Cellulose is passed by D-glucopyranose β- A linear polymer formed by the connection of 1,4 glycoside bonds. The cellulose membrane itself is highly crystalline and cannot be gelatinized in water or formed into a membrane, so it must be chemically modified. The free hydroxyl at the positions C-2, C-3 and C-6 endows it with chemical activity and can be oxidized?reaction, etherification, esterification and graft copolymerization. The solubility of the?modified cellulose can be improved and has good film forming performance.
2. In 1908, Swiss chemist Jacques Brandenberg prepared the first cellulose film cellophane, which pioneered the development of modern transparent soft packaging materials. Since 1980s, people began to study modified cellulose as edible film and coating. Modified cellulose membrane is a membrane material made from the derivatives obtained after chemical modification of cellulose. This kind of membrane has high tensile strength, flexibility, transparency, oil resistance, odorless and tasteless, medium water and oxygen resistance.
3. CMC is used in fried foods, such as French fries, to reduce the absorption of fat. When it is used together with calcium chloride, the effect is better. HPMC and MC are widely used in heat treated food, especially in fried food, because they are thermal gels. In Africa, MC, HPMC, corn protein and amylose are used to block edible oil in deep fried red bean dough based foods, such as spraying and dipping these raw material solutions on red bean balls to prepare edible films. The dipped MC membrane material is the most effective in grease barrier, which can reduce the oil absorption by 49%. Generally speaking, dipped samples show lower oil absorption than sprayed ones.
4. MC and HPMC are also used in starch samples such as potato balls, batter, potato chips and dough to improve the barrier performance, usually by spraying. The research shows that MC has the best performance of blocking moisture and oil.Its water retention ability is mainly due to its low hydrophilicity. Through the microscope, it can be seen that MC film has good adhesion to fried food. Studies have shown that HPMC coating sprayed on chicken balls has good water retention and can significantly reduce the oil content during frying. The water content of the final sample can be increased by 16.4%, the surface content of oil can be reduced by 17.9%, and the internal oil content can be reduced by 33.7%.The performance of the barrier oil is related to the thermal gel performance of HPMC. At the initial stage of the gel, the viscosity increases rapidly, intermolecular binding occurs rapidly, and the solution gels at 50-90 ℃. The gel layer can prevent the migration of water and oil during frying. Adding hydrogel to the outer layer of the fried chicken strips dipped in the bread crumbs can reduce the trouble of the preparation process, and can significantly reduce the oil absorption of the chicken breast and maintain the unique sensory properties of the sample.
5. Although HPMC is an ideal edible film material with good mechanical properties and water vapor resistance, it has little market share. There are two factors that restrict its application: first, it is a thermal gel, that is, a viscoelastic solid like gel formed at high temperature, but exists in a solution with very low viscosity at room temperature. As a result, the matrix must be preheated and dried at high temperature during the preparation process. Otherwise, in the process of coating, spraying or dipping, the solution is easy to flow down, forming uneven film materials, affecting the performance of edible films. In addition, this operation should ensure that the entire production workshop is kept above 70 ℃, wasting a lot of heat. Therefore, it is necessary to reduce its gel point or increase its viscosity at low temperature. Second, it is very expensive, about 100000 yuan/ton.