| The change of food acidity is the first sign of food deterioration,and the development of acid-base indicators has become an important research direction to detect food freshness.Intelligent color film is a kind of membrane material which uses the color indicator to detect the change of food p H value and evaluate the freshness of food.As a rich renewable resource,cellulose has excellent properties and has been widely used in our daily life,such as papermaking,cloth,film,coating,tissue,medicine and polymer materials.Cellulose coloring film can effectively and environmentally friendly use cellulose,through the change of food freshness to release acid and alkaline gas,food packaging environment p H change,to achieve food freshness detection,which provides a new idea for the field of food packaging and food testing.In this work,different types of cellulose were used as matrix,different types of ionic liquids were used as dissolution system,and natural chromogenic agents extracted from natural plants were added.The effects of cellulose matrix,dissolution system and natural chromogenic agent content on p H coloration,crystallization,UV resistance and oxidation resistance of cellulose/shikonin composite films were studied.A multi-functional cellulose/shikonin regenerated composite food color packaging film which can detect food freshness was prepared.The results show that compared with Amim Cl and Emim Ac,the regenerated cellulose membrane treated by Bmim Cl is smoother,has better crystallization and UV resistance,higher color sensitivity and better color performance in the p H range of 6-8.Compared with cotton fiber matrix and microcrystalline cellulose matrix,hemp cellulose matrix has great advantages in p H environmental chromogenic properties,anti-oxidation and anti-UV properties,the L* value of the chromogenic film still changes regularly in the neutral p H environment in the range of 6-8.The change of shikonin content has a certain effect on the p H coloration performance and antioxidant performance of cellulose/shikonin composite film,the shikonin contents reaches 5%,the color performance of composite film is relatively stable,and the value of shikonin begins to have regularity with the change of p H environment.By studying the effects of different cellulose matrix,ionic liquid dissolution system and shikonin content on cellulose chromogenic composite film,the cellulose/shikonin composite film with excellent chromogenic properties was selected to prepare cellulose/shikonin composite membrane.The deterioration process of fresh shrimp meat was detected,and the effect of the color film on the detection of food freshness was verified.And the results show that the prepared color film has a certain application value for the detection of food freshness.In order to enrich the dissolution system of regenerated cellulose and improve the dissolution efficiency of cellulose,DMF and DMSO co-solvents were added to the original ionic liquid solvents.The effects of the two co-solvents on the crystallization,chromogenic properties and UV resistance of cellulose regenerated composite films were studied and compared.The results show that the addition of two kinds of co-solvents can improve the dissolution rate of the fiber.When the addition ratio of DMF is 30% and that of DMSO is 50%,the effect on the degree of dissolution is small,and the dissolution time were significantly reduced.The addition of two kinds of co-solvents effectively improved the dissolution rate of cellulose on the premise of keeping good crystallization,UV resistance and chromogenic properties of cellulose composite membranes,which provided a new dissolution system for the preparation of regenerated cellulose chromogenic films. |
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