Fabrication And Applications Of Layer-by-layer Edible Fresh-keeping Coatings

Recently,the market of fresh fruits including lightly processed fruits has been expanded greatly due to the increase of consumers' demand for fresh-like products.However,the post harvest process may result in consequence such as enzymatic browning,off-flavor and texture breakdown.Those phenomena have prompted researches on prolonging the shelf-life of fruit products.Edible coatings have been particularly considered due to their ability of improving food quality,moreover,it is a healthy and simple method.Layer-by-layer(LBL)electrostatic deposition technique is based on the alternate deposition of oppositely charged polyelectrolytes,the method is very simple and can be operated on fruits easily.Edible coatings were fabricated through LBL electrostatic deposition technique.They were characterized and their preservation effects on fruits were also analyzed.The conducted experiments and conclusions are as following:1)SA,CMC and PAAS were assembled with CS through LBL method respectively to fabricate edible coatings.All those coatings are smooth and laminar.Moreover,the water solubility and transmittance of(CMC/CS)3 coating is lowest between all these coatings and the coating shows good preservation effect on tangerines.Thus,the most reasonable polyanion material among SA,CMC and PAAS is CMC.2)PEM coating(that is(CMC/CS)3 coating)was fabricated.The antibacterial rate of PEM coating against Gram-negative bacteria is more than 95%.Slightly scratched coating can self-heal rapidly after the stimulation of water and its self-healing ability is not related to the layer number.Moreover,the coating can heal damage whose width is far bigger than the thickness.3)Ascorbic acid and calcium chloride(CaCl2)were mixed with CS respectively and the mixed soutions were employed on fresh-cut apples directly to form edible coatings.Both of the coatings have good adhesion to apple slices.Meahwhile,the CaCl2-CS coating shows good anti-browning and fresh-keeping ability.The coating inhibit weight and nutrition loss of fresh-cut apple as well.Thus,CaCl2 is a good option as fresh-keeping agent.4)PEM edible coating containing CaCl2 was fabricated throught LBL method.The coating is imporous and laminar,moreover.the coating can self-heal its morphology and mechanical properties effectively and the self-healing ratio of tensile strength reached to 87.4%.The edible coating shows good fresh-keeping ability.These findings indicate that this work have fabricated and characterized the edible,antioxidative,antibacterial,self-healing coating successfully.The coating have great meaning to the fresh-keeping field.