Study On Pullulan Composite Film Produced By Dip Coating And Film Coating For Keeping Fruit Fresh

In this paper, the edible composite films were made from pullulan, sodium alginate and sodium carboxymethylcellulose by dip coating.The films were determinated with thickness, tensile strength, Water vapor permeability, and oxygen barrier as index. The effects of film-forming medium, film-forming method, colloid formulation, concentration, drying temperature and time on properties of composite films were studied in this paper. The results indicated that the suitable conditions of film-forming were: the proportion of Pul, Alg and CMC(5:2:3); the total concentration of polysaccharides in 100mL Water (2%-2.2%); coating film on glass by dipping it into solution; then drying it for 90min at 60℃.The film forming solutions based on pullulan treated by microwave were studied. The results showed that the tensile strength and oxygen barrier of the edible films increased, the water vapor permeability decreased after the film forming solutions treated by microwave. The microstructure of SEM indicated that the compaction of films was enhanced by microwave treatment. The film could get better mechanical and barrier properties when the film forming solutions were treated by microwave at 450W and 20s.Dangshan pear and Yangshan honey peach coated with pullulan composite film during cold storage were studied in this experiment. Sensory evaluation and chemical analysis were used to evaluate the effect of edible coating for preserving Dandshan pear. Through orthogonal experiment, the best formulation for preserving Dangshan pear was obtained, which was pullulan content 1.15g, sodium alginate content 0.6g and CMC content 0.6g in 100mL water. The results showed that the pullulan coating was effective in keeping Dangshan pear fresh and could significantly extend the shelf life of Dangshan pear stored at 2±0.5℃. The coating treatments could slow down the changes of the sensory quality; control the rates of drop of reducing sugar, total soluble solids and organic acid, and inhibit the activities of enzymes such as POD and PPO. When the film forming solutions of the best preservation formulation were treated by microwave (450W and 20s), each index of pears treated were better than the control. On the basis of these experiments about Dangshan pear, the best preservation formulation could also be used on preserving honey peach. The results based on different fruits with pullulan coating explained the fact that pullulan edible coatings could be used as preservatives on respiratory climacteric fruits.