Preparation And Application Of Two Slow-release Fresh-keeping Packaging Films With Molecular Sieve As Carrier

Because of the thin skin,soft flesh,high sugar and water content,and rich nutrition,grape is easily infected by pathogens and rots,and which results to serious economic losses.SO2 preservation is still the most effective preservation method in grape preservation,however,rapid release rate,short release period,instability,and grape bleaching damage remain unresolved after SO₂ treatment.With the public attention to the residual problem of SO2 in grape fruits,it is imperative to develop safe,non-toxic preservatives for preservation,this manuscript developed a sustained-release preservative with stable performance,long-lasting release and low residual SO₂.At the same time,the essential oil of eugenol replaced SO2 as a fresh-keeping agent was studied in the manuscript.This paper aims to provide a certain technical reference for the development of grape post-harvest preservation.The main research contents and conclusions are as follows:1.In this study,alkali treatment was selected to modify 13X molecular sieve.After design by the single factor and orthogonal tests experiments,the optimum modification process of molecular sieve was:1.5 mol/L of NaOH,90°C immersion temperature for 2 h.BET results showed that the specific surface area of modified molecular sieve increased76%,and the pore size increased 31%,and the pore volume was 4.5 times of the original materials.The hysteresis loop was formed and the number of mesopores was increased after modification in the middle pressure section?0.4<P/P₀<0.8?.The results of FT-IR and XRD showed that the alkali treatment did not destroy the structure of the molecular sieve,the peak shape of the corresponding characteristic peak remained intact,the intensity of characteristic absorption peaks and the relative crystallinity increased after treatment.SEM showed that the surface structure of modified molecular sieve was found to form more regular and smooth,the flocculent irregular species were removed,and the gap was more tidy,smooth,and the porosity was increased after modification.Therefore,it could conclude that adsorption capacity of the modified molecular sieve was significantly improved,it was suitable as a carrier material for the adsorbate2.Based on the matrix resin of LDPE and LLDPE,and 13X molecular sieve/eugenol composite was used as filler,the fresh-keeping films were formed after mixing with appropriate amounts of additives.The results of oxygen permeation and moisture permeability showed that the water vapor transmission and the oxygen transmission increased with the increase of the molecular sieve content,The results of bending and tensile properties showed that the stiffness of the film was slightly reduced with adding molecular sieves,but the flexibility and ductility were enhanced,and the overall mechanical properties were improved.The characteristic peak of PE and molecular sieve were detected in the FT-IR spectrum of the composite film,SEM showed that no obvious agglomeration occurred in the surface and cross section,it indicated that the molecular sieve could be well dispersed in the matrix resin.After applied to the preservation of grape it was found that the film with low molecular sieve content could delay rate,while the film with high molecular sieve content could completely inhibit the growth of Alternaria alternate in grape fruit 5.04%of eugenol was still remained in the composite film at the end of storage.3.Based on the carrier of 13X molecular sieve,a slow-release SO₂-ClO₂ formed in this manuscript.We selected three kinds of membrane materials with different permeability to oxygen and moisture.The components such as sulfite,sodium chlorate,slow-release agent and water absorbent were evenly distributed in the middle of the two layers through adhesives,and formed fast and slow release layers.Through the release rule of the two-component gas of SO₂ and ClO₂,we had determined that the process formula of the composite wrap film was pyrosulfite:sodium chlorate:molecular sieve=5:1:0.3.In addition,the prepared composite film was applied to the in vivo experiment after Alternaria alternata inoculation.The SO₂-ClO₂ film exhibited a significant preservation effect,and the decay rate was 0%throughout the storage period.The maximum SO₂ residue in grape fruits was 7.93 mg/kg,which was lower than the FDA standard for the residue of SO₂ in grape.