Polylactic Acid(PLA) Biodegradable Active Packaging And Its Application In Fruits And Vegetables

According to FAO statistics in 2016,in China,the production of fruits and vegetables was reached 708 million tons,accounting for 39%of the world's output,far exceeding India?10%?and the United States?4%?.Fruits and vegetables are a type of product that can perform respiratory activities and maintain an active metabolism even after harvesting.Because of its soft texture,high physiological activity,high sensitivity to microorganisms and mechanical damage,it is perishable after harvesting,which greatly limits its market demand and consumer access.Therefore,it is necessary to find a way to extend the shelf life and maintain the quality of fruits and vegetables.Modified atmosphere active packaging is a type of packaging that can independently adjust the internal atmosphere.The film has a suitable permeability and incorporated with antibacterial and antioxidant ingredients,delaying the microbial growth and spoilage,which has a positive impact on the quality and safety of fruits and vegetables.By adjusting the gas and water vapor transmission rate,which effectively establishes a suitable atmosphere and avoids the accumulation of harmful gases in the packaging microenvironment.The permeability of the packaging is determined by various factors such as the weight and physiological characteristics of fruits and vegetables?breathing rate,maturity stage?,environmental conditions?temperature,relative humidity?,and characteristics of packaging films.Therefore,the following biodegradable materials were selected:?1?polylactic acid?PLA?,?2?poly?3-hydroxybutyrate-4-hydroxybutyrate??P3,4HB?,?3?poly?butylene succinate adipate??PBSA?,and for the development of new fruit and vegetable fresh-keeping packaging.This article was based on polylactic acid?PLA?,the second and third chapters focused on the modification of PLA-P3,4HB and application in peaches.The fourth chapter was the modification of PLA-PBSA,and the application in broccoli.Both PLA-based active films were prepared by blending extrusion and casting methods.The following were the main research contents and results of this article:?1?PLA-P3,4HB film was prepared by melting extrusion.Different proportions of chain extender?ADR4300?and plasticizer?BXA?were added to regulate the gas and water vapor permeability,and the ginger and angelica essential oil were selected as active ingredients.The barrier properties,mechanical properties,thermal stability,microstructure and infrared characterization were investigated.The results showed that 0.2%chain extender,3%plasticizer,PLA:P3,4HB?4:1?,and 3%essential oil formula,had a good film-forming effect.PLA-P3,4HB based film improved the brittleness,and had higher gas and water vapor transmission rates.The incorporation of two types of active essential oils has no effect on the chemical structure and the microstructure of the composite material.PLA-P3,4HB-AEO film showed the best water vapor and gas transmission rate,showed the optimum application value.?2?Study on the research of PLA-P3,4HB based films on peaches.Through low-field nuclear magnetic resonance?LF-NMR?,high-speed,non-destructive,and visual methods were used to track the moisture migration.Malonaldehyde,membrane permeability,hardness,soluble solids,polyphenol oxidase and lipoxygenase were selected to evaluate the fresh-keeping effect.The results showed that,the peaches packaged with PLA-P3,4HB active films,due to the suitable gas and water vapor permeability?WVP?,which effectively reduced its respiration and maintained the content of hardness and soluble solids.Angelica essential oil as an active substance reduced the process of membrane lipid peroxidation and maintained a high level of antioxidant.The group of PLA-P3,4HB-AEO film,nuclear magnetic resonance imaging showed the lightest proton density color.This indicated that the higher proportion of bound water in the fruit,and exhibited a high nutritional value,which effectively delayed the spoilage process of the peach and extended the shelf life.?3?PLA-PBSA-based active film was prepared using melt extrusion method.PLA as the basic material,PBSA as the modified material,ginger and tea tree essential oil as the active ingredients,then blended with chain extender.Mechanical properties,microstructure,antioxidant and barrier properties were investigated.The results showed that the two active materials did not change the microstructure of the film,had good compatibility,and improved the oxidation resistance of the film.The oxygen transmission rate?OTR?and WVP of the modified film were greatly improved,of which GEO-PLA/PBSA film had a high CO₂/O₂ breathability ratio?30:1?,which was suitable for the application of high respiratory transition fruits and vegetables.In addition,the GEO-PLA/PBSA film showed strong antioxidant properties,effectively delayed the loss of chlorophyll and Vc,suppressed the increase of MDA content,and prolonged the shelf life of broccoli for 2-3 days.