Preparation Of Chlorine Dioxide Cotrolled Release Corrugated Box And Microcapsule And Its Application In Fruit Preservation

Fruit is one of the important sources of carbohydrate,vitamin,antioxidant and other nutrients.Due to rich nutrition,high moisture content,and easy to be damaged by machinery in the process of picking and storage,it is easy to be infected by pathogenic bacteria,resulting in large loss.At present,the strategies to control the microbial infection of fresh fruits and vegetables are cold storage and antimicrobial agents.However,the cold storage demands expensive equipments.At the same time,the direct spraying of antimicrobial agents on the surface of fruits and vegetables has a short acting time and is easy to cause security risks.Therefore,it has become a research hotspot to add antimicrobial agents into packaging materials.When packaging materials are combined with antimicrobial agents,it is usually necessary for antimicrobial agents to closely contact products to effectively inhibit the growth of surface microorganisms.However,fresh fruits and vegetables often have large specific surface area and irregular shape,so it is impossible to ensure their effective contact with packaging materials.Non direct contact volatile or gaseous antimicrobial agents can spread to the exposed surface of products surface.This is a better choice for antibacterial packaging.And the key of this technology is to control the release of antibacterial drugs under appropriate conditions,so that the release is stable and continuous.ClO₂?chlorine dioxide?is a safe and broad-spectrum antibacterial agent.Due to its strong oxidation,it reduces the ethylene release of postharvest fruits and vegetables However,both gaseous and liquid ClO₂ are unstable,which limits their practical application.At room temperature,the solid NaClO₂?sodium chlorite?can release ClO2under acidic conditions.Therefore,in this paper,taking NaClO₂ as the precursor,firstly,the ClO₂ controlled-release corrugated box was prepared by double-layer coating,and the release behavior of ClO₂ was explored,and the fresh-keeping effect of the controlled-release box on strawberry was evaluated.In order to expand the application of ClO₂ controlled-release packaging,ClO₂ controlled-release microcapsules were prepared.Single factor test was used to optimize the preparation process to improve the encapsulation efficiency.The microcapsules prepared under the optimal conditions were characterized.The release behavior of ClO₂ was measured and applied to the packaging of cherry tomatoes to evaluate its fresh-keeping effect.The main research contents and achievements are as follows:?1?Polyvinyl alcohol?PVA?-NaClO₂-diatomite mixture was used to coat the inner surface of the corrugated box,then chitosan acetic acid solution was sprayed for the second coating to prepare the ClO₂ sustained release corrugated box.In the process of testing the release behavior,it was found that the controlled-release box released ClO₂ gas under the condition of high humidity,while the addition of diatomite stabilized and prolonged the release.With the increase of NaClO₂ concentration in the coating,the release concentration of ClO₂ increased.Under the condition of 100%humidity,9 g/L NaClO₂ coated corrugated box continuously released ClO₂ to the 14^thh day with a maximum concentration of 1.8 mg/m³.However,as the coating layer was water absorbent polymer,the compressive properties of the controlled-release box decreased significantly compared with the untreated group.?2?The controlled-release box with 3 g/L,6 g/L and 9 g/L NaClO₂ concentration were used for packaging fresh strawberries.The fresh-keeping effect of the controlled-release cartons on strawberries at room temperature was evaluated with untreated box as the control group.Compared with the control group,the decay rate and quality loss rate of strawberry packaged in 9g/L NaClO₂ controlled-release boxes decreased by21.88%and 6.84%,respectively.And strawberries in 9g/L NaClO₂ controlled-release boxes had better maintaining of surface color and firmness,and delayed the consumption of nutrients.Therefore,after packaging strawberry with ClO₂ controlled-release boxes,it induced the reaction of NaClO₂ to release ClO₂ under the action of CO₂ and water vapor produced by respiration and transpiration of strawberry,so as to prolong the shelf life of strawberry.?3?NaClO₂ was used as the core material and polylactic acid?PLA?was used as the wall material,then dissolving or evenly dispersing in the oil phase of chloroform ethanol mixture together.Polyvinyl alcohol?PVA?was used as the emulsifier and deionized water was used as the water phase.NaClO₂ were successfully encapsulated in PLA.Taking the encapsulation efficiency as the index,the single factor experiment was carried out to optimize the preparation process.The optimal process was obtained as follows:PVA concentration was 0.5%?w/v?,volume ratio of oil-water phase was80:350,mass ratio of core and wall material was 1:10,volume ratio of ethanol and chloroform in oil phase was 1:4,and the encapsulation efficiency of NaClO₂microcapsules was 55.75%.According to the results of FTIR and TGA,NaClO₂ was successfully encapsulated in PLA.The microcapsules were white and spherical,with an average particle size of 498.08?m and the particle size was mainly distributed in400?600?m.The release behavior of ClO₂ from the microcapsules was determined.It was found that in high humidity environment,the mixture of NaClO₂ microcapsules and citric acid microcapsules released ClO₂.The release rate was affected by the ratio of the two microcapsules and temperature.?4?The mixture of NaClO₂ microcapsule and citric acid microcapsule was placed in the boxes with fresh cherry tomatoes.The ratio of the two microcapsules was 3:0?M-3?,1:1.5?MA-1?and 3:4.5?MA-3?,respectively.The boxes without microcapsules were taked as control and record as CK.The fresh-keeping effect of the ClO₂ controlled-release microcapsule of cherry tomatoes was evaluated.When stored at 20?and 90%RH,the decay rate of the control group reached 86.67%,while that of MA-3 was only31.67%,M-3 was 55.00%,and MA-1 was 71.67%,which was still 15%lower than that of CK.On the 18^th day,the weight loss rate of CK reached 7.93%,while that of MA-3was only 5.23%,M-3 was 6.03%,and MA-1 was 6.34%.In addition,the color and hardness of the fruits in the experimental group were better maintained of M-3,MA-1and MA-3.Although ClO₂ was a strong oxidizing gas,the final results showed that it did not cause the decrease of soluble solids,titratable acid content and total antioxidant capacity of the fruits.On the contrary,the ascorbic acid content of CK was the lowest.Therefore,ClO₂ controlled-release microcapsules effectively prolonged the shelf life of the fruit.Compared with MA-1,M-3 had better fresh-keeping effect.This indicated that the water and CO₂ released by the fruit itself also induced the release of ClO₂ to have a good fresh-keeping effect.And since the amount of NaClO₂ microcapsules in M-3 was three times of MA-1,more generated ClO₂ makes the fresh-keeping effect better.