Preparation Of Oregano Essential Oil Inclusion Complex/PBAT Composite Film By Extrusion Blow Molding And Its Application In The Preservation Of Bingtang Orange

China is the largest producer of fruits and vegetables in the world,but the relatively backward postharvest storage and fresh-keeping technology and imperfect cold chain facilities have led to serious postharvest losses（up to 20%to 30%）.At present,the main fresh-keeping methods of fruits and vegetables are the application of chemical fungicides and the use of plastic packaging films/bags and so on.However,chemical fungicides have drug resistance and food safety problems,and almost all of the packaging films/bags are non-degradable synthetic polymer materials,and their wastes aggravate plastic pollution.Therefore,the development of green,safe and efficient biodegradable fresh-keeping film is of great significance to reduce the waste of resources and achieve sustainable development.Poly（butylene adipate-co-terephthalate）（PBAT）is a kind of biodegradable material with good processability,and its mechanical properties are similar to those of polyethylene（PE）,so it is expected to be a substitute for PE as a fresh-keeping packaging film for fruits and vegetables.In addition,adding antimicrobial agents to the packaging film to prepare antibacterial film can effectively delay the decay of fruit,reduce or avoid the direct use of chemical fungicides,and improve food safety.Natural antimicrobial agents such as plant essential oils are not only green and safe,but also have excellent antibacterial and antioxidant properties.The packaging film made of natural antimicrobial agents and polymer materials can be volatilized to the inside of the packaging to effectively exert the antibacterial and fresh-keeping effect.But at the same time,the volatility of plant essential oil makes it difficult for the composite film of plant essential oil and polymer to be processed by industrial molding methods such as extrusion blow molding,which has become one of the bottlenecks limiting its production and application.Using the carrier with high thermal stability to encapsulate the essential oil and then composite with polymer materials is one of the effective measures to solve this problem.Based on this,oregano essential oil/β-cyclodextrin（β-CD）inclusion complex（CD-O）was prepared by coprecipitation method using oregano essential oil as core material andβ-CD as wall material.The preparation process was optimized,and the morphology and properties of CD-O were characterized.Secondly,CD-O was blended with PBAT,and PBAT composite films with different CD-O contents were prepared by extrusion blow molding.The microstructure,mechanical properties,barrier properties,thermal stability and oxidation resistance of the composite films were characterized in order to explore the effect of CD-O addition on the structure and properties of PBAT films.Finally,the composite film with the best comprehensive performance（15%mass fraction of CD-O）was made into a bag for postharvest storage of Bingtang orange（Citrus sinensis Osbeck）.The ability of the composite film to maintain the nutritional quality of Bingtang orange and inhibit the disease of fruit inoculated with pathogens was evaluated.The main conclusions are as follows:（1）After the composition analysis of oregano essential oil,it was found that the percentages of carvacrol and thymol with good antibacterial and antioxidant activity were86.40%and 2.06%,respectively.The results of antioxidant activity determination showed that the free radical scavenging ability of oregano essential oil increased with the increase of essential oil concentration.When the concentration of oregano essential oil is 20μg/m L,its free radical scavenging rate has exceeded 80%.Taking the entrapment efficiency and loading rate of CD-O as optimization indexes,the addition amount of wall material,the core-wall ratio and the mass ratio of essential oil to ethanol were optimized by single factor.The optimal preparation process of CD-O was obtained as follows:the mass fraction of wall material was 7%,the core-wall ratio was 1:6,and the mass ratio of oregano essential oil to ethanol was 1:7.The entrapment efficiency of CD-O prepared by this process is 61.01%,and the loading rate is 10.04%.It has uniform microstructure,maintains good antioxidant activity（the free radical scavenging rate of CD-O solution with 1.0 mg/m L concentration is 52.13%）,and obviously inhibits the growth of Penicillium digitatum（the diameter of bacteriostatic zone is 22.60±1.31 mm）.The results of X-ray diffraction and thermogravimetric analysis showed that oregano essential oil was successfully included byβ-CD,and the thermal stability was improved.At the same time,the essential oil in CD-O could be released slowly within 16 days,and the release curve could be fitted by Higuchi model（R²=0.9964）.（2）CD-O/PBAT composite films（5%CD-O/PBAT,10%CD-O/PBAT,15%CD-O/PBAT）with 5%,10%and 15%mass fraction of CD-O andβ-CD/PBAT composite films（5%β-CD/PBAT,10%β-CD/PBAT,15%β-CD/PBAT）with 5%,10%and 15%mass fraction ofβ-CD were prepared by extrusion blow molding,and their structures and properties were characterized.The results showed that both CD-O andβ-CD aggregated in PBAT to a certain extent,resulting in a small number of micropores in the film,but the CD-O aggregates were smaller,indicating that essential oil encapsulation could promote their dispersion in PBAT.Compared with PBAT film,the mechanical properties and thermal stability ofβ-CD/PBAT composite film decreased obviously.Although the addition of CD-O also decreased the tensile strength,elastic modulus,elongation at break,onset decomposition temperature(T_onset)and maximum decomposition rate temperature(T_max)of the composite film,the decrease was much smaller than that of the composite film withβ-CD.When the mass fraction of CD-O increased from 5%to 15%,the opacity of the composite film gradually decreased,and the free radical scavenging ability was gradually enhanced.In addition,the addition ofβ-CD and CD-O increased the water vapor permeability of the film,but the value of CD-O composite film was more than 50%lower than that ofβ-CD composite film.The oxygen permeability of each composite film increased at first and then decreased with the increase ofβ-CD or CD-O addition,and the value of 15%CD-O/PBAT composite film was not significantly different from that of PBAT（p>0.05）.（3）The single fruit of Bingtang orange was bagged with PBAT and 15%CD-O/PBAT composite film,respectively,and stored in an environment of 20±1℃and 60±5%RH.The quality of Bingtang orange was determined periodically with untreated group（CK）and commercial polyethylene bag packing group（PE）as control.The results showed that compared with CK group,15%CD-O/PBAT film bag could significantly reduce the postharvest respiration of Bingtang orange in the first 8 days,and its effect on fruit weight loss was the same as that of PBAT film bag,but lower than that of PE film bag.Compared with PE film bag,15%CD-O/PBAT film bag can better maintain the hardness of peel and pulp and delay the process of fruit softening.At the same time,compared with other groups,the Bingtang orange of 15%CD-O/PBAT group had significantly higher ascorbic acid content,total soluble solid content and total phenol content during storage（p<0.05）,which maintained the nutritional quality of fruit.In addition,after the fruit was inoculated with Penicillium digitatum,it was found that compared with PBAT group,the onset time of fruit in 15%CD-O/PBAT group was delayed by 2 days,and the diameter of disease spot was significantly lower（p<0.05）.In conclusion,this study usedβ-CD to encapsulate oregano essential oil,which can achieve the slow release of essential oil and can be compounded with PBAT by extrusion blow molding process.And the composite film has certain moisture barrier,oxygen resistance and anti-oxidation activity.When used in Bingtang orange bagging,the composite film can better maintain the nutritional content of fruit and inhibit the occurrence of diseases.It has good application potential in postharvest storage of fruits and vegetables.