Preparation Of Polylactic Acid-based Modified Atmosphere Breathing Film And Its Fresh-keeping Effect On Agaricus Bisporus

Agaricus bisporus is rich in nutrients and delicious in taste.It is the most widely produced and consumed edible fungus in the world,and it is also one of the most cultivated edible fungi in my country.However,the fruiting body of Agaricus bisporus has high water content and no obvious protective tissue on the surface.It will lose water and brown in 1-3 days at room temperature,resulting in a decline in edible quality and commodity value,which poses a huge challenge to the storage and sales of Agaricus bisporus.In this study,Agaricus bisporus was selected as the experimental target,and the key factor of spontaneous modified atmosphere packaging-gas permeability was the fundamental starting point.Biodegradable polylactic acid（PLLA）was used as the base material,and a certain mass of glycolic acid（GA）and polybutylene fumarate（PBF）,were modified by melt copolymerization to improve their mechanical properties and barrier properties,and were prepared into spontaneous modified atmosphere packaging（MAP）applied to Agaricus bisporus.Compared with the commercially available films,the changes of storage quality were discussed in depth from the changes of gas in the package,sensory quality,physiological and biochemical indicators,aging indicators,and antioxidant enzyme activity.The specific research contents and results are as follows:（1）ynthesis of PLLA,PLGA8%and PLBF8%materials and preparation of modified atmosphere films.Taking PLLA as the main body,by adding a certain mass ratio of GA and PBF,it is modified by melt copolymerization to improve its barrier properties,mechanical properties,permeability ratio,etc.,to prepare a modified atmosphere packaging suitable for Agaricus bisporus.（2）Testing the properties of PLLA,PLGA8%and PLBF8%films.The molecular properties,mechanical properties,and barrier properties of the films were systematically analyzed.The results showed that PLLA,PLGA8%and PLBF8%were successfully synthesized.Compared with PLLA,the molecular weights of the copolymer films PLGA8%and PLBF8%had different degrees.Increase,of which PLBF8%can be as high as 58359.The barrier property test shows that the oxygen transmission coefficients of PLGA8%and PLBF8%are reduced by 53.8%and 69.2%,respectively,compared with PLLA,and the CDP/OP is increased by 18.2%and 33.3%;the water vapor transmission coefficients of PLGA8%and PLBF8%ignificantly higher than PLLA,4.07×10^-7cm³·m/m²·d·Pa and 4.51×10^-7cm³·m/m²·d·Pa,respectively,which is higher than the PE film(7.62×10^-9cm³·m/m²·d·Pa)has an order of magnitude improvement.The elongation at break of PLGA8%and PLBF8%films increased to121.1%and 139%,respectively,while their yield strength decreased from 40.3 MPa to23.3 and 25.6 MPa,respectively.The brittleness of the copolymerized material decreased and the flexibility increased significantly.（3）To study the fresh-keeping effect of PLLA,PE,PLGA8%and PLBF8%copolymerized modified atmosphere breathing film on Agaricus bisporus,the results show that the barrier properties of the four materials are significantly different,and the barrier properties of the film are significantly related to the storage physiological characteristics of Agaricus bisporus.All four materials can effectively reduce the browning,weight loss rate,malondialdehyde content,cell membrane permeability and polyphenol oxidase activity of Agaricus bisporus,and can maintain the color,flavor,hardness,soluble sugar,soluble protein,vitamin C,The content of total phenols and flavonoids,and the activity of antioxidant enzymes,etc.Looking at various indicators,the fresh-keeping effect of PLBF8%breathing film packaging is significantly better than the other three kinds of modified atmosphere packaging,which can maintain a stable gas environment inside the packaging for a long time,O₂concentration（<1%）,CO₂concentration（6.33-8.62%）,delaying the physiological metabolic activity of Agaricus bisporus,maintaining good sensory quality and normal physiological indicators,and extending the fresh-keeping period to 15 days.To sum up,it shows that the PLGA8%copolymerized modified atmosphere breathing membrane has the most fresh-keeping effect in the preservation of Agaricus bisporus.