Construction Of Poly(Adipic Acid)/Butyl Terephthalate Based Nanometer Modified Atmosphere Breathing Film And Its Preservation Mechanism Of Agaricus Bernardii

Agaricus bernardii,is a wild edible fungus with gray-brown caps,fish-like stripes,and pure black pleats.Researchers have successfully domesticated it,which was very popular among consumers.However,the postharvest handling of edibel fungi is difficult due to their highly perishable nature.In this paper,Polyadipate/butyleneterephthalate（PBAT）based nanometer modified atmosphere breathing film systems was prepared by adding L-polylactic acid（PLLA）and nano-silica（SiO₂）with different blending mass ratios,and the effects of breathing film on the storage quality,browning mechanism,cell wall metabolic characteristics and changes in flavor substances of Agaricus bernardii were investigated to explore the key factors of Agaricus bernardi preservation and its mechanism.The main results are as follows:1.The domesticated Agaricus bernardii was rich in protein（38.02～39.57%DW）,amino acid composition,mineral elements,functional fatty acids and polyunsaturated fatty acids,which make it has extrmely valuable for utilization.The nutritional value of the fruiting body of Meng baiyin 1 was slightly better than that of the fruiting body of Meng baiyin 2.Compared between two commercial harvesting periods found that the unripened ripening fruiting body showed higher nutritional quality than the ripened ripening fruiting body.2.PBAT/PLLA blends film were prepared by melt blending uniaxial tensile method,and the compatibility,mechanical properties,thermal properties and barrier properties of the blend film were systematically analyzed.The results show that PBAT and PLLA blend system was thermodynamic incompatible systems.with the PLLA content increased,the crystallization temperature of the blend films increases and the crystallinity of PBAT components decreased,The elongation at break decreases,while the tensile strength and young’s modulus increase,indicating that the addition of PLLA enhances the rigidity of the film.The barrier properties of O₂ and CO₂.were improved by the addition of PLLA.PBAT/PLLA30%breathing film restrains a steady-state with low O₂（<1%）and CO₂ concentration（4.85-5.15%）,which can delay the physiological metabolic activity,maintain good sensory quality and storage quality.It indicated that PBAT/PLLA breathing film has the possibility of application in the preservation of Agaricus bernardii.3.PBAT/PLLA/SiO₂ breathing film with different types SiO₂（hydrophilic and hydrophobic）were prepared by melt blend method,and the SiO₂ additional effect on the barrier properties,crystallization properties and thermodynamic properties of blend film was dicucced.The results show that the addition of nano-SiO₂ can improve the mechanical properties by improve the Young’s modulus of the oriented film.The gas permeability and water vapor transmission properties of the blended film showed a trend of decreasing first and then rising,and showed the best barrier performance when the addition amount was 0.5%.A comparison between the two types of SiO₂ reveals that,the gas barrier properties of hydrophilic SiO₂blended films are superior to hydrophobic SiO₂blended films;the hydrophobic group shows better water vapor barrier performance than the hydrophilic group;the addition of SiO₂can promotes the crystallization of the PBAT component and increase the crystallinity of the PBAT and PLLA components.4.To clarify the physicochemical and selected enzyme activities in Agaricus bernardii packed with different barrier packaging materials during storage.The low O₂（<1%）and moderate CO₂ levels（4.65-6.6%）in 0.5S SiO₂film maintained a high level of soluble protein,soluble sugar,ascorbic acid and phenolic contents,inhibited the increase of malondialdehyde,increased the antioxidant enzymes activities of peroxidase and decreased the enzymes activities of polyphenol oxidase.The overall acceptability of mushrooms packed in the 0.5S SiO₂ group remained good and within the limits of marketability after 15 d of storage,Application of 0.5S SiO₂could have potential in maintaining the quality of harvested Agaricus bernardii fruit bodies by maintaining the appropriate gas composition.5.The metabolism of cell wall composition can influence the quality of Agaricus bernardii.Control group showed the highest hardness due to the significant increase of cellulose and chitin.PE group has serious autolysis duo to its high level of Cell wall degrading enzyme activity.0.5S SiO₂ reduce losses of protein,polysaccharides,cellulose and chitin,and has lower level of cell wall degrading enzyme activity,leading to better cell wall integrity.compared to PE group,the shelf life of Agaricus bernardii in 0.5S SiO₂ group prolongs 7 days.6.The flavor substances of Agaricus bernardii and their changes during storage were analyzed by High Performance Liquid Chromatography（HPLC）and Solid-phase micro-extraction（SPME）combined with Gas Chromatography-Mass Spectrometer（GC-MS）.The results showed that alcohols and ketones were mainly the volatile flavor substances of Agaricus bernardii,of which 3-octanol and 3-octanone were higher in content.With the extension of storage period,the kinds of volatile flavor substances was increasing,mainly due to formed more hydrocarbons,esters and other volatile components,non-volatile organic acids and volatile eight carbon compounds contents declined,Compared to other treatment groups,0.5S SiO₂ could reduce the oxidation decomposition and degradation of eight carbon compounds and organic acid content,resulting in the flavor protection of Agaricus bernardii.