Effects Of Nanocomposite Packaging Material On Flammulina Velutipes Preservation And Its Possible Mechanisms

Flammulina velutipes are highly perishable after harvest and have a very short shelf life.In order to solve this problem,a novel polyethylene(PE)based packaging material containing nano-Ag,nano-TiO2,nano-SiO2,and attapulgite was prepared and applied on fresh F.velutipes preservation.The effect on storage stability of F.velutipes packaged with nanocomposite packaging material(Nano-PM)and its possible mechanism was investigated by testing the gas composition inside the package,microbial growth,texture,nutrient substances,favor alteration,ROS metabolism and differentially expressed proteins.More information of each research chapter was shown as follow:1.In this study,Nano-PM was prepared based on PE matrix incorporated with nano-Ag,nano-TiO2;nano-SiO2,and attapulgite.The thickness of the derived film was 40μm.Normal PE packaging material(Normal-PM)in the same thickness and size but without any nanocomposite masterbatch nano-powder was used as the control.The mechanical and barrier properties,particle distribution,safety and production cost of two packaging materials were analyzed.The XRD result showed that Ag and TiO2 exhibited cubic phase and anatase type structure respectively in the composite nanoparticle.According to the microstructural observations,the nanoparticles were well distributed in the molten PE and the majority of them had diameters between 50 and 100 nm,thereby indicating the good dispersivity of the nanoparticles in the matrix.Compared to the control,the addition of nanoparticles improved the longitudinal tensile strength by 26.91%and decreased the gas,vapour or light transmission rate.The result of material sanitation and migration test confirmed that Nano-PM met the national safety standards(GB 9687-1988&GB 9685-2016).The additional cost of producing Nano-PM increased by 35.79%compared to the control,which was acceptable to users.2.Fresh F.velutipes was packaged with Nano-PM and Normal-PM for 21 days of storage at 4℃ in order to study the effect of Nano-PM on mushroom storage stability.The result showed that Nano-PM could eliminated ethylene and regulated the gas composition inside package leading to a better-mixed gases matching of O2 and CO2,which benefited F.velutipes preservation.The weight loss of two packed F.velutipes was all under 1%during cold storage.Compared to the control,the maximum respiration rate of Nano-PM packed F.velutipes was decreased by 19.17%.The cap opening rate,stipe elongation,maximum shear force and browning of Nano-PM packed F.velutipes were decreased by 39.80%,44.08%,16.45%and 22.01%,respectively.Furthermore,Nano-PM improved the retention of vitamin C,soluble protein,total soluble solids and free amino acid contents of F.velutipes.Both two packaged mushrooms showed a continual increase on the counts of mesophilic and psychrophilic bacteria,Pseudomonas,yeasts and molds during the storage time.Nonetheless,Nano-PM was more effective in inhibiting the growth of microbes compared with Normal-PM during the later stage of storage.On the other hand,the results of E-nose and GC-MS exhibited that volatile compounds of fresh F.velutipes mainly consisted ketones and alcohols,and 3-octanone was the predominant compound.After 21-day storage,the main volatile compounds in Nano-PM packed samples were ketones(73.9%).The relative content of hydrocarbon in Nano-PM packed samples was nearly double from 6.2%to 12.7%compared to fresh F.velutipes.In Normal-PM packed samples,heterocyclic and aromatic compounds became the main volatile flavour substances,which contributed to the off-flavour development.The relative content of ethanol in Normal-PM packed samples rose up from 0 to 5.3%because of anaerobic respiration,while only 0.8%ethanol was detected in Nano-PM packed ones.The umami,sourness and salt taste of both Nano-PM and Normal-PM packed F.velutipes were decreased during storage time.Significant(P<0.05)changes of two packaged F.velutipes on sourness and after taste were observed.3.The effect of Nano-PM on ROS metabolism,antioxidant capacity,membrane permeability and lipid peroxidation of F.velutipes during 21 days of postharvest storage at 4℃ was analyzed.The results showed that Nano-PM improved the antioxidant enzyme activities.At the third day of storage,the activities of SOD and POD approached the highest value,which were 134.67 U/mg protein and 44.78 U/mg protein respectively.These SOD and POD values were significantly(P<0.05)higher than that of control.After six days of storage,Nano-PM packed F.velutipes had significant higher CAT activity than Normal-PM,which increased by 15.46%.At the end of storage,the contents of O2·-and H2O2 in Nano-PM were 3.86 mmol/kg FW and 14.65 mmol/kg FW,which were significantly lower than that of Normal-PM.The trend of MDA contents in Nano-PM proved that Nano-PM packed F.velutipes had a lower lipid peroxidation level.The results of relative electrolyte leakage test and microstructure TEM observation indicated that Nano-PM could help mushroom cell maintain the stability and integrality of bio-membranes.Based on LF-NMR analysis,there were four distinct peaks(T21,T22,T23 and T24)distributed in the relaxation times(T2)curve of fresh F.velutipes.T21 stood for bound water in the cell wall,T22 represented cytoplasm water,T23 and T24 were considered as free water in the extra cellular lacuna and vacuole,respectively.After 21 days of storage,compared to that in Nano-PM group,the peaks of the relaxation times in Normal-PM packed F.velutipes were smaller and led to a left-ward shift.Interestingly,it was found that there was a shoulder between T23 and T24 fractions and they had a tendency to merge into one.This result illustrated that cell bio-membrane structure was damaged by ROS resulting in the loss of cell permselectivity.The electrolyte leakage would influence the LF-NMR signal leading to the shifting or merging trend of T2 peaks.4.To gain insights into metabolic changes of F.velutipes packaged with Nano-PM,a comparative proteomic approach based on TMT-coupled 2D LC-MS/MS was applied.In total,2283 proteins were identified from fresh F.velutipes(F),Nano-PM packed F.velutipes(N)and Normal-PM packed F.velutipes(P).Protein abundances that changed more than 1.2-fold and P<0.05 were selected as differentially expressed proteins(DEPs).Following this criterion,429 DEPs were identified.A total of 176 proteins were up-regulated and 5 proteins were down-regulated in the comparison of the N/F groups,117 proteins were upregulated and 28 proteins were downregulated in the P/F comparison,and 232 proteins were up-regulated and 65 proteins were down-regulated in the N/P group comparison.Based on GO annotations,the up-regulated DEPs mainly distributed in the cytoplasm(50%),participating in amino acid synthesis and metabolic,protein transport,signal transduction and response to stress(11%).The down-regulated DEPs were mainly located in the mitochondria(35%),cytoplasm(31%)and membrane(18%),which was involved in carbohydrate metabolic,amino acid synthesis and metabolic,and organic acid metabolic process,suggesting more nutrient consumption happened in Normal-PM packed F.velutipes during storage.By mean of GO,KEGG and PPI analysis,we found that Nano-PM decreased the protein expression related with TCA and glyoxylate cycle including citrate synthase and isocitrate lyase;increased the protein expression of formate dehydrogenase and aldehyde dehydrogenases leading to relatively lower ethanol accumulation.Besides,the cellulose and trehalose degradation were inhibited by the lower protein expression of β-glucosidase and trehalase in N/P group.The ability of Nano-PM packed F.velutipes resistance to stress was enhanced by up-regulating the expression of saccharopine dehydrogenase and tryptophan synthase.Glutamate dehydrogenase expression was also up-regulated to maintain the balance of carbon and nitrogen metabolism in cell.Another up-regulated protein,protein disulfide isomerases,could help mushroom cell fix misfolded proteins.On the other hand,the proteins associated with signaling pathways including mitogen-activated protein kinase,myo-inositol-1-phosphate synthase,regulator of G protein signaling,protein kinase C and bar adaptor protein hob3 were up-regulated in N/P group.Moreover,glutathione peroxidase,superoxide dismutase,methionine sulfoxide reductase B and heat shock proteins of Nano-PM packed F.velutipes increased in abundance during cold storage compared to that of Normal-PM treatment.As a result,the cellular antioxidant system in Nano-PM packed F.velutipes was enhanced and the redox homeostasis in cell would be maintained during storage.