Respiratory Inhibition And Regulating Mechanism Of Composite Coatings Based On Shellac On Fruits Stored At Room Temperature

Traditional postharvest technology only focuses on the appearance quality of fruits and vegetables,while ignoring the nutritional value and safety.Due to the gradual improvement of health awareness,people pay more attention to the intrinsic nutritional quality and safety of postharvest fruits and vegetables.So,the development of green,efficient and safe postharvest technology has become a research focus.The edible coating technique has obvious advantages in postharvest preservation of fruits and vegetables due to its good preservation effects and natural edible properties.However,most edible coating lack biological activity,and the air permeability can not be regulated,resulting in limited variety of fruits and vegetables and preservation effects.Lack of multi-functional coating has become the main challenge in the edible coating technique,which demands further research.The main contents are as follows:(1)Effects of tannic acid-shellac composite coating on preservation of mango at room temperature:The tannic acid-shellac complex preservative was prepared for prolonging mango shelf life at room temperature.The optimum formulation of tannic acid-shellac compound preservative was obtained by response surface methodology based on Central Composite experimental design.Meanwhile,the physical and chemical indexes of compound preservative were also tested.The results showed that the optimal formulation was composed of 7.3%(wt%)of shellac,0.3%(wt%)of tannic acid and 2%(wt%)of glycerol.The weight loss rate and incidence of black spots of mangoes operated with optimal compound preservative were 24.38%and 29.91%respectively at the 18^th day,respectively.The compound preservative could obviously prolong the shelf life of mangoes at room temperature compared to shellac coated and uncoated.And Storage shelf life of mangoes coated with the compound preservative had been prolonged for about 7?10 days.The sensory and physical and chemical indexes of the compound preservative were all in line with the requirements of the national standard,which indicated that the preservative was green and safe and non-toxic.(2)Effect of tannic acid-shellac composite coating on quality of postharvest mango and its preservation mechanism:This study investigated characteristics of tannic acid/shellac compound preservative and the effects of tannic acid/shellac compound preservative on nutritional qualities and physiological changes of mango during room temperature storage.The results showed that tannic acid-shellac composite coating performed lower water vapor permeability,and higher antioxidant capacity than shellac coating due to the the addition of tannic acid.And the composite coating also reduced malondialdehyde content,membrane permeability and the activities of guaiacol peroxidase and polyphenol oxidase of mangoes than that of blank control and shellac treatment.The composite coating treatment could keep lower respiration,weight loss and enzymatic-oxydative browning,and keep higher nutritional contents compared to that of shellac-coated and black control.The vitro experiments showed that tannic acid-shellac composite coating performed strong inhibition against Colletotrichum gloeosporioides and Phomopsis mangiferae,which not only reduced microbial growth,but also prolonged the shelf life of mango fruits.(3)Polylactic acid porous microsphere regulation towards gas barrier property of edible film for postharvest preservation:The polylactic acid(PLA)porous microspheres(PPM)prepared by thermally induced phase separation(TIPS)were embedded into the shellac membranes to obtain PPM/shellac composite membranes,and then the microspheres characteristics and the roles that it plays in adjusting gas permeability of PPM/shellac composite membranes were investigated.Finally,PPM/shellac composite membranes regulation towards coated oranges in respiration metabolism were peformed.The results showed that the polylactic acid porous microspheres fabricated through optimization conditions exhibited more than 77%porosity and pretty antibacterial acyivities.And the toxicology experiment in vivo demonstrated that it was non-toxic.The water vapor permeability and gas permeability of the composite membranes could be adjusted by changing the addition amounts of microspheres,respectively.Besides,the composite membranes had highly mechanical strength and transmittance in visible range.We experimentally demonstrated PPM/shellac composite membranes regulation towards respiration and ethylene release of coated oranges during storage.The composite membranes had the potential applications as an edible and spontaneity-modified atmosphere packaging for prlonging shelf life of fruits and vegetables.(4)Edible membranes with facilely adjustable permeability and selectivity based on self-assembled tannic acid-chitosan porous microspheres for spontaneous modified atmosphere packaging:In this study,a novel method was developed to prepare chitosan porous microspheres using PEG as the pore-forming agent,followed by fabricating tannic acid-chitosan porous microspheres(TA-CSPM)within interface assemblly.The composite membranes based on self-assembled tannic acid-chitosan porous microspheres and shellac were prepared.Then the microspheres characteristics and the roles that it plays in adjusting gas permeability of composite membranes were investigated.Subsquently,The composite membranes regulation towards coated oranges in respiration metabolism were peformed.The results showed that chitosan porous microspheres possessed mesoporous structures with a specific surface area of 62.06 m²/g.The specific surface area of the porous microspheres declined slightly after loading tannic acid,while its bacteriostatic ability against Escherichia coli,Staphylococcus aureus and Bacillus subdue improved.And the toxicology experiment in vivo demonstrated that TA-CSPM was non-toxic.The water vapor and gas permeability and the selectivity of CO₂ and O₂ improves with the increase of the content of microspheres.Finally,we experimentally demonstrated composite membranes regulation towards respiration and ethylene release of coated oranges during storage.