| By applying edible coating to postharvest fruits,the respiration and transpiration of fruits can be delayed and the storage period of fruits can be prolonged by adjusting the exchange rate of water and gas between fruits and the environment.Adding nanomaterials to the coating materials can further regulate the barrier and stability of the coating so as to enhance its preservation effect.This research added nanocrystal cellulose?NCC?to chitosan?CS?,used for keeping fresh citrus film,on the basis of the concentration of NCC was optimized,with the method of secondary coating explores the fruits during storage the changing structure of the coating and the relationship between fruit storage quality,at the same time,through the preparation of stripping of NCC/CS composite coating,has been clear about the nano fiber on the properties of composite coating,thus explores the NCC reinforced CS coating on the mechanism of the effect of preservation of citrus.In this study,NCC/CS composite coatings of different concentrations were firstly applied to the preservation of tangerine.Meanwhile,the flat films with the same NCC content were characterized to explore the influence of NCC on the performance of composite films.Then NCC/CS composite coating used for keeping fresh tangerine,and commercial preservative to contrast with the the tangerine quality during storage,sensory,and pulp and peel test to determine the antioxidant activity of the material changes,and regularly observed coating and microstructure changes on the surface of the peel,to explore the film during fruit storage structure change and its impact on the storage quality of fruit;During the fruit during storage,coating due to the fruit by the impact of respiration and transpiration,microporous coating barrier property destroyed,to explore the coating structure and the relationship between the fruit quality,further after the first coat of tangerine,respectively in coating micropore before and after to the secondary coating of fruit,in monitoring the coating microstructure change at the same time,determination of tangerine fruit during storage quality and antioxidant activity in pulp and peel material changes;Finally,for the further research of nanometer fiber structure and properties of coating,and to explore mechanism of composite coating preservation effect is enhanced,the orange peel for interface was prepared with different NCC content and can be stripped of NCC/CS composite coating?C type film?,on the structure and performance characterization,at the same time using petri dish for preparation of the same content of NCC interface flat membrane?P type film?,and C type thin film were compared.The main research contens and results are as follows:1.The NCC/CS composite coating with mass fraction of 0%,3%,6%and 9%?accounting for the dry weight of CS?was used to preserve tangerine,and the preservation effect of the composite coating was investigated in the untreated group.At the same time,the film with the same NCC content was prepared by petri dish fluidization method,and its tensile and barrier properties were characterized.The results showed that compared with the control group,6NCC/CS?6%concentration of NCC/CS?composite coating could reduce the decay rate of tangerine by 60.5%,reduce the accumulation of malondialdehyde,and be beneficial to the fruit to maintain the firmness and maintain the nutrient content.At the same time,compared with the pure CS film,the addition of NCC with 6%concentration can improve the tensile property of the composite film by 60.2%,reduce the moisture absorption by 26%,and improve the barrier capacity of water vapor and oxygen.2.2NCC/CS composite solution?NCC/CS at 2%concentration of CS?and Prochloraz?OP?were applied to the preservation of tangerine coating film.Various physiological activity indexes,antioxidant substance changes and sensory indexes of tangerine flesh and skin were measured regularly,and the changes of microscopic morphology of the peel surface were observed.The results showed that compared with PC,2NCC/CS coating had a better inhibition effect on decay rate,respiration rate,malondialdehyde and relative conductivity of tangerine.Meanwhile,the 2NCC/CS coating group had the highest sensory evaluation score,which was more conducive to the preservation of nutrients such as acid,sugar,ascorbic acid,total phenols and flavonoids.In addition,2NCC/CS coating could maintain higher DPPH free radical clearance rate,SOD activity and POD enzyme activity,etc.According to the microscopic morphology of the peel coating,on the third day,the hydrophilic coating on the surface of the CS group was destroyed under the transpiration of the fruit,and the pores appeared in the stomata of the fruit,while the coating layer of the 2NCC/CS group appeared in the fifth day.The integrity of chitosan was destroyed by fruit respiration and transpiration,and the addition of NCC could enhance the structural stability of chitosan coating to some extent,thus he preservation effect of citrus is closely related to the stability of coating structure.3.In order to solve the problem that the coating layer is destroyed due to the properties of citrus fruits,and the pores appear near the stomata.After the initial coating of CS and 2NCC/CS,the second coating?CS-3,CS-5,2NCC/CS-3,2NCC/CS-5?was conducted at different times?at day 3 and day 5?to observe the microscopic morphology of the coating layer and periodically determine the physiological and biochemical indexes and antioxidant activity of the pulp and peel of tangential orange.The results showed that,CS group produced micropores on the day 3,2NCC/CS group produced micropores on the day 5.After the secondary coating,the pores of the coating layer are repaired and the surface becomes dense and flat again.On the day 12 of storage,the weight loss and decay rates of 2NCC/CS-3 were the lowest,followed by2NCC/CS and CS-3,which decreased by 35.7%and 41.7%respectively compared with CK.2NCC/CS-3 in the respiratory rate lowest during storage,fruit internal maintains the low concentration of O2 and CO2 gas,has higher firmness,better keep materials such as sugar,acid and chlorophyll content,and total polyphenols,flavonoids,and antioxidants such as ascorbic acid content is higher than other groups,inhibits the generation of reactive oxygen species,to maintain the higher DPPH clearance.It can be concluded that the second composite coating on the third day of storage can maintain the integrity of the coating structure for a long time,so as to improve the preservation effect of citrus.4.Respectively in the two kinds of interface peel of citrus and polystyrene plate)preparation of four different concentrations?NCC accounts for CS quality respectively,0%,2%,4%and 6%,with 1.5%mass concentration of cs in aqueous solution?composite membrane,by Infrared spectrum,UV spectra,scanning electron microscopy,water contact Angle,thermal characterization methods,such as,characterization of the microstructure,structure and properties of film.The film formed by the orange interface was recorded as C-type film,and the film formed by the plate interface was recorded as P-type film.The results show that the C-type film has a stronger barrier to ultraviolet light,and the transmittance of the two films decreases with the increase of the concentration of NCC.P-6NCC/CS?polystyrene plate preparation to get 6%of the concentration of NCC/CS films?compared with P-CS?polystyrene plate preparation of pure chitosan film?,and C-6NCC/CS?orange peel surface preparation to get 6%of the concentration of NCC/CS films?compared with C-CS?orange peel surface preparation of pure CS film?,thin film samples in at 800 nm light transmittance was reduced by15.8%and 5.5%respectively.However,the Infrared spectrum of all films did not change much.The thermal decomposition temperature of C-6NCC/CS is 26.9?higher than that of P-6NCC/CS.At the same time,the water vapor barrier property and hygroscopicity of C-type film are reduced,and the surface morphology is rough and the crystallinity is reduced.Therefore,the structure and properties of P-type film and C-type film are different,and the edible film cannot be completely replaced by the plate film to help explain the preservation mechanism of coating.However,with the change of the content of nanocellulose in the composite film,the change trend of the two films is consistent.It can be proved that the addition of NCC is beneficial to the structural stability of chitosan coating. |
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