Preparation Of Multifunctional Chitosan Composite Film And Its Application On Storage And Preservation Of Chestnut

Chitosan is a natural,non-toxic,biodegradable alkaline polysaccharide with excellent film formation properties.As a new edible packaging material,chitosan has a promising future in the food industry.However,a single chitosan film has poor water resistance,low air permeability,weak mechanical properties,and other shortcomings,making it difficult to meet the comprehensive needs of post-harvest fresh fruit and vegetable preservation.Although chestnut fruits have a distinct flavor and nutritional value,due to their high water content and vigorous respiration,they are prone to water loss and rot during storage.Therefore,based on the storage characteristics of chestnut,this paper used water vapor transmission rate and gas transmission rate as the core indicators,combined with the measurement of mechanical performance indicators,by adding different types of natural products to screen chitosan composite film with moisture barrier and air permeability properties.Basis on the chitosan composite film,a natural antibacterial substance was added to prepare a multifunctional chitosan composite fresh-keeping film with moisture resistance,air permeability,and antibacterial activity.Further evaluation of the preservative and fresh-keeping effect of multifunctional chitosan composite film on chestnut.The main results were shown as follows:(1)Preparation of moisture-resistant and breathable chitosan film.The chestnut was treated with different concentrations of chitosan,and the weight loss rate and decay rate were investigated.The best anti-corrosion and fresh-keeping effect of chitosan was screened when the concentration of chitosan was 1.75%.More than 30substances with different properties were further screened to study their effects on the water vapor transmission rate and gas transmission rate of 1.75%chitosan film.It was found that cinnamaldehyde can significantly reduce the water vapor of 1.75%chitosan film.And it also can improve the oxygen and carbon dioxide permeability of1.75%chitosan film to a certain extent;further research found that adding rosin to the cinnamaldehyde-1.75%chitosan composite film can further improve the oxygen and carbon dioxide permeability of the composite film.(2)Effects of cinnamaldehyde and rosin on the properties of chitosan films.By studying the effects of different concentrations of cinnamaldehyde on the properties of 1.75%chitosan films,it was found that the addition of cinnamaldehyde could improve the comprehensive properties of a single chitosan film to a certain extent.When the addition amount of cinnamaldehyde is 0.8%,the composite membrane has better comprehensive performance.The water vapor transmission rate is612.67g/(m~2·day),the oxygen and carbon dioxide transmission rates are 46.62 and195.34 cm3/m2·24h·0.1MPa,respectively,the tensile strength reaches 35.51MPa,and the elongation at break is 17.31%.The effect of adding different concentrations of rosin on the performance of chitosan-cinnamaldehyde composite membrane was further studied,and it was found that when the concentration of rosin was 1%,the composite membrane had the best comprehensive performance.The lowest water vapor transmission rate reached 577.77 g/(m~2·day),which greatly improved the moisture barrier properties of the chitosan film.In addition,the oxygen and carbon dioxide transmission rates have also been greatly improved,reaching 141.71 and1341.26 cm3/m2·24h·0.1MPa,respectively.In addition,the tensile strength and elongation rate at break are 37.09 MPa and 25%,respectively,which further improves the composite membrane of mechanical properties.The ultrastructure observation results of the chitosan composite film showed that after adding cinnamaldehyde,the original smooth and dense structure of the chitosan film became rough and oily droplets appeared.After further adding rosin,the surface of the composite film appeared uneven.Therefore,the addition of cinnamaldehyde and rosin affected the properties of the 1.75%chitosan film by changing its structure.(3)Screening of natural antibacterial substances and preparation of multifunctional chitosan composite film.By studying the antifungal effects of extracts of natural products such as oldenlandia,eagle tea,folium cortex eucommiae,and poplar bud extract(PBE)on the dominant rot-causing fungi of chestnut,it was found that 1%PBE has the best fungistasis effect.Therefore,1%natural antifungal substance PBE was added to the basis of the optimal ratio of the composite film in order to study the antifungal effect of the chitosan film,cinnamaldehyde-chitosan composite film,cinnamaldehyde-rosin-chitosancomposite film and cinnamaldehyde-rosin-PBE-chitosan composite film on chestnut postharvest dominant pathogenic fungi such as Fusarium brucei and Clostridium neocassis.The results showed that the four composite membranes had different inhibitory effects on the two pathogenic fungi.However,the cinnamaldehyde-rosin-PBE-chitosan composite film had the highest inhibition rate against the two pathogenic fungi,which were 75.96%and77.78%,respectively.(4)Evaluation of the postharvest antiseptic and fresh-keeping effect of the multifunctional chitosan composite film on chestnut.The effect of the multifunctional chitosan composite film treatment on the microbial indicators,quality indicators and physiological indicators of chestnut during storage at normal temperature was determined.It was found that the multifunctional chitosan composite film treatment can effectively reduce the rot rate of chestnut,and the rot inhibition rate under normal temperature and low temperature storage conditions was 37.53%and 60.18%,respectively.Contents of quality indicators such as starch,soluble protein,titratable acid,and soluble solids.In addition,under normal temperature and low temperature storage conditions,the multifunctional chitosan composite film not only effectively inhibited the growth of rot-causing bacteria during the storage process of chestnut,but also inhibited the respiration of chestnut,with the inhibition rates reaching 30.00%and 35.05%,respectively.At the same time,the activities of chestnut polyphenol oxidase(PAL),polyphenol oxidase(PPO)and peroxidase(POD)were improved.Therefore,the multifunctional chitosan composite film has potential application value in effectively reducing the rot of chestnut during storage and maintaining the quality of chestnut.