Study On Preparation Of Lacquer Seed Protein/Chitosan Composite Film And Modification Of Lacquer Wax

Lacquer tree(Toxicodendron vernicifluum(Stokes)F.A.Barkley)is one of the ancient economic tree species in China.It is widely distributed and mainly produces lacquer.Lacquer tree seed is the fruit of lacquer tree,which matures from September to October every year.The annual yield of lacquer tree fruit is about 1.5 million tons in China.However,the utilization of fruit has not attracted people’s attention,and there is little research on the components other than oil.In order to comprehensively develop and utilize lacquer tree seed resources,this paper used lacquer seed meal as raw material to extract lacquer tree seed protein(LSP)by alkali-soluble acid precipitation method,determined the amino acid composition and physicochemical properties of LSP,and evaluated the nutritional value of LSP.Lacquer tree seed protein/chitosan composite film and lacquer seed protein/chitosan/lacquer wax composite film were prepared by casting method.The thermal stability of the composite film was measured by differential scanning calorimetry(DSC);The morphology of the films was observed by scanning electron microscopy(SEM);Fourier transform infrared spectroscopy(FT-IR)was used to analyze the characteristic functional groups of the film components;The crystal structure of the films was analyzed by X-ray diffraction(XRD).The effects of the film-making raw material mass ratio on the mechanical properties,water vapor transmission rate,color,thermal stability,chemical structure,microstructure and crystal structure of the film were discussed.The main results are as follows:1.Lacquer seed meal contains at least 17 kinds of amino acids,among which leucine(3.05%)has the highest content of essential amino acids;The highest content of non essential amino acids was glutamic acid(9.31%).The particle size and zeta potential of LSP at different pH values are significantly different,and the particle size is large in acidic solutions.When the pH value is lower than the isoelectric point,the protein is positively charged,and after the pH value is greater than the isoelectric point,the pH The higher the value,the smaller the particle size and the protein is negatively charged.The water holding capacity and oil holding capacity of LSP are 0.83g/g and 1.85g/g,respectively;The emulsifying ability and emulsifying stability were 15.52 m2/g and 84.90% respectively;the foaming ability was126.67%.The FT-IR and XRD of LSP are similar to soybean protein isolates(SPI),and the denaturation temperature is 88.04 ℃.2.The lacquer tree seed protein/chitosan(CH)composite membrane was prepared by casting method.The water vapor transmission rate of the films increased slightly after adding lacquer seed protein.The tensile strength(TS)of the film decreased significantly,and the elongation at break(EAB)increased significantly.When the ratio of LSP to CH is 1:1,the TS and EAB of the composite film have the maximum value.The surface of the LSP/CH films is uneven,rough,with no pores in the cross section.FT-IR showed that the addition of LSP promoted the breaking of hydrogen bonds in CH and more free hydroxyl groups were found.XRD showed that the crystal structure of the composite membrane and the pure chitosan membrane changed greatly.The DSC curves showed that the new crystalline structure of the composite film was probably formed,and the melting temperature was higher than that of the pure chitosan film.3.Different volumes of lacquer wax emulsion was added to LSP/CH membrane to improve the water barrier properties of the film.When the content of lacquer wax in the composite film increased from 0.1%(m/m)to 0.5%,the water vapor transmission rate decreased accordingly,and the highest water vapor transmission rate can be reduced by77.82%.The mechanical properties of the films were decreased by adding a small amount of wax.The results showed that the surface of the film was smooth and the cross section was rough.The results of contact angle(CA),SEM,IR,DSC,XRD,particle size and zeta potential,as well as the moisture content(MC)and total soluble matter(TSM)of the film were comprehensively analyzed.It was concluded that the wax did not enhance the hydrophobicity of the film surface.The increase of water resistance of the blend film was due to the appearance of large particles with poor hydrophilicity and dense structure composed of lacquer seed protein,chitosan,lacquer wax and surfactant.The new aggregated structure has hydrophilic surface,strong internal hydrophobicity,compact structure and high melting point.