Preparation Of Solid Lipid Aqueous Dispersion And Its Application In Blueberry Coating Preservation

As an efficient,healthy and environment-friendly fresh-keeping method,edible coating has been widely used in the fresh-keeping of fruits and vegetables.At present,edible coating preservation materials are hydrophilic colloidal materials mainly composed of polysaccharides and proteins.When coating preservative is applied in the form of liquid,there are some problems such as too long drying time,accelerating the water loss of fruits and vegetables and easy to be bred by microorganisms.In order to enhance the surface hydrophobicity of hydrophilic colloid based edible coatings,this paper attempted to prepare solid lipid nanoparticles(SLNs)from Chinese white wax(CWX)by polymorphic transition of crystal,and studied the cold-burst Phenomenon of CWX crystal in surfactant aqueous solution during freeze-thaw(FT);Then,the effects of the addition of Chinese white wax solid lipid nanoparticles(CWX-SLNs)on the surface hydrophobicity of bacterial cellulose nanofibers(BCNFs)/chitosan(CS)composite films were investigated;Based on the above,the preservation effect of functional compound coating dispersion in blueberry was evaluated.The main results are as follows:(1)Three-phase contact angle(θ)of CWX crystal in aqueous surfactant solution is the main factor affecting the cold-burst phenomenon in the FT process.The types and concentration of surfactant have an important influence on the cold-burst phenomenon of CWX crystal.The effects of CWX content,surfactant concentration,FT times and ultrasonic time on the properties of CWX-SLNs were investigated by particle size and zeta potential.The particle size changes of CWX crystal during several FT process were investigated by optical microscope,and the stability of CWX-SLNs aqueous dispersion was investigated by static storage;The results showed that the CWX-SLNs prepared under the conditions of CWX content of 2 wt%,Tween 20 concentration of 0.5 wt%,FT times of 4times and ultrasonic time of 20 min had uniform particle size distribution,good storage stability and the best comprehensive properties.(2)The influence of the addition of CWX-SLNs on the surface hydrophobic properties of BCNFs/CS composite films was explored.The influence mechanism was studied by analyzing the effects of CWX-SLNs at different concentration on the infrared structural characteristics,optical properties,water content,water solubility,surface hydrophobic properties,water vapor barrier properties and mechanical strength of the blend films.The results showed that the addition of CWX-SLNs can effectively enhance the surface hydrophobicity of CWX-SLNs/BCNFs/CS composite films.After modified by CWXSLNs,the surface water contact angle of the composite films increased significantly.When addition concentration of CWX-SLNs is 0.3 wt%,the surface water contact angle of the composite films can reach 105°,which is only 76° compared with that of the unmodified composite films;The barrier ability to UV-vis light of the composite film modified by CWX-SLNs is significantly enhanced,and has a concentration effect with the addition amount of CWX-SLNs.(3)The functional compound coating dispersion and CWX-SLNs aqueous dispersions were applied to blueberry surface by immersion and spraying,respectively.The preservation effects of compound coating on weight loss rate,total soluble solids(TSS)content,p H value,titratable acidity(TA),total phenolics content,DPPH radical scavenging rate,malondialdehyde(MDA)content,and cell membrane permeability of blueberry during storage were investigated.The simulation effect of CWX-SLNs aqueous dispersion on blueberry epidermal cuticle was investigated;The results showed that compared with the control group,weight loss rate,TSS content and total phenolics content of blueberry treated with compound coating decreased more slowly,the DPPH free radical scavenging rate was higher,and the permeability of tissue cell membrane was lower;With the extension of storage time,the p H value of blueberry treated with compound coating increased gradually,but it was always slightly lower than that of blueberry in the control group.TA did not change significantly during storage,but it was always slightly higher than that of blueberry in the control group.In a word,compared with the control group,the shelf life of blueberries treated with compound coating was extended to 10 days at room temperature,which still had good commercial value.