Preparation Of Thymol Nanoparticle And Its Application In Keeping Chinese Chestnut Fresh

Chestnut(Castanea mollissima Blume)is China’s major economic crops,the chestnuts are easy to rot and germination during the storage.In this study,thymol-loaded chitosan nanoparticles was achieved by a two-step method to improve the application of thymol in food preservation,oil-in-water emulsion and ionic-linking technique,with chitosan as the drug carrier,sodium tripolyphosphate(TPP)as the crosslinker reagent,Tween-80 as the emulsifier.The effects of thymol-loaded chitosan nanoparticles on the storage efficiency of chestnuts were studied by measuring the physiological and biochemical indexes,sensory evaluation and microbial index of chestnut in storage period.The main conclusions are as follows:(1)The thymol-loaded chitosan nanoparticles were prepared by ion-crosslinking and oil-in-water emulsion technique.The effects of chitosan concentration,thymol concentration,TPP concentration,crosslinking time,pH,stirring speed on the particle size and entrapment efficiency of nanoparticles were studied.The optimal condition for the chitosan nanoparticles was investigated by orthogonal test with encapsulation efficiency(optimization process 1)as response value: the concentration of chitosan is 5mg/mL,the concentration of TPP is 1mg/mL,the concentration of thymol is 0.8mg/mL,the quality of CS: TPP =5:1,the pH is 4.Under the optimal conditions,the encapsulation efficiency of chitosan nanoparticles is 61%.The optimal condition for the chitosan nanoparticles was investigated by orthogonal test with average diameter(optimization process 2)as response value: the concentration of chitosan is 1mg/mL,the concentration of TPP is 1mg/mL,the concentration of thymol is 0.4mg/mL,the quality of CS: TPP =5:1,the pH is 4.Under the optimal conditions,the average diameter of chitosan nanoparticles is 212.51 nm.(2)The characterization and cumulative realease efficiency of thymol nanoparticles obtained by orthogonal test with the entrapment efficiency and particle size as the index were measured respectively.The particle size of optimization 1 is 338.92 nm and the polymer dispersity index(PDI)is 0.213.The particle size of optimization 2 is 232.42 nm and the PDI is 0.271.The spherical morphology of the two kinds of nanoparticles can be visually observed by transmission electron microscopy,and the dispersibility is good and no agglomeration phenomenon.The results of Fourier Transform infrared specttoscopy(FTIR)and X-Ray diffraction(XRD)showed that chitosan was crosslinked with TPP successfully,and thymol was successfully embedded into nano-particles.It was found that the cumulative release rate of thymol was 74.15% at 48 h of optimization 1,and the cumulative release rate of thymol was 50.42% optimization 2.The results showed that thymol was encapsulated into chitosan nanoparticles with a sustained release effect.(3)The nanoparticles optimized with the entrapment efficiency and particle size as the indexes and the corresponding blank nanoparticles were used to preserve the chestnut.The results showed that the chitosan nanoparticles had no significant effect on the weight loss of chestnut,water content,but it could significantly inhibit the activity of amylase in chestnut,the hydrolysis of starch,the increase of soluble sugar content and the growth of bacteria and fungi on chestnut surface,and significantly reduced the decay rate and mildew rate of chestnut,and inhibited the chestnut’s respiratory strength to a certain degree.Based on the comprehensive analysis,the optimal treatment to the chestnut was optimized by using the encapsulation efficiency as the index.