Study On The Preparation Of Polysaccharide-Silver Nanoparticles And Its Application In Litchi Preservation

Litchi is not only taste sweet,but also rich in nutrients,which make it a well-known subtropical fruit.However,due to the respiratory metabolism in harvest season and it is prone to decay.Hence,it’s important to study postharvest technology of litchi.Nanotechnology is a novel technique with physicochemical properties and promising application in pharmaceutical and food industry.In this study,the preparation of silver nanoparticles composite particles(AgNPs)by using emblic polysaccharide as reductant and stabilizer was carried out,and the effects of AgNPs on the postharvest preservation of litchi and the inhibitory of the cells proliferation about three different cells were also evaluated.The major research contents are as follows:1.Response Surface Optimization of the AgNPs preparation and its structure characterizationThe experiment was carried out based on the principle of Box-Benhnken center combination.Response surface methodology was applied to optimize the preparation of AgNPs,with the diameter of bacteriostatic circle as the response value by using three factor and three level analysis method.The optimal conditions for the preparation of AgNPs were as follows:the pH 8.94,the volume ratio of silver nitrate solution to polysaccharide solution 2.3:1(v/v)and the reaction temperature 30℃,and the theoretical maximum diameter of inhibition zone was 16.91 mm.The synthesized AgNPs showed significant under these condictions,with an inhibition zone diameter of 16.89±0.01 mm,indicating that the response surface method was reliable in the preparation of AgNPs.The properties of AgNPs were determined by X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscope(TEM).The results showed the particle size of AgNPs ranged from 5 to 20 nm,displaying a face centered cubic structure with a spherical or nearly spherical shape.2.The effects of AgNPs on postharvest preservation of litchiIn present study,the samples(litchi fruit of ’Feizixiao’)were treated with 0μg/mL(blank control),50 μg/mL,100 μg/mL and 500 μg/mL AgNPs,with 45%prochloraz as positive control.The results showed,the AgNPs treated fruits was well preserved with significant higher rate in healthy and lower rate in browning index and anthocyanin content than that of blank control.The content of TA,the activity of PPO and POD in treated group were higher than that of the blank control group,showing a dose-dependent effect.There was no significant difference between the samples treated with 100 μg/mL and 500 μg/mL,it’s reasonable to take 100 μg/mL dosage in lichi fruit postharvest preservation.The results indicated that,due to the larger surface and other special structure of AgNPs,so it was easy to form a protective film on skin surface,reduced the respiratory metabolism of litchi effectively,alleviated the decayed and browning rate of pericarp,and prolong storage time,increased the value of the goods.3.The Influence of AgNPs on the proliferation of cellsIn this paper,three types of cells,namely HaCaT,LO2 and HepG-2,were applied for cell proliferation analysis by using MTT method.The results showed that the AgNPs solution had a slight effect on the growth of HaCaT cells and LO2 cells.The survival rate of HepG-2 cells was only 6.65%when the AgNPs concentration was 160 μg/mL,this showed that the AgNPs had a greater inhibitory effect on HepG-2 cells.In addition,the morphological changes of cells were consistent with the results detected by MTT method.The intracellular reactive oxygen species(ROS)analysis showed that the HepG-2 AgNPs had a remarkable inhibitory effect on the proliferation of HepG-2 cells with the concentration of 160 μg/mL after 24 h adminstraion.It is concluded AgNPs could suppress HepG-2 proliferation,attributing to the intracellular oxidative damage induced by AgNPs,while non-cytotoxic effect was observed on the growth of normal cells.It’s worthy of further investigation to explore the mechanism in future.