Application Of Sodium Alginate-silver Nanoparticle Composite Antibacterial Coating On Fruit Preservation

Recently,the study of edible coating as matrices for incorporating antimicrobial nanoparticles to prepare composite antibacterial coating on fruit preservation has attracted more and more attention.Sodium alginate(SA)is a natural polysaccharide and can be used as edible coating to preserve fruit by reducing water loss,enhancing appearance and improving mechanical properties,etc..After adding silver nanoparticles(Ag NPs)with antibacterial properties,it can reduce microbial corruption of fruit and thus prolong the shelf life of fruit.In this paper,bio-synthesized silver nanoparticles was added into SA coating to enhance the physical and antibacterial properties of the coating,and improve the fruit preservation ability of the coating.The main results are as follows:1.Sodium alginate-silver nanoparticle(SA-Ag NP)composite antibacterial film was prepared by incorporating silver nanoparticles into sodium alginate and characterized.The chemical composition of film was investigated by X-ray photoelectron spectroscopy(XPS)technique and the thickness was also measured.The surface morphology,hole width,roughness,and elasticity of SA-Ag NP film were evaluated by atomic force microscope(AFM).The swelling rate and the water solubility were measured as well.The representative Gram-negative bacterium(Escherichia coli)and Gram-positive bacterium(Staphylococcus aureus)were selected to evaluate the antibacterial effect of the composite film.The XPS spectrum confirmed the existence of Ag NPs in this composite film.The thickness of SA-Ag NP composite film was 0.01 mm.The results of AFM displayed that the film was covered with hole,the hole width decreased from 443 nm to 396 nm,the surface roughness(Ra)increased from 10.5 nm to 17.3 nm and the slope of force curve increased from 0.13 to 0.48 indicating the enhancement of elasticity after adding Ag NPs.The swelling rate of the SA-Ag NP composite film was 17.95% and the water solubility was 34.33%.The SA-Ag NP composite film showed tremendous antibacterial activity against E.coli and S.aureus with inhibition zone of 11 mm and 13 mm,respectively.2.The effects of sodium alginate coating treatment and sodium alginatesilver nanoparticle composite coating treatment on the physiological and biochemical quality and storage period of banana after harvest were investigated.The results indicated that different treatments affected the changes of banana organoleptic quality,weight loss rate,total soluble sugar,malonaldehyde(MDA),total phenol content and total flavonoid content.The SA-Ag NP treatment during the storage could delay the change of fruit appearance,slow down the decay of banana,reduce the weight loss and total soluble sugar,delay the increase of MDA content and inhibit the decrease of antioxidants such as total phenols and total flavonoids,compared with those of SA treatment and untreated fruit(CF).The composite antibacterial coating prolonged the shelf life of banana.Observed from the appearance change,the banana storage period was 9 d for SA-Ag NP coating treatment,7 d for SA coating treatment,5 d for untreated fruit.3.The effects of sodium alginate coating treatment and sodium alginatesilver nanoparticle composite coating treatment on the physiological and biochemical quality and storage period of mango after harvest were investigated.The results indicated that different treatments affected the changes of mango organoleptic quality,weight loss rate,total soluble sugar,MDA,total phenol content and total flavonoid content.The combination of sodium alginate and silver nanoparticles could significantly delay the development of mango browning,maintain weight loss,inhibit the increase of total soluble sugar and MDA content compared with the SA coating treatment and CF.Furthermore,the total phenol and flavonoid content of SA-Ag NP coating treatment were also higher than that of CF and SA coating treatment.Observed from the appearance change,the mango storage period was above 9 d for SA-Ag NP coating treatment,6 d for SA coating treatment,3 d for untreated fruit.These results showed that the SA-Ag NP composite antibacterial coating developed in this study has great potential in fruit preservation and provides a new approach to utilize the nanobiotechnology for fruit preservation.