| Electrostatic spraying(ES)has received increasing attention in the food industry due to its advantages of material saving,high efficiency,and continuous operation.However,the efficiency of electrostatic spraying is not only affected by operating parameters,but also by the inherent properties of the materials.Chitosan is one of the most popular natural coating film packaging materials.Its good film-forming properties and excellent antibacterial ability make it be a hot spot for food preservation.In this paper,the effects of deacetylation degree(DD,81.0%,88.1%,95.2%)on the properties of chitosan film-forming solution,the characteristics of electrostatic spray film formation and the preservation effect of different foods after film formation were studied.The application of the film provides a theoretical basis in food preservation.The main research contents and results of this paper are as follows:(1)The properties of chitosan film-forming solutions with different DD was measured by surface tension,contact angle,rheological properties and electrical conductivity.The industrial camera and optical microscope system were used to collect the spray angle and spray particle size of the chitosan film-forming solution during the electrostatic spraying process.The matlab software was used to analyze the relationship between the performance of film-forming solution and the electrostatic spraying process.The microstructure of chitosan films prepared by electrostatic spraying was analyzed by SEM,AFM and XRD to correspond to the macroscopic properties(including mechanical properties,water resistance,water solubility,water activity and antibacterialproperties),explaining the chitosan in the electrostatic spraying process.The film formation mechanism and the chitosan formula with the optimal electrostatic spray film formation effect were determined by fuzzy comprehensive evaluation method.The results showed that as the deacetylation degree and concentration increased,the contact angle and conductivity of the film-forming solution on the glass plate increased,and the surface tension and the contact angle on polystyrene plate were decreased.The spray angle of the chitosan solution in the electrostatic spraying process was in the range of10.5-15.9°,and the average median diameter of the droplet size was in the range of 6.4-13.9 ?m.The surface tension and viscosity were the main factors affecting the spraying process.Microstructure analysis of the films showed that the high DD chitosan film had a denser cross section,a rougher surface morphology and more metastable crystalline phases.Therefore,the high DD film had better water blocking ability and mechanical properties.For example,the water vapor permeability value of the 95.2% DD chitosan film was only60% of the 81.0% DD chitosan film.In addition,the 88.1% chitosan film with DD had the best antibacterial properties against Escherichia coli and Listeria monocytogenes.The chitosan film with the concentration of 1.2% and DD of88.1% was the optimal formula calculated by fuzzy comprehensive evaluation.(2)The chitosan film with concentration of 1.2% and different DD was electrostatically sprayed on the mozzarella cheese with uniform composition and appearance and then the cheese was kept at a low temperature(4 °C).The effects of electrostatic spraying on chitosan films with different DD were investigated by evaluating the physical and chemical properties of cheese(including weight loss rate,color,pH value,lipid peroxide value),texture,mold content,and sensory quality.The results showed that the chitosan film with a deacetylation degree of 88.1% improved the total number of molds by 15%compared with the control group,and had a good effect on the sensory quality and peroxide value.(3)The chitosan film with concentration of 1.2% and different DD was electrostatically sprayed on strawberry with irregular appearance and then the strawberry was kept at a low temperature(4 °C).The total number of molds,weight loss rate,pH value,soluble solids,hardness,flavonoids and superoxide dismutase were measured during storage.The effects of chitosan films with different DD on strawberry preservation were studied.The chitosan film with a deacetylation degree of 88.1% had the best effect on the weight retention,pH value,TSS value and hardness of the strawberry.In addition,the malondialdehyde content of the treated group sprayed with the chitosan film with a deacetylation degree of 88.1% reached only 3.28 ?mol/L when stored for11 days,which was only 76% of the control group.For microbial indicators,the antibacterial ability of chitosan had a certain inhibitory effect on mold growth.The chitosan film with a deacetylation degree of 88.1% was the best bacteriostatic agent in this experiment,and the total number of molds reach 6.01 log CFU/g after 11 days' storage,which was about 10% lower than the total number of molds in the control group.In summary,the change of the amino acid concentration and molecular force brought about by the deacetylation degree had a composite effect on the properties of the chitosan film.Considering comprehensive investigation of film formation and insurance effect,the chitosan with concentration of 1.2%,deacetylation degree of 88.1% was the best electrostatic spray film forming formula.It can be a safe,cheap and simple food preservation method. |
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