| Salted duck egg is a kind of famous Chinese traditional egg product, which is loved by masses of consumers in our country, and at present the production and consumption amount is very large. But now the cooked salted duck eggs are commonly packaged using vacuum package, of which the cost is higher than coating package and could cause "white" pollution. In addition, the mechanization degree of traditional process is so low. The coating fresh-keeping package of salted duck eggs could consume lower package material, and easily realized mechanization and automation. Therefore, researching and exploring biodegradable coating material for salted duck egg packaging are of great significance, which could realize modern automated production of traditional salted duck egg, and be characterized by high efficiency saving energy and green environmental protection.Because of polyvinyl alcohol (PVA) is biodegradable and of good safety, so it shows wide application prospect in food packaging area recently. However, its strong hydrophilicity makes a high water permeability of formed film, which greatly impacts its application in food preservation packaging. Nano-SiO2, as a kind of modified material, can compound with many macromolecule polymer resins, thus enhancing the performance characteristics of the polymer film and the preservation effect for foods. In this paper, nano-SiO2 was used to modify PVA-based composite coating packaging material. The properties of formed film and the preservation effect of packaging were determined and analyzed. Based on the previous studies, the preservation effect of coating-packaging salted duck egg, with nano-SiO2composite coating material, for long-term storage was further investigated. The detailed contents are as follows:1.Study on modification for PVA-based composite coating material with nano-SiO2 The PVA-based composite coating material was modified with Nano-SiO2, and its preparation method was optimized by response surface methodology (RSM). The mathematical model was builed by using the water vapor transmission rate of formed film as response and nano- SiO2, steric acid and glutaraldehyde as influencing factors. The main and interactive effects of all three factors on the water vapor transmission rate of formed film were analysed. Furthermore, the microstructure and internal morphology of the formed film of polyvinyl alcohol-based nanocomposite coating material was scaned by infrared spectroscopy (FT-IR) and electron microscopy (SEM), respectively. The FT-IR and SEM results showed that there was an hybridization reaction occurred between nano-SiO2 and PVA by forming Si-O-C bond; nano-SiO2 was well dispersed in the composite coating material, which could effectively enhance the water vapor barrier performance of the PVA-based composite coating materia. Response surface experiment results indicated that the water vapor transmission rate of formed film of optimal group decreased by 31.43% (P<0.05) compared with that of the control group. There were significant interactions among nano-SiO2, stearic acid and glutaraldehyde on the water vapor transmission rate of formed film. The addition of nano-SiO2 could increase the added level of stearic acid and glutaraldehyde in the composite coating material, and thereby decreased the water vapor transmission rate of nanocomposite film. The water vapor transmission rate of composite film decreased and water vapor barrier performance increased with the content increase in nano-SiO2 within a certain range in 100 mL 5% (W/VH2O) of the PVA solution.2. Study on the packaging properties of formed film of PVA-based nanocomposite coating materialThe package efficiency properties of the formed film of PVA-based nanocomposite coating material was investigated by measuring the water vapor transmission rate, water absorption rate, light transmission rate, gas permeability property, and antibacterial property of the film and by comparing with PVA film and common PVA-based composite film (no nano-SiO2). The results showed that the water vapor and gas permeability of nano-SiO2 composite film reduced, water resistance and the light transmission rate were elevated compared with those of single PVA film and nonmodified PVA-based composite film. Whereas, the permeability such as water vapor transmission rate (18.78g·m-2·d-1), water vapor absorption rate (1.40%), O2 penetration rate (0.055g·m-2·d-1) and CO2 penetration rate (0.174g·m-2·d-1) decreased significantly by 8.61 g·m-2·d-1,1.07 times, 17.91% and 18.31%, respectively, compared with those of ordinary PVA-based composite films. In addition, at 600nm wavelength, light transmission rate (23.9%) increased by about 1.34 times, and adding appropriate amount of nano-SiO2 could also strengthen the antibacterial activity of the nano-SiO2 modified composite film.3. Study on the storage preservation effect of salted duck eggs by packaging of PVA-based nanocomposites coating materialThe salted duck eggs coated by ordinary PVA-based composite coating material were used as control experiment, and the salted duck eggs coated by nano-SiO2 modified PVA-based composite coating material were used as experimental treatment group. All the salted duck eggs of the two groups were stored at normal temperature for 6 months, and at the end of the storage, the physical and chemical as well as microbiological and sensory indices of the eggs of each group were measured and compared between two different treatment. The results showed that, after 6 months storage, the average water loss rate (6.53%) of the salted duck eggs coated with PVA-based nanocomposites coating material decreased by 14.53% compared with the control group (7.64%). Moreover, the aerobic plate count (362 CFU·g-1) and total volatile basic nitrogen content (7.97 mg/100g) also decreased significantly (p<0.05). This result indicated that coating the salted duck eggs with PVA-based nano-SiO2 composite coating material could effectively prevent the water loss in salted duck eggs, inhibit microbial growth and reproduction, and reduce the production of total volatile basic nitrogen, which well protected the color and flavor of salted duck eggs for 6 months storage. |
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