| In our country commercially available eggs are mostly dirty eggs. Sample survey showed that about10%in the surface of commercially available eggs carry salmonella, E. coli serious overweight occur on64%of eggs. Therefore, researching and exploring environmental and degradation coating packing material for packaging fresh eggs are great significance to carry out the production of egg products shifting from traditional to modern automated production paradigm, which is carbon emissions, environmental protecting and healthy.Polyvinyl alcohol (PVA) is easily filming and biodegradable, good sanitation and safety, so it shows broad prospect in food coating preservation. However, its good hydrophilic property makes the higher permeability of formed film, that impact its application in food preservation packaging. Liquid paraffin which is hydrophobic oil substance has good barrier fresh performance in the packaging of food preservation. In this subject, composite emulsifier was used to emulsify liquid paraffin and PVA, with nano-SiO2, nano-TiO2modifying, optimized and analyzed the preparation conditions of process and performance, studied the nano-composite coating material influence long-term storage preservation effect of egg, the idiographic content as follows:1. The impact of modification for PVA-liquid paraffin composite coating material by nano-SiO2, nano-TiO2the flim-forming propertiesWith the Box-Benhnken Design response surface test method, studying on modification for PVA with liquid paraffin composite coating material by nano-SiO2, nano-TiO2, optimize this coating material ratio of raw material; establishing a mathematical model, in which water vapor transmission rate of formed filmed film as objective function, nano-SiO2, nano-Ti02and liquid paraffin as experimental factors; analyzed the various factors and their interactions effect on water vapor transmission rate of formed film. The result showed that:The water vapor barrier performance of the PVA based composite coating material for packaging could be effectively enhanced by adding Nano-SiO2, nano-TiO2and liquid paraffin, the water vapor transmission rata of formed film of optimal group decreased by26.42%(p<0.05) compared with the control group; There were significant interactions between nana-SiO2and nano-TiO2and between nano-SiO2and liquid paraffin for the effects on the water vapor transmission of formed film of composite coating-packaging material. With the increase of nano-SiO2addition, the water vapor transmission rate of composite packaging material was decreased with the appropriate increase of the proportion of nano-TiO2or the appropriate decrease of the proportion of liquid paraffin.2. Resurch on optimization of PVA-liquid paraffin nano-compositing coating material preparation process and film-forming propertiesThe orthogonal array design method was used to study the effects of cross-linking time, cross-linking temperature and film-forming temperature on the composite film-forming water vapor transmission rate, optimized composite coating materials preparation process with film-forming water vapor transmission rate value as the objective function; Measured the inhibitory effect of composite film; Studied the microstructure of the film-forming material by infrared spectroscopy(FTIR); Detect the amount of evaporation residue, heavy metals and decolorizing test of the coating packaging materials. The result showed that the primary and secondary order in various process factors affecting the film formation water transmission rate value is that cross-linking temperature> film-forming temperature> cross-linking time (p<0.01). Cross-linking time and film-forming temperature on the water vapor transmission rate have a significant interaction (p<0.05), When cross-linking time and film-forming temperature affecting the film-forming water vapor transmission rate, their respective critical values would be presented with the increase of the other decreased. So improving the film-forming temperature appropriately to shorten cross-linking time could reduce composite film-forming water vapor transmission rate. The best result of comprehensive regression optimization process is that when cross-linking temperature is79.8℃, cross-linking time is45.2min, film-forming temperature is60.3℃. The reaction generating new molecular functional groups between nano-SiO2, nano-TiO2and PVA is that Si-O-C, Ti-O-C and Si-O-Ti. The evaporation residues, heavy metals and the decolorizing testing of nano-modified composite packaging material were in line with the relevant food packaging hygiene standards.3. Studied on Polyvinyl alcohol-liquid paraffin nano-composite coating material effect on the storage and preservation of fresh eggCompared with the control groups is that chitosan coating, ordinary PVA nano-modified coating and nano-modified PVA based liquid paraffin once coating clean eggs, the treatment group is nano-modified PVA based liquid paraffin composite secondary coating. Under the conditions humidity of50±2%, temperature of35±2℃storage and preservation test, measured and analyzed the physical and chemical indicators of storage and sense indicators. The results showed that:Compared with the control group(after10days dispersing yolk), Nano-modified PVA-Liquid paraffin composite packaging materials secondary coating eggs group (after24days dispersing yolk) had significantly improve the shelf life of fresh eggs. after18days of storage, the clean egg water loss rate remained at about2.63%, smaller pH change from storage initial8.2to8.575, Haugh unit and yolk index fell marginally, Haugh unit from the initial84.966dropped to60.305, yolk index decreased from the initial0.468to0.218, the result of sensory evaluation is satisfactory, all indicators were better than the control group. |
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