| With the improvement of living standards, people has higher requirement for the quality of food. Due to the high cost, complex equipment, not easy to operate, many previous methods of food preservation have been unable to meet demand. Functional packaging material is gradually developed in this background, such as modified atmosphere packaging bags, anti-bacterial packaging bags. Because contains antibacterial and antioxidant, the packaging material can effectively inhibit the propagation of microorganisms in food to extend food preservation. Furthermore, due to environmental issues have become increasingly serious, the use of plastic packaging has been limited strictly, so a biodegradable packaging material is particularly important.This thesis was studied with polyvinyl alcohol as base material, citric acid for preservative. By adding different concentrations of citric acid in the mother liquor of polyvinyl alcohol study the effect of citric acid on the indicators of polyvinyl alcohol film. Packaging carp, fresh-cut apples, cherry tomatoes fruit with citric acid modified polyvinyl alcohol films, and then measuring its freshness indicators, to study the preservation effect of citric acid modified film. The main research conclusions are as follows:(1) Citric acid has a certain effect on the physical and chemical properties of polyvinyl alcohol film. With the increase of mass fraction of citric acid, water absorption and solubility of the film has a substantially downward trend. When the mass fraction of citric acid was 7.5%, the film solubility was increased. By scanning electron microscopic analysis, citric acid dispersed evenly in the polyvinyl alcohol film. Antibacterial experiments show that citric acid film has an antibacterial effect on E. coli and Staphylococcus aureus. Citric acid was added to reduce the water vapor permeability.(2) Citric acid crosslinked PVA can improve the performance of color film. With the increase of the mass fraction of citric acid, the tensile strength of the film increased, but elongation decreased. Citric acid has a greater impact on the light transmittance and haze of films. The haze is rising with the increasing amount of citric acid. Citric acid content have a great effect on the color of films. Thermogravimetric analysis showed that citric acid can increase the thermal decomposition temperature of the film, thereby enhancing the thermal stability of the film.(3) The research was found the preservation effect of citric polyvinyl alcohol film was significantly higher than those without citric polyvinyl alcohol film, and extend the shelf life of fish 1-2 days by analyzed the TVB-N value, the total number of colonies, p H, drip loss and thiobarbituric acid value. The experimental group containing 0.5% citric acid had better preservation effect than the other groups on the TVB-N value, the total number of colonies, drip loss of the three indicators, the experimental group. 0.75% polyvinyl alcohol film group obvious effect of citric acid at p H indicators, which may be due to the film itself contains more acidic, so 0.5% citric acid polyvinyl alcohol film has a certain role in the preservation of the fish.(4) According to experiments, fresh-cut apples packaging with the citric acid modified polyethylene film could extend the shelf life. Mass fraction of 2% citric acid modified film can effectively inhibit apples browning, reduce fruit weight loss, maintaining fruit firmness, and soluble solids content, reduce the loss of Apple Vc.(5) Polyvinyl alcohol film added the citric acid had a role in preservation of cherry tomatoes, which could effectively prevent the loss of moisture in the fruit, keep fruit firmness and soluble solids content, while reducing the loss of vitamin C. 1% of citric acid films had good preservation effect in the first four indicators, 0.5% of citric acid films can better maintain the sensory quality of the fruit. |
PDF Full Text Request