| There is increasing interest in the potential application of edible polymers as foodpacking films due to both environmental concerns and consumer demand for high-qualityfood products. Edible films cover the exterior of the food and make the final productsuitable for consumption. These films also offer great potential to extend the shelf lifeand improve the quality of many food systems such as fruits and vegetables through theirability to control moisture, oxygen, carbon dioxide, flavor, and aroma transfer betweenfood components and the surrounding atmosphere. Finally, edible films could be analternative to bio-plastics in packaging applications due to their abundant, renewable,environmentally friendly and biodegradable properties. Soy protein isolate (SPI) is awidely available biopolymer, that is often used to develop edible materials for diverseapplications. Water vapor permeability (WVP) and oxygen permeability (OP) are thebarrier properties that frequently determine the ability of an edible film to protect thefood product from decay due to exposure to environment. Mechanical properties are alsouseful in assessing the ability of the film and coating to protect and maintain the food’smechanical integrity. Although SPI films are a good gas barrier, their application hasbeen limited by poor mechanical properties and the water sensitivity of soy protein-basedmaterials.The objective and results of this work were separated in five parts as follows:(1) To evaluate the effect of temperature (20,60and80°C) and pH (2,7and12) onthe film forming properties, mechanical properties, barrier properties of SPI fims. Themodification treatments (ultrasonic, microwave and ultrasonic/microwave assistedtreatment) was carried out to regulate oxygen and carbon dioxide barrier properties ofSPI films, further control gas-selective permeability of SPI films in this work. In addition,all films obtained were flexible and transparent. Gas-selective permeability coefficientsof SPI film was from0.39to1.25, as indicated that gas-selective permeability of SPIfilm could be regulated according to the actual needs of food systems.(2) Wheat-bran cellulose (WC) and microcrystalline wheat-bran cellulose (MWC)were prepared, and ultrasonic/microwave assisted treatment (UMAT) was used to modifyMWC. The effects of UMAT time, power and temperature on yield rate, length,polymerization degree, swelling water capacity and water holding capacity of MWCwere decided. Response surface analysis was used to optimize UMAT condition. It wasfounded that with UMAT time, power and temperture increased, length, polymerizationdegree, yield rate of MWC decreasd, but swelling water capacity and water holding capacity of MWC increased. According to response surface analysis, when UMAT timewas15min, UMAT power was300W and UMAT temperature was30°C, yield rate ofMMWC was obtained, as87.8%.(3) WC and MWC were successfully prepared, and the WC, MWC, and MMWCcontent in SPI films improved the properties of the films, particularly their mechanicalproperties. Furthermore, the intra-molecular hydrogen bonds between SPI and the fillersare formed, and these interactions led to improved integration of the fillers into theprotein matrix. Ultrasonic/microwave assisted treatment has been used to modify MWCto MMWC that contained smaller particle size, larger surface area, and more freehydroxyls on the surface, all of which improved the film’s abilities as a water vapor andoxygen barrier. In addition, the different thermal properties of each film provide furthersupport for their properties, and were in agreement with the changes in molecularinteractions detected by FTIR analysis, and SEM analysis of film surface morphology.However, it was also found that an excess of fillers can degrade the properties of afilm because this can lead to agglomeration and heterogeneous dispersion in the matrixof the films. Above all, WC and MWC are found to satisfy the food industry’s demandfor a candidate edible film, and ultrasonic/microwave assisted treatment can furtherimprove the properties of these films.(4) Edible films were prepared using soy protein isolate (4g/100g), oleic acid(0-2g/100g) and stearic acid (0-2g/100g). Effects of the ratio of oleic acid to stearic acidand ultrasonic/microwave assisted treatment on the water vapor permeability (WVP) andcontact angle of the prepared films were evaluated. Changes in the ratios of oleic acid tostearic acid had significant effects on WVP and contact angle (p <0.05). It was foundthat the prepared films (oleic acid: stearic acid=2:3) had the lowest WVP value(0.1×10-12g·cm-1·s-1·Pa-1) and highest contact angle value (135°), when the treatmenttemperature, time and power were20°C,15min, and500W respectively. Additionally,when OA and SAwere added, the peak at2920cm-1appeared, indicating a certain degreeof interaction between the lipid and SPI. Additionally, differences in the surfacecharacteristics of the films suggest that the surface microstructure may be partiallyresponsible for differences in the WVP of the films.(5) Soy protein isolate (SPI,5.0g/100mL) films embedded with nano-TiO2(0,0.5,1.0,1.5and2.0g/100mL) were prepared by solution casting and modified byultrasonic/microwave assisted treatment (UMAT). The effects of nano-TiO2content andUMAT time on the films’ physical properties and structure were investigated. Incorporationof nano-TiO2significantly enhanced films’ mechanical properties and barrier properties,because of the intermolecular force between nano-TiO2and SPI. UMAT time≤20minobviously improved films’ tensile strength values (15.77MPa,245%higher than the control), and reduced water vapor permeability (1.8457×10-11g cm-1s-1Pa-1,72.11%lowerthan the control) and oxygen permeability values (0.8897×10-5cm3·m-2·d-1·Pa-1,57.66%lower than the control). SEM images also revealed a more compact and dense structure offilms when UMAT time≤20min. Films’ water adsorption properties were evaluated.GAB and Henderson models exhibited the best to fit experimental data, thus it waspredicted that films (1.5g nano-TiO2/100ml) could be stable at low moisture content (0.27kg of water/kg dry mass). |
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