| There is currently increased interest in the application of renewable and biodegradable polymers in coating and packaging due to concerning over the decline in petroleum-derived resources and the aggravation of environmental pollution caused by the massively use of plastic food packaging materials.Soy protein isolate(SPI)is a by-product obtained from soybean oil processing.SPI owns good film-forming capacity and nutritional value.The SPI-based film has moderate mechanical properties and excellent oxygen and oil barrier properties that allow its application in food packaging and coating.However,the poor strength and high water sensitivity of SPI films have limited their commercial applications.Therefore,the performance enhancement of SPI films is necessary.Moreover,the incorporation of nature antioxidant into SPI films to yield films with antioxidant activities could decline the oxidative deterioration and extend shelf-life of food,which may also improve application values of films.In this work,nano-SiO2 and licorice residue nanocellulose(LNC)were used as reinforcement agents to enhance the mechanical and barrier properties SPI films.Licorice residue extract(LRE)was used as antioxidant to improve the antioxidant activities of SPI films.The main findings are as follows:(1)The effects of different sizes and contents of SiO2 nanoparticles on the structure and physical properties of the SPI-based films were investigated.The results showed that the incorporation of SiO2 significantly improved the mechanical strength and barrier properties of films.The SPI/SiO2 films were compact and exhibited good thermal stability.The films showed the best optimum comprehensive properties when the particle size and content of SiO2 was 8.11 nm and 3%,respectively.In this condition,tensile strength(TS)and contact angle(CA)were 9.04 MPa and 79.7°,increased by 36.3%and 32.4%,respectively.The water vapor permeability(WVP),oxygen permeability(OP),and elongation at break(E%)was 1.28 × 10-5 g m m-2 day-1 Pa-1,7.23×10-5 cm3 mm mm-2 day-1 atm-1,and 105.05%,decreased by 22.4%.14.9%,and 36.9%,respectively.(2)Nanocellulose was extracted from licorice residue.The prepared LNC was incorporated to SPI for the production of eco-friendly nanocomposites.The effects of LNC content on the structure and mechanical and barrier properties of SPI films were characterized.The results revealed that LNC had a short rod-like structure(100-400 nm in length and 10-35 nm in diameter)and had high stability in aqueous media.LNC had a higher crystallinity degree.The microstructure of SPI/LNC films was rough and the crystalline structure of films was enhanced due to the incorporation of LNC.The addition of LNC also significantly improved the properties of SPI films,especially at 6 wt%.In this condition,TS and CA of SPI films were 11.17 MPa and 72.40,increased by 68.5%and 20.3%,respectively.WVP,OP,and E%was 1.20×10-5 g m m-2 day-1 Pa-1,2.81×105 cm3 mm mm-2 day-1 atm-1,and 63.8%,decreased by 27.3%,66.9%,and 61.8%,respectively.(3)The effects of different concentrations of LRE on the microstructure,physical properties,and antioxidant activities of SPI films were investigated.Antioxidant SPI films were also applied to the pork lard preservation.The results showed that the microstructure of SPI films with LRE was rough.The films with LRE had excellent UV barrier properties,the surface color became deeper brown.The incorporation of LRE significantly improved the methanical and barrier properties,especially at 5 wt%.In this condition,TS and E%of SPI films were 10.83 MPa and 101.7%,respectively.CA,WVP,OP,and was 71.4°,1.42×10-5 g m m-2 day-1 Pa-1,and 6.14×10-5 cm3 mm mm-2 day-1,respectively.In addition,the SPI/LRE films have excellent free radical scavenging activities.After room temperature storage for 20 days,the peroxide values and acid values of the grease wrapped with SPI/LRE films were lower than those of grease wrapped with control films and polyethylene plastic,indicating good preservation effect of SPI/LRE films on grease. |
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