Preparation And Performance Analysis Of Zanthoxylum Bungeanum Extract/nano-cellulose/soybean Protein Isolate Based Films

The total production of pepper（Zanthoxylum bungeanum Maxim）in China is the first in the world and the resources are very abundant.As a by-product of the pepper industry,pepper leaves and branches,except for a very small amount of young leaves that have been exploited,have been burned directly as agricultural waste,which not only pollutes the air,but also has not been reflected in its value.On the other hand,the environmental and human health hazards caused by traditional plastic packaging cannot be ignored,and edible biopolymeric packaging films based on natural polymer materials have become increasingly popular.Among them,soy protein isolate（SPI）films have potential applications,however,their poor mechanical properties,high water sensitivity and single function have greatly limited the practical applications of SPI films.To this end,in this paper,we prepared pepper leaf extract and pepper branch nanocellulose,developed a pepper leaf extract/pepper branch nanocellulose/soy protein isolate composite film,defined the amount of pepper leaf extract and pepper branch nanocellulose to be added when the comprehensive performance of the film is optimal,and determined the optimal process conditions for the preparation of pepper branch nanocellulose by sulfuric acid hydrolysis.The main findings are as follows:（1）The effects of different concentrations of pepper leaf flavonoid extracts on the microstructure,physical properties and antioxidant properties of SPI films were investigated.The results showed that pepper leaf flavonoid extract had good compatibility with SPI,and the films added with pepper leaf flavonoid extract had a brown appearance with excellent light transmission and UV-blocking properties.The addition of pepper leaf flavonoid extract significantly improved the mechanical properties and antioxidant properties of the films.The overall performance of the films was optimal when the pepper leaf flavonoid extract was added at 5%（relative to SPI mass）,at which time the tensile strength（TS）and contact angle（CA）were 12.95 MPa and 74.80°,respectively,improving to 1.62 and 1.09 times that of the pure SPI films,respectively.The elongation at break（E）and water vapor transmission rate（WVP）were 85.33%and 0.91 g·s^-1·m^-1·Pa^-1×10^-10,decreasing by 23.35%and 1.32%,respectively.the DPPH radical scavenging rate was 69.98%,the ABTS radical scavenging rate was 85.73%,and the iron atom reduction capacity was 7.10 mg Trolox/g,which increased to 2.64,1.07 and 1.93 times,respectively.（2）SPI/5%antioxidant film provided better preservation effect during storage of sainfoin fruit.The pepper leaf flavonoid extract/SPI film was very important in inhibiting the degree of decay,maintaining color,and retaining its V_Ccontent and moisture in the sainfoin fruit.At day 18,the weight loss rate of sainfoin fruit packed with SPI/5%antioxidant film was 17.49%,which was 10.70%lower than that of pure SPI film;the decay rate was 31.25%,which was 28.47%and 16.67%lower than that of fresh film and pure SPI film,respectively;the V_Ccontent was 28.60 mg/100g,which was 6.39 mg/100g higher than that of fresh film and pure SPI film packaging,respectively.（3）The optimum process conditions for the preparation of pepper branch nanocellulose by sulfuric acid hydrolysis were determined as follows:sulfuric acid mass fraction 60%,acid digestion temperature 55℃,acid digestion time 70 min,acid digestion material-liquid ratio1:25,and the yield of nanocellulose under these conditions was 61.55%±0.45%.The nanocellulose of pepper branches prepared by sulfuric acid hydrolysis was needle-like with two pointed ends,the length distribution ranged from 50 to 400 nm with an average length of166.76 nm,and the diameter distribution ranged from 5 to 50 nm with an average diameter of 13.70 nm,still maintaining the typical cellulose type I crystal structure,and the crystallinity increased to 96.98%.（4）The filling of pepper branch nanocellulose significantly improved the mechanical and hydrophobic properties of the SPI antioxidant films.The overall performance of the film was optimal at 4%（relative to the mass of SPI）,where the tensile strength（TS）was 30.04MPa,which increased to 2.32 times of the original one,the elongation at break（E）was8.53%,which decreased by 90.00%,the contact angle（CA）was 83.33°,which increased by20.70%,and the water vapor transmission rate（WVP）was 0.72 g·s^-1·m^-1·Pa^-1×10^-10,which was reduced to 0.79 times.