| In recent years, the increasing of both environmental problems and people’s environment-protecting awareness fasten the studies of biodegradable film taking place of plastic film. Protein film is made of biomacromolecules. Great attention has been paid to them due to their unique mechanical properties and barrier properties. Due to it has widely sources, highly nutritional value, remarkable functions and the exist of a large number of hydrogen bond, hydrophobic bond, coordination bond and so on, peanut protein become good raw materials to be edible film. But its tensile strength and water resistance are low and poor, so the applications of protein films are limited.In this paper, low denatured defatted peanut meals were used as raw materials to extract peanut protein isolate. Firstly, the modification of glycosylation with xylose to peanut protein and the modification of glycosylation in combination with TGase to peanut protein were studied. The effect of glycosylation and TGase compound modification on the mechanical properties, barrier properties, infrared spectra and microstructure of peanut protein films were studied and the mechanism of compound modification of peanut protein film was discussed. The aim was to improve the mechanical and barrier properties of peanut protein films and provide a theoretical basis for the research and application of protein films.The main conclusions of the study are as follows:1. The preparation process of xylose glycosylated peanut protein to make films were optimized by single factor experiment and orthogonal tests according to tensile strength of PPI, the results showed that:Xylose glycosylated peanut protein condition:PPI concentration was 8%(w/v), xylose concentration was 10%PPI(g/g), glycerol concentration was 15%PPI(g/g), pH value was 9.0, reaction temperature was 70℃, reaction time was 90min. Under these conditions, the TS was 2.63±0.08 MPa, E was 165.33±1.00%, respectively increased by 45.75% and 42.70% compared with control group.2. The preparation process of glycosylation in combination with TGase to peanut protein to make films was optimized by using single factor experiment and response surface methodology, according to tensile strength of PPI, the results showed that:(1) The best complex modification way was that adding xylose and TGase at the same time before a pretreatment on PPI solution due to that the mechanical properties of the films made by this kind of complex modification were the best.(2) Xylose and TGase complex modification condition:protein content:pretreatment temperature was 70℃, pretreatment time was 60min, TGase dosage was 5u/gPPI, complex reaction tempreture was 50℃, complex reaction time was 20min.Under these conditions, the tensile strength was 3.25±0.05MPa, closing to predicted value.(3) Quadratic regression equation of PPI films on TS was established, R2=0.9889.3. The effect of different modifications on the properties of PPI films was studied. Compared different films made from PPI that was modified by xylose(PPI-X), TGase(PPI-T),and both of them complex(PPI-C), the results showed that:(1)The mechanical properties of films made by the three kinds of modified PPI were much better than the control. The TS and E of PPI-XF respectively increased by 45.75% and 42.70% compared with control group. The TS and E of PPI-MF were 2.18MPa and171.40%, respectively increased by 22.47% and 47.63% compared with control group. The TS and E of PPI-CF were 3.25MPa and188.37%, respectively increased by 82.58% and 62.58% compared with control group.(2) The water solubility of PPI-XF, PPI-TF and PPI-CF respectively decreased by 42.68%,32.47% and 53.07% compared with control group.(3) The WVP of PPI-XF, PPI-TF and PPI-CF were significantly reduced compared with control group, but there was no significant differences among the three kinds of modifications.(4) The light transmittance of PPI-XF and PPI-TF were decreased and the films were more yellow and brighter. There was was no Significant differences between PPI-MF and PPI-F and the films were all much red;4. Determined the surface hydrophobicity (S0), SDS-PAGE and FTIR spectrograms of different modified PPI as well as took scanning electron microscopic photographs of these films to expore the mechanism of complex modification PPI, the results showed that:(1)The surface hydrophobicity declined in sequence from PPI-M, PPI-C, PPI-X to PPI.(2) SDS-PAGE electrophoreto gram showed that there was no significant differences between PPI-X and PPI in molecular weight, PPI-T and PPI-C appeared high-molecular-weight components band and weakened the low-molecular-weight components band, but the brightness of PPI-C was much weaker than PPI-T.(3) The 1600-1700cm-1 infrared spectroscopy was analyzed by Pealfit group and showed that modifications increased the content of a-helix and β-corner, while decreased P-folded random coil.(4) The scanning electron microscopic photographs showed that there were more crosslink in PPI-XF, PPI-TF and PPI-CF. PPI-MF showed higher degree of crosslinking and higher roughness on surface microstructures than PPI-XF. SEM picture of PPI-CF showed smooth macromolecular structure. |
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