| The development of new packaging materials of biodegradable polymers is one of the most important and effective ways to solve the problem of environmental pollution caused by petroleum-based plastic packaging and improve the level of food safety.Pectin is considered as an effective biopolymer for producing edible films due to its excellent gel-forming ability,biodegradability,and biocompatibility.Hawthorn is the fruit with the highest pectin content in currently known fruit.With the rapid development of hawthorn processing industry,a large number of processing by-products containing pectin are produced,which provides a good resource for the preparation of pectin.In this paper,hawthorn fragments were used as raw materials to study the effect of different extraction methods,quaternization,and the addition of thyme essential oil on the film-forming properties of pectin.Combining modern analysis technology,modern separation and extraction technology,biomacromolecule modification technology and film-forming technology to develop hawthorn pectin functional film innovatively.The main research work was as follows:1.The effects of four extraction methods:hydrochloric acid method(HA-HP),citric acid method(CA-HP),ultrasonic-assisted method(UA-HP),and microwave-assisted method(MA-HP)on the properties and structure of pectin were studied.It was shown that HA-HP,CA-HP,and UA-HP were all high-methoxy pectin with degree of methylation(DE)of 66.82%,50.88%,and 51.96%respectively,while MA-HP was low-methoxy pectin with DE of 42.96%.The galacturonic acid(Gal A)contents of HA-HP,CA-HP,UA-HP,and MA-HP were 89.14%,90.83%,80.00%and 58.32%,respectively,and the weight-average molecular weights(Mw)were 276.7 k Da,348.91 k Da,379.35 k Da,and 446.03 k Da.Fourier transform infrared(FTIR)spectroscopy and X-ray diffraction(XRD)reflected that there were certain differences in DE and crystallinity among the four pectins.The results of thermogravimetric showed that HA-HP had the best thermal stability,and the temperature under the maximum thermal decomposition rate of it was 249.4?.2.Films prepared by obtained pectin using a solution casting method,and the effects of different extraction methods on the film-forming properties of pectin were studied.Among the films prepared by pectin extracted by hydrochloric acid method(HA-HPF),citric acid method(CA-HPF),ultrasonic-assisted method(UA-HPF),and microwave-assisted method(MA-HPF),the performance of CA-HPF and UA-HPF was better.The characterization results of CA-HPF were as follows:thickness 28.5?m,?E*1.37,the light transmittance at wavelength of 600 nm73.28%,opacity 4.74,tensile strength 47.02 Mpa,and elongation at break 4.67%,water contact angle 79.87°,water vapor permeability 9.21×10-13g·m-1·s-1·Pa-1,oxygen permeability 5.12×10-17cm~2·s-1·Pa-1,the temperature under the maximum thermal decomposition rate 237.1?.The characterization results of UA-HPF were as follows:thickness 40.3?m,?E*1.64,the light transmittance at wavelength of 600 nm 77.63%,opacity 2.73,tensile strength 42.24 Mpa,and elongation at break 5.20%,water contact angle 85.32°,water vapor permeability 2.21×10-13g·m-1·s-1·Pa-1,oxygen permeability 83.61×10-17cm~2·s-1·Pa-1,the temperature under the maximum thermal decomposition rate 231.5?.3.Hawthorn pectin was modified by CHPTAC,and quaternized pectin(QHP)was successfully prepared.The degree of substitution of QHP-1,QHP-2,QHP-3,and QHP-4 was0.11,0.13,0.18,and 0.19,respectively.FTIR,~1H NMR,XRD proved the success of quaternary modification at the structural level.QHP had more lamellar structure than unmodified pectin,and aggregates appeared on their surfaces.With the increase of the degree of substitution,the aggregates gradually increased.The results of thermal analysis exhibited that the quaternization modification resulted in an increase in the capacity of maintaining water and a decrease in thermal stability.The melting temperature of unmodified pectin,QHP-1,QHP-2,QHP-3,and QHP-4 was 90.3?,98.7?,103.6?,111.3?,and 122.1?,respectively,and the temperature under the maximum thermal decomposition rate was 240.1?,215.7?,212.6?,210.5?,and226.5?.QHP had inhibitory effects on Escherichia coli and Staphylococcus aureus,as well as inhibited their biofilm formation.The minimum inhibitory concentration of QHP-1,QHP-2,QHP-3,and QHP-4 against Escherichia coli was 1560,780,100,and 50?g/m L,and the minimum inhibitory concentration against Staphylococcus aureus was 200,100,500,and 390?g/m L.4.Films prepared by four kinds of quaternized pectin using a solution casting method.The related characterization results showed that the performance of the film prepared from QHP-3(QHPF-3)was best.The characterization results of QHPF-3 were as follows:thickness 20.0?m,?E*1.78,the light transmittance at wavelength of 600 nm 87.80%,opacity 2.83,tensile strength 21.69 Mpa,elongation at break 2.05%,water contact angle 87.16°,the temperature under the maximum thermal decomposition rate was 212.4?.5.Composite films were prepared with quaternized pectin as the matrix and the effects of amount of essential oil on the properties and functions of composite films were studied.The results showed that when the amount of thyme essential oil added was 1.0%(QPF/TEO 1.0%),the performance of composite film was best.The characterization results of QPF/TEO 1.0%were as followed:tensile strength 24.24 Mpa,elongation at break 8.33%,water contact angle61.84°,water vapor permeability 2.64×10-12g·m-1·s-1·Pa-1,the inhibition zone diameter against Escherichia coli 10.57 mm,the inhibition zone diameter against Staphylococcus aureus 15.70mm. |
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