Process Optimization Of Starch And Sweet Potato Leaf Polyphenols Edible Film And Its Application In The Preservation Of Potato Steamed Bread

With the characteristics of pollution-free,accessible and edible,the new active packaging made of edible material and natural active constituents is expected to replace traditional plastic packaging.In the present study,the starch materials for edible films were selected from potato starch,sweet potato starch and corn starch.Then the microstructure,mechanical properties,light transmittance and water vapor transmission rate and other physicochemical properties of film were investigated to optimize the process of edible film.Moreover,the effects of sweet potato leaf polyphenol(SPLP)concentration on the physicochemical properties,antioxidant and antibacterial activities of starch/SPLP edible film were measured to optimize the process of active packaging film.In addition,the specific volume,moisture content,brightness and surface microorganism of potato steamed bread(containing 55%of potato flour)were investigated to clarify the effect of PS/SPLP edible film in the preservation of potato steamed bread.The purpose of this study is to provide a theoretical basis for the practical application of starch/SPLP edible film.The main results are as follows:(1)Compared with sweet potato starch and corn starch,PS is most suitable for starch edible film.The PS edible film has a compact structure,high elongation at break(52.21%),good tensile strength(8.92 MPa),low transparency value(0.20)and low water vapor permeability(18.61 g/(m224h)).The optimized process parameters of PS film was as follows:4%potato starch,30%glycerin(dry starch basis),60?film forming liquid temperature.The final product has a dense surface structure,strong mechanical properties,high light transmittance and low water vapor transmission rate.(2)As the increase of SPLP concentration,the surface of the PS/SPLP edible film gradually becomes rough with voids and holes.When the concentration of SPLP in edible film was 0.5%,there were obvious pores and granuls on the film surface.In terms of mechanical properties,with the increase of SPLP concentration,the elongation at break of the film and the light transmittance reduced to 23.79%?45.81%and 28.92%?76.70%,respectively.However,the water vapor transmission rate was not significantly affected by SPLP concentration.FTIR analysis showed that there was no new functional group between SPLP and PS in edible film.The results of DPPH radical scavenging activity and Fe3+reducing ability shows that the PS/SPLP edible film has good antioxidant activity in dose-dependent manner due to the addition of SPLP.The antibacterial results showed that PS/SPLP edible film has great antibacterial activities in dose-dependent manner due to the addition of SPLP.When the concentration of SPLP in edible film was 0.4%,the PS/SPLP film could inhibit Staphylococcus aureus,Escherichia coli,Penicillium griseorum and A spergillus niger.(3)The effects of SPLP,tea polyphenol and potassium sorbate at the concentration of 0.4%in edible film in the preservation of potato steamed bread showed that PS/SPLP edible film has no significant effect on the specific volume of potato steamed bread,and could increase the moisture content and brightness of the steamed bread,and inhibited the growth of mold within 72 h storage.In summary,the PS/SPLP edible film obtained in this study has strong mechanical properties,high light transmittance and water vapor transmission rate,and has good preservation effect on potato steamed bread.This research could promote the development of potato steamed bread industry.