Preparation And Properties Of Highly Hydrophobic Starch/Lipid Edible Films

Traditional petroleum-based packaging materials have brought serious environmental pollution problems.Starch showed great application potential in the field of edible or degradable packaging because of its rich natural reserves,biodegradability and low cost.Acid-modified starch is a kind of modified starch with mature production process and affordable price,which has good film-forming property.However,the inherent humidity sensitivity of starch limits the application of acid-modified starch in food packaging.The composite film prepared by adding lipids could effectively overcome this defect.In this paper,acid-modified starch was selected as the main film-forming substrate,lipid was added as hydrophobic agent,and octenyl succinate starch was used as emulsifier to form a film-forming system.Effects of octenyl succinate starch ratio,content and type of natural wax and lipid crystallization factors,on the physicochemical properties and film-forming mechanism of starch film was investigated.This paper could provide a theoretical basis for reducing the humidity sensitivity of starch edible film.The main findings are as follows:（1）The addition of octenyl succinate starch（OSS）has a significant effect on the distribution of beeswax in acid-modified starch film,and further affects the structure and properties of film.The apparent viscosity and storage modulus of the film-forming solution decreased with the increase of OSS ratio.The results of Attenuated total reflectance-Fourier transform infrared（ATR-FTIR）showed that the hydrogen bond interaction in the film-forming network was weakened by the presence of OSS.The analysis of scanning electron microscope（SEM）,atomic force microscope（AFM）and X-ray diffraction（XRD）showed that the addition of OSS had obvious effect on the formation and distribution of beeswax crystallization.The surface distribution of beeswax could effectively improve the hydrophobicity and water vapor barrier properties of the film,and make the film showing a better elongation at break,but reduce the tensile strength and light transmittance of the film.The film with higher OSS ratio（>12%）showed higher thermal stability.（2）The type and amount of natural wax have a significant effect on the structure and properties of the film.The addition of beeswax（BW）,candelilla wax（CL）and carnauba wax（CB）could increase the apparent viscosity and storage modulus of the film-forming solution.The results of ATR-FTIR showed that the hydrogen bond interaction in the film-forming matrix could be destroyed in the presence of any kind of natural wax.The analysis of SEM and AFM showed that the three natural waxes had different distribution in the film-forming matrix,so that the film formed different microstructure.The addition of BW and CL improved the hydrophobicity and water vapor barrier properties of the film,and made the film showing a better elongation at break,but the tensile strength decreased.Compared with CL and CB,BW showed better compatibility with the film-forming matrix.The S/BW-15film showed the highest hydrophobicity（contact angle 91°）and best water vapor barrier properties.The water vapor permeability decreased by 21.2%compared with the pure starch film.The CB showed poor compatibility with film-forming matrix,which had an adverse effect on the hydrophobicity,water vapor barrier properties and mechanical properties of the film.（3）The ultrasonic time significantly affected the structure and physicochemical properties of the film.The results of ATR-FTIR showed that ultrasonic increased the generation of hydrogen bonding force in the film-forming matrix.The analysis of AFM and XRD showed that ultrasonic promoted the dispersion of beeswax in the film-forming matrix and reduced the formation of beeswax crystallization,so the surface of starch film was more uniform.The results of DSC showed that ultrasonic promoted the fusion of two-phase systems in the film-forming matrix.The extension of ultrasonic time could significantly improve the hydrophobicity,water vapor barrier properties and tensile strength of the film.Compared with pure starch film,the water vapor permeability of US-5 film reduced by 41.6%.However,ultrasonic beyond 7 min destroyed the film structure and reduced the hydrophobicity and water vapor barrier properties of the film.（4）The speed and time of homogenization significantly affect the structure and properties of the film.The results of DSC showed that lower homogenization speed and shorter homogenization time could aggravate the tendency of phase separation in the film-forming matrix.The AFM analysis showed that the trend of beeswax distribution to the surface increased with the shortening homogenization time under the 15000 r/min homogenization speed,so the film showed rougher surface structure.The surface roughness and hydrophobicity of the film increased with the decrease of homogenization time.The S/BW-15000-1 film showed the highest hydrophobicity（contact angle 98.5°）and the lowest water vapor permeability(1.70×10^-10 g m^-1s^-1Pa^-1).However,under the condition of 9000r/min homogenization speed,beeswax could not be effectively dispersed and gathered in the matrix,so the starch film showed poor hydrophobicity and water vapor properties.