Study On Ultrasonic Preparation Technology Of Nisin-oat Protein-polysaccharide Composite Fresh-keeping Film

The widespread development and use of petroleum-based plastics,which has intensified the consumption of oil resources in recent years,has also had a significant impact on the environment.In the field of food packaging,the development of degradable biofilm materials has become a hot research topic and researchers have been exploring new sources for better film-forming properties.Films prepared with oat protein were found to have good film-forming properties and natural degradability;however,the pure oat protein film had the disadvantage of poor mechanical properties,which limited its application in food packaging materials.The addition of pullulan with protein and polysaccharides to prepare composite membranes can improve mechanical and barrier properties.The ultrasonic cavitation effect can promote the interaction between protein and polysaccharide molecules,and further improve the performance of the composite membrane.The natural composite film lacks antibacterial activity and other functional properties,which limits its application.The natural antibacterial agent nisin(Nisin),the only bacteriocin allowed to be used as a food additive in the world,has good antibacterial activity.The addition of nisin in the composite membrane could significantly improve the antibacterial performance of the membrane.Therefore,this paper selected oat protein and pullulan as the film-forming matrix prepared under multi-mode ultrasonic technology to assist complex formation.Furthermore,the whole processing conditions were optimized and natural antibacterial agents were added to prepare Nisin oat protein/pululan composite films.The effect of Nisin and ultrasonic treatment on the performance and structure of the composite membrane were determined,and finally,the composite membrane was used for strawberry preservation to investigate its preservation effect.The main conclusions are as follows:(1)Optimizing the preparation conditions of the oat protein/pullulan composite membrane were as follow:the matrix concentration,4 g/100 m L,the mass ratio of oat protein to pullulan,2:2,and the amount of glycerol additon as the ratio of the solute mass,25%,the heat treatment time,10min,and the heat treatment temperature,70?.Under these conditions,the tensile strength of the composite film was 6.3 MPa,and the elongation at break was 78.92%.The optimal ultrasonic preparation conditions of the composite film were:ultrasonic time,10min;ultrasonic frequency,20/60 k Hz and ultrasonic power,50 W/L.Under these conditions,the tensile strength and elongation at break of the composite film were increased by 16.17%and 70.01%,respectively,compared with those without ultrasound.(2)The results of the synergistic study of Nisin addition concluded that the addition of 0.4 g/L Nisin could improve the mechanical,water vapor barrier,oxygen barrier,moisture barrier,and bacteriostatic properties as well as light resistance of the oat protein/pullulan polysaccharide composite film.Among them,the tensile strength increased to 3.94 MPa,the elongation at break increased to 240.57%,the light transmittance decreased to 51.85%,the color difference value increased to 7.54.The water vapor transmission rate increased to 5.28×10^-11 g/(m·s·Pa),the water content dropped to 11.69%,the oxygen permeability dropped to 4.82 meq/kg,and the water solubility dropped to 19.21%,which had an excellent antibacterial effect on Listeria monocytogenes.Ultrasonic treatment improved the mechanical,oxygen,water vapor,and moisture barrier properties of the composite film.The elongation at break of the composite film was increased to 269.96%,the moisture content was reduced to13.93%,and the oxygen permeability was reduced to 6.33 meq/kg.The water solubility dropped to 77.78%,and the water vapor transmission rate dropped to5.69×10^-11 g/(m·s·Pa).After ultrasonic treatment of the Nisin-loaded composite film,the elongation at break was increased by 8.04%,the light transmittance increased from 54.31%to 62.34%,the color difference value decreased to 6.94,the moisture content increased to 13.65%,and the oxygen permeability decreased from 6.26 meq/kg to 5.97 meq/kg.The water solubility decreased from 74.79%to 66.46%.The results showed that ultrasonic treatment of the Nisin-loaded composite membrane could further improve the mechanical,oxygen barrier,and moisture barrier propertiesof the composite membrane.(3)The structural characterization and surface morphology of Nisin oat protein/pullulan polysaccharide composite film showed that the ultrasonic treatment decreased the surface roughness of the composite film,improved thermal stability,and decreased crystallinity from 42.58%to 34.77%.The CH stretching vibration and CO bond stretching vibration in the membrane were found;after adding Nisin for synergy,the film had a smoother surface with reduced thermal stability.The crystallinity was increased to 57.24%,and the C=O stretching vibration were observed.After the Nisin film was ultrasonically treated,there were obvious small bumps on the surface of the film,the thermal decomposition temperature of the film did not change,and the film still had good thermal stability,the crystallinity dropped to 42.06%,and the CH stretching vibration in the film changed.(4)The results of the fresh-keeping test on strawberries showed that with the increase in storage time,the decay rate,weight loss rate,and p H of strawberries in the control group and the different coating treatment groups showed an upward trend,and the decrease speed of the coating treatment group was lower than that of the control.The coating treatment effectively delayed the spoilage,water loss,and p H rise of strawberry fruit.Among them,the csn-op-pul film group had the best effect.Compared with the uncoated group,the decay occurred after 7 days.The weight loss rate was reduced by 12.95%,and the p H decreased by 0.3%.With the increase of storage time,the hardness of strawberries in the control group and different coating treatment groups showed a downward trend.The decrease in csn-op-pul film was the lowest,57.40%,from 22.82 g/mm² to 9.72 g/mm².The soluble solid content of the uncoated group first increased and then decreased.The soluble solid content of the uncoated group reached the maximum value of 10.3%on the 5th day and then began to decline;and the coated group reached the maximum value on the 9th day and then gradually decreased,indicating that the coating treatment could reduce the spoilage of strawberries and the loss of surface hardness reduced the ripening speed of strawberries.