Study On Emulsion Stability And Emulsification Mechanism Of Eggplant Pulp

Emulsifiers have been widely used in food,medicine,and cosmetics products.However,some widely used synthetic emulsifiers may cause risks on the people’s health.There is increasing consumption of emulsifier that is more natural,green,nutritious and healthy with the improvement of living standard and the awareness of health consciousness.As it is known,eggplant is rich in dietary fiber and it can maintain moisture and absorb the oil in the related foods,which makes it be a good potential candidate for vegetable source emulsifier.In this dissertation,we investigated the emulsifying properties of eggplant.First,we studied the emulsifying activity of eggplant emulsifier prepared in different ways and analyzed the influence of environmental stress on the stability of eggplant pulp homogenate（EPH）emulsions.Second,the emulsifying activity and mechanism of the main components of EPH were analyzed.Finally,the effect of eggplant powder on the processing characteristics of fat-reduced pork sausages was discussed.This dissertation is intent to develop a vegetable source emulsifier that is of wide sources,low cost,and excellent emulsifying activity to enrich the natural food emulsifiers.The specific research contents and results are as follows:1.Comparative study on the emulsifying properties of eggplantIn this part,at first,chemical components of eggplant pulp and full eggplant were analyzed and compared.Results indicate that,for the eggplant pulp and full eggplant,the chemical composition based on dry material were 33.79%and 33.15%for total fiber,35.25%and 34.12%for soluble sugar,11.65%and 11.75%for protein,which has no significant difference（P>0.05）.The pectin content of eggplant pulp is 5.16%,which is significantly lower than that（5.75%）of full eggplant（P<0.05）;Second,the emulsification activity and emulsification stability of eggplant pulp,eggplant,eggplant powder（including low temperature dried eggplant powder（LEP）,high temperature dried eggplant powder（HEP）,and freeze dried eggplant powder（FEP））,and two commercial emulsifiers（natural polysaccharide emulsifier-gum arabic（GA）and synthetic emulsifier-Tween 80（T80））were comparative studied.Results indicate that,when the concentration of EPH is below 1.25%,the creaming index（CI）and mean particle size d_3,2(MPD,d_3,2)of the EPH emulsion are significantly higher than those of eggplant emulsion（P<0.05）,and the zeta-potential of the EPH emulsions was smaller than that of the eggplant emulsion（P<0.05）,which indicated that eggplant has a better emulsifying activity.However,the L*,a*and b*values significantly decreased for the eggplant emulsion（P<0.05）.When the concentration was1.00%,the CI of LEP,HEP and FEP emulsions were increased by 0.6%,2.4%and 7.4%,respectively,compared to that of EPH emulsion（P<0.05）,but the MPD(d_3,2)and zeta-potential had no significant differences（P>0.05）,indicating that low temperature drying can better maintain the emulsifying activity of eggplant when compared to high temperature drying and freeze drying.Through Cryo-scanning electron microscopy,it was found that filamentous fibers were fractured and the network formed by long filamentous fibers became weak,which leading to the decreased of emulsifying activity and emulsifying stability.In regard to the emulsifying properties of EPH and GA,it was found that the CI,MPD(d_3,2)and zeta-potential of EPH emulsion were higher than those of GA emulsion,indicating that GA has a better emulsification activity.However,oil of the GA emulsion spilled out when it is stored for some days,while 1.50%EPH emulsion remain unchanged during same storage.2.Study on the stability of emulsions stabilized by EPHIn this part,we investigate the influence of the storage time,temperature,p H value and Na Cl concentration on the stability of EPH emulsions.Results indicated that the CI and MPD(d_3,2)of EPH emulsion exhibited no significant difference（P>0.05）during the storage compared to that at the 1-day storage when the EPH concentration was 0.50%,0.75%and 1.00%,while had no significant difference when the EPH concentration was 1.25%and1.50%（P>0.05）.For the 0.50%,1.00%and 1.50%EPH emulsions,the particle size distributions,MPD(d_3,2)and zeta potential had no significantly variation when treated by temperature ranging from 4 to 50℃（P>0.05）.However,when the treated temperature was above 75℃,the particle size distribution moves towards higher values and the MPD(d_3,2)significantly increased for the 0.50%EPH emulsion,（P<0.05）,while it had no significant difference for the 1.00%and 1.50%EPH emulsion（P>0.05）.For the 0.50%,1.00%and1.50%EPH emulsions,the CI has no obvious variation when p H is above 5.0,while it significantly increases when the p H is 3.0 and 4.0（P<0.05）.As a result,the MPD(d_3,2)had the smallest value at p H 5.0 and 6.0,and had the biggest value at p H 3.0,when compared with p H 4.0,7.0,8.0 and 9.0 9 for the emulsions with 0.50%and 1.00%EPH.For the 1.50%EPH emulsion,creaming occurs but the particle size distributions and MPD(d_3,2)remain unchanged at p H 3.0 and 4.0（P>0.05）.Microstructure observation found that only flocculation happened in the 1.50%EPH emulsion when p H is 3.0,but both coalescence and flocculation occurred in the 0.50%EPH emulsion.In addition,the MPD(d_3,2)significantly increased from 81.6μm to 95.6μm with the Na Cl concentrations ranging from 0 to 0.5 M for the 0.50%EPH emulsion（P<0.05）,while the particle size distribution and the MPD(d_3,2)had no significant changed for the 1.00%and 1.50%EPH emulsion.The emulsion is easy to be influenced by the temperature,p H and Na Cl concentration at low EPH concentration,while can be resistant to the environment stress and keep stable at high EPH concentration.3.Research on the properties of emulsifying components and emulsification mechanismIn this part,at first,the monosaccharide composition and content of eggplant soluble sugars（ES）and the monosaccharide composition and content,molecular weight,functional group,crystallinity and microstructure of eggplant insoluble sugars（EIS）were analyzed,and the structural information of eggplant polysaccharide was obtained.Results indicated that ESS are mainly monosaccharides,disaccharides or trisaccharides,which is composed by glucuronic acid（46.79%）,fucose（21.29%）,glucose（12.5%）and mannose（10.78%）.The EIS are pyranose withα-glycosidic andβ-glycosidic bonds,which is consisting of galacturonic acid（33.3%）,galactose（25.6%）,glucose（11.9%）,xylose（9.9%）and arabinose（8.69%）.The weight-average molecular weight（Mw）is 21809 and the PD is about 2.41.The structure of the polysaccharides is composed by crystalline and amorphous regions and the resultant crystallinity is 57.7%.The micromorphology of EIS is forming of filamentous and flaky fibers that interweave with each other to form a network;Second,the component of eggplant pulp homogenate（EPH）,eggplant soluble sugars and protein（ESP）,ES,eggplant protein（EP）,EIS,ES+EIS,and EP+EIS were used to prepared emulsion in order to investigate the function of ES,EP and EIS in emulsification,respectively.In addition,the microscope was used to observe the microstructures on the surface and inside of the emulsion droplets for the purpose of exploring the eggplant emulsification mechanism.Results indicate that ESP,ES and EP can form a uniform emulsion,while EIS formed floccule but not emulsion.The CI and MPD(d_3,2)of ESP,ES and EP were significantly higher than that of EPH（P<0.05）,and the MPD(d_3,2)of ES significantly higher than that of ESP（P<0.05）.Microstructural observation showed that ES and EP were adsorbed on the surface of oil droplet,and formed a surface film coating on the oil droplets during the homogenization.The branches chain of EIS were adsorbed on the surface film,and the other side formed a three-dimensional network structure in the continuous phase.Thus,the droplets are physically embedded within the network,and the aggregation of the droplets was restrained,resulting in a stable emulsion.4.Effect of eggplant powder on the physicochemical and sensory characteristics of reduced-fat pork sausagesIn this part,the effects of soybean oil,water,and eggplant powder（EP）as substitutes for pork back fat on the water-and fat-binding properties,color,water distribution,texture,and sensory properties of pork sausages were investigated,and the application prospect of eggplant powder in low-fat meat products was discussed.Results showed that the replacement of fat with soybean oil in sausages decreased the fat and cholesterol proportions and increased the moisture content,but the water-and fat-binding properties,texture properties,and sensory properties became worse.The addition of EP significantly reduced the water release（WR）and oil release（OR）of the emulsified sausages.The WR of the pork sausages decreased from 6.38%to 4.77%,2.86%and 2.52%when the added EP was 1%,2%and 3%.,respectively（P<0.05）.The OR was significantly decreased from2.25%to 0.87%,0.35%and 0.20%when the added EP was 1%,2%and 3%,respectively（P<0.05）.EP addition significantly accelerated T₂ relaxation time,T₂₁ and T₂₂ of the pork gel moved towards fast relaxation direction with the increase of the eggplant powder,increased the immobilized water content,and decreased the free water content of sausages.In addition,EP increased the relaxation peak area P₂₁ for immobile water and reduced the peak area P₂₂ for free water,resulting in the transformation from free water to immobile water and the improvement of the water retention for the pork gel.With the increase of the EP,the L*and a*values of the pork sausages showed a decreasing trend,while the b*values showed an increasing trend.The hardness and chewiness of pork sausages were significantly higher（P<0.05）than R group,while the springiness and cohesiveness had no significantly difference in EP and R group（P>0.05）.The addition of EP to low-fat sausages increased the flavor,texture,mouth feel,and overall acceptability scores,except for the appearance score（P<0.05）.Sensory analysis showed that sausage formulated with2%EP was the most acceptable to the panelists after considering appearance,flavor,texture,and mouth feel.Overall,2%EP can be used to improve the physicochemical and sensory properties of emulsified sausage...