| Total nutrient emulsions（TNEs）,as a type of food for special medical purposes with comprehensive nutrients and easy digestion and absorption,can provide precise nutritional support for people with digestive disorders and have great potential for development in the consumer market.Currently,TNEs are prone to protein flocculation,spotting,fat floating,mineral precipitation and shelf-life gelation and other unstable phenomena during processing and storage.Among them,casein,as a full-valent protein with structural flexibility and thermal stability,is widely used in the food industry as a major source of protein.Maltodextrins have different thickening and emulsifying effects and can effectively supplement glucose and nutrients.Therefore,by studying the interaction mechanism between casein/maltodextrin and clarifying the process conditions of TNEs preparation is the key to improve the stability of TNEs.Based on this,this paper firstly constructed a casein/maltodextrin non-covalent bonding complex system,elucidated the molecular interaction mechanism between casein and maltodextrin,and investigated the physicochemical properties and thermal stability of casein/maltodextrin non-covalent bonding complex;secondly prepared TNEs,and clarified the influence of key control points such as high pressure homogenization on the stability of TNEs;finally evaluated the sensory quality and nutritional quality changes of TNEs under different storage conditions.Finally,we evaluated the changes of sensory quality and nutritional quality of TNEs under different storage conditions,and and predicted the shelf life of TNEs,in order to provide some theoretical basis and guidance value for the efficient preparation and maintenance of TNEs in steady state.The main research contents of this paper are as follows:Firstly,the casein/maltodextrin complex system was prepared,and the interaction of casein/maltodextrin complexes under high-speed shear was investigated by particle size,zeta potential,DSC,fluorescence spectroscopy,Raman spectroscopy and UV spectroscopy.The results showed that the average particle size of the casein/maltodextrin complex increased from 2.12μm to 5.71μm with the increase of shear time（0 to 12 min）,and when the shear time was 4 min,the particle size was normally distributed and the particle size of the complex was uniform;the absolute value of zeta potential showed a trend of increasing and then decreasing,and the maximum value was 22.56 m V;the thermal denaturation temperature of the casein/maltodextrin complex was the highest.The maximum thermal denaturation temperature of the casein/maltodextrin complex was 142.12℃,and the enthalpy change value was 24.61 J/g,which suggested that the shear treatment caused the cross-linking reaction between casein and maltodextrin and the formation of hydrogen bonds.In addition,the fluorescence and Raman spectra showed that the shear treatment shifted the maximum emission wavelength of casein from 347 nm to 336 nm,and the I760value gradually decreased（0.93 to 0.41）,and the I850/I830value first increased and then decreased（the maximum value was 1.24）.The shear treatment affected the hydrogen bonding and hydrophobic interactions between casein and maltodextrin,and had good stability at 4 min of shear treatment.Secondly,TNEs were prepared on the basis of casein/maltodextrin composite system,and the effects of high-pressure homogenization treatment on the stability of TNEs were analyzed by means of particle size,zeta potential,centrifugal precipitation rate,physical stability,and microstructure.The results showed that the particle size distribution index decreased gradually（0.29 to 0.15）with the increase of homogenization pressure（40～100MPa）,and when the homogenization pressure was 80 MPa,the particle size of TNEs showed a single-peak distribution in the range of 1.25～31.11μm.It shows that the shear and turbulent forces generated by homogenization break the droplets into fine particles.The absolute value of zeta potential first increased and then stabilized（the maximum value was 66.84 m V）and remain constant.The TSI value of stability index decreased from 1.3 to 0.7 and the rate of change of backscattered light decreased to 0.6%,which suggested that the local particle concentration decreased.The centrifugal precipitation rate was as low as 1.63%.In addition,the microstructure observation showed that the droplet particles became significantly smaller without clustering phenomenon under homogenization treatment.The above results indicated that the TNEs prepared at 80 MPa has good stability.Finally,we investigate the change pattern of quality characteristics of TNEs under different storage conditions and to perform kinetic-thermodynamic analysis and shelf-life prediction.The results showed that the a*and b*values increased and the brightness decreased with the increase of storage temperature.At the end of storage,the average particle size of the total nutrient emulsion increased from 18.24μm to 32.32μm,39.11μm and 46.83μm,respectively,and the absolute values of zeta potential decreased by 27.36%,34.76%and48.31%,respectively.p H was weakly acidic with a variation range of 6.11-6.23.Degradation of vitamin C was consistent with a primary reaction and the activation energy was 21.75k J/mol.The kinetic analysis showed that the p H,particle size and centrifugal precipitation rate followed zero-level reaction kinetics,and the changes of color difference,potential and vitamin C content followed first-level reaction kinetics at different storage temperatures.The results of thermodynamic analysis showed thatΔH*>0 andΔS*<0,which were non-spontaneously proceeding heat absorption reactions.Gibbs free energy depended on temperature and showed an upward trend with increasing temperature.A model was developed to predict the shelf-life of TNEs using centrifugal sedimentation rate as an indicator,and the shelf-lives were 337 d,295 d and 212 d,respectively. |
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