LF-NMR Characterization Of Oil-containing Food System And Its Application In The Formation Of Oleogel

The new type of oleogel with vegetable oil as the main component reduces or removes the components of saturated fatty acids or trans-fatty acids in the diet as well as maintaining the original texture of the food.It has excellent potential to replace traditional plastic fat.Low-field nuclear magnetic resonance（LF-NMR）technology is widely used in the field of food analysis and detection,but the relationship between the characteristics of various components in food and the relaxation characteristics of LF-NMR needs to be further studied.In this study,two polysaccharides and two phenol were combined with soybean protein isolate（SPI）solid particles to be used as an emulsifier,and a camellia oleogel system was constructed by the emulsion template method.Several factors,such as SPI concentration,processing conditions,oil fractions as well as protein-polyphenol-polysaccharide interactions,which affected the microstructure,interfacial properties,rheological properties,and oxidative stability of oleogel have been investigated.By analyzing the LF-NMR relaxation characteristic information in correspondence with other characterization results,a new and rapid characterization method for the preparation of oleogel was explored.The main results obtained are as follows:Study on the LF-NMR relaxation characteristics of Fried fries with different frying time showed that both the T_cur and T_2W decreased relatively within 2 minutes of frying,and then increased in 3-4 minutes.There were three relaxation peaks appeared in the multi-component（T₂）relaxation spectrum,which shifts to the left as the frying time increased.LF-NMR combined with magnetic resonance imaging（MRI）technology provided visual information for the changes of signal intensity and spatial distribution in internal hydrogen proton of French fries during the frying process.The high correlation between the relaxation characteristic information of French fries and moisture and oil content（R²>0.95）proved the feasibility of LF-NMR technology to predict the moisture and oil content in fried starch system,which also provided theoretical support in the characterization of O/W emulsions and oleogels.During the preparation of SPI-stable oil gels,as the concentration increased from0.5%to 8%,the particle size of the SPI dispersion increased,the attenuation accelerated,and T_2W and T₂ descended.The treatment with Na Cl（300 m M）and further heating（95℃,15 mins）process reduced the particle size of the nanoparticles and enhanced surface hydrophobicity（H_o）,which corresponded the gradually shortened T_cur,T_2W,and T₂relaxation time.With the increase of the oil fractionΦ（0.1-0.6）,both the AP%and the shear viscosity of the emulsion increased,the T_cur and T_2W were gradually reduced,and the three relaxation peaks(T₂₁,T₂₂,and T₂₃)based on the relaxation of the emulsion have significant correlations with the water/oil phase（R²>0.97）.However,when theΦ>0.7,the emulsion was demulsified.The frequency dependence of the constructed oleogel sample showed weak elastic properties（G’>G”）.There was no significant difference in the T_cur of the oleogel groups,and T_2W was relatively concentrated at 90 ms.The T₂₁ peak shifted to the right and the RC₂₁ gradually decreased withΦincreasing from 0.1 to 0.6.It can be proved that the oleogel samples were in a more uniform and stable state,and LF-NMR relaxation characteristic information can be used to successfully monitor changes in this process.During the preparation of protein-polyphenol-polysaccharide oleogel samples,TA and GSP had less effect on the particle size of the nanoparticles in the dispersion,but significantly enhanced DPPH free radical scavenging and Fe²⁺chelating ability.Compared with SPI dispersions,the T_cur,T_2W and T₂of SPI-GG and SPI-FG dispersions were shortened,and this trend is more pronounced in protein-polyphenol-polysaccharide complex dispersions.The particle size of the protein-polyphenol-polysaccharide stabilized emulsion decreased significantly,but the irregularity of droplet arrangement increased,which was most obvious in the SPI-GG-GSP and SPI-FG-GSP groups.The adds of polyphenols and polysaccharides significantly increase emulsion viscosity and mechanical strength（G’>G”）.The shortened T_cur and T_2W,as well as the left shift tendency of T₂ peak of the emulsion,indicated that the hydrogen protons in the emulsion were in a more stable state.The complex oleogel samples has higher mechanical strength（G’>G’’）.The oxidation stability of the oleogel in the polyphenol-added groups were significantly enhanced with the most prominent group SPI-GG-TA.The difference between the T_cur,the T_2W of oleogel were less obvious,and the T₂relaxation characteristics of composite oleogels have similar relaxation distributions overall,indicating that the protein-polyphenol-polysaccharide interaction can be emulsified to obtain a more uniform and stable camellia oleogel.