| Since traditional solid fat products mostly contain higher trans fatty acids and saturated fatty acids,the new oleogel have a wide range of applications in replacing saturated fats.Glyceryl monostearate is a commonly used emulsifier in foods and is widely used as a gel factor in the study of oil gels.Glyceryl monolaurate,as a broad-spectrum and highly effective antibacterial agent,can also be used as an excellent food emulsifier,A single gelling agent usually has certain limitations.The compounding agent can fully play the role of the gelling agent and achieve a synergistic effect.Therefore,this experiment investigated the effects of different compounding ratios of glyceryl monolaurate and glyceryl mono stearate on the properties and structure of oil gels.The presence of water in the oil gel provides a delicate texture to the product,but at the same time it will affect the quality and oxidation stability of the oil gel.Therefore,this experiment also studied the relative influence of the water content on the performance and structure of the oil gel.In this experiment,the moisture content was first fixed at 40%,and the soybean oil oil gel was prepared by adding glyceryl monolaurate and glyceryl monostearate in different compounding ratios,and the properties and structure of the gel compound oil gel were studied.The influence of water content on the properties and structure of the oil gel was studied by using different water content to prepare soybean oil oleogel under the determined compounding ratio of gel agent.The oil gels with different moisture contents were stored at 25 ? and 5 ?,respectively,and the oxidative stability,properties and microstructureof the oil gels was studied,which provided a theoretical basis for the application of oil gel in the food field.The main research results are summarized as follows:1.The effect of the ratio of glyceryl monostearate/glyceryl monolaurate on the microstructure and functional properties of oil gel.The five gelling agent ratios of 1:9,2:8,3:7,4:6,and 1:1were used to prepare oil gels in order to study their hardness,oil and water holding capacity,microstructure,DSC thermal properties,rheological properties,polarized light microstructure analysis,emulsion type identification,XRD analysis,and chemical bond interaction.The results showed that when the ratio of gel agent was 1:9(glycerol monolaurate:glycerol monostearate),the hardness of the oil gel was small and the phenomenon of water-oil separation was easy to occur,therefore,the oil and water holding capacity was relatively poor.When the ratio of gel agent was sequentially from 2:8 to 1:1,the hardness of the oil gel gradually decreased,and the oil and water holding capacity was enhanced.According to rheological analysis,oil gel was a thixotropic fluid.When the ratio of gel agent was 1:9,the thixotropy was large and the structure was the most unstable.The apparent viscosity of the oil gel decreased with the shear rate increasing,which showed the shear thinning characteristic,During the frequency scanning,the elastic modulus of the oil gel was greater than the viscous modulus,showing a stable solid gel characteristic.When the ratio of gelling agent was 3:7,the gel strength was the largest and the particles were arranged most closely.The oil gel was a thermally reversible fluid.The melting temperature of the gel was around 50?,and the melting temperature gradually decreased with the ratio of the gel agent from 1:9 to 1:1.The structure of the oil gel network was observed by polarized light microscope,with the ratio of gel agent from 1:9 to 1:1,the structure of the oil gel network also showed from loose to dense,the birefringence phenomenon was enhanced,and the crystal morphology changed from small and scattered needles toward long and neat needle-like and fibrous development;while staining the water and oil in the oleogel separately,it can be observed by fluorescence microscope that the oleogel system was oil-in-water(O/W)structure;X-ray diffraction analysis showed that homogeneous polycrystals exist in the crystallization of oil gels,mainly in the ? and ?' crystal forms;Fourier infrared analysis showed that the oil gel was a chemical gel that mainly forms a network structure with carbon-hydrogen bonds.2.The effect of moisture content on the microstructure and functional properties of the oil gel.Five different moisture contents of 30%,40%,50%,60%,and 70%were used to prepare oil gels for the purpose of exploring the moisture content on oil gel hardness,oil and water holding capacity,microstructure,thermal properties,rheology influence of nature,emulsion type,chemical bond interaction,crystal type.The results showed that 30%-70%moisture content can form a stable gel system.As the moisture content increased,the hardness of the oil gel gradually decreased,the oil holding capacity was better,and the water holding capacity was decreased with the water content increasing.According to rheological analysis,the oleogel was a thixotropic fluid,its apparent viscosity decreased with the shear rate increasing,and exhibited shear thinning characteristics;the elastic modulus of the oleogel was greater than the viscous modulus during frequency scanning that main the oleogel was always a stable solid state.At low moisture content(30%-50%),the gel strength was large,the coordination number was large,and the particles were closely arranged.The oil gel was a thermally reversible fluid.The melting temperature of the gel was around 50?.With the moisture content increasing,the crystallization enthalpy/melting enthalpy of the oil gel decreased,indicated that the addition of gel factor was beneficial to the crystallization of the oil gel.The structure of the oil gel network was observed by polarized light microscope,the birefringence of oil gel with 40%,50%and 60%moisture content was strong,the network structure was complete,the crystal size was larger than that of oil gel with 30%and 70%moisture content,and the larger crystal size can enhance the strength of the gel;there were strong crystallization peaks at 4.6 (?) and 4.2 (?),indicated that there were mainly ? and ?'crystal forms in the oil gel,and as the moisture content increased,the number was gradually increased;the fluorescence microscopy analysis showed that the oil gel system was oil-in-water(O/W)structure;Fourier infrared analysis showed that a shallow and broad absorption peak appeared at 3350 cm-1,indicated that the oil gel has an intermolecular hydrogen bond which formed a gel network.As the moisture content increasing,the gel content decreased,which resulted in the intensity of the stretching vibration peak of-CH at 2850 cm-1.The hydrogen bonding between them was weakened.3.Study on the oxidative stability and structural properties of oil gel during storage.The oil gels with different moisture contents(40%,50%,60%,70%)were stored at 25? and 5?,and the oxidation stability of the oil gel was studied by detecting the peroxide value and Tbars value.At the same time,through the hardness,oil and water holding capacity,polarized light microstructure,thermal properties,rheological properties,crystal types and chemical bond analysis of oil gel properties.The results showed that with the extension of storage time,the peroxide value and Tbars value of the oleogel were increased.When the storage temperature was 25?,the moisture content of 50%and 70%the peroxide value of the oleogel exceeded the national limit at 25 d,and the oleogel with 60%moisture content exceeded the national limit at 23 d.However,the peroxide value of the oil gel stored at 5? within 60 days did not exceed the national limit.Showed that low temperature storage was conducive to alleviate the oxidative rancidity of oil products.At the same time,as the moisture content increased,the Tbars value also increased.Through the analysis of hardness,oil and water holding capacity,rheological properties,thermal properties and color difference,low temperature storage could better extend the shelf life of the oil gel and showed more excellent stability.Nevertheless,properly the increase of the storage temperature had a positive effect on the thermal stability of the oil gel.During storage,the oil gel with 40%and 50%moisture content showed good stability,strong oil and water holding capacity,moderate hardness,and no separation of water and oil.Yet,due to the poor stability of 60%and 70%moisture content oil gel,the hydrogen bonding force was weakened,and crystal aggregation was likely to occur in the later period of storage,and the phase separation phenomenon was more serious. |
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