Characterization Of Soybean Oil Organogels With High-melting Point Diacylglycerols And Monoacylglycerols

Organogels are new plastic fats with semi-solid viscoelasticities and lower trans and saturated fatty acids which can be widely used in food,medicine,the chemical industry,and other fields.These gels were prepared from soybean oil with diacylglycerols(DAG)obtained by the esterification of immobilized enzyme and with monoacylglycerols(MAG).The effects of DAG and MAG content on the melting,crystallization,and rheological behaviour of organogels were investigated.The properties of organogels developed by mixtures of DAG and MAG were also studied.The results are as follows:(1)DAGs with higher melting points was synthesized through the esterification of immobilized lipase Novozym 435 in a solvent-free system using a stirred reactor.Conditions for the reaction included an enzyme load of 5 wt%,glycerol: stearic acid mole ratio of 9:1,a reaction temperature of 60 ?,and a reaction time of 45 min in order to obtain a DAG content of 43.4wt%.After purification by molecular distillation,a DAG content of 63.5 wt% was achieved.(2)Organogels were prepared from soybean oil with DAG(52.1?)that had higher melting points.The differential scanning calorimetry,pulsed nuclear magnetic resonance,and rotational rheometer were used for the preliminary evaluation of melting,crystallization,and rheological behaviours of thes gels.The effect of DAG content on the properties of organogels was investigated.DAG with higher melting points had the ability to form plastic organogels indicating high nutritive value,desirable spreadability,and stable characteristics.The crystal structure of organogels was dense and homogeneous.Unsaturated fatty acid content was more than 70% and these DAG organogels consisted mostly of ? and ?? crystals.The DAG content induced changes in stability,oil binding capacity,and viscoelasticity of organogels.The addition of 20% DAG may result in oleogels with optimal physicochemical properties.(3)Organogels were prepared by soybean oil and molecular distilled MAG.The effects of MAG content on the melting,crystallization,and rheological behaviours of organogels were investigated.Comparison of DAG and MAG organogel properties showed that type and content of organogelator had a great influence on solid fat content,rheological properties,and crystallization characteristics.The oil binding capacity in MAG organogels was greater in comparison to the DAG organogels.At 7%,8%,and 12% MAG additions,stable organogelshad formed,where a 12% addition gave the bestoil binding capacity and mechanical stability.MAG organogels showed non-Newtonian shear-thinning behaviour and thixotropic behaviour at different shear rates.The elastic modulus(G')values were higher than the viscous modulus(G")values.Unsaturated fatty acid content was more than 77.2% in these MAG organogels.The results of x-ray diffraction indicated that MAG organogels consisted mainly of? crystals and bothneedle-and plate-like morphologies were observed by polarized light microscopy.(4)Soybean oil organogels were prepared from a mixture of both MAG and DAG.The melting,crystallization,and rheological behaviors of MAG-DAG organogels were evaluated.The effects of compound ratio of MAG and DAG on the organogels properties were investigated.Results showed that the ratio of MAG and DAG had a great influence on formation mechanism,rheological properties,and crystallization characteristics of MAG-DAG organogels.At the addition of 8% and 12% organogelator,MAG-DAG organogels were stable,uniform,smooth,and creamy.In comparison to MAG organogels,the MAG-DAG organogels were more uniform.In comparison to DAG organogels,the content of unsaturated fatty acid in the MAG-DAG organogels had increased by reducing the content of organogelator.The experimental data for the shear rate and shear stress at 4 ?and 20 ?were fitted using the Herschel–Bulkley model and showed non-Newtonian shear-thinning behaviour.The polymorphic content of DAG-MAG organogels were mainly ? crystals and the addition of DAG increased ?? crystal formation.In the system with large proportion of MAG,the crystal morphology was dominated by either needle-or plate-like crystal morphologies whears a large proportion of DAG resulted in either spherulitic or rosette-like crystal morphologies.