Studies On Characteristics Of Palm-based Diacylglycerol And Assessment Of Their Storage Stability For Plastic Fats

Diacylglycerol?DAG?oils are attractive not only for their capacity to alleviate obesity and restrain accumulation of body fat,but also for their unique physico-chemical properties,which could be suitable for application as a functional ingredient to produce DAG-enriched plastic fat in the future.In view of this,palm stearin?PS?,palm mid fraction?PMF?,palm oil?PO?,palm olein?POL?and low erucic acid rapeseed oil were employed to study the molecular composition,thermal behaviors,the textural,and viscoelastic characteristics as well as microstructure.We aimed to investigate the crystallization mechanism of palm-based DAG oils and explore how blending of DAG-enriched oils influenced the physico-chemical properties in a solid fat system.The storage stability of DAG-enriched plastic fat was investigated to explore the feasibility of substitute DAG-enriched oils for traditional oils in the application of plastic fat.Given that these informative data will contribute to popularizing functional DAG oils products in the future.The critical conclusions were shown as follows:?1?Lipozyme TL IM immobilized lipase was selected to catalyze the glycerolysis reaction in tert-butanol system.The lipase concentration was 5%?w/w?and the reaction temperature was 70?.For palm-based oils?P-oils?,the ratio of t-butanol to substrate was 4:1 and molar ratio of substrate to glycerol was 1:2.The reaction time for palm mid fraction?PMF?and palm oil?PO?was 36 hours while 36 hours for palm olein?POL?and palm stearin?PS?.Additionally,the ratio of t-butanol to substrate,molar ratio of substrate to glycerol as well as the reaction time were 3:1,1:3,36 h,respectively.With these conditions,both the content of DAG and the conversion of TAG were better.The short-path distillation was carried out to purify the reaction mixture and the DAG content of PS?PMF?PO?POL?RSO were 89.45%?92.61%?90.43%?89.87%?92.67%,respectively.?2?Although the fatty acid composition of palm-based oils after transformation to DAG oils showed no significant differences,DAG oils were observed to have significantly?P<0.05?higher slip melting point?SMP?,flatter solid fat content?SFC?profiles and they were primarily characteristic of ? polymorphism.Additionally,the crystallization and melting profiles showed distinctly different,where the crystallization and melting curves were found to shift to the higher temperature region and new exothermic and endothermic peak were deteceted in the higher temperature region.Palm-based DAG?P-DAG?oils showed higher nucleation and crystallization rate than P-oils with no slight plateau as temperature variated and were less sensitive to temperature.The time scale required for complex modulus values and phase angle to reache an equilibrium was smaller.Furthermore,all P-DAG oils showed extremely similar microstructural images with more compact structures of very small needle-like crystals.?3?1,3-PO,1,3-OO and 1,3-PP were all characteristic by ? polymorphism and SMP were 37.6??22.1? and 68.7?,respectively.The kinetic phase diagrams of 1,3-PO/1,3-OO,1,3-PP/1,3-OO and 1,3-PO/1,3-PP constructed using melting and cooling DSC thermograms indicated that obvious eutectic behaviors were detected for 1,3-PO/1,3-OO and 1,3-PO/1,3-PP,while 1,3-PP/1,3-OO showed an monotectic behavior.The simulation of the liquidus boundaries for two eutectic binary systems of 1,3-PO/1,3-OO and 1,3-PO/1,3-PP produced negative ? values for all their segments apart from the region of 0?X_1,3-PP?X_e at both 1/min and 10?/min cooling rates,which indicated that the molecular interactions between 1,3-PO and 1,3-OO or 1,3-PO and 1,3-PP in region of X_e?X_1,3-PP?1 were inclined to favor the formation of mixed-pairs.The PLM results exhibited that the variations in the microstructure were strongly affected by the adding components,especially apparent at compositions in proximity of the eutectic composition.?4?PO-DAGE/POL-DAGE and PO-DAGE/PS-DAGE binary system showed a better compatibility in comparison with their corresponding original blends and a concurrence of a minor eutectic effect.The melting and crystallization properties were distinctively different from corresponding original blends.DAG-enriched blends displayed a rather high crystallization rate and exhibited no spherulitic crystal growth,which showed more dense and ordered structure with very small needle-like crystals.PO-/POL-/RSO-DAGE,PO-/PS-/RSO-DAGE and PO-/PS-/POL-DAGE tenary system were also exhibited good compatibility.Lastly,PO-/POL-/RSO-DAGE?45:45:10?,PO-/PS-/POL-DAGE?45:10:45?,PO-/PS-/POL-DAGE?10:10:80?,PO-DAGE/POL-DAGE?70:30?,PO-DAGE/POL-DAGE?90:10?and PO-DAGE/PS-DAGE?90:10?were optimally formulated through analysis of SFC profiles,compatibility as well as polymorphism to produce typical bakery shortening.?5?After stored at constant and fluctuant temperatures for 3 months,the POV values and acylglycerol composition for PDAGE-shortening A and B as well as their contron samples and comercial shortening exhibited no significant differences.Compared to control A and B,the SFC values of PDAGE-shortening A and B were less sensitive to the temperature variations and the decline trend of hardness was more gentle.During storage,the viscoelasticity of PDAGE-shortening A and B more stable,with less sensitiveness to time and temperature,which showed smaller variation scale.During constant 5?,the storage time showed no significant effect on enthalpy values.However,the effect became obvious when stored at higher temperatues and more obvious at fluctuant temperatures.Additionally,the enthalpy of PDAGE-shortening A and B was significantly less sensitive to time and temperature.Furthermore,the rate of crystal form transitions for PDAGE-shortening A and B was slower,which showed ?? and ? cyrstals after 3 months.During storage,the evolution of crystal growth,migration and aggregation for DAG-enriched shortening was slower,which was not easy to aggregate to form larger granular crystals or large fat bulk.