The Effect Of Emulsifier On The Mechanical Properties And Crystalline Structure Of Plastic Fat

With the increasing demand for food diversity,high quality fat is absolutely necessary.Food can be endowed with fine taste,flavor and color by plastic fats,which have become major products by oil factories.Palm oil is widely applied in the manufacture of plastic fats due to its advantages such as large production,low price and fine processing characteristics.During processing or storage,sandiness is easily appeared in the crystallization of fat due to inappropriate processing conditions and ambient temperature,which generates worse tastes and results in losing its proper functional characteristics and operational performance.This quality defect is remarkably obvious in palm oil and beef tallow-based plastic fats,which leads to huge economic loss every year.Till now,as constant temperature during cold chain transportation hasn't been achieved in food industry,emulsifier has been widely used to solve the problem of sandiness in plastic fats.However,the application of emulsifier in plastic fats is largely based on experience,thus,there has not been any definite conclusion for the functional rule or mechanism of emulsifier yet.It is obvious that any material's special function is completely decided by its structure.Therefore,it is of great importance to discuss the effect of emulsifier on the plastic fats'structure from the multiple perspectives of structure for the rational control of plastic fats quality.In this paper,palm stearin is taken as the research object,which is added with 1%,2%,4%concentration of sorbitol monopalmitate,glycerol monostearate and glycerol monopalmitate,respectively.The effect of emulsifier's structure and dosage on fat's solid-liquid conversion,crystalline evolution,crystalline structure and mechanical properties is systemically discussed.The relationship between emulsifier molecule,plastic fats'crystalline structure and macrophysics properties is investigated.The mechanism of emulsifier molecule-induced multi-scale structural changes of lipid crystal network is revealed,so as to be rational to control the quality of plastic fats.?1?Effects of emulsifiers on thermal properties and the homogeneous poly-crystalline evolution of palm stearin during quenching process.Effects of emulsifiers with different types and concentrations on the thermodynamics of crystallization and on the homogeneous poly-crystalline evolution of palm stearin during quenching process was investigated by means of the DSC combining with XRD method.When the fat samples were cooled down at the rate of 5?/min,10?/min,or 20?/min,it is found that the crystallization peaks shifted to the high temperature zone at low cooling rate.Addition of emulsifiers facilitated the crystallization of the saturated components in fat.Three emulsifiers with the addition dose of 2%or 4%all increased the T_onset and T_p level of palm stearin comparing with the untreated samples.Two crystallization peaks were observed for all tested samples and the first one corresponded to the?form consisting of the saturated components in fat while the other comprised of the unsaturated components was the?'form.The?'form was evolved from the?form or directly produced from the fat,and the?form was not detected during quenching process.?2?Effect of emulsifiers on the isothermal crystallization dynamics and the micro-structure of palm stearinThe crystallization dynamics,mechanical properties,and microstructure of palm stearin with different emulsifiers were investigated during isothermal crystallization process at 15?,20?,25?,or?m?,respectively.The level of SFC and hardness of palm stearin remarkably decreased along with increasing the temperature of isothermal crystallization.The fat system formed instantaneous nuclei and the isothermal crystallization curves against time showed typical hyperbolic pattern at 15?-25?.Meanwhile,the emulsifier which contained the same fatty acids and similar structure as palm stearin postponed the transition from?to?'form.The crystallization rate of palm stearin was low at 30?.The structure of crystallization network and the fat hardness were affected by the emulsifier which changed the crystallization mechanism of the fat system.Besides,the influence of emulsifiers was structure and dose-dependent.Addition of 4%GMS or GMP prompted the instantaneous nucleation and facilitated the formation of compact fat crystallization with tiny nuclei and high hardness.Moreover,similar results were observed when 1%of SMP was applied,which was attributed to the steric hindrance of sorbitol anhydride in SMP.?3?Effect of emulsifiers on the crystallization behavior of palm stearin-based model shorteningThe palm stearin-based model shortening was prepared in terms of the simulated industrial production process.Then the hardness,SFC,crystalline structure,and crystalline form of the model shortening were investigated at 25?.It is found that the?-crystal was evolved from crystal during the ripening process.Emulsifiers improved the yield resistance of fat by affecting the size of nano-plates which had influence on the size and congestion of crystal beams.All three emulsifiers facilitated the superposition of nano-scale molecular layer structure,inhibited the congestion of nano-plates,and reduced the size of crystal beams.But they showed different impact on the length of nano-plates.This confirmed that the emulsifier binds to the oil crystallization network and plays a role in the crystallization site at the nanostructure level.On the basis of divergence of the fatty acid composition and molecular structure,it is suggested that emulsifiers with different molecular structure had higher extent of impact on the crystal morphology of plastic fat whereas emulsifiers with the same molecular structure but various fatty acids effectively inhibited the transition of crystal form from?'to?and sand-out.Therefore,it is of importance on the modulation of plastic fat.?4?Effect of emulsifiers on the quality of model shortening in storageThe SFC value of the model shortening decreased along with time during storage?4?/12 h followed by 28?/12 h in a cycle period of 24 h?.At the later stage in storage?7 d and 14 d?,the shortening without emulsifiers severely deteriorated owing to the aggregation of crystals,separation of liquid oil,reduction of hardness,and high proportion of?crystals.SMP,GMS,and GMP effectively ameliorated the production of?crystals and GMS showed the best capability in multiple cycles?14 times?.When GMS was used,it absorbed the triglyceride molecules melted at high temperature to form crystals with large size during recrystallization process.This phenomenon prompted the growth and cross-link of crystals.The showed higher hardness at the later stage of storage and had the less proportion of?crystals than other shortenings.Besides,the liquid-solid separation was not observed in the GMS shortening.