Study On Crystalization Mechanism Of Cocoa Butter And Application Of Its Fractionation

As a solid fat with complex crystallization behavior,cocoa butter is widely used in food,cosmetics and other industries.However,due to its unique crystal structure,cocoa butter products often experience "blooming" during storage,which seriously affects the product quality.Therefore,this experiment focuses on the formation mechanism of frost phenomenon and strives to find a suitable solution.First,the changes in the chemical composition of cocoa butter at different crystallization stages were studied,and the relationship between the chemical composition and the micro structure of the crystals was explored to clarify the dynamic crystallization behavior of cocoa butter.Then,by studying the change of crystal characteristics of cocoa butter products made by different processing methods during storage,the blooming mechanism of cocoa butter products was clarified.Finally,the use of high melting point fractions distilled from cocoa butter as an inhibitor to delay the appearance of frosting in cocoa butter products.In addition,attempts have been made to add low melting point fractions of cocoa butter to the gel oil,so as to produce an oleogel that can replace artificial shortening,and improve the value of cocoa butter utilization.The main results are summarized as follows:(1)According to the ways of ctystal growth,the crystallization process was divided into the induction stage,primary crystallization stage,and secondary crystallization stage.At the early primary crystallization stage,the crystals contained large proportions of 1,3-dipalmitoyl-2-oleoylglycerol(POP),1-palmitoyl-2-oleoylglycerol-3-stearoyl(POSt),1,3-distearoyl-2-oleoylglycerol(StOSt)and tristearin(StStSt).As crystallization progressed,the relative content of POP increased from 12.08%to 29.84%,and the relative content of StOSt and StStSt decreased from 37.11%to 20.21%and from 4.86%to 0.19%,respectively.The melting point of the crystals decreased from 57.4? to 33.1? during crystallization.Circular crystals were formed at the induction and primary crystallization stages,and ?-? form and ?'-? form polymorphisms were exhibited.When crystallization entered the secondary crystallization stage,the crystal morphology was transformed from circular to acicular,and their polymorphism was transformed from ?'-? form and ?'-?form to ?-form.(2)Control of tempered procedures is the critical factor influencing quality during cocoa butter products manufacture.The improper tempered procedure results in crystallization of inner part of unfilled cocoa butter product later than the outer part of that.In the inner part of the cocoa butter product,there were mainly concentrated of the low melting point triacylglycerol and the unstable ?'-? form crystals.They cause the inside of the unfilled cocoa butter product were significantly differ from the outside in triacylglycerol composition,hardness,crystallinity,melting point and crystal form.During storage,the concentration differences drive the low-melting triacylglycerol from the inner part to the outer part of the product,accompanied by the conversion of polymorphism between ?'-? form and ?-? form and the fat bloom were formed.(3)The addition of high-melting fractions significantly delayed the occurrence of frosting in cocoa butter.Cocoa butter samples with 9%high-melting fractions did not show significant blooming in 60 days.High-melting fractions significantly increase the density of the cocoa butter crystal network,resulting in products with higher hardness,melting points,and crystallinity.(4)The unsaturated fatty acids of oleogels(range from 60.42%to 71.25%)were significantly higher than the shortening(38.08%).With the raising content of low-melting-point fractions of cocoa butter(LFCB),the hardness,solid fat content,viscoelasticity of oleogels increased.The polymorphisms of oleogels were both were ?'-Form and ?-Form.During the crystallization process,the rice bran wax was first crystallized,and then induced a part of LFCB formed ?'-Form crystals,and another LFCB formed the?-Form crystals.The results show that the properties of the organogel prepared by adding 30%of the LFCB are the closest to the shortening.