Mechanism Of Bloom In Lauric Cocoa Butter Substitutes Based Chocolate And Its Modification

Since its physical properties resembling those of cocoa butter (CB), as well as its widely cheap sources, lauriccocoa butter substitute (CBS) becomes an important material which has an extensive application prospect in theconfectionery industry. CBS, which doesn’t need tempering when processing, can be used in place of a major part ofCB that is present in normal chocolate and endue the chocolate with good glossiness. However, bloom formation, aworldwide difficulty in confectionery industry, is one of the outstanding problems of these chocolate products. Thisresearch focused on the bloom problem of CBS chocolate, speculated the mechanism by using static and dynamicanalysis, then discussed the correlation among based fat, dispersed phase and the physical properties of chocolate,finally evaluated the contribution of emulsifiers on modifying the crystallization properties of based fat, as well as theireffects on delaying the bloom formation. The main results are as follows:1. The morphological and microstructure properties of fresh and bloom chocolate were evaluated by using atomicforce microscopy (AFM), scanning electric microscopy (SEM), and extended depth-of-field3-dimension microscopymethods. Bloom and chocolate matrix were carefully separated without destroying the crystallization to determine theirtriacylglycerol (TAG) composition, melting curve, polymorphism transformation, and crystallize shape. The resultsshowed that: fat crystals evenly distributed on the fresh chocolate surface, forming a dense crystal network, othercomponents were locked inside the network. Bloomed chocolate showed a coarse surface, phase separation occurredbetween fat phase and the dispersed phase, some fat crystals aggregated and outreached from the chocolate surface,scattered light leading to bloom appearance. Compared with the chocolate matrix, bloom showed a decline of saturatedTAG and increment of monounsaturated TAG,19.7%and130.1%separately. Polymorphism results showed acombination of β and β′forms for bloom while a β′form for chocolate matrix. XRD results of model chocolate after6weeks temperature fluctuation storage showed that no polymorphism translation appeared among the chocolate.2. Phase behaviors of CBS (two typical types, hydrogenated palm kernel olein (HPKO) and hydrogenated palmkernel stearin (HPKS)), cocoa butter (CB), and milk fat (MF) were systematic analyzed, meanwhile its correlation withmodel chocolate properties were evaluated. Both CBS/CB binary blends displayed significant eutectic behaviors, butHPKO showed better incorporation with CB than HPKS. Dilution effect was observed in both CBS/MF blends,indicated that MF decreased the solid fat content (SFC) of CBS. For the ternary mixtures of CBS/CB/MF, when CB andMF addition were both under10%, the mixture showed a β′form. SFC showed a relationship with the chocolatehardness, for the HPKS based model chocolate, there was a linear correlation between SFC and hardness. Bloomformation closely related with the phase behavior of based fat, for the HPKO/CB/MF ternary mixtures, in which thedilution effect significantly affected the system, a mist-like bloom was induced after11weeks storage, while eutecticshowed a more significant impact on the HPKS/CB/MF mixture than dilution effect, with5%CB addition, a largewhite spot-like bloom was induced after4weeks storage.3. SEM and DSC were introduced to determine the effect of dispersed phase particles on the fat crystallization,meanwhile, dynamic analysis were done for the crystallize curve. The dispersed particles had a significant effect on themelting properties of the system. Cocoa powder could provide heterogeneous nucleation sites for the fat crystals andinduce a stable polymorphism formation, leading to the crystallize temperature increased3oC; crystallization enthalpyof sugar powder was20J/g higher than that of crystal sugar; skim milk powder promoted steep melting andcrystallizing peaks, while whole milk powder showed a broad melting range with low melting enthalpy. Addition oflecithin decreased the crystallizing temperature of both cocoa powder fat mixture and sugar fat mixture, but increasedthe crystallizing temperature (0.4oC) of milk powder fat mixture. The Avrami n value indicated that, sugar increased nfrom3.4to4.4~7.4, inducing a multidimensional space growth; cocoa powder decreased the n value, although thisdecrease effect disappeared with the addition of lecithin; whole milk powder did not change the nuclear and crystalgrowth mechanism, while skim milk powder changed the crystallization to spherical growth with a sporadic nucleation.4. These results suggested that the mechanism of bloom formation in CBS chocolate was as follows: both fatcrystals and liquid oil existed in the CBS chocolate system, during storage, fat crystals kept growth under the drivingforce of the subcooling, crystal lattice of CB was larger than that of CBS, they tended to separate from each other, thesame crystals gathered to form new dense network, while liquid oil migrated freely inside the system; along with thefurther separation of CB and CBS crystals, dispersed particles became more close and finally aggregated under thedriving of van der waals forces, fat phase and dispersed phase separated from each other, among the fat phase TAG ofCB and CBS separated from each other, migration liquid oil brought the CB TAG and CBS LLL (trilaurin) to thesurface of chocolate, with a polymorphism transformation, then large crystals outreached from the surface.5. Five types of emulsifiers were chosen to evaluate their effects on the based fat crystallization, three additionlevels,0.5%,1.0%, and1.5%, for single emulsifier and three ratios,1:3,1:1, and3:1, for combination of emulsifierwere chosen to evaluate their effects on model chocolates by crystallization thermal dynamics and crystallizationkinetics analysis. Addition of emulsifiers changed the nucleation and crystal growth mechanisms of based fat, amongwhich span60and monoglyceride accelerated the nucleation speed, and promoted the two dimension plate growth ofcrystallization. Emulsifier type and additional level also affected the physical properties of chocolate. Addition oflecithin significantly improved the rheology property of molten chocolate; monoglyceride softened the model chocolate,as the additional level increased, the soften effect increased; addition of span60showed a bloom delay effect within16weeks storage, however, its yield stress, apparent viscosity, and thixotropism were high, which had a negative impact on the processing procedure, when molten chocolate was combined with monoglyceride or lecithin in ratios of3:1, itsrheological properties were improved, and also had an effectively bloom delay effect.