The Effect Of Emulsifiers On Crystallization Behavior Of Palm Oil

This research used a palm oil-based blend (palm oil/palm stearin=2/1, POST) toinvestigate the effects of different emulsifiers on the isothermal crystallization and thermalmelting behavior of POST, and study the effects of emulsifiers on crystallization behavior ofpure oil system and emulsified system under different supercooling degrees in order to find anuniversal rule of emulsifiers affecting oil crystallization and try to give a guidance for theselection of emulsifiers to avoid the crystal defects of palm oil and improve product quality.The effects of temperature, emulsifiers type and the amounts of emulsifiers on isothermalcrystallization behavior of the palm oil-based blend were studied. The conclusions are:(1)The effects of emulsifiers at low temperature (0oC)was not significant, while at higertemperature (30oC), it was difficult to form nucleus and the effects of emulsifiers wasambiguous. At25oC, all emulsifiers had significant effects.(2) The amount of emulsifieraffected the isothermal crystallization of POST at25oC and the solid fat content, and theeffects were enhanced by the increase of emulsifiers amount. When it was1.0%, allemulsifiers showed the strongest effects (p<0.05).(3) The SEs with different acyl chain toPOST affected the crystal morphology and crystal network:(3.1) Adding SEs with similaracyl chain length to POST, i.e. stearoyl (S-070, S-170) and palmityl (P-170) into POSTaccelerated oil crystallization, shortened existence of α crystals, enhanced the transition tofiner β′crystals, increased viscosity and prevented oil migration and linear growth of cystalson nucleus, and then formed many finer crystals and were easy to melt when heated.(3.2) Theaddition of SEs lauroyl (L-195), erucyl (ER-190and ER-290), which had dissimilar acylchain to POST, delayed the appearance of α and the transition to β′. The sporadic nucleationmade crystals had enough time to linearly grow on nucleus and form well-organized and largecrystals.(3.3) Adding SEs POS-135with similar acyl chain to POST, the acyl chain cancombine with oil but the existence of sucrose prevented the growth of other triacylglycerolson its surface. It delayed the appearance of α crystals and transition to β′crystals and formedsome certain size spherical crystals. Although SEs of oleoyl (O-170) had similar acyl chain toPOSt, but it could not form crystal at room temperature. Thus it had little effects on the blend crystallization.(4) Adding vegetable oil, monoglycerides, polyglycerol esters and sorbitanesters with the same acyl chain length and melting point to SEs, they didn’t have prominenteffects on isothermal crystallization and thermal melting behavior of POST like SEs, and thismay be related to polar groups of SEs which can also affect crystallization behavior of POST.POST formed β′and β crystals under low supercooling degree. Samples with adding SEsL-195, ER-190, ER-290and POS-135delayed the crystallization of POST, they had littleeffect on polymorphism and microstructure of POST. Adding SEs S-070, S-170and P-170ledto high MP, accelerated the crystallization of POST, and formed finer crystals. The addition ofSEs P-170mainly promoted samples presented in β′forms, which had a positive effect toovercome crystallization defections of palm oil.POST both in pure oil, and emulsified systems formed β′crystals under highsupercooling degree. Temperature fluctuation between25oC and4oC had little effect on thepolymorphism, microstructure and melting curves for both systems. When temperaturefluctuation was carried out between30oC and4oC, crystal transformation was observedwhich β′crystals transformed to β crystals. The addition of SE S-170and SE P-170did notonly promote samples to form finer crystals, but also stabilized β′crystal after temperaturefluctuation in a very wide range. They improved crystallization behavior of palm oil-basedplastic fats and maintained their quality.