A Preliminary Study On The Crystallization Properties Of Branched Chain Fatty Acids Triglycerides And Their Applications In Shortening

Branched chain fatty acids are functional fatty acids that have recently attracted attention.Due to their branched chain characteristics,their oils and fats can have special solid crystalline characteristics and are of particular values for specialized oils and fats,especially shortenings.In this work,branched-chain fatty acid triglyceride（BCFA-TAG）was synthesized using branched-chain fatty acids as the acyl donor material,and the palm oil-based blend PO-PS（Palm Olein/Palm Stearin=7/3,w/w）was used as the shortening based oil.The crystallization properties of BCFA-TAG were first investigated to provide basic data for further analysis of the effect of BCFA-TAG addition on the crystallization behavior of PO-PS and its application in shortening.BCFA-TAG was then added to shortening-based oils PO-PS at appropriate concentrations（0%,1%,2%,5%,8%,10%）to investigate the effect of BCFA-TAG on the crystallization behavior of shortening-based oils PO-PS from the macroscopic（solid fat content,hardness,crystallization kinetics and thermal properties）and microscopic（crystalline shape and microstructure）perspectives respectively.Subsequently,BCFA-TAG was mixed with shortening base oil PO-PS to prepare simulated shortening by rapid cooling kneading process.Under different temperature procedures（low temperature,normal temperature,high temperature and variable temperatures）,the shortening containing BCFA-TAG and ordinary shortening were subjected to shelf experiments（time points:0 days,7 days,21 days,40 days,90 days）to further investigate the application value of BCFA-TAG in shortening.Finally,PO-PS with 10%BCFA-TAG was selected for chemical interesterification（CIE）to investigate the effect of the random distribution of branched fatty acids on the crystallization behavior of oils and fats,expanding the application of triglycerides of branched fatty acids in the modification of oils and fats.The main points and conclusions are as follows:1.A preliminary investigation of the molecular composition,solid fat content,crystallization kinetics,crystal form and crystalline morphology of the branched fatty acid triglycerides and a comparative analysis with palm oil-based blends（PO-PS）showed that:The fatty acid composition of BCFA-TAG was very complex.The carbon number of fatty acids ranges from C₁₀ to C₂₉,and they were all saturated fatty acids,including branched and linear fatty acids,of which branched fatty acids account for the main part.The triglycerides of BCFA-TAG were mainly distributed in the C42:0 to C71:0,and the content was in a normal distribution state.The high melting point triglycerides appeared in the C48-C71 range（taking the triglyceride of C48 as an example,12:0-20:0 indicated that its fatty acids are triglycerides formed by the combination of fatty acids of C12:0-C20:0）,and its content reached 91.66%.Thus,the presence of high melting point triglycerides provided BCFA-TAG with good crystallization properties,providing certain structural properties for the formation of fatty crystalline networks.However,due to the branched characteristics of branched fatty acids which give them similar physicochemical properties to unsaturated fatty acids,BCFA-TAG will have some specific solid crystallization characteristics,making BCFA-TAG not exhibiting high melting point properties during melting after complete crystallization.Moreover,BCFA-TAG showed an instantaneous nucleation mechanism during isothermal crystallization.At temperatures up to 30°C,the nucleation mechanism of BCFA-TAG did not change much and showed fine,dense needle-like crystals,which may be related to the branched structure of the branched fatty acid glycerides,and the branched structure retarded the formation of coarse crystals.Meanwhile,the crystalline network of BCFA-TAG was denser than that of PO-PS,with a higher fractal dimension value than PO-PS,a higher degree of filling and an orderly crystal arrangement,while the crystal morphology tended towards theβ’crystal type.2.The effects of BCFA-TAG on the solid fat content（SFC）,hardness,crystallization rate,crystal nucleation growth and thermal properties of shortening-based oils PO-PS were investigated macroscopically by differential scanning calorimeter（DSC）,pulsed nuclear magnetic resonance（p-NMR）and texture analyzer（TA）.Polarizing light microscope（PLM）and X-ray diffraction（XRD）were used to investigate the effect of BCFA-TAG on the crystal form and microstructure of PO-PS in shortening base oil from a microscopic perspective.The results showed that:（1）The addition of BCFA-TAG significantly affected the crystallization of PO-PS,primarily reflected in the fact that BCFA-TAG accelerated the onset of PO-PS crystallization and promoted the nucleation of PO-PS crystals but delayed the growth of the crystals as a whole.The delay in the crystallization process was also well demonstrated by the reduction in the crystallization half time t_1/2,with the effect of high concentrations of 10%BCFA-TAG being the most pronounced.（2）BCFA-TAG was involved in the crystallization of PO-PS.After 48 h of crystallization at 25°C,BCFA-TAG induced a more compact and orderly crystalline network of PO-PS and an increase in space filling,resulting in an increase in hardness.（3）The crystal density of the higher concentration samples（PO-PS+10%）decreased with storage time,suggesting that the high concentration of BCFA-TAG acted as a fat dilution during subsequent storage.（4）The crystalline form of sample PO-PS+10%maintained theβ’crystalline form throughout the 30 days of storage and no conversion ofβ’to theβcrystalline form occurred,thus having a positive effect in alleviating the post-hardness of the palm oil.3.Model shortening with 5%and 10%BCFA-TAG was used for the study of the hardness,crystalline diffraction,crystalline nature of melting and the diffraction pattern of crystal morphology of shortening samples during storage by constant temperature storage mode（15°C,25°C,37°C）and temperature fluctuation storage mode（5°C 12 h-25°C 12 h cycle reciprocal,37°C 12 h-25°C 12 h cycle reciprocal）,and blank model shortening was selected as control for comparative analysis.The results showed that:（1）During storage at a constant temperature of 15°C and 25°C,the blank model shortening showed a significant hardening,while the model shortening with a high concentration of 10%BCFA-TAG did not show any hardening.The addition of BCFA-TAG had no effect on the hardness of the shortening when the constant storage temperature rose to37°C,during which time most of the internal crystals of all samples melted and the hardness decreased significantly after 7 days of storage.Over time,after 90 days,the only solid fat remaining was beyond the detection limit of the instrument due to too low a hardness.The hardness of the model shortening with a high concentration of 10%BCFA-TAG decreased more gently when stored at fluctuating temperatures.（2）The effect of time on the enthalpy change of the melting curves of model shortening samples with 5%and 10%BCFA-TAG during storage at a constant temperature of 15°C was not significant.The effect of time on the enthalpy change of the 5%-shortening sample was relatively significant when the temperature of constant storage was increased to 25°C,while the enthalpy change of the 10%-shortening sample did not change significantly and only changed significantly at 90 days.When the temperature increased to 37°C,the time had a significant effect on the enthalpy change of all samples.The effect of time on the enthalpy changes of shortening samples with 10%BCFA-TAG was not significant when stored at fluctuating temperatures（15°C 12 h-25°C 12 h）,while the melting properties of all samples changed significantly when stored at fluctuating temperatures（25°C 12 h-37°C 12 h）.In conclusion,the model shortening samples with a high concentration of 10%BCFA-TAG were significantly less sensitive to temperature and time than the blank model shortening and 5%-shortening samples.（3）The shortening samples supplemented with a high concentration of 10%BCFA-TAG at a certain temperature（15°C-25°C）showed a significantly slower rate of crystal diffraction than the blank model shortening,both at constant and fluctuating temperatures,andβ′crystals were still present in the samples after 90 days of storage.（4）The shortening with 10%BCFA-TAG showed a slower growth and aggregation of crystals during storage than the blank shortening control sample,both at constant and fluctuating temperatures（15°C-25°C）,and was less likely to form larger granular crystals or large fat blocks,indicating that the shortening with a high concentration of 10%BCFA-TAG deteriorated relatively slowly during storage.4.The crystallization properties of BCFA-TAG after chemical interesterification with shortening-based oils PO-PS:（1）The chemical interesterification of the sample with 10%BCFA-TAG resulted in an increase in the solid fat content of the sample,an increase in hardness,a shift in the non-isothermal crystallization melting curve towards the high temperature region and an increase in the crystallization rate,corresponding to a decrease in the crystallization half time t_1/2,corresponding to an increase in both the trisaturated TAGs and the monosaturated TAGs in the glycerol composition of the sample after the interesterification.（2）Meanwhile,the random distribution of branched fatty acids facilitated the transformation of theα-crystalline form toβ′crystals but did not change the nucleation and growth pattern of the crystals,which were transient nucleation and linear growth;the crystals grew into coarse crystals but did not change the crystalline form of the sample system,which remained asβ′crystals.Comparison of the crystalline properties of BCFA-TAG with shortening-based oils PO-PS after chemical interesterification with PO-PS（CIE）revealed that:The peak temperature of the high melting point component of the samples containing BCFA-TAG after chemical interesterification increased with the decrease in enthalpy change due to the increased content of trisaturated triglycerides in the samples after the addition of BCFA-TAG interesterification,but the presence of branched chains interfered with the stacking of TAG to form a high melting point structure,making the crystal structure formed during its crystallization less strong,resulting in a lower absorption of heat used for melting during melting and easier melting.After chemical interesterification of BCFA-TAG with PO-PS,the solid fat content and crystallization rate increased and the hardness increased,while the microstructure changed significantly.According to the above results it indicated that the physicochemical properties of the samples after chemical interesterification with and without the addition of BCFA-TAG were significantly different,suggesting that the random distribution of branched fatty acids on TAGs had a significant effect on the grease system,which is an interesting finding and provides some guidance for further expansion of the application of branched fatty acid triglycerides in lipid modification.