Short spacings and polymorphic forms of natural and commercial solid fats: A review

Enzymatic Esterification of Functional Lipids for Specialty Fats: 1,3-Dipalmitoylglycerol and 1,3-Distearoylglycerol

High-melting point 1,3-diacylglycerols not only provide health benefits, but are also suitable for manufacture of foods containing various specialty fats. It is difficult to prepare such high-melting point diacylglycerols, as the activities of specific enzymes will severely reduce at their melting points. In the present study, a combined technique was developed to prepare 1,3-dipalmitoylglycerol (1,3-DPG) and 1,3-distearoylglycerol (1,3-DSG) using selective esterification, molecular distillation, and solvent fractionation. Lipozyme TL IM was suitable for use as the optimal enzyme to maintain relatively high activity levels at esterification temperatures of 73-75 °C. 1,3-DAG/(DAG + TAG) was selected as the most important index to monitor the esterification and to evaluate the synthesized fats. The obtained 1,3-DPG and 1,3-DSG showed high purities, at more than 83%, and possessed hard attributes at room temperature. Both 1,3-DPG and 1,3-DSG exhibited fat crystals with β' and β crystals. Needle-like and rod-like crystals were observed at 5-25 °C for 1,3-DPG, and closely packed feather-like crystals were found at 5-20 °C for 1,3-DSG, indicating their multiple abilities in modifying the crystallization stabilization of the fat matrix during food processing.

Diet-Induced Obesity Modulates Close-Packing of Triacylglycerols in Lipid Droplets of Adipose Tissue

Adipose-derived lipid droplets (LDs) are rich in triacylglycerols (TAGs), which regulate essential cellular processes, such as energy storage. Although TAG accumulation and LD expansion in adipocytes occur during obesity, how LDs dynamically package TAGs in response to excessive nutrients remains elusive. Here, we found that LD lipidomes display a remarkable increase in TAG acyl chain saturation under calorie-dense diets, turning them conducive to close-packing. Using high-resolution X-ray diffraction, solid-state NMR, and imaging, we show that beyond size expansion LDs from mice under varied obesogenic diets govern fat accumulation by packing TAGs in different crystalline polymorphs. Consistently, LDs and tissue stiffen for high-calorie-fed mice with more than a 2-fold increase in elastic moduli compared to normal diet. Our data suggest that in addition to expanding, adipocyte LDs undergo structural remodeling by close-packing rigid and highly saturated TAGs in response to caloric overload, as opposed to liquid TAGs in a low-calorie diet. This work provides insights into how lipid packing within LDs can allow for the rapid and optimal expansion of fat during the initial stages of obesity.

The relationship between nonlinear viscoelasticity and baking performance in low-saturated puff pastry margarine

The oil phase obtained by blending and oleogel methods has potential for the production of non‑hydrogenated and low-saturated puff pastry margarine, thereby reducing intakes of both types of dietary fat. The crystal form, microstructure, rheology, and baking applications of puff pastry margarines prepared with anhydrous milk fat (AMF)/palm stearin (POs), POs/palm oil (PO), beef tallow (BT)/PO, or AMF/POs/diacetyl tartaric acid ester of mono(di)glycerides (DATEM) oleogels were investigated using X-ray scattering, polarized light microscope, and rheometer, respectively. All margarines exhibited β'-form crystal and strongly viscoelastic at low strain. With the addition of DATEM oleogel, their crystal microstructure became more uniform and finer, and the croissants were less hard (1690) and chewiness (160). The chewiness of croissants produced using the margarines was significantly improved with POs content. The theoretical basis for preparation and application in non‑hydrogenated and low-saturated puff pastry margarine was provided in the present study.

Improving the crystallization and melting characteristics of cocoa butter substitute by blending with krabok seed fat

This work investigated the crystallization and melting behavior of a commercial cocoa butter substitute (CBS) blended with 10-80% (by weight) of a hard lauric fat called krabok seed fat (KSF). The aim was to find CBS-KSF blends with improved crystallization and melting characteristics from that of the CBS. It was found that the addition of 10-80% KSF to CBS improved the melting properties of the CBS. However, 10-20% KSF resulted in too high solid fat content (SFC) values at the body temperature (37 °C) which would lead to waxy mouth feel. Adding 30-40% KSF resulted in better melting profiles than 10-20% KSF with SFC values < 3% at 37 °C and SFC curves most similar to cocoa butter. However, 40% KSF led to a significant decrease in the crystallization rate from that of CBS and a significant increase in the average crystal size. With 60-80% KSF, although the blends melted completely at the body temperature, their crystallization rates were significantly reduced. All CBS-KSF blends crystallized into β' structure. Therefore, the addition of 30% KSF to the CBS is recommended for industrial use to obtain compound chocolate with improved quality.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05513-1.

Polymorphism of a Highly Asymmetrical Triacylglycerol in Milk Fat: 1-Butyryl 2-Stearoyl 3-Palmitoyl-glycerol

Milk fat has more than 200 triacylglycerols (TAGs), which play a pivotal role in its crystallization behavior. Asymmetrical TAGs containing short butyryl chains contribute to a significant portion of milk fat TAGs. This work aims to elucidate the crystallization behavior of asymmetrical milk fat TAGs by employing the pure compound of 1-butyryl 2-stearoyl 3-palmitoyl-glycerol (BuSP). The structural evolution of BuSP after being cooled down to 20 °C from the melt is evaluated by small- and wide-angle X-ray scattering (SAXS and WAXS) and differential scanning calorimetry (DSC). The temporal structural observation shows that BuSP crystallizes into the α-form with short and long spacings of 4.10 and 56.9 Å, respectively, during the first hour of isothermal hold at 20 °C. The polymorphic transformation of the α to β' phase occurred after 4 h of isothermal hold, and the β'- to α-form fraction ratio was about 70:30 at the end of the isothermal experiment (18 h). Pure β'-form X-ray patterns are obtained from the BuSP powder with short spacings of 4.33, 4.14, and 3.80 Å, while the long spacing of 51.2 Å depicts a three-chain-length lamellar structure with a tilt angle of 32°. Corresponding DSC measurements display that BuSP crystallizes from the melt at 29.1 °C, whereas the melting of α- and β'-forms was recorded at 30.3 and 47.8 °C, respectively. In the absence of the β-form, the β'-polymorph is the most stable observed form in BuSP. This work exemplarily explains the crystallization behavior of asymmetrical milk fat TAGs and thus provides new insights into their role in overall milk fat crystallization.

Quantifying cooperative flow of fat crystal dispersions

We quantify the cooperative flow behaviour of fat crystal dispersions (FCDs) upon varying crystallization conditions. The latter enabled altering the multiscale microstructure of the FCDs, from the nanometer-sized platelets, and the dispersed fractal aggregates, up to the strength of the mesoscopic weak-link network. To the goal of characterizing strongly-confined flow in these optically-opaque materials, we acquire high-resolution rheo-magnetic-resonance-imaging (rheo-MRI) velocimetry measurements using an in-house developed 500 μm gap Couette cell (CC). We introduce a numerical fitting method based on the fluidity model, which yields the cooperativity length, ξ, in the narrow-gap CC. FCDs with aggregates sizes smaller than the confinement size by an order of magnitude were found to exhibit cooperativity effects. The respective ξ values diverged at the yield stress, in agreement with the Kinetic Elasto-Plastic (KEP) theory. In contrast, the FCD with aggregates sizes in the order of the gap size did not exhibit any cooperativity effect: we attribute this result to the correspondingly decreased mobility of the aggregates. We foresee that our optimized rheo-MRI measurement and fitting analysis approach will propel further similar studies of flow of other multi-scale and optically-opaque materials.

Characterization of sheep tail fat dry fractionation at the pilot scale

Two-step dry fractionation was employed to prepare the liquefied sheep tail oil at the pilot scale. Sheep tail oil was separated into fat residuals, crude oil, stearin A, stearin B, olein A, and olein B. The extracted rates for crude oil, olein A, and olein B were 66.7, 45.9, and 35.0%, respectively. The ratios of saturated/unsaturated fats in the crude oil, olein A fractions, and olein B fractions were 0.62, 0.63, and 0.60, respectively. The olein B was liquid at ambient temperature and its melting point was 5.32 °C. The iodine values of stearin samples were significantly decreased compared to the crude oil samples (P < 0.05). For the stearin fractions, the polymorphic form was mainly β’ form, and the solid fat content was significantly higher than the olein fractions (P < 0.05), which can be used to make the shortening product.

Rhizomucor miehei lipase-catalysed synthesis of cocoa butter equivalent from palm mid-fraction and stearic acid: Characteristics and feasibility as cocoa butter alternative

In this study, cocoa butter equivalents (CBEs) were prepared through enzymatic interesterification of palm mid-fraction (PMF) with stearic acid (SA). The reaction process parameters were experimented and the performance of the product was analysed. PMF and stearic acid (at a mass ratio of 1:2) were catalysed by 80 g kg^-1 enzyme loading of Lipozyme RM IM fromRhizomucor mieheiat 60 °C for 120 min. The yield of the CBE product was more than 92%, and the CBE resembled cocoa butter (CB) in terms of its triacylglycerol composition. The hardness of the CBE product was higher than that of CB at different storage temperatures, but this difference was not obvious at 25 °C. The polymorphic structures and SFC curve of the CBE were similar to those of the CB. In addition, the CBE could be mixed with CB in any ratio without an obvious eutectic phenomena. Up to 40% CBE could be added to CB without significantly affecting the thermodynamic properties of CB. Thus, replacing CB with the CBE product is feasible.

The Effect of Hard Lauric Fats on the Crystallization Behavior of Cocoa Butter Substitute

This work investigated the crystallization and melting behavior of cocoa butter substitute (CBS) blended with two hard lauric fats: fully hydrogenated palm kernel oil (FHPKO) and krabok seed fat (KSF). The aim was to find a way to increase the heat resistance of CBS for the production of heat-resistant compound chocolate (HRCC). Adding FHPKO to CBS increased the crystallization rate with a decrease in crystallization induction time but did not increase the heat resistance. In contrast, all KSF-CBS blends exhibited higher heat resistance than CBS and crystallized into β' form, a preferred polymorph for fats used in compound chocolate. Only the blends with 10-60% KSF melted completely at the body temperature, indicating that they would leave no waxy mouthfeel, but the blends with 30 and 40% KSF exhibited a significant decrease in the crystallization rate compared to the original CBS. Therefore, the KSF-CBS blends with 10, 20 and 60% KSF are recommended for future use as fats for HRCC production.

Interesterified blend-based and physical blend-based special fats: storage stability under fluctuating temperatures

BACKGROUND

Temperatures that special fat faces in a real environment fluctuate, thus, understanding the property changes of special fats under fluctuating temperatures will be helpful in guiding how to keep its high quality in the production and application process. Therefore, a comparative study was carried out on the storage stability of physical blend-based and interesterified blend-based special fats (PBSFs and IBSFs) and their oxidative stability, crystallization and physical properties were studied under fluctuating temperatures.

RESULTS

The peroxide values of IBSFs and PBSFs were less than 10.0 mmol kg^-1 after 4 weeks of storage, and IBSFs had better oxidative stability. There was little change in the solid fat content, and the hardness decreased when IBSFs and PBSFs were stored for 4 weeks. X-ray diffraction results indicated that PBSFs had only β-crystal, but IBSFs had β- and β'-crystal after storage. Moreover, in IBSFs, the transformation from β'- to β-form in PS:RO-IBSF was more obvious than that in PS:SO-IBSF (PS, palm stearin; SO, soybean oil; RO, rapeseed oil) after 4 weeks of storage, and the good integrity of crystalline network in fast-frozen special fats during fluctuating temperature storage followed the order: IBSF > PBSF, PS:RO-PBSF > PS:SO-PBSF.

CONCLUSION

The results suggest IBSF can better maintain its quality during fluctuating temperature storage than PBSF. © 2019 Society of Chemical Industry.

Storage stability studies on interesterified blend-based fast-frozen special fats for oxidative stability, crystallization characteristics and physical properties

The storage stability of two kinds of interesterified blend-based fast-frozen special fats (PS:SO-IBSF, PS:RO-IBSF) with varied triacylglycerols (TAGs) compositions under different temperatures for 4 weeks was investigated. Rancimat and peroxide values experiments indicated that both IBSFs display good oxidation stability throughout a 4-week storage. As for the physical properties of both IBSFs, the solid fat content and hardness decreased with the increase of storage temperature, and IBSFs still exhibited a viscoelastic solid-like behavior. X-ray diffraction results showed that crystal transformation from β'- to β-form was more serious when stored at 25 °C. The more content of ECN 50-type TAGs in PS:RO-IBSF is helpful to reduce its crystal transformation from β'-to β-form compared to PS:SO-IBSF. On the other hand, storage at 4 °C was beneficial for both IBSFs to keep their crystal network integrity, and the PS:RO-IBSF maintained better quality under the same storage conditions.

Effects of wax concentration and carbon chain length on the structural modification of fat crystals

Natural waxes are cost-effective and potential fat crystallization modifiers; however, there is limited information about their implementation in solid triacylglycerol (TAG) oil. Herein, we investigated the effects of two natural waxes, namely, candelilla wax (CLW) and rice bran wax (RW), with different concentrations (2, 4, 6, and 8 wt%) and carbon chains on the crystal growth and structure of palm kernel stearin (PKS85). CLW significantly accelerated the PKS85 crystallization process. Both waxes could induce a new hydrocarbon chain with the lengths of 3.70 and 4.15 Å during the TAG crystallization, respectively. Particularly, X-ray diffraction (XRD) indicated that PKS85 combined with CLW showed a similar lamellar thickness (d₀₀₁) and crystal domain size (ξ) with pure PKS85, whereas that of PKS85 containing RW was 1.7-1.8 and 1.5-1.8 fold higher, respectively. This result corresponded to the carbon chain length of CLW and RW, which was double and quadruple that of PKS85, respectively. Further, these variations were reflected in the crystal microstructures of PKS85 with CLW and RW, where the former showed small homogeneous crystals, while the latter displayed large rod-like layered crystals. In addition, the firmness significantly increased when CLW and RW were added, which is possibly attributed to the fact that the waxes became the backbone of the crystal "fence". Our findings give clear insight into the interaction between TAGs and wax molecules in the crystallization process, which can help guide the utilization of natural waxes in the modification of fats.

Synthesis of cocoa butter substitutes from Cinnamomum camphora seed oil and fully hydrogenated palm oil by enzymatic interesterification

Cinnamomum camphora trees have a vast range of distribution in southern China and the seed oil has unique fatty acid (FA) properties and various bio-activities. In this work, Cinnamomum camphora seed oil (CCSO) was utilized to synthesize value-added cocoa butter substitute (CBS) by enzymatic interesterification. The synthesis was conducted in a solvent-free system by blending CCSO with fully hydrogenated palm oil under the catalysis of Lipozyme RM IM. The reacted products were assessed with physicochemical properties, i.e. FA composition, slip melting point (SMP), triacylglycerol (TAG), crystal polymorphism, microstructure, melting and crystallization properties and solid fat content (SFC). It showed that MCFAs (capric acid plus lauric acid) was the main fatty acid in products, accounting for over 45%. Comparing to physical blends, some novel TAG species such as LaLaLa and LaMLa/LaLaM were observed after enzymatic interesterification whereas SSS TAGs were reduced. IP presented a ball-like, well-distributed and nearly round crystal microstructure and a smaller crystal size. Moreover, it should be mentioned that SFC of IP ranging from 31.85 to 38.47% at 25 °C with most β' crystal forms, was beneficial to improve the spreadability in term of confectionery products and baked goods. The SMP of the interesterified products was 35.75-36.15 °C which closed to the commercial CBS. Hence, the products synthesized can be used to as CBS, and the results in this study also showed CCSO have value-added applications.

Physicochemical characterization of organogels prepared from menhaden oil or structured lipid with phytosterol blend or sucrose stearate/ascorbyl palmitate blend

Phytosterol blend and sucrose stearate/ascorbyl palmitate blend organogelators and different oil phases formed organogels with different physicochemical properties.

Insights into the mechanism of the formation of the most stable crystal polymorph of milk fat in model protein matrices

The effect of incorporation and presence of various ingredients in a model sodium caseinate-based imitation cheese matrix on the polymorphism of milk fat was comprehensively described using powder x-ray diffraction, differential scanning calorimetry, and microscopy. With anhydrous milk fat (AMF) in bulk used as control, the embedding of AMF as droplets in a protein matrix was found to result in a greater extent of formation of the β polymorph than AMF alone and AMF homogenized with water and salts solution. The use of other protein matrices such as soy and whey protein isolate gels revealed that the nature of the protein and other factors associated with it (i.e., hydrophobicity and molecular structure) do not seem to play a role in the formation of the β polymorph. These results indicated that the most important factor in the formation of the β polymorph is the physical constraints imposed by a solid protein matrix, which forces the triacylglycerols in milk fat to arrange themselves in the most stable crystal polymorph. Characterization of the crystal structure of milk fat or fats in general within a food matrix could provide insights into the complex thermal and rheological behavior of foods with added fats.

Crystallinity properties and crystallization behavior of chocolate fat blends

Cocoa butter (CB) provides unique crystallization characteristics to chocolates and confectionary products; hence, it is an important value-add product. However, other alternative fats that minimally affect the crystallization behaviour of chocolates and confectionary products are now being increasingly used. This study analyzed the crystallization behaviour of CB, cocoa butter substitutes (CBSs), and their blends. Blends were prepared using CBS concentrations: 5, 10, 15, 20 and 37.5%. CB, CBS, and their blends were evaluated by following analysis: solid fat content, isothermal analysis, polarized light microscopic, thermal behaviour, X-ray diffraction and consistency. Crystallization analysis showed an incompatibility between the 2 fats, with a reduction in the crystallinity and increase in liquid content in all the blends. Eutectic crystallization at 20 °C was only observed for the blend containing 20% CBSs. This was considered as a positive result because previous studies have indicated that CBS concentration in CB blends should not be more than 5%.

Trans-free margarine fat produced using enzymatic interesterification of rice bran oil and hard palm stearin

Trans-free interesterified fats were prepared from blends of hard palm stearin (hPS) and rice bran oil (RBO) at 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, and 80:20 weight % using immobilized Mucor miehei lipase at 60°C for 6 h with a mixing speed of 300 rpm. Physical properties and crystallization and melting behaviors of interesterified blends were investigated and compared with commercial margarine fats. Lipase-catalyzed interesterification modified triacylglycerol compositions and physical and thermal properties of hPS:RBO blends. Slip melting point and solid fat contents (SFC) of all blends decreased after interesterification. Small, mostly β' form, needle-shaped crystals, desirable for margarines were observed in interesterified fats. Interesterified blend 40:60 exhibited an SFC profile and crystallization and melting characteristics most similar to commercial margarine fats and also had small needle-like β' crystals. Interesterified blend 40:60 was suitable for use as a transfree margarine fat.

Formation of β Polymorphs in Milk Fats with Large Differences in Triacylglycerol Profiles

In this study, we characterized the polymorphism of milk fat (MF) with various TAG compositions during isothermal crystallization at 20 °C. TAG composition of MF from seven individual cows was determined using GC-FID and MALDI-TOF MS, and MF polymorphism was studied using X-ray diffraction. Results showed that TAG profile determines the polymorphic behavior of MF. Saturated TAG with carbon numbers 34-38 promoted the formation of α polymorphs, whereas unsaturated TAG with 52-54 promoted the formation of the β polymorphs. Furthermore, MFs with unsaturated fatty acid profiles were increased in unsaturated TAG with 52-54 carbons. The presence of MF crystals in the β polymorph has been controversial over the years as most authors mainly find MF crystals in the α and β' form. In our work, we showed that the β polymorph is formed in MF on the basis of its TAG composition.

Characterization of the nanoscale structure of milk fat

The nanoscale structure of milk fat (MF) crystal networks is extensively described for the first time through the characterization of milk fat-crystalline nanoplatelets (MF-CNPs). Removing oil by washing with cold isobutanol and breaking-down crystal aggregates by controlled homogenization allowed for the extraction and visualization of individual MF-CNPs that are mainly composed of high melting triacylglycerols (TAGs). By image analysis, the length and width of MF-CNPs were measured (600 nm × 200 nm-900 nm × 300 nm). Using small-angle X-ray scattering (SAXS), crystalline domain size, (i.e., thickness of MF-CNPs), was determined (27 nm (d001)). Through interpretation of ultra-small-angle X-ray scattering (USAXS) patterns of MF using Unified Fit and Guinier-Porod models, structural properties of MF-CNPs (smooth surfaces) and MF-CNP aggregations were characterized (RLCA aggregation of MF-CNPs to form larger structures that present diffused surfaces). Elucidation of MF-CNPs provides a new dimension of analysis for describing MF crystal networks and opens-up opportunities for modifying MF properties through nanoengineering.