Comparison of ultrasonic and pulsed NMR techniques for determination of solid fat content

In this work an ultrasonic velocity technique was compared to direct pulsed NMR (pNMR) spectroscopy for the determination of the solid fat content (SFC) of anhydrous milk fat (AMF), cocoa butter (CB), and blends of AMF and CB with canola oil (CO) in the range 100 to 70% (w/w). In situ measurements of ultrasonic velocity were carried out during cooling (50–5°C) and heating (5–50°C) of the fat samples, and SFC values were calculated. The SFC were also determined simultaneously by pNMR. Peak melting temperatures determined by DSC were used as an indicator of the polymorphic state of the different fats and fat blends. Estimates of SFC obtained using pNMR and ultrasonic velocimetry did not agree. Our results suggested that ultrasonic velocity was highly dependent on the polymorphic state of the solid fat. Ultrasonic velocity in fat that contained crystals in a more stable polymorphic form was consistently higher than in fat that contained crystals in a less stable polymorphic modification. A high attenuation of the signal was observed in milkfat and CB at lower temperatures, particularly after sitting for 24 h. This high attenuation could be a product of scattering by crystallites or by microscopic air pockets formed upon solidification of the material, or it could be due to high ultrasonic absorption associated with phase transitions. This research highlights some of the problems associated with applying ultrasonics to the determination of SFC.     

<Emphasis Type="Italic">In situ</Emphasis> monitoring of solid fat content by means of pulsed nuclear magnetic resonance spectrometry and ultrasonics

An ultrasonic technique was developed to study the crystallization process of edible fats on-line. A chirp wave was used instead of the conventional pulser signal, thus achieving a higher signal-to-noise ratio. This enabled measurements to be made in concentrated systems [≈20% solid fat content (SFC)] through a 8.11-cm thick sample without significant signal loss. Fat samples were crystallized at 20, 25, and 30°C at a constant agitation rate of 400 rpm for 90 min. The crystallization process was followed by ultrasonic spectroscopy and a low-resolution pulsed nuclear magnetic resonance spectrometer. Specific relationships were found between ultrasonic parameters [integrated response, time of flight (TF), and full width half maximum] and SFC. TF, which is an indirect measurement of the ultrasonic velocity (v), was highly correlated to SFC (r ²>0.9) in a linear fashion (v=2.601 SFC+1433.0).     

Dispersed phase destabilization in table spreads

Commercially available butter, regular-fat margarine, and a fat-reduced margarine (38% fat w/w) were stored between 10 and 35°C for up to 4 d to elaborate on the relationship between droplet size and solid fat content (SFC) that exists in these spreads. At 10°C, the mean volume-weighted droplet size for butter was 4.22±0.40 μm followed by margarine (6.22±0.10 μm) and fat-reduced margarine (12.62±0.28 μm). At higher temperatures, as a result of decreasing SFC, the mean droplet size increased as did the droplet size distribution, leading to eventual coalescence and destabilization in all spreads. In butter, the critical SFC was ∼9%, whereas in margarine notable coalescence occurred at ∼5% SFC. The fat-reduced margarine destabilized at lower temperatures than the other spreads (∼20°C vs. ∼30°C), at an SFC of ∼6.5%. In these spreads, two different mechanisms influenced dispersed phase stability: (i) steric stabilization against coalescence via fat crystals located at the droplet interface, known as Pickering stabilization, and (ii) stabilization against droplet sedimentation (and droplet encounters) due to the presence of the fat crystal network.     

Effect of emulsion temperature on physical properties of palm oil-based margarine

Margarines made from refined, bleached, and deodorized palm oil at different emulsion temperatures showed no significant difference in their consistency, polymorphic behavior, and solid fat content (SFC) during storage, although differences were observed during processing. The emulsion temperatures studied were 40, 45, and 50°C, with other parameters such as emulsion flow rates, tube cooler temperature, and pin rotor speed kept constant. The SFC developed during processing and storage at 28°C was measured to evaluate the quality of margarine. The emulsion contained no SFC at any emulsion temperature studied. However, the amount of SFC in the perfector or tube cooler unit increased to 15.9, 13.9, and 15.6% in margarine produced at emulsion temperatures of 40, 45, and 50°C, respectively. At 40°C, the lowest SFC was developed during storage even though this margarine had the highest consistency. The softening point of this sample was moderately high and closely related to the type of crystal developed, which was a mixture of β′ and β crystals. Emulsion at 45°C gave the most stable margarine consistency and SFC with crystal in the β′ form even after the fourth week. At 50°C, moderately soft product was produced, which might be undesirable for some applications, although the crystals were in the β′ form.     

<Emphasis Type="Italic">Trans</Emphasis>-Free Plastic Shortenings Prepared with Palm Stearin and Rice Bran Oil Structured Lipid

Rice bran oil structured lipid (RBOSL) was produced from rice bran oil (RBO) and the medium chain fatty acid (MCFA), caprylic acid, with Lipozyme RM IM as biocatalyst. RBOSL and RBO were mixed with palm stearin (PS) in ratios of 30:70, 40:60, 50:50, 60:40 and 70:30 v/v (RBOSL to PS) to formulate trans-free shortenings. Fatty acid profiles, solid fat content (SFC), melting and crystallization curves and crystal morphology were determined. The content of caprylic acid in shortening blends with RBOSL ranged from 9.92 to 22.14 mol%. Shortening blends containing 30:70 and 60:40 RBOSL or RBO and PS had fatty acid profiles similar to a commercial shortening (CS). SFCs for blends were within the desired range for CS of 10–50% at 10–40 °C. Shortening blends containing higher amounts of RBOSL or RBO had melting and crystallization curves similar to CS. All shortening blends contained primarily β′ crystals. RBOSL blended with PS was comparable to RBO in producing shortenings with fatty acid profiles, SFC, melting and crystallization profiles and crystal morphologies that were similar. RBOSL blended with PS can possibly provide healthier alternative to some oils currently blended with PS and commercial shortening to produce trans-free shortening because of the health benefits of the MCFA in RBOSL.     

Physical and textural characteristics of some North American shortenings

A number of North American vegetable and animal fat shortenings were evaluated for their melting, crystallization, textural and polymorphic crystal characteristics and solid fat content (SFC). The majority of the dropping points and crystallization temperatures of the fats ranged from 42 to 46°C and from 27 to 31°C, respectively. Softening points of the products were higher than the dropping points of their fats, especially for the vegetable shortenings. Differential scanning calorimetry melting curves of the products were different for the various products. The animal fat shortenings were mainly in theβ-polymorphic form, while vegetable shortenings containing palm oil were in theβ′ form. Textural evaluation was carried out on the products with the cone penetrometer, constant speed penetration and constant speed compression. Constant speed compression supplied a measure of brittleness and a degree of viscosity. Lard and shortenings containing high levels of palm oil were able to withstand large deformations without breakage. The effect of tempering temperature of the fat in the SFC determination was evaluated and the values obtained were compared with the SFC of the actual product. SFC of fat and product were determined by pulse nuclear magnetic resonance. Correlation of values within textural methods was significant (P<..01), but were not significant between texture and SFC of the fat, indicating that the nature of the crystal network also plays a role in texture.     

Ultrasonic Attenuation Measurements of the Mixing,Agglomeration, and Sedimentation of Sucrose Crystals Suspended in Oil

The structure and properties of solid-in-oil dispersions are important in many industrial products, notably chocolate, yet are difficult to characterize by existing methodologies. Sensors based on ultrasonic attenuation measurements offer potential to characterize changes in these systems. Sucrose crystals (d ~ 29.8 μm) were dispersed into corn oil (8–16 wt%) in a stirred tank. The dispersed crystals were agglomerated by the addition of small volumes of water (<1%) and finally allowed to sediment quiescently. The processes were monitored continuously by ultrasonic attenuation measurements (2.25 MHz). Ultrasonic attenuation increased with increasing sucrose crystal concentration and with the degree of agglomeration. Adding water also decreased the equilibrium sediment density and decreased the time taken for the sucrose to sediment out quiescently. Water-induced agglomeration led to the formation of a few very large particles as inferred from sedimentation kinetics and confirmed by micrometer measurements of crystal agglomerates. In conclusion, ultrasonic attenuation measurements provide a variety of novel approaches that can be used to characterize suspensions of particles in oil.     

The effect of supercooling on crystallization of cocoa butter-vegetable oil blends

The solid fat content (SFC), Avrami index (n), crystallization rate (z), fractal dimension (D), and the pre-exponential term [log(γ)] were determined in blends of cocoa butter (CB) with canola oil or soybean oil crystallized at temperatures (T _Cr) between 9.5 and 13.5°C. The relationship of these parameters with the elasticity (G′) and yield stress (σ^*) values of the crystallized blends was investigated, considering the equilibrium melting temperature (T _M ^o) and the supercooling (i.e., T _Cr ^o−T _M ^o) present in the blends. In general, supercooling was higher in the CB/soybean oil blend [T _M ^o=65.8°C (±3.0°C)] than in the CB/canola oil blend [T _M ^o=33.7°C (±4.9°C)]. Therefore, under similar T _Cr values, higher SFC and z values (P<0.05) were obtained with the CB/soybean oil blend. However, independent of T _Cr TAG followed a spherulitic crystal growth mechanism in both blends. Supercooling calculated with melting temperatures from DSC thermograms explained the SFC and z behavior just within each blend. However, supercooling calculated with T _M ^o explained both the SFC and z behavior within each blend and between the blends. Thus, independent of the blend used, SFC described the behavior of G′_eq and σ^* and pointed out the presence of two supercooling regions. In the lower supercooling region, G′_eq and σ^* decreased as SFC increased between 20 and 23%. In this region, the crystal network structures were formed by a mixture of small β′ crystals and large β crystals. In contrast, in the higher supercooling region (24 to 27% SFC), G′_eq and σ^* had a direct relationship with SFC, and the crystal network structure was formed mainly by small β′ crystals. However, we could not find a particular relationship that described the overall behavior of G′_eq and σ^* as a function of D and independent of the system investigated.     

Regulating the β′→β polymorphic transition in food fats

Hydrogenated cottonseed oil (HCSO) is commonly used as a β′-stable fat in margarines and shortenings. In the present study, the crystallization behavior of HCSO is altered via dilution, agitation, tempering regime, and the addition of an emulsifier [polyglycerol polyricinoleate (PgPr)]. Key properties assessed include crystal morphology (with polarized light microscopy), polymorphic behavior (with X-ray diffraction), and crystallization kinetics (with DSC). It is demonstrated that on considerable dilution with canola oil (4% w/w), HCSO can be crystallized in the β′ or β polymorph with associated changes in crystal morphology, depending on tempering regime. Crystallization from the melt to 25°C results in the β′-form, as there is insufficient supercooling to form the β polymorph but enough to form the metastable β′. With cooling from the melt to 5°C, there is adequate supercooling for the δ polymorph to form, with the presence of the canola oil facilitating the transformation toward this stable phase. Static vs. crystallization under agitation does not lead to visible changes in either polymorphic behavior or crystal morphology. However, there is extensive secondary nucleation and growth as a result of crystals breaking off accreting agglomerates. The presence of PgPr, added as a crystal modifier, does not affect the final crystal polymorph or morphology, except under one set of conditions—crystallization from the melt to 5°C with agitation, whereby it considerably alters crystallization behavior.     

Kinetics of nucleation and growth of L-sorbose crystals in a continuous MSMPR crystallizer with draft tube: Size-independent growth model approach

The experimental data concerning kinetics of a continuous mass crystallization in L-sorbose - water system are presented and discussed. Influences of L-sorbose concentration in a feeding solution and mean residence time of suspension in a working volume of laboratory DT MSMPR crystallizer on the resulting crystal size distributions, thus on the nucleation and growth kinetics, were determined. The kinetic parameter values were evaluated on the basis of size-independent growth (SIG) kinetic model (McCabe’s ΔL law). It was observed that within the investigated range of crystallizer productivity (220–2,200 kg of L-sorbose crystals m⁻³ h⁻¹), a crystal product of mean size Lm from 0.22 to 0.28 mm and CV from 68.8 to 44.0% was withdrawn. The values of linear growth rate show increasing trend (from 6.6·10⁻⁸ to 7.6·10⁻⁸ m s⁻¹) with the productivity enlargement (assuming constant residence time τ=900 s). Occurrence of secondary nucleation phenomena within the circulated suspension, resulting from the crystals attrition and breakage was observed. The parameter values in a design equation, matching linear growth rate and suspension density with nucleation rate were determined.     

Phase Behavior of Palm Oil in Blends with Palm-Based Diacylglycerol

Phase behavior of palm oil (PO) in blends with different concentrations (10% intervals) of palm-based diacylglycerol oil (PO-DAG) was studied using the iso-solid diagram, solid fat content (SFC) with the hardness thermal protocol, DSC melting and crystallization curves, X-ray diffraction curves, and texture analysis (hardness). Minor eutectic effects were observed at around 20–50% PO-DAG in 20–50% SFC iso-lines. The phase behavior predicted by the iso-solid diagram as well as SFC with the hardness thermal protocol did not account for hardness variations observed between PO and PO blends with 10–40% PO-DAG. Nevertheless, the latter could be attributed to the corresponding DSC data as well as crystal polymorphism. However, as the concentration of PO-DAG increased from 40% to 100%, iso-line temperatures, SFC with the hardness thermal protocol, and also hardness were found to steadily increase. PO-DAG at 10% concentration was found to have a β′-stabilizing effect on the polymorphism of PO, while a β-tending effect was observed as the concentration of PO-DAG increased from 10% to 90%.     

Rheological and Microscopic Properties of Fat Blends with Similar Solid Fat Content but Different Trans Composition

In this study, two different groups of fat samples were prepared in a way that samples of each group had different trans fatty acid (TFA) composition but similar solid fat content (SFC). Samples of the first group (named group A) had TFA between 0.0 and 56.23 %, while the samples of the second group (group B) contained trans isomers ranging from 0.0 to 44.4 %. A polarized microscope was used to monitor the differences between the samples in terms of crystal size and crystal number during isothermal crystallization. In general, increasing TFA resulted in formation of larger crystals in a shorter time. Similar findings were also observed when small deformation time and frequency sweep experiments were conducted. A higher TFA content led to higher complex modulus values during isothermal crystallization. On the other hand, when the samples were stored at 4 °C for 48 h, the samples with the lower trans isomer had higher hardness values.     

Weak gels of fat crystals in oils at low temperatures and their fractal nature

The formation of fat crystal gels in soybean oil has been studied by sedimentation in a low concentration region at 10–25°C. At 10°C, weak gels were formed with 1% crystals, and no gels formed at concentrations of 2–5%. At temperatures of 15–25°C, no gels were formed at concentrations of 1–5%, and samples sedimented. Stronger gels of fat crystals were formed with ∼10% fat crystals at all temperatures examined. Formation of weak gels is a consequence of the fractal nature of fat crystal aggregates and sediments. At low temperature, the interaction is weak. The fractal dimension is then high, and the floc size is large for low crystal concentrations. These large flocs form a three-dimensional network that act as a weak gel and withstand gravitational force. When the temperature is increased, the fat crystal interaction becomes stronger, fractal dimension decreases, and floc size decreases. Smaller flocs have a higher density, pack more easily, and sediment. Similar effects are observed when the concentration of fat crystals is increased at low temperature due to a decrease in floc size.     

The Effect of Phospholipids on Butter Physical and Sensory Properties

The addition of phospholipids (PL), either in the form of the milk fat globule membrane (MFGM) or soy lecithin, had a significant influence on butterfat crystal morphology. At low concentrations, PL addition increased spherulite size, but as PL levels reached 2 wt%, spherulite formation was inhibited and the microstructure consisted of well dispersed individual crystals. This change in crystal structure made the butter harder, less grainy at low temperatures, and less prone to oiling-off above room temperature. PL addition was also shown to affect the relative concentrations of the various species created during crystallization. Of the two 2L β′ species that form at crystallization onset, the presence of PL shifted the balance towards the first species at the expense of the second. PL also facilitated the polymorphic transition of the 3L α species to a 2L β′ structure. It is unclear, however, whether the inhibition of spherulite formation was due directly to the inhibition of secondary nucleation by PL at the crystal surface, or indirectly by the reduction of supercooling resulting from a more rapid polymorphic transition. Evidently, PL concentration must be properly controlled during manufacturing in order to optimize butter functional properties.     

Effect of Triacylglycerol Compositions and Physical Properties on the Granular Crystal Formation of Fat Blends

The effect of triacylglycerol (TAG) compositions and physical properties related to solid fat content (SFC) on the behavior of granular crystal formation was investigated. Four fat blends involving different 1,3-dipalmitoyl-2-oleoyl-sn-glycerol (POP) and 1-palmitoyl-2,3-dioleoyl-sn-glycerol (POO) compositions or SFC were prepared, and crystallization was investigated using polarizing microscopy, X-ray diffraction, SFC, whereas hardness was determined using a texture analyzer. Samples containing a higher saturated fatty-acid content from palm and higher SFC showed higher β-type crystals in the initial period, yielding a number of small-sized crystals, with no growth occurring afterward. Growth of the granular crystals as a function of time was observed in the samples, transforming from the β’- to β-type polymorph gradually. Large granular crystals at the initial stage were observed in the sample with a higher POO content and lowest SFC. These results suggested that POO promotes the rate of the crystals’ polymorphic transformation, resulting in the growth of granular crystals. In contrast, excess high-melting-point TAG content, such as tripalmitin and POP, retarded granular crystal growth regardless of the increased β’ to β transition rate. We concluded that the behavior of the growth of granular crystals is influenced by the combined effect of TAG composition and SFC.     

In Situ Rheo-NMR Measurements of Solid Fat Content

The properties of crystallized fats depend on their solid fat content (SFC) and their fractal structures. The SFC and the structures are dramatically affected during crystallization under shear flow. A mini-Couette cell was developed to crystallize fat samples under shear. The cell was tested with blends of canola stearin (CS) in canola oil (CO) in a 20-MHz NMR spectrometer. The blends were placed in the cell, melted at 80 °C, and then crystallized under different shear rates (58–460 s⁻¹) at 40 °C inside the spectrometer for 4 h. Time averaged NMR free induction decay (FID) curves were captured at 20 s intervals. SFC values were calculated using parameters determined by a calibration procedure. The SFC values determined by the direct method with and without the shaft of the Couette device were reasonably close. Similar results were observed with and without shear in the Couette device. The FID curves did not show a significant difference either. Therefore this system is accurate for in-situ time-resolved determination of SFC under shear flow. Furthermore, a combination of the direct and the indirect methods was successfully used to estimate the temperature increase due to viscous heating. The system developed will help in understanding the effects of shear flow on SFC of nanostructured lipid multicomponent systems. This will permit the optimization of the manufacturing processes.     

Effect of processing conditions on crystallization kinetics of a milk fat model system

Crystallization behavior of three blends of 30, 40, and 50% of high-melting fraction (MDP=47.5°C) in low-melting fraction (MDP=16.5°C) of milk fat was studied under dynamic conditions in laboratory scale. The effect of cooling and agitation rates, crystallization temperature, and chemical composition of the blends on the morphology, crystal size distribution, crystal thermal behavior, polymorphism, and crystalline chemical composition was investigated by light microscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD) and gas chromatography (GC). Different nucleation and growth behavior were found for different cooling rates. At slow cooling rate, larger crystals were formed, whereas at fast cooling rate, smaller crystals appeared together. Slowly crystallized samples had a broader distribution of crystal size. Crystallization temperatures had a similar effect as cooling rate. At higher crystallization temperatures, larger crystals and a broader crystal size distribution were found. Agitation rate had a marked effect on crystal size. Higher agitation rates lead to smaller crystal size. Cooling rate was the most influential parameter in crystal thermal behavior and composition. Slowly crystallized samples showed a broader melting diagram and an enrichment of long-chain triacylglycerols. Crystallization behavior was more related to processing conditions than to chemical composition of blends.     

Crystallization kinetics and technology of 2-chloro-4,6-dinitro-resorcinol

The crystallization kinetics of 2-chloro-4,6-dinitro-resorcinol were studied by the method of intermittent dynamic analysis. The nucleation rate and crystal growth rate of 2-chloro-4,6-dinitro-resorcinol under three groups of conditions (27°C, 180 rpm; 33°C, 180 rpm; 33°C, 240 rpm) were estimated. The results show that, by increasing the temperature of the solution, both the nucleation rate and crystal growth rate increase. It is further found that, when the stirring rate increases, the nucleation rate increases and the crystal growth rate decreases. On the basis of the study of the crystallization kinetics, the effect of the operational parameters on the crystallization was studied. It is proved that, when the stirring rate is 180 rpm and the solution is cooled slowly to −8°C, the particle size of the crystals is even, the quality of the crystals is good, and the yield of the crystals is 40.6%. Published in Russian in Teoreticheskie Osnovy Khimicheskoi Tekhnologii, 2007, Vol. 41, No. 3, pp. 338–342. The text was submitted by the authors in English.     

Effects of High Intensity Ultrasound Frequency and High-Speed Agitation on Fat Crystallization

The objective of this research was to examine the effect of ultrasound frequency and high-speed agitation on lipid crystallization. Interesterified soybean oil was crystallized at 44 °C without and with the application of high intensity ultrasound (HIU—20 and 40 kHz) or with high-speed agitation (6000 and 24,000 rpm). Two tip amplitudes (24 and 108 µm) and three pulse durations were evaluated (5, 10, and 15 s) for the acoustic frequencies tested. Sonication at 20 kHz of frequency significantly reduced crystal size, increased (p < 0.05) elasticity (435.9 ± 173.3–80,218 ± 15,384 Pa) and SFC (0.2 ± 0.0–4.5 ± 0.4%). No significant difference was observed in the crystallization behavior of these samples when sonicated at different amplitudes for 5 and 10 s. The crystallization behavior was significantly delayed (p < 0.05) in samples sonicated using 108 µm amplitude for 15 s. Larger crystals were formed in samples sonicated at 40 kHz compared to those obtained with 20 kHz and lower SFC (3.7 ± 0.0%) and elasticity (3943 ± 1459 Pa) values were obtained. High-speed agitation at 24,000 rpm increased SFC (5.5 ± 0.1%) and crystallized area and decreased the elasticity (42,602 ± 11,775 Pa) compared to the samples sonicated at 20 kHz.     

Characterizing cocoa butter seed crystals by the oil-in-water emulsion crystallization method

Unambiguous quantitative evidence for the catalytic action of seed crystals in cocoa butter is presented. We used an ultrasound velocity technique to determine the isothermal growth of solid fat content in cocoa butter oil-in-water emulsions, in which the probability of finding a seed crystal in any one droplet was around 0.37 at 14.2°C. The upper limit for the size of seed crystals in West African cocoa butter was around 0.09 μm, the Gibbs free energy for nucleation was 0.11 mj m⁻², and the concentration of seed crystals was in the range of 10¹⁶ to 10¹⁷ m⁻³. X-ray diffraction measurements showed that emulsified cocoa butter crystallizes in the α polymorph and does not appear to transform to the β′ form within the first 25 min of crystallization. Primary nucleation events in cocoa butter emulsions are accounted for by seed crystals. Collision-mediated nucleation, a secondary nucleation mechanism, in which solid droplets (containing seed crystals) catalyze nucleation in liquid droplets, is shown to account for subsequent crystallization. This secondary nucleation mechanism is enhanced by stirring.