Fat Globule Size Distribution Research Articles

Effects of processing conditions on the texture and rheological properties of model acid gels and cream cheese

Manufacture of cream cheese involves the formation of an initial acid-induced gel made from high-fat milk, followed by a series of processing steps including shearing, heating, and dewatering that complete the conversion of the acid gel into a complex cheese product. We investigated 2 critical parameters for their effect on the initial gel: homogenization pressure (HP) of the high-fat cheese milk, and fermentation temperature (FT). The impact of a low (10 MPa) and high (25 MPa) HP, and low (20°C) and high (26°C) FT were investigated for their effects on rheological and textural properties of acid-induced gels. Intact acid gels were sheared and heated to 80°C, and then their rheological properties were analyzed to help understand the effect of shearing/heating processes on the gel characteristics. The effect of HP on fat globule size distribution and the amount of protein not involved in emulsion droplets (i.e., in the bulk phase) were also studied. For cream cheese trials, a central composite experimental design was used to explore the effect of these 2 parameters (HP and FT) on the texture, rheology, and sensory properties of experimentally manufactured cream cheese. Storage modulus (G') and hardness values of cream cheeses were obtained from small amplitude oscillatory rheology tests and texture profile analysis, respectively. Quantitative spectrum descriptive sensory analysis was also performed. Consistency of acid gels (measured using a penetration test) increased with an increase in FT and with an increase in HP. Although stiffer acid-induced gels were formed at high FT, after the heating and shearing processes the apparent viscosity of the samples formed at high FT was lower than those formed at low FT. For the cream cheeses, significant prediction models were obtained for several rheological and textural attributes. The G' values at 8°C, instrumental hardness, and sensory firmness attributes were significantly correlated (r > 0.84); all these attributes significantly decreased with an increase in FT, and HP was not a significant parameter in the prediction models developed for these attributes. Significant interactions were observed between the HP and FT terms for these prediction models. Higher HP increased the amount of protein adsorbed at interface of fat globules but decreased bulk phase protein content (which may be important for crosslinking this gelled emulsion system). At higher FT temperature, coarser gel networks were likely formed. The combined effect of a coarser acid gel network at high FT, and less bulk phase casein available for crosslinking the acidified emulsion gel with an increase in HP, could have contributed to the lower stiffness/firmness observed in cream cheese made under conditions of both high FT and high HP. Stickiness of cream cheese greatly increased under conditions of high FT and high HP, whereas the sensory attributes cohesiveness of mass and difficulty to dissolve decreased. This study helped to better understand the complex relationships between the initial acid-induced gel phase and properties of the (final) cream cheese.

Effect of temperature on the microstructure of fat globules and the immunoglobulin-mediated interactions between fat and bacteria in natural raw milk creaming

Natural creaming of raw milk is the first step in production of Grana Padano and Parmigiano Reggiano Protected Denomination of Origin cheeses. This process decreases the fat content and plays an important role in the removal of clostridia species that may cause late-blowing defects in ripened cheeses. Partial coalescence of fat globules-that may influence fat behavior in cheese making and affect the microstructure of fat in the final cheese product-was observed at creaming temperatures higher than 22°C by confocal laser scanning microscopy. The widespread practice of heating of milk at 37°C before creaming at 8°C resulted in important changes in the size distribution of fat globules in raw milk, potentially altering the ability of fat to entrap clostridia spores. We investigated the role of immunoglobulin classes in both the clustering of fat globules and the agglutination of Clostridium tyrobutyricum to fat globules during creaming. Immunogold labeling and transmission electron microscopy showed that IgA and IgM but not IgG were involved in both clustering and agglutination. Both vegetative cells and spores were clearly shown to agglutinate to fat droplets, a process that was suppressed by thermal denaturation of the immunoglobulins. The debacterization of raw milk through natural creaming was improved by the addition of purified immunoglobulins. Overall, these findings provide not only a better understanding of the phenomena occurring during the natural creaming but also practical insights into how the process of creaming may be optimized in cheese production plants.

Milk fat globule size affects Cheddar cheese properties

Cheddar cheese was prepared using milk separated into large (d4,3 = 5.07 ± 0.06 μm) and small (d4,3 = 2.76 ± 0.07 μm) milk fat globule (MFG) size distributions using microfiltration. MFG size did not influence the moisture-adjusted yield or the amount of protein and lactose. However differences in the texture, microstructure, lipolysis and other compositional factors were found between cheeses. Notably, the small MFG milk (SMM) cheese retained more salt and contained more moisture and polar lipids, observed through a novel confocal staining regime, compared with the large MFG milk (LMM) cheese. Fewer intact MFG and more pockets of coalesced milk fat were observed in the LMM cheese. However both SMM and LMM cheese were softer, and less resistant to melting than the Control. These findings show that MFG separation can influence cheese mechanical behaviour and allow for the development of differentiated cheese products.

0040 Ultrasonic separation of milk to select for fat globule size distribution

0040 Ultrasonic separation of milk to select for fat globule size distribution

Effect of Pasteurization, Freeze-drying and Spray Drying on the Fat Globule and Lipid Profile of Human Milk

Human milk is the ideal food to nourish newborn babies; it contains important nutrients: proteins, carbohydrates, fat, vitamins and minerals, which are needed to provide agood health to the infants. Milk fat provides about 50% of energy to infants and its fatty acids are essential for brain and retina development. Therefore, analysis of the lipid fraction of human milk is an important task, especially when this milk is processed. The objective of this research was to study the effect of pasteurization, freeze-drying and spray drying on some characteristics of human milk fat. The fatty acid profile was analyzed by HPLC and gas chromatography. Fat content, globule size and distribution were measured. The HPLC method for the analysis of fatty acids showed accuracy, precision and linearity in the concentration range studied. Non-significant differences in fat content between the different processes were found; however, there was a decrease of 23% in the fat content of spray dried milk. The fat mean globule size decreased considerably in all treatments, varying from 2138 to 529 nm. The size distribution of fat globules increased during pasteurization and drying from 0.24 in raw milk to 0.78 in pasteurized milk. With respect to the fatty acid profile, we found that human milk samples had an elevated content of palmitic (27%), and oleic (30%) acids and significant variations were observed in the pasteurized samples for oleic and linoleic acid. Preservation processes applied to human milk caused a decrease on the fat globule diameter; the change in size increased the surface area and could improve the bioavailability of the fat components. This is the first report of human milk drying as a preservation method.

Influence of casein as a percentage of true protein and protein level on color and texture of milks containing 1 and 2% fat

Combinations of fresh liquid microfiltration retentate of skim milk, ultrafiltered retentate and permeate produced from microfiltration permeate, cream, and dried lactose monohydrate were used to produce a matrix of 20 milks. The milks contained 5 levels of casein as a percentage of true protein of about 5, 25, 50, 75, and 80% and 4 levels of true protein of 3.0, 3.76, 4.34, and 5.0% with constant lactose percentage of 5%. The experiment was replicated twice and repeated for both 1 and 2% fat content. Hunter color measurements, relative viscosity, and fat globule size distribution were measured, and a trained panel documented appearance and texture attributes on all milks. Overall, casein as a percentage of true protein had stronger effects than level of true protein on Hunter L, a, b values, relative viscosity, and fat globule size when using fresh liquid micellar casein concentrates and milk serum protein concentrates produced by a combination of microfiltration and ultrafiltration. As casein as a percentage of true protein increased, the milks became more white (higher L value), less green (lower negative a value), and less yellow (lower b value). Relative viscosity increased and d(0.9) generally decreased with increasing casein as a percentage of true protein. Panelists perceived milks with increasing casein as a percentage of true protein as more white, more opaque, and less yellow. Panelists were able to detect increased throat cling and mouthcoating with increased casein as a percentage of true protein in 2% milks, even when differences in appearance among milks were masked.

Improving thermal stability of hydrolysed whey protein-based infant formula emulsions by protein–carbohydrate conjugation

Whey protein hydrolysate (WPH) ingredients are commonly used in the manufacture of partially-hydrolysed infant formulae. The heat stability of these emulsion-based formulae is often poor, compared with those made using intact whey protein. The objective of this study was to improve the heat stability of WPH-based emulsions by conjugation of WPH with maltodextrin (MD) through wet heating. Emulsions stabilised by different protein ingredients, whey protein isolate (WPIE), whey protein hydrolysate (WPHE), heated WPH (WPH-HE), and WPH conjugated with MD (WPH-CE) were prepared and heat treated at 75°C, 95°C or 100°C for 15min. Changes in viscosity, fat globule size distribution (FGSD) and microstructure, evaluated using confocal laser scanning microscopy (CLSM), were used to monitor the effects of hydrolysis, pre-heating and conjugation on the heat stability of the emulsions. Heat stability increased in the order WPHE<WPIE<<WPH-HE<<<WPH-CE; emulsions WPHE, WPIE and WPH-HE destabilised on heating at 75°C, 95°C or 100°C, respectively. Flocculation and coalescence of oil droplets were mediated by protein aggregation (as evidenced by CLSM) on heat treatment of WPH-HE emulsion at 100°C, while no changes in FGSD or microstructure were observed in WPH-CE emulsion on heat treatment at 100°C, demonstrating the excellent thermal stability of emulsions prepared with the conjugated WPH ingredient, due principally to increased steric stabilisation as a result of conjugation.

Ptychographic X-ray computed tomography of extended colloidal networks in food emulsions

As a main structural level in colloidal food materials, extended colloidal networks are important for texture and rheology. By obtaining the 3D microstructure of the network, macroscopic mechanical properties of the material can be inferred. However, this approach is hampered by the lack of suitable non-destructive 3D imaging techniques with submicron resolution. We present results of quantitative ptychographic X-ray computed tomography applied to a palm kernel oil based oil-in-water emulsion. The measurements were carried out at ambient pressure and temperature. The 3D structure of the extended colloidal network of fat globules was obtained with a resolution of around 300 nm. Through image analysis of the network structure, the fat globule size distribution was computed and compared to previous findings. In further support, the reconstructed electron density values were within 4% of reference values.

Influence of lecithin on the processing stability of model whey protein hydrolysate‐based infant formula emulsions

Whey protein hydrolysate (WPH)‐based oil‐in‐water (O/W) emulsions containing lecithin (0–5%, w/w, oil) were produced and stored at 4 °C for 14 days. Surface tension and interfacial tension of these systems were measured for formulation development. Fat globule size distribution (FGSD) analysis and confocal laser scanning microscopy (CLSM) were used to assess the physical stability of emulsions during storage and identify mechanisms of instability. Lecithin decreased interfacial tension between oil and aqueous phases of model emulsions and allowed formation of smaller oil droplets on homogenisation. However, low‐intermediate levels (1–3%) of lecithin caused coalescence and shift to bimodal FGSD during storage of emulsions.

Effect of fat and protein-in-water concentrations on the properties of model processed cheese

Model processed cheeses with variable protein (10–20%, w/w, total protein/18–45% protein-in-water) or fat concentrations (0–40%, w/w, total fat) were prepared. With increasing protein-in-water concentrations, cheese firmness increased markedly and the rheology changed from a concentrated liquid to a weak gel. A small increase in firmness was observed with increasing fat concentration and all samples were concentrated liquids. The tendency of the cheese to melt decreased as the protein-in-water concentration increased. For samples with variable fat concentrations, the tendency to melt was highest at intermediate fat concentrations; differences among samples were smaller than for the variations in protein-in-water concentrations. There were small differences in fat globule size distributions among samples. Microstructural images suggested some poorly emulsified fat in the samples at the lowest protein-in-water and highest fat concentrations. Overall, the protein-in-water concentration had a large impact on the rheological properties; fat concentration had a relatively small impact.

Effect of ultrasonic homogenization on the Vis/NIR bulk optical properties of milk

The size of colloidal particles in food products has a considerable impact on the product's physicochemical, functional and sensory characteristics. Measurement techniques to monitor the size of suspended particles could, therefore, help to further reduce the variability in production processes and promote the development of new food products with improved properties. Visible and near-infrared (Vis/NIR) spectroscopy is already widely used to measure the composition of agricultural and food products. However, this technology can also be consulted to acquire microstructure-related scattering properties of food products. In this study, the effect of the fat globule size on the Vis/NIR bulk scattering properties of milk was investigated. Variability in fat globule size distribution was created using ultrasonic homogenization of raw milk. Reduction of the fat globule size resulted in a higher wavelength-dependency of both the Vis/NIR bulk scattering coefficient and the scattering anisotropy factor. Moreover, the anisotropy factor and the bulk scattering coefficients for wavelengths above 600nm were reduced and were dominated by Rayleigh scattering. Additionally, the bulk scattering properties could be well (R2≥0.990) estimated from measured particle size distributions by consulting an algorithm based on the Mie solution. Future research could aim at the inversion of this model to estimate the particle size distributions from Vis/NIR spectroscopic measurements.

English

Innovative and eco-friendly food technologies in practical usage today like Ultrasound (US) and High Hydrostatic Pressures (HHP) are feasible to adequately maintain various food properties while processed, such as texture, sensorial and organoleptic characteristics, and microbiological issues as well. Benchmarked attribute of the mentioned approach lies in the ability of US and HHP to control and withhold both temperature and treatment duration. While temperature could be controlled within room ambient, treatment time is mostly below 30 minutes. US and HHP treatment were performed as separate treatments in order to obtain better homogenization. Goat milk was exposed to ultrasonic propagation up to 100 W of nominal power and high pressures up to 600 MPa. Maximum treatment time was 9 minutes. Ultrasonic homogenization indicates enhanced homogeneity of fat globules while high pressure process parameters have a significant influence on the observed mean particle diameter (fat globules). Improved stability and quality of emulsions (goat milk) was obtained by both applied processes. Statistical analysis indicated the influence of process parameters on fat globule size distribution between 0.3 – 4 µm and variance lower than 0.6.

Effects of high pressure homogenisation of ice cream mix on the physical and structural properties of ice cream

This study investigated the effect of high pressure homogenisation (HPH) on the physical and structural properties of ice cream. Samples were produced from mixes differing in fat content (5% and 8%) and subjected to different homogenisation pressures (15/3 MPa and 97/3 MPa). Ice creams were compared for fat globule size distribution, overrun, melting behaviour, and hardness. No influence of HPH on fat structure destabilisation with respect to the conventional homogenisation (CH) was observed. The HPH ice cream samples with high fat content were characterised by the lowest overrun, the highest hardness and improved resistance to melting; the HPH ice creams with low fat content showed higher resistance to meltdown, but were not clearly differentiated for hardness with respect to the CH samples.

Blends of delactosed permeate and pro-cream in ice cream: Effects on physical, textural and sensory attributes

Various blends of delactosed whey permeate (DLP) and pro-cream, a by-product of microfiltration during whey protein isolate production, were made and assessed for application in ice creams as a source of protein and fat. These blends were compared with control ice cream containing nonfat dried milk (NFDM) as the primary source of protein. Textural properties of ice creams were influenced by partial replacement of NFDM with DLP-pro-cream blends. Compared with control ice cream, those containing DLP-pro-cream blends showed similar mean ice crystal size, relatively higher melt rate, and reduced fat destabilization. Melt rate (based on linear portion of melting curve) correlated well with the fat globule size distribution or extent of fat destabilization. In sensory analysis, ice creams containing the DLP-pro-cream blends (30:70 and 50:50) were slightly less accepted by panelists than the control ice cream for most of the attributes, with an off-flavor more noticeable with increasing DLP content.

Fat Globule Size Effect on Visible and Shortwave near Infrared Spectra of Milk

Step-wise homogenisation has been applied to raw milk samples of different composition to investigate the effect of fat globule size distribution on diffuse transmission spectra in the region 400–1100 nm. Homogenisation results in significant spectral changes with two distinct phases. Initial even growth of spectral intensity across the whole spectral range, observed at lower degrees of homogenisation, was followed by a drastic fall in absorbance at the long-wave end of spectrum as the fat globules reached some critical size. Fat and protein content in the sample significantly affected the observed dependences of spectra on the applied homogenisation time. These observations have been explained as a superposition of two effects: growing fat globule density and changes in scatter nature as the particle sizes approach the light wavelengths in a corresponding spectral range. The representative layer theory has been used to illustrate the nature of the spectral effects.

Estimation of Fat Globule Size Distribution in Milk Using an Inverse Light Scattering Model in the near Infrared Region

The determination of particle characteristics from light scattering patterns is a challenging inversion problem and, not least, a demanding instrumentation problem. Despite the importance of the knowledge of size distribution in several technological dairy processes, often laser diffractometers and other instrumentation for particle size analysis are not available in dairy laboratories and, therefore, such information is not easily available, except for research purposes. Near infrared (NIR) instrumentation, instead, is largely available in dairy labs. Laser granulometers are based on the principle that particles scatter light from one or two laser beams with an angular pattern directly related to their size. Consequently, a suspension of particles forms an angular pattern of scattered light that is characteristic of its size distribution. In a similar manner, a NIR spectrometer in transmission mode can be considered as a tool for studying the behaviour of forward scattering at different wavelengths. In this work, a model based on an approximation of Mie scattering was developed for the calculation of scattering due to fat globules in the NIR transmission spectrum of milk. The inversion of the model was applied to raw milk spectra in the spectral regions from 1000 nm to 1360 nm and from 1580 nm to 1800 nm, free from strong absorption bands, in order to estimate the fat particle size distribution. More than 700 samples, collected monthly for two years from 50 Friesian–Holstein, 7 Jersey and 5 Brown cows, were analysed. Four hundred of these samples were also analysed using a laser granulometer. The correlation ( r2) between NIR and laser granulometric data was equal to 0.95 for the mean volume surface diameter ( d3,2) with a root mean square error ( RMSE) of 0.11 microns. A sub-class of Weibull distribution with only one freedom parameter proved to be sufficient in order to describe milk fat globule distribution and fit spectral data. The method developed in this work can be useful both for genetic selection and technological purposes and easily extended to the analysis of other dietary fat emulsions.

Preparation of Recombined Milk Using Modified Butterfats Containing α‐Linolenic Acid

Modified butterfats (MBFs) were produced by lipase-catalyzed interesterification with 2 substrate blends (6:6:8 and 4:6:10, by weight) of anhydrous butterfat (ABF), palm stearin, and flaxseed oil in a stirred-batch type reactor after short path distillation. The 6:6:8 and 4:6:10 MBF contained 21.7% and 26.5%α-linolenic acid, respectively. Total saturated fatty acids of the MBFs ranged from 41.4% to 47.4%. The cholesterol contents of the 6:6:8 and 4:6:10 MBFs were 21.0 and 12.1 mg/100 g, respectively. In addition, the melting points of the 6:6:8 and 4:6:10 MBFs were 32 °C and 31 °C, respectively. After preparation of recombined milks (oil-in-water emulsions) with MBFs, the stability of emulsions prepared with the MBFs (6:6:8 and 4:6:10) was compared to those with ABF during 10-d storage at 30 °C. Skim milk powder (containing 1% protein) was added to prepare emulsions as an emulsifier. Microstructures of emulsions freshly prepared with the ABF and the MBFs consisted of uniform fat globules with no flocculation during 10-d storage. With respect to fat globule size distribution, the volume-surface mean droplet diameter (d(32)) of the 6:6:8 and 4:6:10 MBF emulsions ranged between 0.33 and 0.34 μm, which was similar to the distribution in ABF emulsion. Milk, an expensive dairy food, has been widely used in various milk-derived food products. Modified butterfats (MBFs) contain α-linolenic acid as an essential fatty acid. Emulsion stability of recombined milks (oil-in-water emulsions) with MBFs was similar to that in anhydrous butterfat emulsion during 10-d storage. They may be a promising alternative for reconstituted milks to use in processed milk-based products.

Changes in Protein Components and Size Distribution of Bovine Milk Fat Globules Caused by Heat Treatment

The effects of heat treatment on the changes in the protein components and size distribution of bovine milk fat globules were investigated. The results of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that some membrane proteins, such as xanthine oxidase and butyrophilin, had disappeared or were weakly stained in the gel due to heating of milk. The volume surface average diameter of raw milk fat globules ranged from 1.15 to 7.42 μm. When the heating temperature was above 90 °C or the heating time was prolonged above 10 min, the average diameters of heated milk fat globules increased significantly (P &lt; 0.05).

Modeling of particle size distribution of heat assisted high-pressure treated reconstituted cow milk: Effect of high pressure, pressurization time and heat treatment temperature

A study was conducted to investigate the effect of high pressure, pressurization time and heat treatment temperature on particle size distribution of fat globules in reconstituted cow milk during heat assisted high-pressure (HAHP) processing of milk. The high pressure, pressurization time and heat treatment temperature were varied between 200 and 600MPa, 0 and 25min, and 15 and 65°C, respectively. Particle size distribution of the HAHP-treated milk showed that the number of fat globules below 1×10−6m increased as pressure and pressurization time increased. However, higher temperature had a negative effect on the particle size due to aggregation of casein micelles around the fat globule at higher temperature. Modeling of particle distribution by Rosin–Rambler–Sperling–Bennet equation was observed to be a good fit for prediction of uniformity of index n and average statistical diameter Ds. The values of n ranged from 0.931 to 1.318, and Ds from 1.68×10−6 to 3.12×10−6m. Linear regression fitting of n and Ds as a function of high pressure, pressurization time and heat treatment temperature showed a good fit with relative deviation percent (Rd) value of 6.02% and 8.12%, respectively.

Association of plasma insulin concentration to fatty acid distribution between milk fat and membrane synthesis

We examined the association between plasma insulin concentration and fatty acid distribution to milk fat and membrane fractions (triglyceride and phospholipid, respectively) in dairy cows. Thirty-seven Holstein cows at 60 to 70 d postpartum were synchronized by 2 PGF2α injections 14 d apart. Plasma samples were taken before morning and evening milkings and milk samples were obtained at morning milking. Plasma insulin concentrations were determined and cows were retrospectively assigned to low insulin (LI; 2.8±0.2ng/mL, n=6) or high insulin (HI; 5.9±0.6ng/mL, n=7) experimental groups. Fatty acid analysis of milk samples demonstrated a possible association between plasma insulin concentration and the fatty acid composition in phospholipid and triglyceride fractions. In the HI group, monounsaturated fatty acid concentration tended to be higher in the triglyceride (Tg) fraction than the phospholipids (Pl) fraction. In the LI group, the concentrations of short- and medium-chain saturated fatty acids (<16 carbon chain length), considered de novo-synthesized fatty acids, were higher in the triglyceride fraction than the phospholipid fraction. These results imply that the primary source of saturated fatty acids for phospholipid synthesis, in both HI and LI groups, is the circulation, as reflected by a higher concentration of longer saturated fatty acids (>16 carbon chain length) in the phospholipid fraction. Finally, the phospholipid-to-triglyceride ratio was higher in the HI group than in the LI group. Together, the results indicate that fatty acid distribution between phospholipid (membrane) and triglyceride (fat) synthesis by the mammary gland is associated with fatty acid length, degree of unsaturation, and origin, and might be subject to metabolic hormone regulation. Furthermore, a lower triglyceride-to-phospholipid ratio in the HI group implies that high plasma insulin and low milk fat concentrations are associated with a shift in the size distribution of milk fat globules.