Fat Globule Size Distribution Research Articles

Human milk fat globule size distributions: comparison between laser diffraction and 3D confocal laser scanning microscopy

Milk fat globules (MFGs) in human milk provide energy to breastfed infants and support infant development. Accurate measurements of MFG size distributions are important to better understand MFG function and origin, as well as the influence of MFG size on milk composition analysis methods. Nevertheless, commonly used laser diffraction systems have never been thoroughly validated for size distribution measurements in human milk. Here, we introduce a new method for determining the size distribution of milk fat globules in human milk, using 3D confocal laser scanning microscopy (CLSM) in combination with fluorescent labeling of MFGs. We validate and compare 3D CLSM to laser diffraction (Mastersizer 2000, Malvern Panalytical), using polystyrene microsphere size standards. Next, we apply both methods to evaluate MFG size distributions in human milk. We show that 3D CLSM can be used to obtain more accurate size distributions between 500 nm and 10 μm compared to laser diffraction. Importantly, MFG size distributions obtained with 3D CLSM contain no secondary population around 1 μm, in contrast to laser diffraction measurements. This suggests that the bimodal MFG distribution obtained by laser diffraction can be an artifact of the built-in fitting algorithm, instead of an actual feature of human milk. This work demonstrates that care should be taken when interpreting size distributions of MFGs measured with laser diffraction and that 3D CLSM is an accurate alternative for measuring size distributions in lactation and dairy research.

Effect of Inulin on Rheological Properties and Emulsion Stability of a Reduced-Fat Salad Dressing.

This study is aimed at investigating the potential use of inulin in a reduced-fat salad dressing to improve its rheological properties, fat globule size distribution, and emulsion stability. The reduced-fat salad dressing, which has 50% less fat compared to the full-fat counterpart (control), was prepared with varying inulin concentrations (10, 12.5, 15, 17.5, and 20% w/w). The full-fat and reduced-fat salad dressings exhibited a non-Newtonian shear-thinning behavior. Power law model was used to describe the rheological properties. Results showed that the flow behavior index (n) and consistency coefficient (K) were greatly affected by the concentration of inulin. A greater pseudoplasticity and apparent viscosity of the reduced-fat samples were achieved with a higher concentration of inulin. Oscillatory tests showed that the storage modulus (G') and loss modulus (G ″) values increased with increasing inulin concentration. All samples displayed characteristics of a viscoelastic solid, as evidenced by a greater G' than G ″. Regarding the size distribution of the oil droplets, the reduced-fat salad dressing containing a higher inulin content was observed to have a larger droplet size. All reduced-fat samples, similar to the full-fat counterparts, exhibited stability with no cream separation over one month of storage at 4°C, as determined by visual observation. Additionally, the reduced-fat salad dressings supplemented with 17.5 and 20% inulin exhibited stability against cream separation, comparable to the full-fat counterpart (p > 0.05), as measured by the thermal stress test (80°C for 30 min) with centrifugation. The sensory acceptance scores for reduced-fat salad dressing with 15 and 17.5% inulin, ranging from approximately 6.28 to 7.63 on a 9-point hedonic scale for all evaluated attributes (appearance, color, aroma, texture, taste, and overall acceptability), were not significantly different from those of the full-fat counterpart (p > 0.05). This study demonstrated that inulin may be a suitable ingredient in reduced-fat salad dressings.

Kinetics of size change in air bubble and fat globule during ice cream freezing process

AbstractUsing a batch‐type freezer, this study investigated the influence of agitation speed on the time course change in the size of air bubbles and fat globules to establish kinetics of those during freezing. Higher agitation is advantageous not only for mixing enhancement but also for preventing local freezing and undesirable solidification, according to the results of flow visualization and time‐course change in the Reynolds number during freezing. Air bubbles and fat globule size were measured using samples obtained during freezing. For each agitations speed, the time‐course change in air bubble size was clearly different. Because of significant shear force, a smooth reduction in air bubble size was observed at a relatively high agitation speed. However, at the later stage of freezing, the increased collision frequency of the bubbles induced an undesirable increase in size. Aggregation of fat globules occurred immediately after the aqueous phase begin to be frozen. In addition, a greater agitation speed improved fat destabilization and hence increased the degree of aggregation (DA) as measured by the fat globule size distribution. At all agitation speeds, a decrease in DA was observed after a temporary increase in DA. This decrease can be explained by the breakup of the aggregates. At higher agitation speed, more serious decrease in DA was found. It was found that agitation speed significantly affects the kinetics of air bubbles and fat globules during freezing.Practical ApplicationsAfter freezing, air bubbles and fat globules size are important factors in determining ice cream quality. Nevertheless, no time‐course change in size has been constructed from the perspective of kinetics. To the best of our knowledge, this is the first study to investigate the effects of agitation speed on the time‐course change in air bubbles and fat globules size. The kinetics of air bubbles and fat globules are important in determining process parameters such as freezing time and agitation speed in the process design of freezers for ice cream manufacturing. Although this study was conducted using a bath‐type freezer, the kinetics of size change can be applied to process design with a continuous‐type freezer.

Physical and sensory properties of soy-based ice cream formulated with cold-pressed high oleic low linolenic soybean oil.

The effect of cold-pressed SOYLEIC™ soybean oil (SOYLEIC) on the physical and sensory properties of soy-based ice cream was compared to commercial vegetable oil (COM-VO), commercial high oleic soybean oil (COM-HO), and heavy cream (CREAM). Fat sources had no significant effect on viscosity and fat globule size distribution of ice cream mixes. Ice cream made with COM-VO had the lowest overrun (p <0.05) and higher degree of fat destabilization; however, no difference in hardness was found. Despite similar melting rate, the shape retention behavior during melting was different for SOYLEIC, COM-VO, and COM-HO compared to CREAM. No significant differences were found in texture attributes except mouth coating, which was higher for CREAM than COM-HO and SOYLEIC (p <0.05). There was no significant difference in flavor attributes between SOYLEIC and CREAM, while COM-VO and COM-HO had higher off-flavor intensities (p <0.05). Consumer acceptability results revealed that SOYLEIC and CREAM had significantly higher flavor liking and overall liking scores than COM-VO and COM-HO (p <0.05). SOYLEIC and CREAM also had higher texture liking than COM-VO (p <0.05). Overall, liking had the highest positive significant correlation with flavor liking (r=0.996). PRACTICAL APPLICATION: Cold-pressed HOLL soybean oil has the potential to be used in formulating plant-based frozen desserts with equivalent texture but more acceptable flavor.

Effect of the Application of Ultrasound to Homogenize Milk and the Subsequent Pasteurization by Pulsed Electric Field, High Hydrostatic Pressure, and Microwaves.

The efficacy of applying ultrasound (US) as a system to homogenize emulsions has been widely demonstrated. However, research has not yet shown whether the effect achieved by homogenizing milk with US is modified by subsequent pasteurization treatments that use new processing technologies such as pulsed electric fields (PEF), microwaves (MW), and high hydrostatic pressure (HPP). The aim of this study was, therefore, to optimize the application of US for milk homogenization and to evaluate the effect of PEF, HPP, and MW pasteurization treatments on the sensorial, rheological, and microbiological properties of milk throughout its shelf life. To homogenize whole milk, a continuous US system (20 kHz, 0.204 kJ/mL, 100%, 40 °C) was used, and different ultrasonic intensities (0.25, 0.5, and 1.0 kJ/mL) were evaluated. The optimal ultrasonic treatment was selected on the basis of fat globule size distribution and pasteurization treatments by MW (5800 W, 1.8 L/min), PEF (120 kJ/kg, 20 kV/cm) and HPP (600 MPa, 2 min, 10 °C) was applied. The ultrasound intensity that achieved the highest reduction in fat globule size (0.22 ± 0.02 µm) and the most homogeneous distribution was 1.0 kJ/mL. Fat globule size was smaller than in commercial milk (82% of volume < 0.5 µm for US milk versus 97% of volume < 1.2 µm for commercial milk). That size was maintained after the application of the different pasteurization treatments, and the resulting milk had better emulsion stability than commercial milk. After 28 days of storage, no differences in viscosity (4.4-4.9 mPa s) were observed. HPP pasteurization had the greatest impact on color, leading to higher yellowness values than commercial milk. Microbial counts did not vary significantly after 28 days of storage, with counts below 102 CFU/mL for samples incubated at 15 °C and at 37 °C. In summary, the homogenization of milk obtained by US was not affected by subsequent pasteurization processes, regardless of the technology applied (MW, PEF, or HPP). Further research is needed to evaluate these procedures' effect on milk's nutritional and functional properties.

Monitoring cheese ripening by single-sided nuclear magnetic resonance

The noninvasive, longitudinal study of products and food processing is of interest for the dairy industry. Here, we demonstrated that single-sided nuclear magnetic resonance (NMR) can be used for noninvasive monitoring of the cheese ripening process. The maturation of soft-ripened Camembert-like molded cheese samples was monitored for 20 d measuring 1-dimensional and 2-dimensional NMR relaxation and diffusion data at various depths, ranging from the hard surface layer to the soft center. Gelation and gel shrinkage were observed throughout ripening, and a complete loss of free water signal was observed at the cheese rind. Transversal (T2) relaxation distributions include 3 components that evolve with ripening time and position, corresponding to water inside the casein gel network, water trapped in casein, and fat. Two-dimensional T1-T2 relaxation experiments provided enhanced resolution of the 3 components, allowing quantification of the relative proportions of each phase. Furthermore, diffusion (D)-T2 relaxation correlation experiments revealed the bimodal size distribution of fat globules. The study demonstrated that single-sided NMR can provide spatially resolved signal intensity, relaxation, and diffusion parameters that reflect structural changes during the ripening process and can be exploited to understand and monitor the ripening of cheeses.

Prediction of size distribution in dairy cream homogenization

The size distribution of fat globules in homogenized concentrated dairy cream has been measured in High-Pressure Homogenizers ( HPH ), working at 80 °C and various operating pressures. For each pressure, the outlet size distribution is found to be self-similar to the inlet distribution, and can be accurately predicted dividing each class diameter of the inlet distribution by a single proportionality factor, which can be interpreted using a simplified deformation model of the fat globules as elongated filaments. The evolution of the factor with the operating pressure is consistent with a scaling analysis of the average shear rate in the HPH as well as with the value predicted from numerical simulations of the flow in the HPH , supporting the physical interpretation of the fragmentation model. • Homogenized fat globules size distribution in cream can be deduced from the entry size distribution with a single parameter. • A simple viscous shear dominated breakup model is proposed to interpret this result. • The breakup model parameter can be explicitely related to the HPH pressure.

Bovine colostrum: Postpartum changes in fat globule size distribution and fatty acid profile

Although "zero waste" valorization concepts are gaining increasing attention, colostrum, a byproduct of milk production, remains underused due to technological challenges. Information about the fat fraction and the size of fat globules is needed to address these challenges, but such information is currently lacking. This study aimed to fill this gap in the knowledge by measuring the size distribution of bovine colostrum fat globules (CFG) and analyzing its relationships with postpartum milkings, parity, and fatty acids (FA) profile. Four sequential postpartum colostrum samples were collected from 44 cows and analyzed for the abovementioned parameters. The results indicated that CFG size increases almost twice during postpartum milkings (from ∼5 to ∼10 µm), whereas lactation has little, if any, effect on CFG size. The FA profile analyses showed that the content of most FA in the fourth postpartum milking was different from the previous milkings. The correlation analyses between CFG size and FA profile also demonstrated that the fourth milking was clearly distinguishable from the first 3 postpartum milkings. For example, the saturated FA content from the first 3 milkings had a positive correlation with smaller CFG (and a negative correlation with larger CFG), whereas the fourth milking demonstrated no correlations. Based on these CFG size and FA profile analyses, the results of this study suggest that the first 3 postpartum milkings can be considered as colostrum, whereas the fourth milking represents transition milk. Information about CFG size distribution enables modification of the FA profile of colostrum products and the ability to create better valorization technologies for colostrum-based food and feed supplements.

Ultrasonication retains more milk fat globule membrane proteins compared to equivalent shear-homogenization

Ultrasonication, like common shear homogenization, can reduce the milk fat globule size and may change the milk fat globule membrane (MFGM). This work compared the effect of ultrasonication to equivalent shear homogenization on MFGM proteins and lipid-derived volatile components. Results showed that treating milk with ultrasound at 35 kJ/L would realize a similar size distribution of the milk fat globules as shear-homogenization at 20 MPa. Proteomics analysis revealed that in total 192 MFGM proteins were identified and quantified and a number of these proteins were lost after both treatments; however, more MFGM proteins remained after ultrasonication than after shear-homogenization. SDS-PAGE results showed that milk plasma proteins, and especially caseins, were absorbed on the milk fat globules after both treatments. In addition, the amount of the volatile free fatty acids increased after both treatments.Industrial relevance: Ultrasonication, as an innovative food processing technology, in comparison to traditional homogenization, was shown to equally efficiently decrease the MFG size, but lead to less damage to native MFGM proteins, which may be due to its longer homogenization time window. These results increased knowledge on the biochemical changes of milk fat globules after their size reduction and showed that ultrasonication could be used as a novel approach to improve dairy product quality.

Effect of chia seed mucilage as stabiliser in ice cream

An ice cream formulation was evaluated in which extracted chia seed gum (mucilage) (CSG) was used to replace a commercial stabiliser. The pH, viscosity of the ice cream mix, overrun, fat globule size distribution, destabilised fat index, meltdown rate and hardness of ice cream were determined in the prototype samples. The ice cream samples were also evaluated by a focus sensory group. The best ice cream according to the focus group contained 0.2% CSG (w/w) with an overrun of ∼103%, 41.0 ± 5.3% destabilised fat index, 40.7 ± 8.9 μm fat globule size (d4,3), low meltdown rate (0.9 ± 0.1 g min−1) and hardness of 40.1 ± 7.2 N. The focus group results showed that the ice cream had desirable hardness, smooth texture and creamy mouthfeel without sensation of ice crystals and off-flavour.

Effect of κ‐carrageenan/milk protein interaction on rheology and microstructure in dairy emulsion systems with different milk protein types and κ‐carrageenan concentrations

We investigated the effect of κ-carrageenan (κ-CG) addition and supplementation with Na-CN, WPI, and MPI on the rheological properties, microstructure, fat globule size distribution, and stability of low-fat cream (LFC) emulsions containing 19% milk fat. Rheological parameter (ηa,10, K, and G′) values of LFCs increased with κ-CG addition. At 0.1% κ-CG concentration, MPI-stabilized LFC had higher G′ value (64.8 Pa) than those of WPI-stabilized LFC (51.3 Pa) and Na-CN-stabilized LFC (34.8 Pa), indicating the strong interaction between MPI and κ-CG. Cryo-SEM images showed the protein layers on milk fat globule membrane in dairy emulsions and revealed that κ-CG led to depletion-flocculation of milk fat globules and promoted clustering of globules. The creaming index values of LFCs with 0.10% κ-CG were lower than those of LFCs with 0.05% κ-CG. Thus, high κ-CG concentrations can contribute to the physical stability in dairy emulsions stabilized by milk proteins. Practical applications Milk proteins are widely used as emulsifiers, and κ-carrageenan (κ-CG) is added to dairy emulsion products to improve their physical properties and stability. Therefore, in this study, the effect of κ-CG addition on physical properties and stability of low-fat creams (LFCs) supplemented with different milk protein types (Na-CN, WPI, and MPI) was investigated. The strong synergistic interaction between proteins and κ-CG was observed in MPI-stabilized LFCs when compared to Na-CN- and WPI-stabilized LFCs. We found that the presence of κ-CG in MPI-stabilized LFCs improved the stability of LFCs by inhibiting the phase separation due to the high viscosity of the continuous phase. These findings suggest that dairy cream-based food products with desirable physical properties can be realized through κ-CG addition to LFC emulsions with milk proteins such as ice cream mix, coffee creamer, and light cream.

Composition, Structure, and Digestive Dynamics of Milk From Different Species-A Review.

Background: The traditional dairy-cattle-based industry is becoming increasingly diversified with milk and milk products from non-cattle dairy species. The interest in non-cattle milks has increased because there have been several anecdotal reports about the nutritional benefits of these milks and reports both of individuals tolerating and digesting some non-cattle milks better than cattle milk and of certain characteristics that non-cattle milks are thought to share in common with human milk. Thus, non-cattle milks are considered to have potential applications in infant, children, and elderly nutrition for the development of specialized products with better nutritional profiles. However, there is very little scientific information and understanding about the digestion behavior of non-cattle milks.Scope and Approach: The general properties of some non-cattle milks, in comparison with human and cattle milks, particularly focusing on their protein profile, fat composition, hypoallergenic potential, and digestibility, are reviewed. The coagulation behaviors of different milks in the stomach and their impact on the rates of protein and fat digestion are reviewed in detail.Key findings and Conclusions: Milk from different species vary in composition, structure, and physicochemical properties. This may be a key factor in their different digestion behaviors. The curds formed in the stomach during the gastric digestion of some non-cattle milks are considered to be relatively softer than those formed from cattle milk, which is thought to contribute to the degree to which non-cattle milks can be easily digested or tolerated. The rates of protein and fat delivery to the small intestine are likely to be a function of the macro- and micro-structure of the curd formed in the stomach, which in turn is affected by factors such as casein composition, fat globule and casein micelle size distribution, and protein-to-fat ratio. However, as no information on the coagulation behavior of non-cattle milks in the human stomach is available, in-depth scientific studies are needed in order to understand the impact of compositional and structural differences on the digestive dynamics of milk from different species.

Sodium hexametaphosphate’s impact on hydrodynamic parameters of milk fat globule membrane

Being able to stabilise milk fat globule particles after pasteurisation over time and reduce the phase separation and migration rate of the cream layer would be of great interest. This study examined the prolonged destabilisation of MFGM emulsions after blending with sodium hexametaphosphate (SHMP) with respect to particle migration, fat globule size distribution, phase separation, variations in the raw signal and serum‐phase protein levels. Low SHMP levels in blended MFGM reduced the interactions between fat droplets during heating. Low SHMP concentrations are recommended for stabilising MFGM.

Milk homogenization monitoring: Fat globule size estimation from scattering spectra of milk

The fat globule size distribution of raw milk and milk with an increasing degree of homogenization was estimated based on their bulk light scattering properties in the Vis/NIR wavelength range. The particle size distribution (PSD) was approximated as a lognormal distribution, of which the parameters were estimated simultaneously with the fat concentration. This resulted in a good agreement between the estimated PSDs and the reference PSDs obtained by laser diffraction in case of raw and strongly homogenized samples. The accuracy increased if a known fat concentration was incorporated, or when the scattering coefficient and anisotropy factor spectra were used simultaneously as input. For mildly homogenized samples, the lognormal distribution was unable to fit the bimodal PSD correctly and focused on the largest fat globules. In this case, the estimated PSDs provided still relatively accurate information on D90, D32 and the right distribution tail, which contains the largest fat globules. Industrial relevanceThe presented estimation method demonstrates the potential of bulk scattering spectra for determining the PSD and concentration of scattering particles in turbid media. Further development of this technology can lead to new solutions for spectroscopic PSD determination, allowing on-line monitoring systems for a wide range of food and non-food products.

Lipid metabolic differences in cows producing small or large milk fat globules: Fatty acid origin and degree of saturation

This study compared cows that consistently produce milk with small (volume-weighted mean diameter of 2.92-3.83 µm, with an average diameter of 3.29 µm) or large (volume-weighted mean diameter of 4.58-5.67 µm, with an average diameter of 4.92 µm) milk fat globule (MFG) size distributions in terms of the fatty acid (FA) composition of the MFG core. Selected cows fell into the respective size group over at least 3 independent measurements, including an observation period before the experiment. Further selection criteria were similar milk production traits between cows (milk yield, fat yield, fat/protein ratio) and established lactation (>50 d in milk). However, the selected groups differed in parity (parity 1-3 and 3-5 in the small and large MFG groups, respectively), and the small MFG group was an average of 25 d in milk later in their lactation period. All cows were under the same nutritional management and environmental conditions. Here, we show that cows with the small or large MFG phenotype differed in their lipid metabolism in terms of the FA composition of the MFG core. Our results indicate that cows with the small MFG phenotype produced milk with higher concentrations of unsaturated FA despite being fed the same diet. We suggest that this characteristic of the small MFG phenotype is the result of increased uptake of long-chain FA from the blood circulation. A relationship between the degree of unsaturation and MFG size was also identified in preliminary studies across other species-namely, camels, sheep, and goats. These findings show the potential for on-farm selection of cows (and potentially other dairy species) based on MFG size to produce milk with improved nutrient composition. This could lead to purpose-specific separation of milk based on MFG size and FA profile, both known to alter the technological properties of milk.

The effect of dietary forage to concentrate ratio and forage type on milk fatty acid composition and milk fat globule size of lactating cows

We examined the effects of 2 grass silage-based diets differing in forage:concentrate (FC) ratio and those of a red clover silage-based diet on intake, milk production, ruminal fatty acid (FA) biohydrogenation, milk FA composition, and milk fat globule (MFG) size distribution. Ten multiparous Nordic Red cows received the following treatments: grass silage-based diets containing high (70:30, HG) or low (30:70, LG) FC ratio or a red clover silage-based diet with an FC ratio of 50:50 (RC) on a dry matter basis. Determinations of MFG were performed from fresh milk samples without addition of EDTA so the results of fat globules >1 µm in diameter are emphasized instead of the entire globule population. Lower FC ratio in grass silage-based diets increased milk production with no effect on daily fat yield, leading to 13% lower milk fat concentration. The effect of FC ratio on MFG size was moderate. It did not affect the volume-weighted diameter in grass silage-based diets, although LG lowered the volume-surface diameter of MFG in the size class >1 µm compared with HG. Compared with HG, feeding LG moderately decreased the biohydrogenation of 18:2n-6, leading to a higher level of polyunsaturated fatty acids in milk fat. Feeding RC lowered milk fat concentration and daily milk fat yield compared with grass silage-based diets. The volume-weighted diameter of MFG in the size class >1 µm was smaller in RC milk compared with grass silage-based diets. Feeding RC increased the flow of 18:3n-3 at the omasum by 2.4-fold and decreased the apparent ruminal 18:3n-3 biohydrogenation compared with grass silage-based diets despite similar intake of 18:3n-3. It also resulted in the lowest amount of saturated FA and the highest amounts of cis-9 18:1, 18:3n-3, and polyunsaturated FA in milk. In conclusion, LG decreased milk fat content and induced minor changes in MFG size distribution compared with HG, whereas RC lowered milk fat production, altered milk FA composition to nutritionally more beneficial direction, and led to smaller MFG compared with grass silage-based diets.

Effects of milk fat, casein, and serum protein concentrations on sensory properties of milk-based beverages

Our goal was to determine the effect of systematically controlled variation in milk fat, true protein, casein, and serum protein concentrations on the sensory color, flavor and texture properties, instrumental color and viscosity, and milk fat globule size distribution of milk-based beverages. Beverage formulations were based on a complete balanced 3-factor (fat, true protein, and casein as a percentage of true protein) design with 3 fat levels (0.2, 1.0, and 2.0%), 4 true protein (TP) levels (3.00, 3.67, 4.34, and 5.00%) within each fat level, and 5 casein as a percentage of true protein (CN%TP) levels (5, 25, 50, 75, and 80%) within each protein level (for a total of 60 formulations within each of 2 replicates). Instrumental measures of Hunter L and a values and Commission Internationale de l'Éclairage (CIE) b* values, instrumental viscosity, particle size, flavor, sensory texture and sensory appearance evaluations were done on each pasteurized/homogenized beverage formulation. Within each of the 3 fat levels, higher serum protein concentration drove higher aroma intensity, sweet aromatic, cooked/sulfur, cardboard/doughy flavors, and sensory yellowness scores, whereas higher casein concentration drove higher instrumental viscosity in milk protein beverages. Increasing serum protein concentration increased yellowness, sweet aromatic, aroma intensity, cooked/sulfur, and cardboard/doughy flavors across all fat levels and also had the largest effect on L, a, and b* values, sensory whiteness, and opacity within each fat level. Increases in true protein increased throat cling and astringency intensities. Increases in fat concentration were correlated with higher L, a, and b* values, larger particle size, and increased sensory whiteness, mouth coating, cooked/milky, and milkfat flavors. Multiple linear regression of L, a, and b* values produced better predictions of sensory whiteness and yellowness of pasteurized milk protein beverages than simple linear regression of L or b* values, respectively. Formulating milk protein beverages to a higher true protein level increased astringency regardless of fat level. When formulating milk protein beverages, a product developer has a wide range of milk-based protein ingredient choices that differ in price and change price relationship across time. Understanding the expected relative effect of different milk protein ingredients on the textural and flavor characteristics of milk-based beverages could be used to help guide product reformulation decisions and ingredient choices to achieve a specific sensory profile while controlling total beverage ingredient cost.

Optical properties of human milk.

With human milk being the most important source of infant nutrition, the protection and support of breastfeeding are essential from a global health perspective. Nevertheless, relatively few objective methods are available to investigate human milk composition and lactation physiology when a mother experiences breastfeeding problems. We argue that optics and photonics offer promising opportunities for this purpose. Any research activity within this new application field starts with a thorough understanding on how light interacts with human milk. Therefore, the aim of this study was to investigate the full set of optical properties for human milk and the biological variability therein. Using a novel approach that combines spatially resolved diffuse reflectance spectroscopy (SR-DRS) and spectroscopic optical coherence tomography (sOCT) between 450 and 650 nm, we quantified the absorption coefficient µa , scattering coefficient µs , reduced scattering coefficient µs', anisotropy g and backscattering coefficient µb,NA of mature human milk from 14 participants released at different stages during a breastfeed (foremilk, bulk milk and hindmilk). Significant correlations were found between µa , µs , µs' and µb,NA and the biochemically determined fat concentration per sample (Rs = 0.38, Rs = 0.77, Rs = 0.80, Rs = 0.44 respectively). We explained the observed variations in the optical properties of human milk using Mie theory and the biological variability in both the concentration and size distribution of milk fat globules. In conclusion, we have provided a full set of optical properties for human milk, which can hopefully serve as a starting point for future biophotonic studies on human milk and the milk containing lactating breast.

Acceleration of acid gel formation by high intensity ultrasound is linked to whey protein denaturation and formation of functional milk fat globule-protein complexes

Ultrasonic homogenization of full fat milk is known to provide changes in the acid-induced gelation behavior, in terms of acceleration of gel formation and increased gel strength. In this study, the dependency of this behavior on ultrasonic power level and treatment temperature was illustrated using an ultrasonic flow cell system, which minimizes temperature increase during treatment. Gel formation was studied by acidification with glucone-δ-lactone at 30 °C using small deformation rheology and effects of ultrasonication on whey protein denaturation, milk fat globule size distribution and proteins associated with the milk fat globule membrane were evaluated. Results illustrate how increased acid-gel strength upon ultrasonication, partly, was attributed to denaturation of whey proteins, but also indicate that changes in the milk fat globule membrane, in terms of increased association of caseins with the milk fat globule membrane, can be of importance by facilitating the formation of highly functional milk fat globule/protein complexes.

Physicochemical Properties of Liquid Infant Formula Stored at Different Temperatures.

Changes in the physicochemical properties of ready-to-feed liquid infant formula (LIF) stored at different temperatures (10, 20, 30, and 40°C) for 6 mon, focusing on 5-hydroxymethylfurfural (HMF) content, color, pH, fat globule size distribution, and rheological properties were determined. The HMF content increased with storage time, and LIF stored at 40°C had a higher HMF content than that of LIF stored at 10°C. The lightness (L*) decreased while redness (a*) and yellowness (b*) increased with increasing HMF content. The fat globule size and pH of LIF stored at 10°C did not change. However, in the case of LIF stored at 30°C and 40°C, the fat globule size increased and the pH decreased during storage for 6 mon. LIF stored at 40°C had a higher apparent viscosity (ηa,10) than that of LIF stored at 10°C, and the shear-thinning behavior of LIF stored at higher temperature was stronger than that of LIF stored at low temperature. The physicochemical changes of LIF during storage were accelerated by Maillard reaction (MR) at higher storage temperatures. Therefore, even if LIF is aseptically manufactured, we recommend that sterilized LIF should be stored at low temperature in order to minimize quality changes during storage.