Fat globules selected from whole milk according to their size: Different compositions and structure of the biomembrane,revealing sphingomyelin-rich domains

Milk fat globules are unique delivery systems for biologically active molecules in the gastrointestinal tract. However, their properties have not yet been fully investigated. In this study, we performed a comparative analysis of the polar lipid and fatty acid compositions of milk fat globules as a function of their size and investigated the structure of the milk fat globule membrane (MFGM). An optimised process of microfiltration was used to select the small milk fat globule (SMFG; 1.6 μm) fractions and the large milk fat globule (LMFG; 6.6 μm) fractions from the same initial whole milks (4.2 μm). The SMFG-fractions contained significantly (i) higher amounts of polar lipids, 8.9 ± 0.9 vs 2.7 ± 0.3 mg/g fat for LMFG-fractions and 6.3 ± 0.5 mg/g fat for whole milks, (ii) lower relative proportions of phosphatidylcholine and sphingomyelin in the MFGM, (iii) higher amounts of C12:0, C14:0, C16:0, C18:1 trans, C18:2 c9 tr11, and lower amounts of C18:0 and C18:1 c9 than did LMFG-fractions and whole milks. Whatever the size of native milk fat globules, the biophysical characterisation performed in-situ, using confocal laser scanning microscopy, showed heterogeneities in the MFGM. The lateral segregation of sphingomyelin in rigid liquid-ordered domains, surrounded by the fluid matrix of glycerophospholipids in the liquid-disordered phase, was revealed. The heterogeneous distribution of glycolipids and glycoproteins was also observed in the MFGM. A new model for the structure of the MFGM is proposed and discussed. The physical, chemical and biological consequences, (i) of the differences in milk fat globule compositions according to their size and (ii) of the specific structure of the MFGM due to sphingomyelin remain to be elucidated.     

Size distribution of fat globules in human colostrum, breast milk, and infant formula

Only a few results are available on the size of human milk fat globules (MFG), despite its significance regarding fat digestion in the infant, and no data are available at <24 h postpartum (PP). We measured the MFG size distribution in colostrum and transitional human milk in comparison with fat globules of mature milk and infant formula. Colostrum and transitional milk samples from 18 mothers were collected regularly during 4 d PP and compared with mature milk samples of 17 different mothers and 4 infant formulas. The size distribution was measured by laser light scattering. For further characterization, the ζ-potential of some mature MFG was measured by laser Doppler electrophoresis. The MFG diameter decreased sigmoidally in the first days. At <12 h PP, the mode diameter was 8.9 ± 1.0 μm vs 2.8 ±0.3 μm at 96 h PP. Thus, the surface area of MFG increased from 1.1 ±0.3 to 5.4 ±0.7 m²/g between colostrum and transitional milk. In mature milk, the MFG diameter was 4 μm on average and increased with advancing lactation, whereas the droplets in infant formula measured 0.4 μm. The ζ potential of mature MFG was −7.8 ± 0.1 mV. The fat globules are larger in early colostrum than in transitional and mature human milk and in contrast with the small-sized fat droplets in infant formula. Human MFG also have a low negative surface charge compared with bovine globules. These structural differences can be of nutritional significance for the infant.     

Behaviour of homogenized fat globules during the spray drying of whole milk

The changes in milk fat globule size and fat globule surface proteins of both low-preheated and high-preheated concentrated milks, which were homogenized at low or high pressure prior to spray drying using a disc atomization drier, were examined. The average fat globule size (d₃₂) of the spray-dried milk powders was smaller than that of the corresponding concentrates, but a small proportion of very large globules (4–80 μm) was also formed during spray drying. As a consequence, total surface protein (mg protein g⁻¹ fat) increased due to the adsorption of casein micelles at the fat globule surface during spray drying. Confocal micrographs of the powders showed some apparent spreading of the fat on the surface of the powder particles, particularly when the concentrates were homogenized at low pressure. These results indicate disruption of the milk fat globules during spray drying, which consequently causes changes in the fat globule surface protein layer.     

Buffalo vs. cow milk fat globules: Size distribution,zeta-potential,compositions in total fatty acids and in polar lipids from the milk fat globule membrane

Although buffalo milk is the second most produced milk in the world, and of primary nutritional importance in various parts of the world, few studies have focused on the physicochemical properties of buffalo milk fat globules. This study is a comparative analysis of buffalo and cow milk fat globules. The larger size of buffalo fat globules, 5 vs. 3.5 μm, was related to the higher amount of fat in the buffalo milks: 73.4 ± 9.9 vs. 41.3 ± 3.7 g/kg for cow milk. Buffalo milks contained significantly lower amount of polar lipids expressed per gram of lipids (0.26% vs. 0.36%), but significantly higher amount of polar lipids per litre of milk (+26%). Buffalo and cow milk fat globule membranes contain the same classes of polar lipids; phosphatidylethanolamine, sphingomyelin (SM) and phosphatidylcholine (PC) being the main constituents. A significant higher percentage of PC and lower percentage of SM were found for buffalo milks. The fatty acid analysis revealed that saturated fatty acids, mainly palmitic acid, trans fatty acids, linolenic acid (ω3) and conjugated linolenic acid were higher in buffalo milk than in cow milk. Such results will contribute to the improvement of the quality of buffalo milk-based dairy products.     

Physicochemical Properties of Milk Fat Emulsions Stabilized with Bovine Milk Fat Globule Membrane

Milk fat globules (MFG) were reconstituted with milk fat globule membrane (MFGM) and milk fat (MF). Viscosity of the reconstituted MFG was highest at pH 5.0 and 4 min emulsifying, and rose with an increase of MFGM between 40–80 mg/g fat. Adsorbed protein/unit fat increased at acid pH with increase of MFGM. The composition of proteins adsorbed on the surface of MFG was not influenced by factors of reconstitution. The size and specific surface area of globules were influenced by emulsifying time, MFGM and MF concentrations, and pH. The size range of MFG prepared by standard method was 0.9–17 μm in diameter. Median diameter was 5 μm and specific surface area was 15,600 cm²/cm³ of emulsion.     

Size-based fractionation of native milk fat globules by two-stage centrifugal separation

A two-stage centrifugal separation method, at various separation temperatures and feed rates, was employed to fractionate milk and cream on the basis of fat globule size. It involved a modified and a conventional centrifugal separation in first and second stages, respectively. In the first stage, two streams of milk: one rich in larger fat globules and another rich in smaller fat globules, were obtained by fractionation in a modified cream separator. In the second stage, the two streams from the first stage were each further fractionated in a conventional cream separator. Depending on the temperature and feed rate of the first stage, this double separation method was able to create streams with mean fat globule size (D [4, 3]) as small as 1.35 μm and as large as 4.28 μm without affecting the droplet integrity. The developed method has potential for size-based fractionation of native fat globules in industrial scale.Industrial relevanceThe developed method has potential for size based fractionation of native fat globules in industrial scale.     

Milk quality and automatic milking: fat globule size, natural creaming, and lipolysis

Thirty-eight Italian Friesian first-lactation cows were allocated to 2 groups to evaluate the effect of 1) an automatic milking system (AMS) vs. milking in a milking parlor (MP) on milk fat characteristics; and 2) milking interval (≤480, 481 to 600, 601 to 720, and >720 min) on the same variables. Milk fat was analyzed for content (% vol/vol), natural creaming (% of fat), and free fatty acids (FFA, mEq/100 g of fat). Distribution of milk fat globule size was evaluated to calculate average fat globule diameter (d₁), volume-surface average diameter (d₃₂), specific globule surface area, and mean interglobular distance. Milk yield was recorded to calculate hourly milk and milk fat yield. Milking system had no effect on milk yield, milk fat content, and hourly milk fat yield. Milk from AMS had less natural creaming and more FFA content than milk from MP. Fat globule size, globular surface area, and interglobular distance were not affected by milking system per se. Afternoon MP milkings had more fat content and hourly milk fat yield than AMS milkings when milking interval was >480 min. Milk fat FFA content was greater in AMS milkings when milking interval was ≤480 min than in milkings from MP and from AMS when milking interval was >600 min. Milking interval did not affect fat globule size, expressed as d₃₂. Results from this experiment indicate a limited effect of AMS per se on milk fat quality; a more important factor seems to be the increase in milking frequency, generally associated with AMS.     

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.     

Effect of nonthermal technologies on the native size distribution of fat globules in bovine cheese-making milk

Milk-fat globule membranes are susceptible to damage by mechanical and thermal processes. This damage is translated into alterations of milk fat structure and functionality of cheese-making milk. The objective of this work was to evaluate the effect of pulsed electrical fields (PEF), high hydrostatic pressure (HHP), and conventional thermal treatments on fat globule size distribution and ζ-potential. Milk was processed by HHP at 400 and 500 MPa for 0–20 min, and with PEF at 36 kV/cm and 42 kV/cm up to 64 pulses. The ζ-potential of HHP and PEF treated milk were − 15.47 mV and − 14.63 mV respectively. HHP treatments induced fat globules flocculation, increasing their mass moment mean diameter. Although PEF processing did not modify the true mean diameter of MFG, it induced small globules to clump together, causing an apparent increment in the population of larger milk-fat globules.

Industrial relevance

The market for traditional raw dairy products has increased in recent times in several regions of the world due to their unique flavor and texture attributes. However, the potential negative implications of consuming raw products limit the growth of this market segment. Manufacture of raw-like cheese from thermally pasteurized milk is not feasible, among other things, because of milk fat globule membrane damage caused by elevated temperatures. Nonthermal food preservation technologies offer the potential to produce milk technically suitable for the industrial manufacture of microbiologically safe raw-like dairy products.     

Composition of milk fat from cows selected for milk fat globule size and offered either fresh pasture or a corn silage-based diet

The objective of this study was to examine the synthesis and composition of milk produced by dairy cows that secrete either small milk fat globules (SMFG) or large milk fat globules (LMFG), and to study their response to diets known to alter milk composition. Four groups of 3 multiparous dairy cows were assigned to 2 isoenergetic feeding treatments: a corn silage treatment supplemented with soybean meal, and fresh pasture supplemented with cereal concentrate. The 4 groups comprised 2 groups of 3 dairy cows that produced SMFG (3.44 μm) and 2 groups of 3 dairy cows that produced LMFG (4.53 μm). The SMFG dairy cows produced higher yields of milk, protein, and calcium. Nevertheless, their milk had lower fat and protein contents. Both SMFG and LMFG cows secreted similar amounts of milk fat; therefore, higher globule membrane contents in milk fat were observed in SMFG cows. Higher calcium mineralization of the casein micelles in SMFG cows suggests that it may be possible to improve cheese-making properties even if the lower protein content may lead to lower cheese yields. The SMFG cows secrete milk fat with a higher concentration of monounsaturated fatty acids and a lower concentration of short-chain fatty acids. They also have a higher C18:1/C18:0 ratio than LMFG cows. This suggests that SMFG cows have more significant fatty acid elongation and desaturation. The pasture treatment led to an increase in milk and protein yields because of increased energy intake. It also resulted in lower milk fat yield and fat and protein contents. The pasture treatment led to a decrease in milk fat globule size and, as expected, an increase in monounsaturated and polyunsaturated fatty acid contents. However, it induced a decrease in the protein content, and in calcium mineralization of casein micelles, which suggests that this type of milk would be less suitable for making cheese. This study also shows that there is no correlation between the cows, based on milk fat globule size and diet. These results open up possibilities for improving milk fat quality based on milk fat globule size, and composition. The mechanisms involved in milk fat globule secretion are still to be determined.     

Milk fat globule membrane proteins are involved in controlling the size of milk fat globules during conjugated linoleic acid–induced milk fat depression

Milk fat globule membrane (MFGM) proteins surround the triacylglycerol core comprising milk fat globules (MFG). We previously detected a decrease in the size of fat globules during conjugated linoleic acid (CLA)-induced milk fat depression (MFD), and other studies have reported that some MFGM proteins play a central role in regulating mammary cellular lipid droplet size. However, little is known about the relationship between MFD, MFG size, and MFGM proteins in bovine milk. The aim of this study was to investigate the profile of MFGM proteins during MFD induced by CLA. Sixteen mid-lactating Holstein cows (145 ± 24 d in milk) with similar body condition and parity were divided into control and CLA groups over a 10-d period. Cows were fed a basal diet (control, n = 8) or control plus 15 g/kg of dry matter (DM) CLA (n = 8) to induce MFD. Cow performance, milk composition, and MFG size were measured daily. On d 10, MFGM proteins were extracted and identified by quantitative proteomic analysis, and western blotting was used to verify a subset of the identified MFGM proteins. Compared with controls, supplemental CLA did not affect milk production, DM intake, or milk protein and lactose contents. However, CLA reduced milk fat content (3.73 g/100 mL vs. 2.47 g/100 mL) and the size parameters volume-related diameter D_[4,3] (3.72 μm vs. 3.35 μm) and surface area-related diameter D_[3,2] (3.13 μm vs. 2.80 μm), but increased specific surface area of MFG (1,905 m²/kg vs. 2,188 m²/kg). In total, 177 differentially expressed proteins were detected in milk from cows with CLA-induced MFD, 60 of which were upregulated and 117 downregulated. Correlation analysis showed that MFG size was negatively correlated with various proteins, including XDH and FABP3, and positively correlated with MFG-E8, RAB19, and APOA1. The results provide evidence for an important role of MFGM proteins in regulating MFG diameter, and they facilitate a mechanistic understanding of diet-induced MFD.     

Natural variation of bovine milk fat globule size within a herd

Native milk fat globule (MFG) size, pH, total fat, protein, and lactose composition in milk from individual cows was examined in autumn and spring 2012 and autumn 2013. Mean MFG diameters ranged between 2.5 and 5.7 µm. Some cows were observed to consistently produce small or large MFG throughout the sampling period, though trends were not consistent across all cows. Small-MFG milk contained more total polar lipids; however, the relative proportion of individual polar lipids did not differ with MFG size, with the exception of phosphatidylcholine, which was greater in small-MFG milk. No significant correlation between MFG size and proximate composition, including calculated fat yield or pH, was found. This work revealed a natural cow-to-cow variation in MFG size exists, which could potentially be exploited to improve the functionality of milk for manufacturing and some products.     

Effect of the size and interface composition of milk fat globules on their in vitro digestion by the human pancreatic lipase: Native versus homogenized milk fat globules

Although the bioavailability of dietary lipids is of primary importance in human nutrition and health, the mechanisms involved in lipid digestion are not fully understood and are of growing interest. The objective of this study was to determine the effect of the size of milk fat globules and of the composition of their interface on the activity of the human pancreatic lipase (PL). Native milk fat globules of various sizes covered by their biological membrane (MFGM) and homogenized fat globules of various sizes covered by milk proteins were prepared from whole milk and underwent lipolysis by the human PL with colipase and bile salts. A lag phase preceding the hydrolysis of milk TAG occurred with all native milk fat globules samples but not with homogenized milk samples. The kinetic parameters of human PL were determined by measuring the enzyme activity either after the lag phase for native milk fat globules samples or immediately after the addition of the enzyme for homogenized milk samples. The catalytic efficiency of human PL is 4.6-fold higher on small (1.8 μm) than large (6.7 μm) native milk fat globules, related to a 3.6-fold larger available surface. Despite the 25-fold larger available surface, milk TAG from homogenized milk are only 2-fold better hydrolyzed compared to native milk fat globules, as a possible result of a less favourable interface covered by milk proteins. The potential mechanisms involved in native vs. homogenized milk fat globules digestion by the human PL are discussed. Our study highlights the crucial role of the MFGM in the efficient digestion of milk fat globules and brings new insight for the design of dairy products and infant formulas.     

High-pressure homogenisation of raw bovine milk. Effects on fat globule size distribution and microbial inactivation

Whole raw milk was processed using a 15 L h⁻¹ homogeniser with a high-pressure (HP) valve immediately followed by a cooling heat exchanger. The influence of homogenisation pressure (100–300 MPa) and milk inlet temperature T_in (4°C, 14°C or 24°C) on milk temperature T₂ at the HP valve outlet, on fat globule size distribution and on the reduction of the endogenous flora were investigated. The T_in values of 4–24°C led to milk temperatures of 14–33°C before the HP valve, mainly because of compression heating. High T_in and/or homogenisation pressure decreased the fat globule size. At 200 MPa, the d_4.3 diameter of fat globules decreased from 3.8±0.2 (control milk) to 0.80±0.08 μm, 0.65±0.10 or 0.37±0.07 μm at T_in=4, 14°C or 24°C, respectively. A second homogenisation pass at 200 MPa (T_in=4°C, 14°C or 24°C) further decreased d_4.3 diameters to about 0.2 μm and narrowed the size distribution. At all T_in tested, an homogenisation pressure of 300 MPa induced clusters of fat globules, easily dissociated with SDS, and probably formed by sharing protein constituents adsorbed at the fat globule surface. The total endogenous flora of raw milk was reduced by more than 1 log cycle, provided homogenisation pressure was ⩾200 MPa at T_in=24°C (T₂∼60°C), 250 MPa at T_in=14°C (T₂∼62°C), or 300 MPa at T_in=4°C (T₂∼65°C). At all T_in tested, a second pass through the HP valve (200 MPa) doubled the inactivation ratio of the total flora. Microbial patterns of raw milk were also affected; Gram-negative bacteria were less resistant than Gram-positive bacteria.     

Elevated concentrate-to-forage ratio in dairy cow rations is associated with a shift in the diameter of milk fat globules and remodeling of their membranes

We examined the effects of concentrate-to-forage ratio in dairy cow rations on milk-fat composition, with a specific focus on the structure of milk fat globules (MFG). Twenty-four Holstein cows, 153 d in milk, were assigned to 2 dietary treatments in a crossover design study. Treatments were (1) high-concentrate (65%), low-forage (35%; HCLF) diet and (2) low-concentrate (35%), high-forage (65%; LCHF) diet. The mean diameter of the MFG; plasma concentrations of insulin, glucose, and nonesterified fatty acids (FA); and the composition and concentrations of milk FA and polar lipids were determined. Concentrations of insulin were 56% higher, and those of nonesterified FA 46% lower, in the HCLF than in the LCHF diet. The milk yield was 8.5 kg/d higher and yields of fat, protein, and lactose were 180, 350, and 403 g/d higher, respectively, in the HCLF versus LCHF diet. Milk FA composition differed between treatments, with 1.5 and 1.0 percentage units higher saturated and polyunsaturated FA concentrations, respectively, in the HCLF versus LCHF diet. Mean MFG diameter tended to be smaller (0.2 μm) in the HCLF diet than in the LCHF diet, associated with increased daily phospholipids yield (34%), lower phosphatidylserine and higher phosphatidylcholine concentrations. In conclusion, the decreased milk and fat yields in the LCHF diet were associated with remodeling of the MFG membrane and with the secretion of larger MFG. Membrane remodeling of the mammary epithelium membranes seems to play a role in regulating MFG size.     

Pilot-scale crossflow-microfiltration and pasteurization to remove spores of Bacillus anthracis (Sterne) from milk

High-temperature, short-time pasteurization of milk is ineffective against spore-forming bacteria such as Bacillus anthracis (BA), but is lethal to its vegetative cells. Crossflow microfiltration (MF) using ceramic membranes with a pore size of 1.4 μm has been shown to reject most microorganisms from skim milk; and, in combination with pasteurization, has been shown to extend its shelf life. The objectives of this study were to evaluate MF for its efficiency in removing spores of the attenuated Sterne strain of BA from milk; to evaluate the combined efficiency of MF using a 0.8-μm ceramic membrane, followed by pasteurization (72°C, 18.6 s); and to monitor any residual BA in the permeates when stored at temperatures of 4, 10, and 25°C for up to 28 d. In each trial, 95 L of raw skim milk was inoculated with about 6.5 log₁₀ BA spores/mL of milk. It was then microfiltered in total recycle mode at 50°C using ceramic membranes with pore sizes of either 0.8 μm or 1.4 μm, at crossflow velocity of 6.2 m/s and transmembrane pressure of 127.6 kPa, conditions selected to exploit the selectivity of the membrane. Microfiltration using the 0.8-μm membrane removed 5.91 ± 0.05 log₁₀ BA spores/mL of milk and the 1.4-μm membrane removed 4.50 ± 0.35 log₁₀ BA spores/mL of milk. The 0.8-μm membrane showed efficient removal of the native microflora and both membranes showed near complete transmission of the casein proteins. Spore germination was evident in the permeates obtained at 10, 30, and 120 min of MF time (0.8-μm membrane) but when stored at 4 or 10°C, spore levels were decreased to below detection levels (≤0.3 log₁₀ spores/mL) by d 7 or 3 of storage, respectively. Permeates stored at 25°C showed coagulation and were not evaluated further. Pasteurization of the permeate samples immediately after MF resulted in additional spore germination that was related to the length of MF time. Pasteurized permeates obtained at 10 min of MF and stored at 4 or 10°C showed no growth of BA by d 7 and 3, respectively. Pasteurization of permeates obtained at 30 and 120 min of MF resulted in spore germination of up to 2.42 log₁₀ BA spores/mL. Spore levels decreased over the length of the storage period at 4 or 10°C for the samples obtained at 30 min of MF but not for the samples obtained at 120 min of MF. This study confirms that MF using a 0.8-μm membrane before high-temperature, short-time pasteurization may improve the safety and quality of the fluid milk supply; however, the duration of MF should be limited to prevent spore germination following pasteurization.     

Effects of Size and Stability of Native Fat Globules on the Formation of Milk Gel Induced by Rennet

Rennet‐induced gelation crucially impacts cheese structure. In this study, effects of the size and stability of native fat globules on the kinetics of rennet‐induced coagulation were revealed by determining the caseinomacropeptide release rate and rheological properties of milk. Moreover, the mobility and stability of fat globules during renneting was revealed using diffusing wave spectroscopy and confocal laser scanning microscopy. By use of a 2‐stage gravity separation combined centrifugation scheme, native fat globules were selectively separated into small (SFG, D_4,3 = 1.87 ± 0.02 μm) and large fat globules (LFG, D_4,3 = 5.65 ± 0.03 μm). The protein and fat content of SFG and LFG milk were then standardized to 3.2 g/100 mL and 1.2 g/100 mL, respectively. The milk containing different sized globules were then subjected to renneting experiments in the laboratory. Reduction of globule size accelerated the aggregation of casein micelles during renneting, giving a shorter gelation time and earlier 1/l^* change. The gel produced from LFG milk was broken due to coalescent fat globules and generated coarser gel strands compared to the finer strands formed with SFG milk. Structural differences were also confirmed with a higher final storage modulus of the curd made from SFG milk than that from the LFG. In conclusion, the size of fat globules affects the aggregation of casein micelles. Moreover, fat globule coalescence and creaming during renneting, also affects the structure of the rennet gel. A better understanding of the size of globules effect on milk gelation could lead to the development of cheese with specific properties.     

Influence of particle size on lipid digestion and β-carotene bioaccessibility in emulsions and nanoemulsions

The interest in incorporating carotenoids, such as β-carotene, into foods and beverages is growing due to their potential health benefits. However, the poor water-solubility and low bioavailability of carotenoids is currently a challenge to their incorporation into many foods. The aim of this work was to study the influence of particle size on lipid digestion and β-carotene bioaccessibility using corn oil-in-water emulsions with different initial droplet diameters: large (d₄₃ ≈ 23 μm); medium (d₄₃ ≈ 0.4 μm); and small (d₄₃ ≈ 0.2 μm). There was a progressive increase in the mean particle size of all the emulsions as they passed through a simulated gastrointestinal tract (GIT) consisting of mouth, stomach, and small intestine phases, which was attributed to droplet coalescence, flocculation, and digestion. The electrical charge on all the lipid particles became highly negative after passage through the GIT due to accumulation of anionic bile salts, phospholipids, and free fatty acids at their surfaces. The rate and extent of lipid digestion increased with decreasing mean droplet diameter (small ≈ medium ? large), which was attributed to the increase in lipid surface area exposed to pancreatic lipase with decreasing droplet size. There was also an appreciable increase in β-carotene bioaccessibility with decreasing droplet diameter (small > medium > large). These results provide useful information for designing emulsion-based delivery systems for carotenoids for food and pharmaceutical uses.     

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.     

Interactive Effects of Milk Fat Globule and Casein Micelle Size on the Renneting Properties of Milk

The size of the casein micelles (CM) and the milk fat globules (MFG) vary depending on farming factors, such as seasonal variation and stage of lactation, and cow genetics. The MFG and CM size of milk can influence the renneting behavior and texture of manufactured dairy products. In this work, we investigated the combined effects of MFG and CM size on the onset of gelation, the maximum rate of gelation, the value for G′_60 min (the final storage modulus) and G″_60 min (the final loss modulus), and tan δ upon renneting. Fractionation of MFG on the basis of size was carried out using laboratory-based centrifugation, whereas milk of predominantly large (184–218 nm) or small (147–159 nm) CM was selected naturally on-farm. Casein micelle size had the dominant effect on curd firmness and gelation rates of milk, where small CM milk formed rennet gels earlier and resulted in a firmer gel than milk with large CM. However, MFG size also influenced the renneting properties. The strongest rennet gels were obtained when large MFG (3.88–5.78 μm) was combined with small CM (153–159 nm). Selecting milk on the basis of the microstructure of key milk components could be achieved by natural selection of dairy cows or via fractionation technologies. Selection may provide a useful tool for efficient manufacturing of different dairy products based on the desirable characteristics specific to each.