Milk Emulsions Research Articles

Homogenization Conditions Affect the Oxidative Stability of Fish Oil Enriched Milk Emulsions: Oxidation Linked to Changes in Protein Composition at the Oil−Water Interface

Fish oil was incorporated into milk under different homogenization temperatures (50 and 72 degrees C) and pressures (5, 15, and 22.5 MPa). Subsequently, the oxidative stability of the milk and changes in the protein composition of the milk fat globule membrane (MFGM) were examined. Results showed that high pressure and high temperature (72 degrees C and 22.5 MPa) resulted in less lipid oxidation, whereas low pressure and low temperature (50 degrees C and 5 MPa) resulted in faster lipid oxidation. Analysis of protein oxidation indicated that especially casein was prone to oxidation. The level of free thiol groups was increased by high temperature (72 degrees C) and with increasing pressure. Furthermore, SDS-PAGE and confocal laser scanning microscopy (CLSM) indicated that high temperature resulted in an increase in beta-lactoglobulin adsorbed at the oil-water interface. This was even more pronounced with higher pressure. Less casein seemed to be present at the oil-water interface with increasing pressure. Overall, the results indicated that a combination of more beta-lactoglobulin and less casein at the oil-water interface gave the most stable emulsions with respect to lipid oxidation.

Homogenization Conditions Affect the Oxidative Stability of Fish Oil Enriched Milk Emulsions: Lipid Oxidation

In this study fish oil was incorporated into commercial homogenized milk using different homogenization temperatures and pressures. The main aim was to understand the significance of homogenization temperature and pressure on the oxidative stability of the resulting milks. Increasing homogenization temperature from 50 to 72 degrees C decreased droplet size only slightly, whereas a pressure increase from 5 to 22.5 MPa decreased droplet size significantly. Surprisingly, emulsions having small droplets, and therefore large interfacial area, were less oxidized than emulsions having bigger droplets. Emulsions with similar droplet size distributions, but resulting from different homogenization conditions, had significantly different oxidative stabilities, indicating that properties of significance to oxidation other than droplet size itself were affected by the different treatments. In general, homogenization at 72 degrees C appeared to induce protective effects against oxidation as compared to homogenization at 50 degrees C. The results thus indicated that the actual composition of the oil-water interface is more important than total surface area itself.

Modeling of particle size distribution of sonicated coconut milk emulsion: Effect of emulsifiers and sonication time

Abstract Coconut milk was extracted from grated coconut meat with addition of water by a hydraulic press. This milk was mixed with emulsifiers (Gum Acacia and maltodextrin) at different ratios of emulsifier to fat (4, 2.75, and 1.5) and different maltodextrin (MD) to Gum Acacia (GA) ratio (0.67, 1.085, and 1.5). The emulsion was sonicated for different time durations (0.5–3.0 min). Particle size analysis of the sonicated coconut milk emulsion revealed that the number fraction of fat globules below 2 × 10 −6 m increased as the emulsifier to fat ratio increased. However, at the highest ratio of emulsifier to fat this trend reversed even at higher sonication times. Similar slump in the increasing trend of globules below 2 × 10 −6 m were observed at the highest value of ratio of MD to GA (1.5) studied. Modeling of particle size distribution by Rosin–Rambler–Sperling–Bennet relation was found to be a good tool for prediction of uniformity of distribution n and statistical average globule diameter M . The n values varied between 0.981 and 1.318 where as M values lied between 2.11 × 10 −6 and 4.12 × 10 −6 m. Linear regression fitting of n and M values as function of ratio of emulsifier to fat, ratio of MD to GA and the sonication time resulted in a good fit with relative deviation of 3.96% and 10.77%, respectively. These linear regression equations provided a suitable model to predict the sonication time required to achieve certain degree of size reduction with a relative deviation of 2.33%.

Effect of Heating and Homogenization on the Stability of Coconut Milk Emulsions

ABSTRACT: The effects of homogenization and heat treatment on the colloidal stability of coconut milk were studied. Fresh coconut milk (15% to 17% fat, 1.5% to 2% protein) was extracted and stored at 30 °C before homogenization at 40/4 MPa (stage I/stage II). Both homogenized and non‐homogenized samples were heated at 50 °C, 60 °C, 70 °C, 80 °C, and 90 °C for 1 h. Homogenization reduced the size of the primary emulsion droplets from 10.9 to 3.0 μm, but increased the degree of flocculation, presumably via a bridging mechanism. This flocculation was also responsible for increased viscosity of the homogenized samples. Heating increased the degree of flocculation in both non‐homogenized and homogenized samples. A slight amount of coalescence was also observed after heating above 80 °C. All samples creamed after 24 h of storage, but the heated samples formed a larger cream layer, presumably because the flocculated droplets packed together less efficiently. Optical microscopy was used to confirm the combination of flocculation and creaming responsible for changes in coconut milk quality. The information obtained from this study provides a better understanding of the emulsion science important in controlling coconut milk functionality.

Emulsiones tipo crema preparadas a base de leche de soja 3: Efecto de ciclos de temperatura

In this work, the effect of temperature cycling on emulsions formulated with reconstituted soy milk, sunflower oil and high melting point milk fat was analysed. The emulsions were prepared at 60 oC , stored at 4 oC (3 h), warmed at 40 oC or 50 oC (30 min) and afterwards recooled at 4 oC (2h). Although solid fat content of emulsions did not raised after tempering at 40 oC , increase of G' and G'' was observed only in those formulated with 40 % lipid phase. This phenomenon was attributed to droplet aggregation due to partial melting, recrystallization and reordering of fat crystals in oil droplets. The main droplet destabilization mechanism was the partial coalescence; it was corroborated by nuclear magnetic resonance, differential scanning calorimetry and droplet size distribution studies. On the other hand, the consistency of 20 % of lipid phase emulsion did not increased. Low droplet concentration disfavoured the partial coalescence of droplets. Similar assays on cream at 40 oC and cream-like soy milk emulsions at 50 oC , did not show rheological modifications, due to almost total melting of milk fat during tempering.

Protection against Oxidation of Fish-Oil-Enriched Milk Emulsions through Addition of Rapeseed Oil or Antioxidants

The ability of rapeseed oil and/or different antioxidants (alpha- and gamma-tocopherol mixture, ascorbyl palmitate, and EDTA) to protect fish-oil-enriched milk emulsions against oxidation was investigated. Tocopherol isomers in concentrations similar to those found in natural rapeseed oil were added to rapeseed oil stripped of natural tocopherols. The rapeseed oil with added tocopherols significantly inhibited oxidation in the fish-oil-enriched milk emulsions. In contrast, the emulsions with only fish oil and added alpha- and gamma-tocopherol were less stable than the emulsions with fish oil alone. When added individually, the gamma-tocopherol seemed to inhibit oxidation more efficiently than alpha-tocopherol. Ascorbyl palmitate (AP) almost completely retarded oxidation in the fish-oil-enriched milk emulsions, as determined by PV, volatile oxidation products, and sensory evaluation. AP also prevented the otherwise prooxidant effect of tocopherols added to fish oil before emulsification. No interactions between AP, tocopherols, and EDTA were observed, and EDTA added alone to fish oil did not show antioxidant properties in the milk emulsions. Overall, the results showed that addition of AP or rapeseed oil containing natural tocopherols to fish oil was equally efficient in inhibiting oxidation in the fish-oil-enriched milk emulsions.

Modeling and simulation of milk emulsion drying in spray dryers

This work aims at modeling and simulating the drying of whole milk emulsion in spray dryers. Drops and particles make up the discrete phase and are distributed into temporal compartments following their residence time in the dryer. Air is the continuous and well-mixed phase. Mass and energy balances are developed for each phase, taking into account their interactions. Constitutive equations for describing the drop swelling and drying mechanisms as well as the heat and mass transfer between particles and hot air are proposed and analyzed. A set of algebraic-differential equations is obtained and solved by specific numerical codes. Results from experiments carried out in a pilot spray dryer are used to validate the model developed and the numerical algorithm. Comparing the simulated and experimental data, it is shown that the model predicts well the individual drop-particle history inside the dryer as well as the overall outlet air-particle temperature and humidity.

Effect of Spray-Dryer Operating Variables on the Whole Milk Powder Quality

This work aims at identifying the effects of the main operational spray-dryer variables on the milk powder quality. Experiments have been performed in a pilot spray-dryer following the full-factorial design technique to provide data and correlations that predict the whole powder properties as function of the main operational variables of the spray-dryer. The emulsion feed flow rate, the atomization rotation and the inlet air temperature have been chosen as the independent variables while the residual moisture content, the tapped bulk density, the cohesion force enhancement between particles as well as size distribution of agglomerate and its morphology are the response variables that quantify the powder quality. Correlations obtained are analyzed and incorporated into a mathematical model previously developed for simulating the spray-drying of whole milk emulsion.

Sensory stability and oxidation of fish oil enriched milk is affected by milk storage temperature and oil quality

Abstract The experiments evaluated the influence of fish oil quality and cold storage temperature on the oxidative stability of milk emulsions containing 1.0% w/w milk fat and 0.5% w/w of either a pure fish oil or a fish oil:rapeseed oil mixture. The results showed that it was possible to produce a pasteurised milk product enriched with the important n-3 PUFA from fish oil with acceptable sensory characteristics if (1) the emulsions were based on a mixture of fish oil and rapeseed oil and (2) the initial peroxide value (PV) of the added oil blend was below 0.5 meq kg −1 . The sensory analysis showed a clear distinction between emulsions based on oil with PV 0.1 and 0.5 meq kg −1 , whereas the PV and the gas chromatographic (GC) analysis of volatile oxidation products were not sensitive enough to reveal these differences clearly. The GC analyses showed that the onset of formation of the volatiles was earlier with increased storage temperature in the range of 2–9 °C.

Effects of fish oil type, lipid antioxidants and presence of rapeseed oil on oxidative flavour stability of fish oil enriched milk

AbstractAs a part of our ongoing experiments on optimization of the oxidative stability of fish oils in genuine food systems, this study investigated the oxidative deterioration of fish oil enriched milk emulsions during cold storage. The experimental data showed that addition of rapeseed oil to fish oil (1:1) prior to emulsification into milk significantly protected the emulsions against oxidative deterioration. Addition of propyl gallate and a citric acid ester to the fish oil prior to emulsification also protected the fish oil enriched milk during storage. Emulsions containing a rapeseed:fish oil mixture were oxidatively stable during 11 d at 2 °C. Thus, no additional inhibitory effect of the added antioxidants was observed. The peroxide value and concentrations of five selected volatiles derived from n‐3 PUFA degradation in rapeseed:fish oil mixture emulsions were not significantly different from the corresponding levels in neither the emulsion containing only rapeseed oil nor the milk. It is proposed that the tocopherols in rapeseed oil may be the protective factor. Three‐way chemometric exploratory data analysis was implemented in form of a parallel factor analysis (PARAFAC). The PARAFAC model provided an overview of the obtained data with significantly enhanced interpretability, and revealed information about groupings and correlations in our data.

Chemical and olfactometric characterization of volatile flavor compounds in a fish oil enriched milk emulsion.

Development of objectionable fishy off-flavors is an obstacle in the development of fish oil enriched foods. Only little is known about the sensory impact of specific volatile fish oil oxidation products in food emulsions. This study examined the volatiles profiles of fish oil enriched milk during cold storage (2 degrees C) for 14 days by dynamic headspace sampling followed by gas chromatography-mass spectrometry analyses. Different volatiles (n = 60) comprising alkenals, alkadienals, alkatrienals, and vinyl ketones were identified in the fish oil enriched milk. The potent odorants identified by gas chromatography-olfactometry were 1-penten-3-one, (Z)-4-heptenal, 1-octen-3-one, (Z)-1,5-octadien-3-one, (E,E)-2,4-heptadienal, and (E,Z)-2,6-nonadienal, but despite their potency, none of the separated volatiles imparted a fishy or metallic odor. Two isomers, (E,Z,Z) and (E,E,Z) of 2,4,7-decatrienal were identified in fish oil enriched milk emulsions with peroxide values 0.8 and 3.4 meq/kg, respectively. To our knowledge, this is the first report on appearance of these decatrienals in food emulsions having a relatively low peroxide value.

Oxidative flavour deterioration of fish oil enriched milk

AbstractThe oxidative deterioration of milk emulsions supplemented with 1.5 wt‐% fish oil was investigated by sensory evaluation and by determining the peroxide value and volatile oxidation products after cold storage. Two types of milk emulsions were produced, one with a highly unsaturated tuna oil (38 wt‐% of n‐3 fatty acids) and one with cod liver oil (26 wt‐% of n‐3 fatty acids). The effect of added calcium disodium ethylenediaminetetraacetate (EDTA) on oxidation was also investigated. Emulsions based on cod liver oil with a slightly elevated peroxide value (1.5 meq/kg) oxidised significantly faster than the tuna oil emulsions, having a lower initial peroxide value (0.1 meq/kg). In the tuna oil emulsions the fishy off‐flavour could not be detected throughout the storage period. Addition of 5—50 ppm EDTA significantly reduced the development of volatile oxidation products in the cod liver oil emulsions, indicating that metal chelation with EDTA could inhibit the decomposition of lipid hydroperoxides in these emulsions. This study showed that an oxidatively stable milk emulsion containing highly polyunsaturated tuna fish oil could be prepared without significant fishy off‐flavour development upon storage, provided that the initial peroxide value was sufficiently low.

MICROSTRUCTURE AND TEXTURE OF MANCHEGO CHEESE‐LIKE PRODUCTS MADE WITH CANOLA OIL, LIPOPHILIC AND HYDROPHILIC EMULSIFIERS

ABSTRACTThe effect of lipophilic and hydrophilic low‐molecular weight emulsifiers on microstructure and textural characteristics of Manchego cheese‐like products (MCLP) made from canola oil‐skim milk emulsions were studied. Nine emulsifier blends comprised of different proportions of polyoxyethylene sorbitan monostearate (P), sorbitan monostearate (S) and glycerol monostearate (G) were used to prepare the emulsions. A control cheese (MCFF) was made from whole milk. The cheeses were matured thirty days prior to Instrumental Texture Profile Analysis and Scanning Electron Microscopy analysis. High proportions of P in the emulsifier blend resulted in MCLP cheeses having smaller and individual oil droplets surrounded by a dense protein structure, which exhibited elevated values of hardness, springiness and chewiness, but low values of adhesiveness and cohesiveness. High proportions of G″ and S in the emulsifier blend yielded MCLP cheeses with larger and more agglomerated oil droplets immersed in a relaxed and porous protein matrix associated with less hard, springy and chewy, but higher cohesive and adhesive texture. The microstructural arrangement of the MCLP‐4 cheese (0.5P‐0.2S‐0.3G) showed texture closer to the MCFF cheese. Polynomial models were obtained that estimate the textural characteristics of the MCLP cheeses as a function of emulsifiers’ concentration.

Analysis of Dispersed Phase of Coconut Milk Emulsion

Experiments were conducted to study the dispersed phase of coconut milk emulsion. They were optical microscopy analysis using a Nikon Microscope and particle size analysis using a Coulter Counter Multisizer. Particle size analysis using a Coulter Counter Multisizer on both original coconut milk and homogenized coconut milk at T = 19 °C indicated that they had a wide range of particle size with average value of 5.988 + 1 .0 pm and 6.696 + 1 . 1 pm in diameter respectively. Optical microscopy analysis showed that homogenization of coconut milk after it was heated in a water bath at T = 35 °C for about 15 minutes resulted in changes of particle size, the particle size became smaller. The result lead to a conclusion that the coconut milk emulsion may be considered as a polydisperse emulsion and it indicates that the system should not be sensitive to small variations in preparation or subsequent handling.

Heat stability of milk emulsions: phospholipid–protein interactions

Abstract Certain types of lecithin increase the heat stability of recombined and conventional full-cream evaporated milk but the mechanism is unknown. Previous studies have indicated the importance of fat in the system. New studies have indicated the nature of protein–lecithin interactions involved in improving heat stability. Two likely mechanisms were considered: (a) that lecithin increases heat stability by displacement of or by interaction with surface-adsorbed protein and (b) that lecithin interacts with free protein in solution thereby influencing heat-induced free protein/bound protein interactions. These possibilities were investigated by examining the effect of lecithin on the heat stability of fresh whole milk, unhomogenized and homogenized, and the corresponding skim milk and recombined milk in the absence and presence of indigenous serum protein. Lecithin does not require fat per se to affect heat stability. In addition, it does not exercise its effect on heat stability by interaction with free protein in solution but changes heat stability by targeting the membrane proteins. These findings were obtained for lecithins containing non-acidic and acidic phospholipids.

Electroacoustic determination of size and zeta potential of fat globules in milk and cream emulsions

Measurements of the zeta potential and droplet size of fat globules in milk and cream emulsions at natural pH have been made using the technique of electroacoustics. This technique requires no dilution or change of environment of the fat globules. Commercial and recombined milk and cream emulsions were studied. A zeta potential of −19 mV was obtained for homogenized fat globules from a commercial milk emulsion, a zeta potential of −22 mV was obtained for natural fat globules from a commercial cream emulsion and a zeta potential of −36 mV was obtained for the fat globules from a recombined milk emulsion. Electroacoustics gives reasonable estimates of median size and zeta potential but at present is unable to give a true indication of the spread of the distribution.

Gastric emptying of oil from solid and liquid meals. Effect of human pancreatic insufficiency.

Digestion of fat in pancreatic insufficiency (PI) is strongly affected by how rapidly fat enters the duodenum. We postulated that: (1) oil empties faster in PI than in normals and (2) in both, it empties in a load-dependent fashion. We used a gamma camera to test these ideas by comparing gastric emptying of iodine-123 iodinated oil in normal and pancreatic-insufficient subjects after 15 g of free oil were ingested in a small spaghetti meal and 60 g of oil were ingested in a large spaghetti meal and in a milk emulsion. Indium-113m marked gastric emptying of water in the milk. In both groups after all meals, oil emptied fastest initially, slowing later; and oil emptied three to four times faster when 60 g vs 15 g were ingested. There were no significant differences between the groups of subjects with respect to gastric emptying of the spaghetti meals, but the pancreatic-insufficient subjects emptied both oil and water faster from the milk emulsion than did the normal subjects. The slower emptying of oil in the normal subjects was associated with significantly more layering of oil to the top of the intragastric milk emulsion.

Homogenization of milk emulsions:use of microfluidizer

The operating efficiency of a laboratory scale microfluidizer had been compared to that of a high pressure valve homogenizer using either pasteurized whole milk or recombined milk. Microfluidization was found to be a very effective method for reducing fat globule size and was only slightly affected by changes in operating pressure. The back pressure module on the microfluidizer had a marginal effect on particle size increase. As a result, the homogenization effect was always greater than that of conventional homogenization. Only very small amounts of serum protein but high levels of casein were found on fat surfaces after microfluidization. The protein load was higher than predicted on the basis of decreases in globule size. Microfluidization had little effect on the formation of fat clusters in milk. The higher protein load probably inhibited fat clustering.

The role of homogenization in the manufacture of halloumi and mozzarella cheese from recombined milk*

When halloumi and mozzarella cheese are made from normal recombined milk, neither product exhibits the characteristic stretch and melt behaviour of the fresh milk cheeses. The present study demonstrates that this problem may be overcome either by using low homogenization pressures to prepare the recombined milk or by coating the fat in the recombined milk emulsion with phospholipid and homogenizing at the usual pressure. The influence of homogenization of milk on the properties of the cheese is discussed in terms of a polymer network model.

A MECHANISM FOR NON-NEWTONIAN FLOW OF MILK IN A CAPILLARY

The apparent viscosity of human milk, fresh cow's milk, homogenized milk, skim milk and oleic acid emulsion have been determined in a Maron-Belner type low shear capillary viscometer using capillaries of different radii combined with a photomicroscope. Photomicrographs of the flowing fluids have been obtained and analyzed by a densitometer. Each suspension examined showed different apparent viscosities and the viscosities depended also on capillary radius. This capillary radius effect was traced to migration of milk fat droplets during flow through the capillary. By assuming that the wall layer is composed of double layers in a flowing liquid in a capillary tube this radius effect may be attributed to geometric hindrance of the capillary wall against the thermal motion of fat droplets near the wall, Values of the wall thickness were calculated.