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Innovative processing technologies, such as ultrasonication, can change the properties of milk, allowing for the improvement or development of dairy foods. Yet taking bench-scale equipment to pilot plant scale has been challenging. Raw milk, standardized to 3% fat and warmed to inlet temperatures of 42 or 54°C, was exposed to continuous, high-intensity, low-frequency ultrasonication (16/20 kHz, 1.36 kW/pass) at flow rates of 0.15, 0.30, and 0.45 L/min that resulted in resident times within the reaction cell of 6, 3, and 2 min per pass, respectively. Multiple passes (3, 5, and 7, respectively) were required to obtain a total exposure time of 14 to 18 min. Evaluation of fat droplet sizes, enzyme coagulation properties, and microstructure of milk and milk gels, as well as determining compositional and lipid properties, were conducted to determine the potential of the ultrasound system to effectively modify milk. Laser scanning particle sizing and confocal microscopy showed that the largest droplets (2.26 ± 0.13 µm) found in raw milk were selectively reduced in size with a concomitant increase in the number of submicron droplets (0.37 ± 0.06 µm), which occurred sooner when exposed to shorter bursts of ultrasonication (0.45 L/min flow rates) and at an inlet temperature of 54°C. Ultrasound processing with milk entering at 42°C resulted in faster gelling times and firmer curds at 30 min; however, extended processing at inlet temperature of 54°C reduced curd firmness and lengthened coagulation time. This showed that ultrasonication altered protein-protein and protein-lipid interactions, thus the strength of the enzyme-set curds. Scanning electron microscopy revealed a denser curd matrix with less continuous and more irregular shaped and clustered strands, whereas transmission electron microscopy showed submicron lipid droplets embedded within the protein strands of the curd matrix. Processing at inlet temperature of 54°C with flow rates of 0.30 and 0.45 L/min also reduced the total aerobic bacterial count by more than 1 log cfu/mL, and the number of psychrophiles below the limit of detection (10 cfu/mL) for this study. Ultrasonication exposures of 14 to 18 min had minimal effect on the milk composition, fatty acid profiles, and lipid heat capacity and enthalpy. The findings show that this continuous ultrasound system, which is conducive to commercial scale-up, modifies the physical and functional properties of milk under the parameters used in this study and has potential use in dairy processing., (Copyright © 2019 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Feeding livestock with n-3 fatty acid (FA) sources (linseed, for example) is a common strategy to improve lipid quality of meat and milk products. However, in monogastric animals, linseed tegument decreases digestibility and alphalinolenic acid (ALA) uptake, while the whole linseed is well used by ruminants. In a context of increasing sustainability of feeding systems, providing monogastric animals and ruminants with linseed products adapted to their digestive systems is an important issue. This research paper addresses the hypotheses: (i) sieved extruded linseed (SEL) specific for ruminants is as or more effective than standard extruded linseed (ii) microalgae DHA Gold® is an interesting source of docosahexaenoic acid (DHA) in feedstuff and (iii) the effects of SEL and microalgae on milk characteristics are complementary and additive. Thirty-two cows were divided into 4 groups with different dietary n-3 fatty acid sources using a continuous design. All the diets were fed as mixed rations based on maize silage, energy concentrate and soybean meal. The first group received a control diet (CTRL) with no additional fat. The 3 other groups received SEL, microalgae DHA Gold® (ALG) and a mixture of microalgae DHA Gold® and SEL (SEL/ALG). Milk was collected from morning milkings after six weeks of dietary treatment. In SEL and SEL/ALG, ALA increased (+0·32 and +0·26% unit, respectively), and DHA increased in ALG and SEL/ALG (+0·43 and +0·15% unit, respectively) compared to CTRL, as a consequence of the initial composition of the n-3 FA sources. In SEL, milk yield, fat and protein contents, milk fat globule size and spontaneous lipolysis (measured to evaluate suitability for milk processing) were not different compared with CTRL. In ALG and SEL/ALG, milk yield decreased (-2·8 and -6·0 kg/d, respectively), fat content was halved, and fat globule size was reduced (-1·46 and -1·31 µm, respectively) compared to CTRL. Spontaneous lipolysis increased in ALG (+0·12 mEq/kg of milk) compared to CTRL. Protected microalgae and the doses of microalgae in the diet need further investigation to prevent FA modification in the rumen and the consequent deleterious effects on milk fat.

The impact of washing on the release of proteins from the milk fat globule membrane (MFGM) was examined by applying washing procedures with different degrees of stringency to milk fat globule (MFG) surfaces in simulated milk ultrafiltrate buffer solution. Three washing methods, M1 (3000g, 5 min, three washes), M2 (3750g, 15 min, one wash), and M3 (15000g, 20 min, three washes) were chosen. MFG ζ-potential increased after M3 washing (P < 0.05), suggesting surface damage. For M1, in which the native MFG surface was least damaged, cluster of differentiation 36 (CD 36) and periodic acid schiff 6/7 proteins were more strongly bound to the MFGM compared with other major membrane proteins. For M3, CD 36 together with fatty acid-binding protein was more strongly bound to the MFGM. Washing by centrifugation and redispersal of the fat globules damaged the MFGM, with release into the aqueous phase of some membrane-associated proteins. The current results show the impact of washing processes on retention of functional MFGM proteins.

Confocal laser scanning microscopy (CLSM) was successfully used to observe the effect of milk processing on the size and the morphology of the milk fat globule in raw milk, raw ultrafiltered milk, and standardized and pasteurized milk prepared for cheese manufacture (cheese-milk) and commercial pasteurized and homogenized milk. Fat globule size distributions for the milk preparations were analyzed using both image analysis and light scattering and both measurements produced similar data trends. Changes to the native milk fat globule membrane (MFGM) were tracked using a MFGM specific fluorescent stain that allowed MFGM proteins and adsorbed proteins to be differentiated on the fat globule surface. Sodium dodecyl sulfate polyacrylamide gel electrophoresis confirmed the identity of native MFGM proteins isolated from the surface of fat globules within raw, UF retentate, and cheese-milk preparations, whereas only casein was detected on the surface of fat globules in homogenized milk. The microstructure, porosity, and gel strength of the rennet induced gel made from raw milk and cheese-milk was also found to be comparable and significantly different to that made from homogenized milk. Our results highlight the potential use of CLSM as a tool to observe the structural details of the fat globule and associated membrane close to its native environment.

We present an extensive description and analysis of a microfiltration process patented in our laboratory to separate different fractions of the initial milk fat globule population according to the size of the native milk fat globules (MFG). We used nominal membrane pore sizes of 2 to 12 microm and a specially designed pilot rig. Using this process with whole milk [whose MFG have a volume mean diameter (d43) = 4.2 +/- 0.2 microm] and appropriate membrane pore size and hydrodynamic conditions, we collected 2 extremes of the initial milk fat globule distribution consisting of 1) a retentate containing large MFG of d43 = 5 to 7.5 microm (with up to 250 g/kg of fat, up to 35% of initial milk fat, and up to 10% of initial milk volume), and 2) a permeate containing small MFG of d43 = 0.9 to 3.3 microm (with up to 16 g/kg of fat, up to 30% of initial milk fat, and up to 83% of initial milk volume and devoid of somatic cells). We checked that the process did not mechanically damage the MFG by measuring their zeta-potential. This new microfiltration process, avoiding milk aging, appears to be more efficient than gravity separation in selecting native MFG of different sizes. As we summarize from previous and new results showing that the physico-chemical and technological properties of native milk fat globules vary according to their size, the use of different fat globule fractions appears to be advantageous regarding the quality of cheeses and can lead to new dairy products with adapted properties (sensory, functional, and perhaps nutritional).

A novel method for the separation of milk-fat globule membrane (MFGM) isolate by microfiltration in the presence of citrate was applied to prepare a fraction to be used to stabilize oil-in-water emulsions. The emulsifying properties of this fraction, containing high amounts of MFGM, were compared with a buttermilk concentrate (BMC) prepared in a similar manner but still containing the original ratio of proteins (caseins, whey proteins, and MFGM). The objective of this work was to determine if the isolation procedure would result in an ingredient with different functionality when compared with BMC. These fractions were incorporated into oil-in-water emulsions at various isolate and oil concentrations. At low concentrations of isolate, MFGM emulsions showed better creaming stability and smaller oil droplet size distribution than whole buttermilk concentrate samples. The difference in stability was attributed to the compositional difference between the 2 ingredients prepared. A selective concentration of MFGM in buttermilk by microfiltration has the potential for the development of ingredients that differ substantially from the ingredients deriving from milk or whey.

Mozzarella cheese was manufactured from milk containing either a low (olein) or a high (stearin) melting point fraction of milk fat or anhydrous milk fat. The fat was dispersed into skim milk by homogenization at 2.6 MPa before being manufactured into cheese. The melting point of the milk fat did not affect the size or shape of the fat globules, nor was there any effect of homogenization on the polymorphic state of the milk fat. There were no changes in milk fat globule size and shape concomitant with the amount of free oil formed. The polymorphic state of the milk fat did affect the amount of free oil formed and the apparent viscosity of the cheese. The lower melting point fraction yielded a larger amount of free oil. The higher melting point fraction yielded a higher viscosity of melted cheese at 60 degrees C. Mozzarella cheese was also manufactured from homogenized milk, nonhomogenized milk, and a 1:1 ratio of the two, without altering the milk fat composition. Increasing the proportion of homogenized milk yielded a lower free oil content and higher viscosity of the cheese.