Changes in the surface protein of the fat globules during homogenization and heat treatment of concentrated milk

Effect of processing methods on the distribution of mineral elements in goat milk fractions

Milk and dairy products are excellent sources of mineral elements, including Ca, P, Mg, Na, K, and Zn. The purpose of this study was to determine the effect of nonthermal (homogenization) and thermal (heat treatment) treatments on the distribution of mineral elements in 4 milk fractions: fat, casein, whey protein, and aqueous phase. The study results revealed that the distribution of mineral elements (such as Mg and Fe) in fat fractions is extremely low, whereas significant mineral elements such as Ca, Zn, Fe, and Cu are mostly dispersed in casein fractions. For nontreated goat milk, Mo is the only element identified in the whey protein fraction, whereas K and Na are mostly found in the aqueous phase. Mineral element concentrations in fat (K, Zn, and so on) and casein fractions (Fe, Mo, and so on) increased dramatically after homogenization. Homogenization greatly decreased the concentration of mineral elements in the whey protein fraction (Ca, Na, and so on) and aqueous phase (Fe, Cu, and so on). After heat treatment, the element content in the fat fraction and casein fraction increased greatly when compared with raw milk, such as Cu and Mg in the fat fraction, Na and Cu in the whey protein fraction, the concentration of components such as Mg and Na in casein fraction increased considerably. In contrast, after homogenization, Zn in the aqueous phase decreased substantially, whereas Fe increased significantly. Therefore, both homogenization and heat treatment have an effect on the mineral element distribution in goat milk fractions.

Microwave vacuum drying of dairy cream: Processing, reconstitution, and whipping properties of a novel dairy product

Traditional ways to preserve cream involve processing it into butter, butter oil, or frozen storage. These technologies do not preserve the unique functionality of cream with respect to whipping or processing into butter. In this work, microwave vacuum drying (MVD) was investigated as a method to manufacture dehydrated cream. Dehydrated cream microstructure, color, and free fat were evaluated using scanning electron microscopy, colorimetry, and solvent extraction, respectively. Effects of homogenization on reconstituted cream microstructure and functionality were investigated using confocal laser scanning microscopy, color, particle sizing, and texture analysis of whipped cream. Reconstituted MVD cream whipped faster, and the whipped cream was more cohesive and firmer when 2-step homogenization at 3.5/7 MPa was used. Fat globules in reconstituted MVD cream were covered by phospholipids, explaining MVD cream's similar functionality compared with pasteurized cream. These results may foster the development of novel shelf stable and highly functional dairy products using MVD.

Composition and interfacial properties play key roles in different lipid digestion between goat and cow milk fat globules in vitro

The different TAG, interfacial properties and digestion rate between goat and cow milk fat globules were investigated. The mechanism of their different lipid digestion was also elucidated. Raw goat milk fat globules had smaller size, less large molecular weight and unsaturated TAG, larger liquid-ordered region and fewer glycoproteins, which contributed to the higher digestion rate than cow milk. After homogenization, the goat lipids also had higher digestion rate that was attributed to the special structure of easy-to-digest TAG and less glycosylated molecules not globule size. More integrated phospholipid layers and glycosylated molecules of HTST milk fat globules resulted in a lower lipid digestion rate than other processed milks. No difference in digestion rate between pasteurized goat and cow milk fat globules might be explained by the more denatured proteins and glycosylated molecules, respectively. Therefore, the TAG and interfacial properties contributed to different digestion between goat and cow milk fat globules.

Dynamic In Vitro Gastric Digestion of Sheep Milk: Influence of Homogenization and Heat Treatment

Milk is commonly exposed to processing including homogenization and thermal treatment before consumption, and this processing could have an impact on its digestion behavior in the stomach. In this study, we investigated the in vitro gastric digestion behavior of differently processed sheep milks. The samples were raw, pasteurized (75 °C/15 s), homogenized (200/20 bar at 65 °C)-pasteurized, and homogenized-heated (95 °C/5 min) milks. The digestion was performed using a dynamic in vitro gastric digestion system, the human gastric simulator with simulated gastric fluid without gastric lipase. The pH, structure, and composition of the milks in the stomach and the emptied digesta, and the rate of protein hydrolysis were examined. Curds formed from homogenized and heated milk had much looser and more fragmented structures than those formed from unhomogenized milk; this accelerated the curd breakdown, protein digestion and promoted the release of protein, fat, and calcium from the curds into the digesta. Coalescence and flocculation of fat globules were observed during gastric digestion, and most of the fat globules were incorporated into the emptied protein/peptide particles in the homogenized milks. The study provides a better understanding of the gastric emptying and digestion of processed sheep milk under in vitro gastric conditions.

An Integrative Approach of an In Vitro Measurement of the Digestibility of Triacylglycerols of Human Milk

Several studies have been published regarding the effect of different factors on the digestion of milk lipids, considering their natural structural arrangement as milk fat globules and the efficiency of the digestive enzymes in the lipolysis of such complex structures. During digestion, the lipolytic products are dispersed in vesicles and micelles, which are the source for absorption of digested lipids. Therefore, it is necessary to consider the isolation of the micellar phase from the digesta to appropriately determine the amounts and classes of lipids which are bioaccessible. This study presents an integrative approach that included an isolation procedure to separate the micellar fraction from undigested and non-micellar parts, and the distribution of digested milk lipids in micelles determined directly through chromatographic techniques. Four groups of five full term mothers donated colostrum or mature milk. Two sets of samples were analyzed directly (raw), and two sets were pasteurized and then analyzed. Our data revealed that the profile of digested milk lipids is different depending on the lactation period and processing stage, while the carbon atom number distribution of the digested triacylglycerols in the micellar fraction provides a substantial information regarding the acylglycerols species that are less available for absorption.

Coagulation behaviour of milk under gastric digestion: Effect of pasteurization and ultra-high temperature treatment

The digestion behaviours of pasteurized and UHT homogenized milks were investigated in in vivo rat stomach and in an in vitro dynamic human gastric simulator. The formation of coagulum under gastric conditions and the protein digestion profiles were similar in both systems. UHT milk formed curds with fragmented and crumbled structures, compared with the more cohesive curds formed from unheated or pasteurized milk. UHT milk had faster rates of protein hydrolysis and of the release of fat globules during digestion. These results are attributed to the differences in the structures of the curds formed from the samples with different treatments. The fragmented and crumbled structure of the curds obtained from UHT milk was probably the result of β-lactoglobulin binding with casein micelles during processing, which sterically hindered aggregation of the casein micelles under gastric conditions. This study provides knowledge for understanding the gastric emptying and digestion of processed consumer milk.

Milk fat globules and associated membranes: Colloidal properties and processing effects

The composition and physical-chemical properties of the milk fat globule membrane (MFGM) is a subject that has gained increased interest in the field of food colloids, mainly because the nutritional and technological value of the MFGM. In fact, related changes in integrity and structure during milk processing pose a huge challenge as far as efforts directed to isolate the components of the fat globule membrane. MFGM characteristics and potential utilization are subjects of dissension. Thus, the effects of processing and the colloidal interactions that exist with other milk constituents need to be better understood in order to exploit milk fat and MFGM, their functionality as colloids as well as those of their components. These are the main subjects of this review, which also reports on the results of recent inquiries into MFGM structure and colloidal behavior.

Oil-in-water emulsion system stabilized by protein-coated nanoemulsion droplets

Nanoemulsion droplets (average size of about 150 nm) coated with micellar casein were used as an emulsifying agent to stabilize oil (n-hexadecane)-in-water emulsions. We found that these nanodroplets adsorbed at the oil-water interface and formed stable emulsions, with the size of the droplet-stabilized emulsions being dependent on the concentration of nanodroplets in the dispersions. Stable emulsions were still formed at low concentrations, even though the interface was not fully covered by the nanodroplets. The nanodroplets fully covered the interface at higher concentrations, resulting in a transition from a thick interfacial layer to a multilayer containing a network of assembled nanodroplets. Because of their soft and elastic nature, the adsorbed nanodroplets showed strong deformation at the oil-water interface. The morphology of the interfacial nanodroplets was dependent on their location inside the network interfacial layer. The adsorption and deformation of the droplets at the oil-water interface and the formation of network structures, as observed in the present study, provide new, useful fundamental knowledge with potential applications for microencapsulation and emulsion stabilization.

Multiscale structures of lipids in foods as parameters affecting fatty acid bioavailability and lipid metabolism

On a nutritional standpoint, lipids are now being studied beyond their energy content and fatty acid (FA) profiles. Dietary FA are building blocks of a huge diversity of more complex molecules such as triacylglycerols (TAG) and phospholipids (PL), themselves organised in supramolecular structures presenting different thermal behaviours. They are generally embedded in complex food matrixes. Recent reports have revealed that molecular and supramolecular structures of lipids and their liquid or solid state at the body temperature influence both the digestibility and metabolism of dietary FA. The aim of the present review is to highlight recent knowledge on the impact on FA digestion, absorption and metabolism of: (i) the intramolecular structure of TAG; (ii) the nature of the lipid molecules carrying FA; (iii) the supramolecular organization and physical state of lipids in native and formulated food products and (iv) the food matrix. Further work should be accomplished now to obtain a more reliable body of evidence and integrate these data in future dietary recommendations. Additionally, innovative lipid formulations in which the health beneficial effects of either native or recomposed structures of lipids will be taken into account can be foreseen.

Redox proteomics of fat globules unveils broad protein lactosylation and compositional changes in milk samples subjected to various technological procedures

The Maillard reaction between lactose and proteins occurs during thermal treatment of milk and lactosylated β-lactoglobulin, α-lactalbumin and caseins have widely been used to monitor the quality of dairy products. We recently demonstrated that a number of other whey milk proteins essential for nutrient delivery, defense against bacteria/virus and cellular proliferation become lactosylated during milk processing. The extent of their modification is associated with the harshness of product manufacturing. Since fat globule proteins are also highly important for the health-beneficial properties of milk, an evaluation of their lactosylation is crucial for a complete understanding of aliment nutritional characteristics. This is more important when milk is the unique dietary source, as in the infant diet. To this purpose, a sequential proteomic procedure involving an optimized milk fat globule (MFG) preparation/electrophoretic resolution, shot-gun analysis of gel portions for protein identification, selective trapping of lactosylated peptides by phenylboronate chromatography and their analysis by nanoLC-ESI-electron transfer dissociation (ETD) tandem MS was used for systematic characterization of fat globule proteins in milk samples subjected to various manufacturing procedures. Significant MFG protein compositional changes were observed between samples, highlighting the progressive adsorption of caseins and whey proteins on the fat globule surface as result of the technological process used. A significant lactosylation of MFG proteins was observed in ultra-high temperature sterilized and powdered for infant nutrition milk preparations, which well paralleled with the harshness of thermal treatment. Globally, this study allowed the identification of novel 157 non-redundant modification sites and 35 MFG proteins never reported so far as being lactosylated, in addition to the 153 ones ascertained here as present on other 21 MFG-adsorbed proteins whose nature was already characterized. Novel MFG proteins include components involved in nutrient delivery, defense response against pathogens and cellular proliferation/differentiation. Nutritional, biological and toxicological consequences of these findings are here discussed, highlighting their possible impact on children's diet.