This study investigated the changes in sheep milk lipids during in vitro gastrointestinal digestion in response to heat treatment (75°C/15 s and 95°C/5 min) and homogenization (200/50 bar) using lipidomics. Homogenized and pasteurized sheep milk had higher levels of polar lipids in gastric digesta emptied at 20 min than raw sheep milk. Intense heat treatment of homogenized sheep milk resulted in a reduced level of polar lipids compared with homogenized–pasteurized sheep milk. The release rate of free fatty acids during small intestinal digestion for gastric digesta emptied at 20 min followed the order: raw ≤ pasteurized < homogenized–pasteurized ≤ homogenized–heated sheep milk; the rate for gastric digesta emptied at 180 min showed a reverse order. No differences in the lipolysis degree were observed among differently processed sheep milks. These results indicated that processing treatments affect the lipid composition of digesta and the lipolysis rate but not the lipolysis degree during small intestinal digestion.

The effect of milk fat globule (MFG) size and species (sheep versus cow) on the lipid and protein compositions of sheep and cow milks was studied. The MFGs in raw cow and sheep milks were separated into six significantly different-sized (1.5–5.5 μm) groups by a gravity-based separation method, and their fatty acids, their lipidomes and the protein compositions of their MFG membranes were determined. The proportions of polar lipids increased but glycoproteins decreased with decreasing MFG size in both sheep milk and cow milk; the fatty acid composition showed few differences among the MFG groups. The average size of each MFG group was comparable between sheep milk and cow milk. Sheep milk contained higher proportions of short-chain fatty acids, medium-chain fatty acids and sphingomyelin than cow milk in all MFG groups. The proportion of glycoproteins was higher in cow MFG membrane than in sheep MFG membrane. The results suggested that the lipid and protein compositions were markedly species and size dependent.

Plants store triacylglycerols in the form of oil bodies (OBs) as an energy source for germination and subsequent seedling growth. The interfacial biomaterials from these OBs are called OB membrane materials (OBMMs) and have several applications in foods, e.g., as emulsifiers. OBMMs are preferred, compared with their synthetic counterparts, in food applications as emulsifiers because they are natural, i.e., suitable for clean label, and may stabilize bioactive components during storage. This review focuses mainly on the extraction technologies for plant OBMMs, the functionality of these materials, and the interaction of OB membranes with other food components. Different sources of OBs are evaluated and the challenges during the extraction and use of these OBMMs for food applications are addressed.

Sheep's milk proteins are susceptible to heat-induced coagulation, but the protein interactions under high heat treatment have not been determined. Heat stability and protein interactions of sheep's skim milk (SSM) at pH 6.2-7.2 were examined at 140 degrees C. SSM had the longest heat coagulation time at pH 6.9, but became very unstable at higher or lower pH. Protein aggregates formed consisted mainly of whey proteins and K-casein (K-CN)-depleted casein micelles. Modification of SSM pH alters ionic calcium concentration, dissociation of caseins and electrostatic interactions, resulting in different extents of protein interactions. The extent of dissociation of K-CN from casein micelles increased with increasing pH (from-6.6 to 7.0) before and after heat treatment, contributing to K-CN-depleted casein micelle aggre-gation. High ionic calcium concentrations, low levels of K-CN on casein micelles and ready dissociation of K-CN from casein micelles may be responsible for the low heat stability of sheep's milk.(c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Sheep milk is considered unstable to UHT processing, but the instability mechanism has not been investigated. This study assessed the effect of UHT treatment (140°C/5 s) and milk pH values from 6.6 to 7.0 on the physical properties of sheep skim milk (SSM), including heat coagulation time, particle size, sedimentation, ionic calcium level, and changes in protein composition. Significant amounts of sediment were found in UHT-treated SSM at the natural pH (∼6.6) and pH 7.0, whereas lower amounts of sediment were observed at pH values of 6.7 to 6.9. The proteins in the sediment were mainly κ-casein (CN)–depleted casein micelles with low levels of whey proteins regardless of the pH. Both the pH and the ionic calcium level of the SSM at all pH values decreased after UHT treatment. The dissociation levels of κ-, β-, and αS2-CN increased with increasing pH of the SSM before and after heating. The protein content, ionic calcium level, and dissociation level of κ-CN were higher in the SSM than values reported previously in cow skim milk. These differences may contribute to the high amounts of sediment in the UHT-treated SSM at natural pH (∼6.6). Significantly higher levels of κ-, β-, and αS2-CN were detected in the serum phase after heating the SSM at pH 7.0, suggesting that less κ-CN was attached to the casein micelles and that more internal structures of the casein micelles may have been exposed during heating. This could, in turn, have destabilized the casein micelles, resulting in the formation of protein aggregates and high amounts of sediment after UHT treatment of the SSM at pH 7.0.

During gastric digestion, bovine milk forms a curd, which consists largely of proteins and lipids. However, it is unknown how processing-induced changes to curd structure affects the gastric emptying of milk proteins and lipids. This study aimed to determine the impact of heat treatment and homogenization on gastric curd for-mation, and gastric emptying of dry matter (DM), proteins and lipids from bovine milk fed to pigs as a human model. Growing pigs (n = 180, mean +/- standard error of the mean (SEM) bodyweight 22.4 +/- 0.13 kg) consumed raw, or pasteurized non-homogenized (PNH), or pasteurized homogenized (PH), or ultra-high temperature treated homogenized (UHT) milk diets. A protein-lipid-free lactose (PLFL) solution was also fed as a test diet. At 0, 20, 60, 120, 180 and 300 min postprandially the entire gastrointestinal tract was dissected out. The gastric chyme (curd and liquid) fractions were collected after separation using a mesh screen. The DM, protein, and lipid contents of these fractions were quantified. Confocal, transmission electron microscopy, cryo-scanning electron microscopy and rheological analyses were conducted to determine the micro-and macrostructure of the curd. Overall, both heat treatment and homogenization influenced the in vivo gastric curd structure formed of bovine milk, although to different extents. The gastric emptying of DM, proteins, and lipids increased with the extent of processing. Gastric emptying rates of DM and proteins followed the pattern UHT > PH > PNH = raw, while emptying rates of lipid also differed between PNH and raw milk. Curd structure was the main gastric parameter affected in PNH milk.

In an increasingly diversified global market, milk of minor dairy species has gained interest as a novel and premium source of nutrition. Relative to the major dairy species, much is lacking in our understanding of red deer (Cervus elaphus) milk. In this study, we characterized the compositions (macronutrients, minerals, fatty acids, and proteins) of red deer milk and their variations throughout lactation. We also investigated the structures, physical properties, and gelation (acid- and rennet-induced) properties of deer milk and how they are impacted by typical processing treatments (e.g., homogenization and pasteurization). We identified unique features in the composition of deer milk, including being richer in protein, fat, calcium, zinc, iodine, branched-chain fatty acids, and α-linolenic acid than other ruminant milks. Different deer milk components displayed diverse variation patterns over the lactation cycle, many of which were different from those demonstrated in other ruminant species. Other physicochemical features of deer milk were identified, such as its markedly larger fat globules. Processing treatments were demonstrated to alter the structural and gelation properties of deer milk. Most of the gelation properties of deer milk resembled that of bovine milk more than ovine and caprine milks. This study furthers our understanding of red deer milk and will aid in its processing and applications in novel products.

Gelation is an important functional property of milk that enables the manufacture of various dairy products. This study investigated the acid (with glucono-δ-lactone) and rennet gelation properties of differently processed sheep, goat, and cow milks using small-amplitude oscillatory rheological tests. The impacts of ruminant species, milk processing (homogenization and heat treatments), seasonality, and their interactions were studied. Acid gelation properties were improved (higher gelation pH, shorter gelation time, and higher storage modulus (G') by intense heat treatment (95°C for 5 min) to comparable extents for sheep and cow milks, both better than those for goat milk. Goat milk produced weak acid gels with low G' (<100 Pa) despite improvements induced by heat treatments. Seasonality had a marked impact on the acid gelation properties of sheep milk. The acid gels of late-season sheep milk had a lower gelation pH, no maximum in tan δ following gel formation, and 70% lower G' values than those from other seasons. We propose the potential key role of a critical acid gelation pH that induces structural rearrangements in determining the viscoelastic properties of the final gels. For rennet-induced gelation, compared with cow milk, the processing treatments of the goat and sheep milks had much smaller impacts on their gelation properties. Intense heat treatment (95°C for 5 min) prolonged the rennet gelation time of homogenized cow milk by 8.6 min (74% increase) and reduced the G' of the rennet gels by 81 Pa (85% decrease). For sheep and goat milks, the same treatment altered the rennet gelation time by only less than 3 min and the G' of the rennet gels by less than 14 Pa. This difference may have been caused by the different physicochemical properties of the milks, such as differences in their colloidal stability, proportion of serum-phase caseins, and ionic calcium concentration. The seasonal variations in the gelation properties (both acid and rennet induced) of goat milk could be explained by the minor variation in its protein and fat contents. This study provides new perspectives and understandings of milk gelation by demonstrating the interactive effects among ruminant species, processing, and seasonality.

In recent years, plant-based milk alternatives have become increasingly desirable because of their sustainability and proposed health benefits. There is a need to understand the behavior of plant-based milks during gastric digestion, including protein digestibility, structural changes, and macronutrient accessibility. The aim of this study was to investigate the gastric digestive behaviors of oat milk and an oat milk‒bovine skim milk blend (1:1, v/v), using an in vitro dynamic human gastric simulator. During gastric digestion with pepsin, the oat milk did not show significant changes in structure and physical stability. In contrast, the oat milk‒bovine skim milk blend formed coagulated, curd-like particles, which were induced by the action of pepsin on the milk proteins. The oat oil bodies were incorporated into the curd particles. This difference in gastric digestive behavior significantly altered the rate of gastric emptying. Coagulation of the oat milk‒bovine skim milk blend slowed the gastric emptying of macronutrients, leading to a delay in the release of protein and lipids into the small intestine compared with the oat milk. This study provides insight into the way the food structure modification during gastric digestion impacts nutrient delivery.

Substitution of commercial milk powders by fluid milk concentrates as ingredients in dairy products, may improve product quality and increase sustainability. This study compared the functional properties of skim milk concentrates made by reverse osmosis (SMC) with standard reconstituted high- and low-heat skim milk powders (POW-SMC). SMC had larger Z-average size values, higher viscosities, wider particle size distributions and lower extent of whey protein denaturation than POW-SMC. During storage, SMC showed no acid-induced gelation, but improved rennet-induced gelation compared with POW-SMC. Emulsification activity improved at 20 compared with 10% solids in all concentrates, while emulsion stability was lowest for SMC. Better foaming was observed for high-heat POW-SMC, except after 30 days, where SMC showed highest overrun. In certain dairy products, SMC can thus replace commercial powders to reduce processing costs and improve functionality. SMC showed to be especially advantageous for rennet-gelled products.

Ruminant milks coagulate during gastric digestion, which plays an important role in controlling digestion kinetics. Previous studies on cow milk showed that the structural and rheological properties of the clots formed in the gastric environment affect their breakdown and consequently their emptying rate into the intestine. This study investigated the impacts of homogenisation and heat treatment on the structural and rheological properties of the clots formed by sheep, goat and cow milks during simulated dynamic gastric digestion, with empasis on the non-bovine milks. Overall, with increasing intensity of processing, the gastric clots formed by ruminant milk became more fragmented, contained more moisture and had lower consistency. The consistency of the clots appeared to be associated with the presence of colloidal calcium phosphate in the casein micelles and the moisture content of the clot. A structural rearrangement of the clots may occur during the early stages of digestion because the forces maintaining the clot network change as the pH decreased. Between different species, we observed different impacts of individual processing treatments on the macrostructure and the consistency of the clots. Homogenisation had greater impacts on goat and sheep milk clots than cow milk clots whereas heat treatment (95 degrees C for 5 min) had the most effect on homogenised cow milk clots. Differences in the physicochemical properties of the ruminant milks, e.g. casein micelle size and ionic calcium concentration, may have been responsible for the variations observed between species. This study furthered our understanding of the gastric coagulation of ruminant milk and highlighted the species-specific processing impacts (processing x species interactions) on the structural and rheological properties of gastric milk clots.

The interactions among the proteins in sheep skim milk (SSM) during heat treatments (67.5-90°C for 0.5-30 min) were characterized by the kinetics of the denaturation of the whey proteins and of the association of the denatured whey proteins with casein micelles, and changes in the size and structure of casein micelles. The relationship between the size of the casein micelles and the association of whey proteins with the casein micelles is discussed. The level of denaturation and association with the casein micelles for β-lactoglobulin (β-LG) and α-lactalbumin (α-LA) increased with increasing heating temperature and time; the rates of denaturation and association with the casein micelles were markedly higher for β-LG than for α-LA in the temperature range 80 to 90°C; the Arrhenius critical temperature was 80°C for the denaturation of both β-LG and α-LA. The casein micelle size increased by 7 to 120 nm, depending on the heating temperature and the holding time. For instance, the micelle size (about 293 nm) of SSM heated at 90°C for 30 min increased by about 70% compared with that (about 174.6 nm) of unheated SSM. The casein micelle size increased slowly by a maximum of about 65 nm until the level of association of the denatured whey proteins with casein micelles reached 95%, and then increased markedly by a maximum of about 120 nm when the association level was greater than about 95%. The marked increases in casein micelle size in heated SSM were due to aggregation of the casein micelles. Aggregation of the casein micelles and association of whey protein with the micelles occurred simultaneously in SSM during heating.

There has been growing consumer interest in sheep and goat milk products as alternatives to cow milk products. The physicochemical characteristics of milk vary not only between ruminant species, but also during different seasons; they determine the nutritional quality and processing properties of the milk. In this study, we characterized sheep and goat milks from New Zealand over the seasons for their composition (macronutrients, macro- and micro-minerals, fatty acids, and proteins) and physicochemical properties (e.g., ionic calcium, fat globule size, casein micelle size, viscosity, and melting behavior of milk fat). Heat-induced (95 °C for 5 min) protein interactions and changes in the physical properties of the milks were also investigated. The compositional and structural features of sheep and goat milks were identified and compared with those reported for cow milk. Seasonal variations in the milk characteristics were more pronounced for sheep milk than goat milk and were probably affected by the production systems. Sheep milk, particularly in the late season, had the largest heat-induced increases in casein micelle size and viscosity, probably arising from the greater casein–whey protein and casein–casein interactions during heat treatment. This study provides comprehensive information on the properties of sheep and goat milks and highlights the interaction effects between species, season, and processing.

This study investigated the structural and physicochemical changes that occur in milk, a naturally designed complex structured emulsion, during gastric digestion using the bottle-fed piglet as an animal model. The gastric digestions of cow, goat, and sheep milk were compared in male piglets euthanized at different postfeeding times to collect the stomach chyme. The cow and noncow milks separated into curd (aggregated caseins) and liquid (mostly soluble whey) phases in the piglet's stomach. For milk from all the species, the curd remained longer in the stomach because of its slow disintegration, whereas the liquid phase emptied readily. The majority of the fat globules were found to be entrapped within the protein network of the curd. The rate of release of fat globules was strongly dependent on the breakdown of the surrounding protein network of the curd. The consistency of the gastric curds changed as digestion progressed, with goat and sheep milk curds having relatively softer curd consistency and less fused protein networks, especially toward the end of digestion. This might have led to the lower protein and fat retention in the goat and sheep milk curds and relatively faster gastric emptying of these nutrients from goat and sheep milk in comparison to cow milk. This in vivo study provided new and enhanced understanding of the mechanisms of the gastric digestion of milk from different species. It may have implications for developing bioinspired structures for the controlled digestion and delivery of nutrients.

Plant-based beverages (PBB) are often marketed and used by consumers as alternatives to ruminant milks, particularly bovine milk (hereafter referred to as milk). However, much research has established that there is variation in nutritional composition among these products, as well as demonstrating that they are largely not nutritional replacements for milk. A survey of the prices and nutrition labels of PBB available in New Zealand supermarkets was undertaken. Selected almond, coconut, oat, rice, and soy PBB products were then analyzed for nutritional content, including energy, fat, protein, amino acid, bioavailable amino acid, and trace element contents. Finally, the protein and calcium contents of well-mixed and unshaken products were analyzed to ascertain the impact of colloidal stability on nutrient content. All PBB groups were more expensive than milk on average, while their declared nutrient contents on package labels was highly variable within and between groups. Analyses of selected PBB revealed that soy products had the most similar proximate composition to milk, while all other PBB groups contained less than 1.1 g protein per 100 mL on average. Many PBB were fortified with calcium to a similar concentration as that in milk. Shaken and unshaken samples showed divergent protein and calcium content for several PBB products but had no effect on the composition of milk, indicating that the nutrient content of PBB at the point of consumption will be dependent on whether the product has been shaken. Only the soy PBB had comparable amino acid content and bioavailability to milk. Overall, our results demonstrate the diversity in composition and nutritional properties of PBB available in New Zealand. While the existent environmental footprint data on PBB shows that they generally have lower carbon emissions than milk, milk currently accounts for approximately 1% of the average New Zealand resident’s consumption-based emissions. Except for calcium-fortified soy PBB, none of the commercially available PBB had nutritional compositions that were broadly comparable to milk.

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.

International Journal of Dairy TechnologyVolume 74, Issue 4 p. 627-628 Editorial Structure of milk and milk products – A need of present era Anant Dave, Anant DaveSearch for more papers by this authorBhavbhuti M. Mehta, Corresponding Author Bhavbhuti M. Mehta bhavbhuti5@yahoo.co.in Search for more papers by this author Anant Dave, Anant DaveSearch for more papers by this authorBhavbhuti M. Mehta, Corresponding Author Bhavbhuti M. Mehta bhavbhuti5@yahoo.co.in Search for more papers by this author First published: 25 October 2021 https://doi.org/10.1111/1471-0307.12824Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume74, Issue4November 2021Pages 627-628 RelatedInformation

The natural structure of whole food plays an important role in the physiological impact of bioactive compounds present within the food, also known as the "matrix effect". Long-chain omega-3 polyunsaturated fatty acids (LCn-3PUFAs) are one example of a food-derived nutrient, mostly found in fish, that is believed to be influenced by the food matrix. However, most previous studies have compared only the long-term bioavailability of fish versus fish oil and have used commercial sources of fish oil. The present study aimed to investigate whether fish (salmon) matrix influences the transit of LCn-3PUFAs during in vitro digestion and affects bioavailability in healthy females. Meals containing intact salmon (intact structure), minced salmon (some structure) and defatted salmon + oil (no structure) with identical macronutrient compositions were developed. Healthy female participants (n = 13) consumed the meals in a postprandial crossover study and blood was collected at regular time points for 6 h post meal consumption. In parallel, in vitro digestion of the meals was performed using a human gastric simulator (HGS) and digesta samples were collected at regular time points for 6 h. Results: showed that plasma concentration of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were significantly higher after participants consumed intact salmon compared to the other meals (covariate analysis p < 0.001). The in vitro digestion results showed defatted salmon + oil meal had a faster decrease in pH and faster fat emptying from the HGS than the other two meals. The defatted salmon + oil meal more closely followed fat emptying of a homogeneous unstructured meal, whereas the other meals exhibited phase separation with a delay in fat emptying. Conclusion: The fish matrix (salmon) plays an important role in the bioaccessibility and bioavailability of EPA and DHA. The differences are partly explained by fat digestion and emptying from the stomach. This study suggests that the natural structure of fish has a functional effect on the absorption and bioavailability of fish oil.

The structural and physicochemical characteristics of oil bodies from hemp seeds were explored in this study. Oil bodies from several plant-based sources have been previously studied; however, this is the first time a characterisation of oil bodies from the seeds of industrial hemp is provided. The morphology of oil bodies in hemp seeds and after extraction was investigated using cryo-scanning electron microscopy (cryo-SEM), and the interfacial characteristics of isolated oil bodies were studied by confocal laser scanning microscopy (CLSM). Proteins associated with oil bodies were characterised using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The effect of pH and ionic strength on colloidal properties of the oil bodies was investigated. Oil bodies in hemp seeds appeared spherical and sporadically distributed in the cell, with diameters of 3 to 5 μm. CLSM images of isolated oil bodies revealed the uniform distribution of phospholipids and proteins at their interface. Polyunsaturated fatty acids were predominant in the lipid fraction and linoleic acid accounted for ≈61% of the total fatty acids. The SDS-PAGE analysis of washed and purified oil bodies revealed major bands at 15 kDa and 50–25 kDa, which could be linked to membrane-specific proteins of oil bodies or extraneous proteins. The colloidal stability of oil bodies in different pH environments indicated that the isoelectric point was between pH 4 and 4.5, where oil bodies experienced maximum aggregation. Changes in the ionic strength decreased the interfacial charge density of oil bodies (ζ-potential), but it did not affect their mean particle size. This suggested that the steric hindrance provided by membrane-specific proteins at the interface of the oil bodies could have prevented them from flocculation at low interfacial charge density. The results of this study provide new tertiary knowledge on the structure, composition, and colloidal properties of oil bodies extracted from hemp seeds, which could be used as natural emulsions or lipid-based delivery systems for food products.