Massey Research Online - Browsing by Author "Ye A"

Browsing by Author "Ye A"

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Acid and rennet gelation properties of sheep, goat, and cow milks: Effects of processing and seasonal variation
(Elsevier Inc on behalf of the American Dairy Science Association, 2023-03) Li S; Delger M; Dave A; Singh H; Ye A
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.
Characteristics of Red Deer (Cervus elaphus) Milk: Lactational Changes in Composition and Processing Impacts on Structural and Gelation Properties
(MDPI (Basel, Switzerland), 2023-04-03) Li S; Saharawat A; Ye A; Dave A; Singh H; Zhou P; Miao S
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.
Characterizations of emulsion gel formed with the mixture of whey and soy protein and its protein digestion under in vitro gastric conditions
(Elsevier B V, 2024-01-06) Cheng Y; Ye A; Singh H; Marangoni AG
Partially replacing animal proteins with plant proteins to develop new products has much attention. To get knowledge of their application in emulsion gels, heat-induced composite protein emulsion gels were fabricated using the mixtures of whey protein isolate (WPI) and soy protein isolate (SPI) with the final total protein concentration of 10% (w/w). The water holding capacity (WHC), mechanical and rheological properties and microstructure of mixed protein emulsion gels prepared at different WPI to SPI ratios (100:0, 90:10, 70:30, 50:50, 30:70, 10:90, 0:100, w/w) were investigated. The ratios of WPI to SPI showed little effect on the WHC of the mixed protein emulsion gels (p > 0.05). Increasing the ratio of SPI decreased the hardness and storage modulus (G') of mixed protein emulsion gels, whereas the porosity of mixed protein emulsion gels in the microstructure increased, as shown by CLSM. Both β-lactoglobulin and α-lactalbumin from WPI and 7 S and 11 S from SPI participated in forming the gel matrix of mixed protein emulsion gels. More protein aggregates existed as the gel matrix filler at the high soy protein levels. Interestingly, the G' of mixed protein emulsion gels at the WPI to SPI ratio of 50:50 was higher than the sum of G' of individual WPI and SPI emulsion gels. The whey protein network predominated the gel matrix, while soy protein predominated in the active filling effect. When subjected to an in vitro dynamic gastric digestion model, soy protein in the gels (WPI:SPI = 50:50) degraded faster than whey protein during gastric digestion. This study provided new information on the characteristics of composite protein emulsion gel fabricated with the WPI and SPI mixture.
Comparative lipidomics analysis of different-sized fat globules in sheep and cow milks
(Elsevier B V, 2024) Pan Z; Ye A; Fraser K; Li S; Dave A; Singh H
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.
Comparative lipidomics analysis of in vitro lipid digestion of sheep milk: Influence of homogenization and heat treatment
(Elsevier Inc on behalf of the American Dairy Science Association, 2024-02) Pan Z; Ye A; Fraser K; Li S; Dave A; Singh H
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.
Corrigendum to "Kinetics of pepsin-induced hydrolysis and the coagulation of milk proteins" (J. Dairy Sci. 105:990-1003)
(Elsevier Inc on behalf of the American Dairy Science Association, 2023-11) Yang M; Ye A; Yang Z; Everett DW; Gilbert EP; Singh H
In equation [3] (page 994), “1−” was placed incorrectly. The corrected equation reads as follows: [Formula Presented] The authors regret the error.
Delivery of encapsulated bioactive compounds within food matrices to the digestive tract: recent trends and future perspectives
(Taylor and Francis Group, 2024-05-31) Qazi HJ; Ye A; Acevedo-Fani A; Singh H
Encapsulation technologies have achieved encouraging results improving the stability, bioaccessibility and absorption of bioactive compounds post-consumption. There is a bulk of published research on the gastrointestinal behavior of encapsulated bioactive food materials alone using in vitro and in vivo digestion models, but an aspect often overlooked is the impact of the food structure, which is much more complex to unravel and still not well understood. This review focuses on discussing the recent findings in the application of encapsulated bioactive components in fabricated food matrices. Studies have suggested that the integration of encapsulated bioactive compounds has been proven to have an impact on the physicochemical characteristics of the finished product in addition to the protective effect of encapsulation on the fortified bioactive compound. These products containing bioactive compounds undergo further structural reorganization during digestion, impacting the release and emptying rates of fortified bioactive compounds. Thus, by manipulation of various food structures and matrices, the release and delivery of these bioactive compounds can be altered. This knowledge provides new opportunities for designing specialized foods for specific populations.
Differences in small intestinal apparent amino acid digestibility of raw bovine, caprine, and ovine milk are explained by gastric amino acid retention in piglets as an infant model
(Frontiers Media S.A., 2023-09-04) Ahlborn NG; Montoya CA; Roy D; Roy NC; Stroebinger N; Ye A; Samuelsson LM; Moughan PJ; McNabb WC; Gallier S
BACKGROUND: The rate of stomach emptying of milk from different ruminant species differs, suggesting that the small intestinal digestibility of nutrients could also differ across these milk types. OBJECTIVE: To determine the small intestinal amino acid (AA) digestibility of raw bovine, caprine, and ovine milk in the piglet as an animal model for the infant. METHODS: Seven-day-old piglets (n = 12) consumed either bovine, caprine, or ovine milk diets for 15 days (n = 4 piglets/milk). On day 15, fasted piglets received a single meal of fresh raw milk normalized for protein content and containing the indigestible marker titanium dioxide. Entire gastrointestinal tract contents were collected at 210 min postprandially. Apparent AA digestibility (disappearance) in different regions of the small intestine was determined. RESULTS: On average, 35% of the dietary AAs were apparently taken up in the small intestine during the first 210 min post-feeding, with 67% of the AA digestibility occurring in the first quarter (p ≤ 0.05) and 33% in the subsequent two quarters. Overall, except for isoleucine, valine, phenylalanine, and tyrosine, the small intestinal apparent digestibility of all AAs at 210 min postprandially in piglets fed ovine milk was, on average, 29% higher (p ≤ 0.05) than for those fed bovine milk. Except for lysine, there was no difference in the apparent digestibility (p > 0.05) of any AAs between piglets fed caprine milk or ovine milk. The apparent digestibility of alanine was higher (p ≤ 0.05) in piglets fed caprine milk than those fed bovine milk. When apparent digestibility was corrected for gastric AA retention, only small differences in the small intestinal apparent digestibility of AAs were observed across milk types. CONCLUSION: Bovine, caprine and ovine milk had different apparent small intestinal AA digestibility at 210 min postprandially. When corrected for gastric AA retention, the differences in apparent digestibility across species largely disappeared. The apparent AA digestibility differed across small intestinal locations.
Digestion behaviour of capsaicinoid-loaded emulsion gels and bioaccessibility of capsaicinoids: Effect of emulsifier type
(Elsevier B V, 2023-03-06) Luo N; Ye A; Wolber FM; Singh H; Sun Q
In this study, the effect of emulsifier type, i.e. whey protein versus Tween 80, on the digestion behaviour of emulsion gels containing capsaicinoids (CAPs) was examined. The results indicate that the CAP-loaded Tween 80 emulsion gel was emptied out significantly faster during gastric digestion than the CAP-loaded whey protein emulsion gel. The Tween-80-coated oil droplets appeared to be in a flocculated state in the emulsion gel, had no interactions with the protein matrix and were easily released from the protein matrix during gastric digestion. The whey-protein-coated oil droplets showed strong interactions with the protein matrix, and the presence of thick protein layer around the oil droplets protected their liberation during gastric digestion. During intestinal digestion, the CAP-loaded Tween 80 emulsion gel had a lower extent of lipolysis than the CAP-loaded whey protein emulsion gel, probably because the interfacial layer formed by Tween 80 was resistance to displacement by bile salts, and/or because Tween 80 formed interfacial complexes with bile salts/lipolytic enzymes. Because of the softer structure of the CAP-loaded Tween 80 emulsion gel, the gel particles were broken down much faster and the oil droplets were liberated from the protein matrix more readily than for the CAP-loaded whey protein emulsion gel during intestinal digestion; this promoted the release of CAP molecules from the gel. In addition, the Tween 80 molecules displaced from the interface would participate in the formation of mixed micelles and would help to solubilize the released CAP molecules, leading to improved bioaccessibility of CAP. Information obtained from this study could be useful in designing functional foods for the delivery of lipophilic bioactive compounds.
Digestive diversity and kinetic intrigue among heated and unheated β-lactoglobulin species.
(ROYAL SOC CHEMISTRY, 2014-11) Loveday SM; Peram MR; Singh H; Ye A; Jameson GB
Food processing often alters the structure of proteins, and proteins are deliberately denatured and aggregated to improve technological functionality in many cases. However, the digestive consequences of processing-induced alterations to protein structure have only recently been studied. Here we explored the process-structure-digestibility relationship in the context of heat-processing effects on the structure and gastric digestibility of the bovine whey protein β-lactoglobulin (β-lg). Heating β-lg produces an array of non-native monomers, dimers and aggregates, and we have characterised these with reverse-phase high performance liquid chromatography (RP-HPLC) as a complement to our earlier work using polyacrylamide gel electrophoresis (PAGE) techniques. Using a combination of SDS-PAGE and RP-HPLC we have identified pepsin-resistant dimers and peptides that appear early in digestion. In an unexpected finding, native β-lg underwent complete hydrolysis during prolonged incubation (48 h) with pepsin. Two phases of hydrolysis were identified, and the transition between phases appears to result from alterations to the secondary structure of β-lg at 3-4 h, as measured with circular dichroism spectroscopy, and/or the binding and release of a pepsin inhibitor peptide. This work has unpacked some of the complexities of the processing-structure-digestibility relationship in a highly simplified system; further work is needed to explore the implications of these findings for food processors, regulatory authorities and consumers.
Dynamic Gastrointestinal Digestion of Bovine, Caprine and Ovine Milk Reconstituted from Commercial Whole Milk Powders
(MDPI AG, 2024-05-02) Li S; Ye A; Cui J; Zhang Y; Ware L; Miller JC; Abbotts-Holmes H; Roy NC; Singh H; McNabb W; Polidori P
The global dairy market has been increasingly diversified with more dairy product offerings of milk products from different animal species. Meanwhile, milk powders remain the main exported dairy product format due to their ease of transportation. In this work, we studied the structural changes, protein hydrolysis and nutrient delivery during dynamic gastric digestion and small intestinal digestion of cow, goat and sheep milk reconstituted from commercial whole milk powders. The results show that the reconstituted milks digest similarly to processed fresh milk. The digestion behaviors of the three reconstituted ruminant milks are broadly similar (gastric coagulation, kinetics of gastric emptying of protein and fat and the high digestibility in the small intestine) with some differences, which are likely contributed by the processing history of the milk powders. The delivery of individual amino acids to the small intestine differed between the early and late stages of gastric digestion, which were primarily affected by the abundance of amino acids in caseins and whey proteins but also by the difference between milk types associated with their gastric coagulation behaviors. This work showed that powdered milk is similar to fresh processed milk in digestion behavior, and the inherent differences between ruminant milks can be modified by processing treatments.
Dynamic in vitro gastric digestion behavior of goat milk: Effects of homogenization and heat treatments.
(Elsevier Inc on behalf of the American Dairy Science Association, 2022-02) Li S; Ye A; Pan Z; Cui J; Dave A; Singh H
The gastric digestion behavior of differently processed goat milks was investigated using a dynamic in vitro gastric digestion model, the human gastric simulator. Homogenization and heat treatment of goat milk resulted in gastric clots with highly fragmented structures. They also delayed the pH reduction during digestion, altered the chemical composition of the clots and the emptied digesta, promoted the release of calcium from the clots, and accelerated the hydrolysis and the emptying of milk proteins. The apparent density of the protein particles and the location of the homogenized fat globules changed during the digestion process, as shown in the emptied digesta of the homogenized goat milks. The effects of processing on the digestion behavior of goat milk were broadly similar to those previously reported for cow milk. However, the overall gastric digestion process of goat milk was more affected by homogenization than by heat treatments.
Dynamic in vitro gastric digestion behaviour of camel milk
(Elsevier Ltd, 2023-08) Li S; Ayyash M; Ye A; Singh H
This study investigated the dynamic in vitro gastric digestion behaviour of camel milk. Coagulum that was retainable in the stomach was not formed during the digestion of camel milk, whereas bovine milk reconstituted to the same protein concentration (2.9%, w/w) underwent pronounced gastric coagulation into structured clots. During early digestion, the camel milk formed small particles, resulting from its weak coagulation, that were preferentially emptied from the stomach. These particles became more compact and spherical in the first hour of digestion and then gradually decreased in size. Protein analysis indicated that the main camel milk proteins were digested in the order αS1-casein > β-casein > α-lactalbumin, which may have been modulated by the decreasing pH during the dynamic gastric digestion. This unique coagulation behaviour of camel milk resulted in its rapid gastric digestion and emptying, which may have nutritional implications.
Dynamic In Vitro Gastric Digestion Behaviour of Commercial Infant Formulae Made with Cow, Goat and Sheep Milk
(MDPI (Basel, Switzerland), 2024-04-23) Song X; Wang X; Yang M; Acevedo-Fani A; Singh H; Ye A; De Noni I
There are a wide range of commercial infant formulae available on the market. These are made using milk from different species, such as goat, sheep, and cow. The different protein compositions of these milks and the process used during infant-formulae manufacture, such as heat treatment, may impact the digestion of nutrients. This study compared the effect of protein composition and heat treatment on the in vitro gastric digestion behaviour of commercial infant formulae made with cow, goat, and sheep milk using a dynamic infant human gastric simulator (IHGS). During the simulated dynamic gastric digestion, the goat milk infant formula (GIF) showed earlier signs of aggregate formation compared to cow milk infant formula (CIF) and sheep milk infant formula (SIF). In addition, the microstructures of GIF chyme showed fragmented and porous structures. On the contrary, CIF formed dense protein networks that trapped oil droplets, whereas SIF exhibited a microstructure of smooth oil droplets surrounded by fewer protein networks. The different aggregation behaviours and aggregate structures of the three infant-formulae chyme were related to their different protein compositions, especially the different casein compositions. Furthermore, the open fragile structure of GIF aggregates provided easier access to pepsin, allowing it to hydrolyse protein. The results from the present study provided some information to assist in understanding the coagulation and digestion behaviours of commercial infant formulae made from different species of milk.
Dynamic In Vitro Gastric Digestion of Sheep Milk: Influence of Homogenization and Heat Treatment
(MDPI (Basel, Switzerland), 2021-08-20) Pan Z; Ye A; Li S; Dave A; Fraser K; Singh H; Velickovic TC
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.
Effect of Gel Structure on the In Vitro Gastrointestinal Digestion Behaviour of Whey Protein Emulsion Gels and the Bioaccessibility of Capsaicinoids
(MDPI (Basel, Switzerland), 2021-03-04) Luo N; Ye A; Wolber FM; Singh H; Kontominas MG
This study investigated the effect of gel structure on the digestion of heat-set whey protein emulsion gels containing capsaicinoids (CAP), including the bioaccessibility of CAP. Upon heat treatment at 90 °C, whey protein emulsion gels containing CAP (10 wt% whey protein isolate, 20 wt% soybean oil, 0.02 wt% CAP) with different structures and gel mechanical strengths were formed by varying ionic strength. The hard gel (i.e., oil droplet size d4,3 ~ 0.5 μm, 200 mM NaCl), with compact particulate gel structure, led to slower disintegration of the gel particles and slower hydrolysis of the whey proteins during gastric digestion compared with the soft gel (i.e., d4,3 ~ 0.5 μm, 10 mM NaCl). The oil droplets started to coalesce after 60 min of gastric digestion in the soft gel, whereas minor oil droplet coalescence was observed for the hard gel at the end of the gastric digestion. In general, during intestinal digestion, the gastric digesta from the hard gel was disintegrated more slowly than that from the soft gel. A power-law fit between the bioaccessibility of CAP (Y) and the extent of lipid digestion (X) was established: Y = 49.2 × (X - 305.3)0.104, with R2 = 0.84. A greater extent of lipid digestion would lead to greater release of CAP from the food matrix; also, more lipolytic products would be produced and would participate in micelle formation, which would help to solubilize the released CAP and therefore result in their higher bioaccessibility.
Effect of ingestion temperature on the pepsin-induced coagulation and the in vitro gastric digestion behavior of milk
(Elsevier Ltd, 2023-05) Yang M; Ye A; Yang Z; Everett DW; Gilbert EP; Singh H
Pepsin-induced protein coagulation occurs in the gastric environment when the milk pH is above the isoelectric point of casein proteins. In this study, the effect of milk temperature (4–48 °C) on the hydrolysis of κ-casein by pepsin and the consequent protein coagulation was studied at pH 6.0 for 120 min. Quantitative determination of the released para-κ-casein showed that both the κ-casein hydrolysis reaction rate constant and the pepsin denaturation rate constant increased with an increase in temperature. The temperature coefficient (Q10) of the specific hydrolysis of κ-casein was calculated to be ∼1.95. The coagulation process was investigated by the evolution of the storage modulus (Gʹ). At higher temperature, the milk coagulated faster but had a lower firming rate and Gʹmax with larger aggregates and voids were observed. The digestion behavior of the milk ingested at 4 °C, 37 °C, or 50 °C was investigated for 240 min in a human gastric simulator, in which the milk temperature increased or decreased to 37 °C (body temperature) over ∼ 60 min. The coagulation of the 4 °C milk was slower than for the 37 °C and 50 °C milk. The curd obtained from the 4 °C milk had a looser and softer structure with a significantly higher moisture content at the initial stage of digestion (20 min) which, in turn, facilitated the breakdown and hydrolysis of the caseins by pepsin. During the digestion, the curd structure became more cohesive, along with a decrease in moisture content. The knowledge gained from this study provides insight into the effect of temperature on the kinetics of pepsin-induced milk coagulation and the consequent digestion behavior.
Formation and properties of highly concentrated oil-in-water emulsions stabilized by emulsion droplets
(Elsevier Ltd, 2023-12) Cheng L; Ye A; Yang Z; Hemar Y; Singh H
70% (v/v) concentrated emulsion has been prepared using Ca2+-cross-linked sodium caseinate particles (Ca-CAS) or Ca-CAS coated nano-sized primary emulsion droplets as emulsifiers. The primary droplet-stabilised emulsion (DSE) was compared with the conventional Ca-CAS stabilised-emulsion (PSE) in terms of viscoelasticity as affected by aging (30 days) and heating (80 °C, 30 min) at pH 5.8 and 7.0. DSE at pH 5.8 showed the highest complex modulus (G* = 1174 ± 39 Pa), approximately was six-times higher than other emulsions (G* ≤ ∼250 Pa) due to the thick emulsifier layer consisting of primary droplet increasing the effective volume faction of core droplets by a factor of ∼1.21. After aging, G* of DSE at pH 5.8 increased to 1685 ± 68 Pa, while G* of other three emulsions were ∼400 Pa. After heating, G* of DSE reached 1801 ± 69 Pa and 1312 ± 205 Pa at pH 5.8 and pH 7.0, respectively, while G* of PSE were ∼600 Pa at both pHs. The possible mechanism for aging-induced gelation was the gravity-driven microphase separation, in which the droplets flocculate together with the entrapped aqueous phase increasing the effective volume fraction. The heat-induced gelation was attributed to the increase in droplet interactions through protein aggregates and/or primary droplets forming three-dimensional networks at elevated temperature. This study suggests that the mechanical strength of food-grade concentrated emulsions can be effectively improved using nano-sized primary emulsions as emulsifying agent and can be further modulated by aging or
Heat stability of sheep's skim milk: Aggregation and interaction of proteins
(Elsevier Ltd, 2023-09) Pan Z; Ye A; Fraser K; Dave A; Singh H
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 °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 κ-casein (κ-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 κ-CN from casein micelles increased with increasing pH (from ∼6.6 to 7.0) before and after heat treatment, contributing to κ-CN-depleted casein micelle aggregation. High ionic calcium concentrations, low levels of κ-CN on casein micelles and ready dissociation of κ-CN from casein micelles may be responsible for the low heat stability of sheep's milk.
Heat treatment and homogenization of bovine milk loosened gastric curd structure and increased gastric emptying in growing pigs
(Elsevier Ltd, 2023-04) Ahlborn NG; Montoya CA; Hodgkinson SM; Dave A; Ye A; Samuelsson LM; Roy NC; McNabb WC
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 formation, 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.

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