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The impact of amino acid mutations within the peptide structure of bovine milk protein is important to understand as it can effect processability and subsequently effect its physiological properties. Genetic polymorphisms of bovine caseins can influence the chemical, structural, and technological properties, including casein micelle morphology, calcium distribution, network creation upon gelation, and surface activity. The A1 and A2 genetic variants of β-casein have recently acquired growing attention from both academia and industry, prompting new developments in the area. The difference between these two genetic variants is the inclusion of either proline in β-casein A2 or histidine in β-casein A1 at position 67 in the peptide chain. The aim of this review was to examine the extent to which milk and ingredient functionality is influenced by β-casein phenotype. One of the main findings of this review was although β-casein A1 was found to be the dominant variant in milks with superior acid gelation and rennet coagulation properties, milks comprised of β-casein A2 possessed greater emulsion and foam formation capabilities. The difference in the casein micelle assembly, hydrophobicity, and chaperone activity of caseins may explain the contrast in the functionality of milks containing β-casein from either A1 or A2 families. This review provides new insights into the subtle variations in the physicochemical properties of bovine milks, which could potentially support dairy producers in the development of new dairy products with different functional properties.

Background Complex polymorphisms in the polypeptide chain of bovine β-casein are responsible for the genetic variants that give rise to different bioactive peptides during in vitro and ex vivo digestion, or food fermentation. One specific group of bioactive peptides, known as β-casomorphins, are opioid-agonists for μ-receptors and have been suggested to assume an active role in the development of various non-communicable diseases, including diabetes mellitus, cardiovascular diseases, neurological disorders, pulmonary inflammation, to name a few. Their potential bioactivity and role in human health is dependent on their release from the latent form within the primary structure of β-casein, which can occur during the manufacture of dairy products or during gastric and intestinal digestion. Consequently, β-casomorphins can be either completely hydrolysed or absorbed in the gut or be transferred into the blood stream and internal organs in their intact form. Their biological function as opioid agonists is expressed in the gut, thus upon epithelial translocation they may affect various physiological states, such as causing gastrointestinal issues, bloating, and lactose intolerance. Scope and approach This review evaluated the possible disadvantages and potential beneficial effects of β-casomorphins on human health, within the scope of in vitro and ex vivo studies. Applying a systematic approach, a literature search was performed across four electronic databases (Scopus, Web of Science, PubMed, and Cochrane) to identify suitable studies. Key findings and conclusions The data mined from in vitro and ex vivo trials on the health impact of β-casomorphins is both inconclusive and limited to completely support the possible adverse or potential beneficial health effects of β-casomorphins. These peptides are usually further cleaved in the gut, which prevents their migration across the gut-blood-brain barrier. Nevertheless, in some individuals that are immunocompromised, their condition increases permeability of the gut barrier often referred to as a "leaky gut" condition. Thus, the absorption of β-casomorphins appears possible. This may indicate that the presence of β-casomorphins can affect gastrointestinal functions only. However, since the overall concern with β-casomorphins appears debatable and not well defined, more experimental trials are required to investigate the metabolic pathways of these identified peptides, their release during digestion, and subsequent fate after the digestion process. Consequently, repeatability of the findings under a number of other laboratory conditions is required before the data can be fully substantiated. Due to the rapidly evolving nature of the issue and emerging studies in this field, further exploration into the bioactivity of β-casomorphins is warranted.

Worldwide milk production is predominantly founded on indoor, high-concentrate feeding systems, whereas pasture-based feeding systems are most common in New Zealand and Ireland but have received greater attention recently in countries utilizing conventional systems. Consumer interest in 'pasture-fed' dairy products has also increased, arising from environmental, ethical, and nutritional concerns. A substantial body of research exists describing the effect of different feeding strategies on the composition of milk, with several recent studies focusing on the comparison of pasture- and concentrate-based feeding regimes. Significant variation is typically observed in the gross composition of milk produced from different supplemental feeds, but various changes in the discrete composition of macromolecular components in milk have also been associated with dietary influence, particularly in relation to the fatty acid profile. Changes in milk composition have also been shown to have implications for milk and dairy product processability, functionality and sensory properties. Methods to determine the traceability of dairy products or verify marketing claims such as 'pasture-fed' have also been established, based on compositional variation due to diet. This review explores the effects of feed types on milk composition and quality, along with the ultimate effect of diet-induced changes on milk and dairy product functionality, with particular emphasis placed on pasture- and concentrate-based feeding systems.

Background A number of randomised in vivo trials have to date investigated the health impacts of the genetic variants A1 and A2 of bovine β-casein. The primary difference between these two genetic variants is the mutation leading to an amino acid exchange at a position 67 in the peptide chain. This systematic review evaluated the effects of bovine milk, β-casein and pure β-casomorphin7, in the form of orally administered nutritional ingredients, on possible incidence and risk for chronic digestive discomfort and development of incurable conditions and diseases in human and animal randomised controlled trials. Scope and approach Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist, searches were performed for publications across 7 electronic databases (Scopus, Embase, Web of Science, Medline, EBSCO, PubMed, and Cochrane) up to and until July 2020, to identify randomised controlled trials. The subsequent search results were screened for relevance firstly by title, then abstract, and the chosen ones by full text, with additional screening of included articles reference lists. Key findings and conclusions In total 2006 peer-reviewed journal articles were identified and after applying exclusion criteria, 19 studies were deemed suitable for inclusion. Human-based and animal-based results from the clinical in vivo studies demonstrated that consumption of A2 β-casein milk can lead to improved tolerance of milk via decline in the ubiquity of gut related discomfort. However, the exact mechanism for these effects or specific individuals that may benefit from A2 β-casein milk as opposed to A1 β-casein milk is still poorly understood. Notably, consumption of A2 β-casein milk had very low to completely no effect on the other health statuses investigated, particularly non-communicable diseases, such as cardiovascular diseases, neurological disorders, and diabetes. Based on current data, there is not sufficient evidence to merit public health authority recommendations related to the consumption and health associations of A1 β-casein milk or A2 β-casein milk. Interestingly, regardless of the scientific evidence between A2 β-casein milk and health, this milk continues to gain prominence on the market, thus further functional research is required to understand the mechanisms of action of these identified peptides and gene variants and any implications A1 or A2 β-casein milk may have on human health and techno-functional properties of milks.

Changes in the pH of skim milk and skim milk ultrafiltration permeate on heating from 25 to 140 °C were examined. Results showed that the decrease in pH with increase in temperature up to 140 °C was not linear. Hydrogen ion release due to changes in the milk mineral balance were responsible for the reduction in pH with increase in temperature. The presence of milk proteins offered little buffering against the drop in pH. The precipitation of calcium phosphate resulted in sediment in milk permeate heated above ∼70 °C, but this did not occur in skim milk, with the pH remaining lower in milk permeate after heat treatment when measured at 25 °C. This study has shown that in-line pH measurements of milk at ultra-high temperatures is feasible, and could prove useful at laboratory and pilot-scale for studying interactions within, and stability of, more complex formulations with added minerals.

Poor solubility of high protein milk powders can be an issue during the production of nutritional formulations, as well as for end-users. One possible way to improve powder solubility is through the creation of vacuoles and pores in the particle structure using high pressure gas injection during spray drying. The aim of this study was to determine whether changes in particle morphology effect physical properties, such as hydration, water sorption, structural strength, glass transition temperature, and α-relaxation temperatures. Four milk protein concentrate powders (MPC, 80%, w/w, protein) were produced, i.e., regular (R) and agglomerated (A) without nitrogen injection and regular (RN) and agglomerated (AN) with nitrogen injection. Electron microscopy confirmed that nitrogen injection increased powder particles’ sphericity and created fractured structures with pores in both regular and agglomerated systems. Environmental scanning electron microscopy (ESEM) showed that nitrogen injection enhanced the moisture uptake and solubility properties of RN and AN as compared with non-nitrogen-injected powders (R and A). In particular, at the final swelling at over 100% relative humidity (RH), R, A, AN, and RN powders showed an increase in particle size of 25, 20, 40, and 97% respectively. The injection of nitrogen gas (NI) did not influence calorimetric glass transition temperature (Tg), which could be expected as there was no change to the powder composition, however, the agglomeration of powders did effect Tg. Interestingly, the creation of porous powder particles by NI did alter the α-relaxation temperatures (up to ~16 °C difference between R and AN powders at 44% RH) and the structural strength (up to ~11 °C difference between R and AN powders at 44% RH). The results of this study provide an in-depth understanding of the changes in the morphology and physical-mechanical properties of nitrogen gas-injected MPC powders.

peer-reviewed This work aimed to model the effect of heat treatment on viscosity of milk protein concentrate (MPC) using kinetic data. MPC obtained after ultrafiltration was subjected to different time-temperature heat treatment combinations. Heat treatment at high temperature and short time (i.e., 100 or 120 °C×30 s) led to a significant increase in viscosity in MPC systems. Second-order reaction kinetic models proved a better fit than zero- or first-order models when fitted for viscosity response to heat treatment. A distinct deviation in the slope of the Arrhenius plot at 77.9 °C correlated to a significant increase in the rate of viscosity development at temperatures above this, confirming the transition of protein denaturation from the unfolding to the aggregation stage. This study demonstrated that heat-induced viscosity of MPC as a result of protein denaturation/aggregation can be successfully modelled in response to thermal treatment, providing useful new information in predicting the effect of thermal treatment on viscosity of MPC.

peer-reviewed Direct supersonic steam injection, direct steam infusion, and indirect tubular heating were each applied to protein-enriched skim milk-based beverages with 4, 6 and 8% (w/w) total protein, and the effect of final heat temperature on the physical properties of these beverages was investigated. Supersonic steam injection resulted in significantly lower levels of denaturation of β-lactoglobulin (34.5%), compared to both infusion (76.3%) and tubular (97.1%) heating technologies. Viscosity, particle size and accelerated physical stability of formulations did not differ significantly between the heating technologies, while noticeable colour differences due to heat treatment (mainly attributed to increasing b* value) were observed, particularly for tubular heating. Overall, the extent of protein denaturation in high-protein dairy products was significantly influenced by the particular heating technology applied. The application of supersonic steam injection technology, with rapid heating and high shear characteristics, may enable differenciated product characteristics for ready-to-drink ambient-delivery high-protein dairy beverages. Industrial relevance: The design and application of novel direct supersonic steam injection technology was comprehensively studied and found to provide significant benefits over direct steam infusion and indirect tubular heating technologies for skim milk-based protein beverages. This type of injection heating system resulted in heat-treated formulations with lower levels of denatured whey proteins, compared to tubular and infusion heating, offering an alternative opportunity to the industry in terms of producing shelf-stable dairy protein beverages.

This study evaluated the effect of high-pressure nitrogen (N2) gas injection prior to spray drying on the subsequent rehydration properties of regular and agglomerated milk protein concentrate (MPC) powders. Conductivity measurements demonstrated a slower release of ions for powders produced using N2 injection (NI) as they took longer to wet and sink due to their lower density. However, analysis of particle size distribution on reconstitution at both 23 and 50 °C showed an improvement in powder dispersion with NI. Powder solubility, when measured at 23 °C, was higher for the NI powders, while agglomeration negatively impacted solubility. Confocal laser scanning microscopy analysis showed a faster diffusion of dye into MPC powder particles produced using NI. The improvement in powder dissolution with NI was attributed to higher porosity and the presence of air voids which facilitated increased water transfer and accelerated the breakdown of primary powder particles.

peer-reviewed Low and high protein dairy powders are prone to caking and sticking and can also be highly insoluble; with powder storage conditions an important factor responsible for such issues. The aim of this study focused on the bulk and surface properties of anhydrous and humidified spray-dried milk protein concentrate (MPC) powders (protein content ~40, 50, 60, 70 or 80%, w/w). Water sorption isotherms, polarized light and scanning electron micrographs showed crystallized lactose in low protein powders at high water activities. High protein systems demonstrated increased bulk diffusion coefficients compared to low protein systems. Glass transition temperatures, α-relaxation temperatures and structural strength significantly decreased with water uptake. CLSM measurements showed that humidified systems have slower real time water diffusion compared to anhydrous systems. Overall, the rate of water diffusion was higher for low protein powders but high protein powders absorbed higher levels of water under high humidity conditions.

This study highlights differences in conformational and physicochemical characteristics of bovine skim milk and micellar casein from cows of different β-casein phenotypes. These genetic variants have been one of the predominant topics among dairy researchers due to their differences in β-casein structure, and thus their potential effects on dairy processing and human health. For characterising differences in milk protein structure, Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (1H NMR) spectroscopies combined with chemometric analysis were used. Additionally, physiochemical properties such as mineral content, particle size, and electrostatic charge in skim milk and micellar casein samples were analysed at 4 and 20 ᵒC. Results showed variation in the secondary structure of all three genetic variants independent of temperature. Moreover, the main differences involved a higher level of β-turn and α-helical structures in A1/A1 β-casein milk, while intermolecular β-sheets were more numerous in A1/A2 β-casein milk, whereas random or polyproline II (PPII) structures were more common in A2/A2 β-casein milk. Temperature slightly affected these differences, which was due to the dissociation of β-casein from the micelle at low temperature. In addition, A2/A2 β-casein milk and its micellar casein had a larger average particle size, which resulted in a lower negative ζ-potential. The A2/A2 β-casein samples contained greater amounts of phosphorus and less calcium compared to the other genetic variants of milk and their micellar caseins. The results also indicated that a combination of FTIR and 1H NMR spectroscopies could be used to establish conformational differences in milk and micellar caseins of different genetic variants.

peer-reviewed The effect of pH, adjusted using either hydrochloric acid (HCl), citric acid or sodium hydroxide, on calcium ion (Ca2+) activity, and consequent changes in viscosity and heat coagulation time (HCT) of milk protein concentrate (MPC) was investigated. Reducing the pH of MPC dispersions resulted in a reduction in their viscosity, which subsequently increased during heat treatment. The maximum heat stability of MPC was observed at pH 6.7. Reducing the pH of MPC from 6.7 to 6.2 resulted in a significant (P < 0.05) increase in Ca2+ activity, and reduction in HCT. Such changes were more extensive using HCl compared with citric acid. Increasing the pH greater than 6.7 also led to a reduction in HCT but a decrease in Ca2+ activity. These results demonstrate the importance of pH adjustment, and choice of acidulant, on Ca2+ activity, viscosity, and heat coagulation properties of MPC concentrates during processing.

peer-reviewed Microfiltration (MF) of skim milk, when combined with diafiltration (DF), facilitates the manufacture of liquid micellar casein concentrate (MCC), which can be spray-dried into high-protein (≥80% protein, dry-basis) powders. MCC powders rehydrate slowly, which is typically considered a defect by end-users. This study compared the impact of cold (

The aim of this study was to evaluate the effectiveness of an in-line hydrodynamic cavitation (HC) system, for rehydration of milk protein concentrate powders (MPC) at semi-industrial pilot scale. MPC powder was dispersed in water at 50 °C at 20% (w/w) dry matter (DM) with two commonly used high-shear powder inductors/mixers. The MPC dispersions created were then passed through the HC system to assess subsequent hydration behaviour of the MPC powders. Particle size distribution (PSD) of MPC dispersions prepared using conventional high-shear mixing indicated that complete rehydration of MPC powders was not achieved, with an average D90 and D[4,3] values of 21.17 μm and 5.62 μm respectively, observed in MPC dispersions. In contrast MPC dispersions subjected to HC had a PSD indicative of complete rehydration, with an average D90 and D[4,3] values of 0.45 μm and 0.19 μm, respectively. Apparent viscosity decreased significantly (p≤.05) post HC compared to dispersions subjected to conventional high shear mixing. Phase separation profiles showed that HC treated MPC dispersions had increased stability to sedimentation compared to high-shear treated samples. Wetting, immersion, dissolution and solubilisation of high protein powders occurred instantaneously (and simultaneously) during HC. This emerging technology has the potential to achieve complete rehydration of powders in significantly less time than conventional rehydration processes employed by dairy and other industries.

Rheological modeling as a function of temperature is a useful tool for describing products undergoing thermal processing. The rheological behavior of a range of dairy-based (4%, w/w) protein beverages was investigated for applicability to semi-empirical temperature-dependent viscosity equations. The viscosity at 16.8 rad/s of the beverages was measured during heating, holding, and cooling over a temperature range of 25 to 90 o C using a rheometer with starch pasting cell geometry. Five established fitting methods were applied based on the Arrhenius and Williams-Landel-Ferry (WLF) equations using nonlinear regression analysis. A two-parameter WLF (WLF2 ) model, using viscosity at a reference temperature of 25 o C resulted in high R2 values (0.974 to 0.988) and a statistically superior fit compared to the Arrhenius, Generalized Arrhenius, and exponential equations (P

Due to their excellent nutritional (e.g., high calcium) and functional (e.g., heat stability and gelation) properties, the use of protein-enriched, micellar casein-dominant dairy powders, including milk protein concentrate/isolate and micellar casein concentrate, has increased considerably among food and beverage manufacturers. However, the poor and often inconsistent rehydration properties of these powders in water, specifically their low dispersibility and solubility (attributed to protein–protein interactions related to the high proportion of micellar casein), remains a significant challenge. This review provides a detailed analysis of the main physical (e.g., injection of gas, ultrasonication) and chemical (e.g., ion exchange, pH adjustment) processing strategies that have been applied, at both laboratory and pilot-scale, to enhance the rehydration performance of high-protein, micellar casein-dominant dairy powders. The information provided will support the advancement of dairy ingredient research and the technological development of nutritional powders that can be used across several industrial applications.

Milk concentrate (MC) viscosity is a key process control parameter in the manufacture of dairy based powders that affects both process efficiency and powder functionality. If the viscosity of MC is too high, various processing issues can arise, i.e., pump blockages, fouling, poor atomisation, product rework and production downtime. Viscosity of MC is dependent on various intrinsic (e.g., total solids content, protein: lactose ratio, mineral profile, pH) and extrinsic (e.g., temperature, agitation, high shear) parameters. It is therefore necessary to understand the effects of these parameters on the viscosity of MC to maintain an optimal process. This review focuses on outlining the parameters that affect the viscosity of MC and recent advances in processing strategies to reduce viscosity of MC prior to spray drying during powder manufacture.

Reconstituted milk protein concentrate (MPC; 80% protein) was mixed with lactose (MPC-Lac) or milk permeate (MPC-Perm) to 20% dry matter (DM) before been evaporated to 45% DM and subsequently spray dried. The pH of protein solutions, measured during evaporation from 20 to 45% DM at 50 °C, decreased from pH 6.64 to pH 6.53 and from 6.1 to 5.95 for MPC-Lac and MPC-Perm, respectively. The particle size and viscosity were greater in MPC-Perm than MPC-Lac solutions after evaporation. However, the heat stability of rehydrated MPC-Perm powder (3.5% protein) were significantly higher than MPC-Lac at pH values between 6.4 and 6.8, which may be attributed to the lower calcium ion concentration in MPC-Perm than in MPC-Lac. This study highlighted the complexity of mineral addition and phase distribution in protein-standardised milk systems; whereby higher levels of mineral addition contribute to viscosity and age thickening, but not necessarily lower heat stability.

The protein composition of bovine skim milk was modified using pilot scale membrane filtration to produce a whey protein-dominant ingredient with a casein profile closer to human milk. Bovine skim milk was processed at low (8.9 °C) or high (50 °C) temperature using ceramic microfiltration (MF) membranes (0.1 μm mean pore diameter). The resulting permeate stream was concentrated using polyethersulfone ultrafiltration (UF) membranes (10 kDa cut-off). The protein profile of MF and UF retentate streams were determined using reversed phase-high performance liquid chromatography and polyacrylamide gel electrophoresis. Permeate from the cold MF process (8.9 °C) had a casein:whey protein ratio of ∼35:65 with no α S - or κ-casein present, compared with a casein:whey protein ratio of ∼10:90 at 50 °C. This study has demonstrated the application of cold membrane filtration (8.9 °C) at pilot scale to produce a dairy ingredient with a protein profile closer to that of human milk.

The aim of this study was to determine the effects of calcium chelating agents on the dissolution and functionality of 10% (w/w) milk protein concentrate (MPC) powder. MPC powder dissolution rate and solubility significantly (P > 0.05) increased with addition of sodium phosphate, trisodium citrate (TSC) and sodium hexametaphosphate (SHMP), compared to MPC dispersions alone. Trisodium citrate and SHMP addition increased viscosity as a result of micelle swelling. However, dispersions containing SHMP showed a decrease in viscosity after prolonged time due to micelle dissociation. Overall, MPC powder dissolution was aided by the addition of calcium chelating agents.

The influence of bovine diet on the metabolome of reconstituted skim milk powder (SMP) and protein ingredients produced from the milk of cows fed on pasture or concentrate-based diets was investigated. Cows were randomly assigned to diets consisting of perennial ryegrass only (GRS), perennial ryegrass/white clover sward (CLV), or indoor total mixed ration (TMR) for an entire lactation. Raw milk obtained from each group was processed at pilot scale, to produce SMP and sweet whey, and SMP was further processed at laboratory scale, to yield ideal whey and acid whey. The total amino acid composition and metabolome of each sample were analyzed, using high-performance cation exchange and a targeted combination of direct-injection mass spectrometry and reverse-phase liquid chromatography&ndash, tandem mass spectrometry (LC&ndash, MS/MS), respectively. The nitrogen composition of the products from each of the diets was similar, with one exception being the significantly higher nonprotein nitrogen content in TMR-derived skim milk powder than that from the GRS system. Total amino acid analysis showed significantly higher concentrations of glycine in GRS- and CLV-derived sweet whey and acid whey than in those from TMR. The cysteine contents of CLV-derived ideal whey and acid whey were significantly higher than for TMR, while the valine content of GRS-derived acid whey was significantly higher than TMR. The phenylalanine content of GRS-derived ideal whey was significantly higher than that from CLV. Metabolomic analysis showed significantly higher concentrations of the metabolites glutamine, valine, and phosphocreatine in each ingredient type derived from TMR than those from GRS or CLV, while the serine content of each GRS-derived ingredient type was significantly higher than that in TMR-derived ingredients. These results demonstrate that the type of bovine feeding system used can have a significant effect on the amino acid composition and metabolome of skim milk and whey powders and may aid in the selection of raw materials for product manufacture, while the clear separation between the samples gives further evidence for distinguishing milk products produced from different feeding systems based on LC&ndash, MS/MS.

Shiga toxin-producing Escherichia coli (STEC) outbreaks involving ready-to-eat salad products have been described in the scientific literature since 1995. These products typically do not undergo a definitive control step such as cooking to eliminate pathogens. To reduce the number of STEC infections from salad products, efforts will need to focus on preventing and reducing contamination throughout the food chain. We performed a systematic review of STEC outbreaks involving sprouted seeds, salad, or leafy green products to determine whether there were recurrent features, such as availability of microbiological evidence or identification of the contamination event, which may inform future investigations and prevention and control strategies. Thirty-five STEC outbreaks linked to contaminated leafy greens were identified for inclusion. The outbreaks occurred from 1995 to 2018 and ranged from 8 to more than 8,500 cases. Detection of STEC in the food product was rare (4 of 35 outbreaks). For the remaining outbreaks, the determination of leafy greens as the source of the outbreak mainly relied on analytical epidemiology (20 of 35) or descriptive evidence (11 of 35). The traceback investigation in 21 of 32 outbreaks was not able to identify possible routes leading to where the STEC bacteria came from or how the leaves were contaminated. Investigations in eight outbreaks found poor practice during processing that may have contributed to the outbreak, such as insufficient postharvest disinfection of the product. Six outbreak investigations were able to identify the outbreak strain in animal feces near the growing fields; two of these were also able to find it in irrigation water on the farms, providing a likely route of contamination. These results highlight the limitations of relying on microbiological confirmation as a basis to initiate investigations of upstream production to understand the source of contamination. This review also demonstrates the importance of, and difficulties associated with, food-chain traceback studies to inform control measures and future prevention.

peer-reviewed This study examined the effect of dietary factors on compositional and functional properties of whole milk powder (WMP) produced from bovine milk. Raw milk samples were obtained from 3 groups of 18 Holstein Friesian spring-calving cows randomly assigned to diets based on perennial ryegrass (GRS), perennial ryegrass/white clover sward (CLV), and total mixed ration (TMR). Raw milks obtained in late lactation were subsequently standardized for fat, heat-treated (90°C for 30 s), evaporated, and homogenized before spray drying. The WMP produced from each diet were analyzed to determine differences in color, particle size distribution, heat coagulation time, yogurt gelation, texture profile, and protein profile due to each diet. Significant differences in heat coagulation time were observed between the CLV and TMR samples, whereas color values were significantly different between GRS and TMR samples. No significant differences in gross composition, protein profile, or whey protein nitrogen index were found between the 3 WMP samples. Average D90 values (the particle size at which 90% of the particles were smaller than the specified size) for fat globules were significantly lower in the TMR sample compared with the GRS and CLV samples. Yogurts produced from GRS- and CLV-derived WMP had significantly higher elastic moduli (G′) than those produced from TMR-derived WMP. Similarly, texture profile analysis revealed significantly higher firmness values in yogurt samples derived from CLV compared with TMR samples. Our data characterize the effect of these diets on the composition and functional properties of fat-standardized WMP, suggesting better yogurt functionality and thermal stability in WMP derived from pasture-based bovine diets.

peer-reviewed Milk protein concentrate (MPC) and sodium caseinate (NaCas) were hydrolysed using the enzyme trypsin and the subsequent physical properties of the two ingredients were examined. Trypsin hydrolysis was carried out at pH 7 and at 45 °C on 11.1% (w/w) protein solutions. Heat inactivation of trypsin was carried out when the degree of hydrolysis reached either 10 or 15%. Size-exclusion chromatography and electrophoresis confirmed a significant reduction in protein molecular weight in both ingredients. However, whey proteins in MPC were more resistant to trypsin hydrolysis than casein. Oil-in-water emulsions were prepared using intact or hydrolysed protein, maltodextrin, and sunflower oil. Protein hydrolysis had a negative effect on the subsequent physical properties of emulsions, compared with non-hydrolysed proteins, with a larger particle size (only for NaCas stabilised emulsions), faster creaming rate, lower heat stability, and increased sedimentation observed in hydrolysed protein emulsions.

The purpose of this study was to examine the impact of a variety of supplemental feeds on the composition and quality of milk in a pasture-based dairy system. Four pasture-supplemented feeding systems were compared: Group 1 supplementation with 16% crude protein parlour concentrate (CONC), Group 2 supplementation with palm kernel expeller plus parlour concentrate (PKE), Group 3 supplemented with soya hulls plus parlour concentrate (SOYA), Group 4 was supplemented with molassed beet pulp plus parlour concentrate (BEET). Supplemental feeding system was demonstrated to have a significant effect on the size of native casein micelles and the gelation properties of milks. While CONC feeding produced significantly higher casein micelle size, gel strength (Young&rsquo, s Modulus) was significantly negatively correlated with casein micelle size. Supplemental feeding system had a significant effect on a number of fatty acids (FA) and indices derived therefrom, including total saturated and unsaturated fatty acids, de novo produced FA, omega 3, and omega 6 FA. The volatile profile of milks was also affected by supplemental feed choice, whereby multivariate analysis demonstrated that the CONC diet was distinctly different to that of the PALM, SOYA, and BEET milks. Multivariate analysis demonstrated that it is possible to distinguish milks from different pasture-supplemented feeding systems by their FA profile.

A new method for the visualisation and determination of local diffusion coefficients in dairy powders is described based on real-time visualisation of penetration of fluorescent dyes into individual particles of spray-dried dairy powders including skim milk powder, milk protein concentrate and whey protein isolate. The rehydration process was controlled by adding polyethylene glycol (PEG) as a viscosity modifier to the aqueous phase in ratios of 1:0, 1:1, 1:3 and 1:4 aqueous rhodamine to PEG, respectively. Real-time effective diffusivity values were obtained from analysis of confocal laser scanning microscope images. Particle size was measured optically. Results indicated that for all dairy powders, rehydration rates were highly dependent on particle size. Effective diffusivity increased linearly with increasing particle size and average effective diffusivity of the liquid phase was calculated for all particle size distributions using this dependence. The Guggenheim-Anderson-de Boer (GAB) water sorption relationship was used to model water sorption isotherms over a broad range of water activities. Vapour phase systems had significantly higher effective diffusivity than liquid phase systems. The results obtained by this new method is broadly in agreement with previously published works, suggesting this new method may be used to measure the hydration of individual powder particles.

One of the most common industrial applications for whey protein is in infant formula (IF) as a source of essential amino acids and other nutrients. While breast milk is considered the optimal source of nutrition for an infant, it is not always a viable option and IF can provide a suitable alternative. Whey protein is used to adjust the whey protein:casein level of bovine milk-based 1st stage formulas from a ratio of 20:80 to mimic that of human breast milk, i.e., 60:40. Human milk has many functions in addition to nutrition which include immune response, reduction in acute/chronic diseases, and allergic responses. IF manufacturers attempt to incorporate these biological functions into formulations through enriched whey ingredients, whereby the physiological characteristics of their constituents (e.g., major and minor proteins, enzymes, growth factors, cytokines, and oligosaccharides) determine the type and level used. Consequently, the inclusion of any whey protein ingredient (e.g., α-lactalbumin (α-La) and/or lactoferrin (Lf)) into IF requires understanding of complex interactions with other nutrients and ionic species to ensure in-process stability during heating, emulsification, concentration, and drying. It is clear that the thermal history of whey protein ingredients has a direct impact on the physicochemical behavior of liquid IF formulations during processing with β-lactoglobulin (β-Lg) having a modulating role. Ultimately, nutritional and functional properties of whey protein-based ingredients have an important function in ensuring the quality of an IF.

This study investigated the influence of injecting nitrogen (N2) gas under high pressure into milk protein concentrate (80%, w/w, protein; MPC) prior to spray drying and examining the physical and bulk handling properties of regular (non-agglomerated) and agglomerated powders. MPC powders produced using the N2 injection (NI) process had significantly lower bulk density and flowability, higher wall friction angles and increased levels of interstitial and occluded air. Agglomerated MPC powders had higher flow index values, lower wall friction angles, but were more friable, compared to regular powders. Surface composition analysis of MPC powders showed that NI caused fat to preferentially migrate to the surface in comparison to powders spray dried without NI. The results obtained in this study demonstrate that the injection of N2 into liquid MPC directly prior to spray drying, as well as agglomeration by fines return, can produce ingredients with unique particle and bulk powder properties.

Pea protein isolate (PPI) is used in many food formulations, due to its low cost, commercial availability and excellent amino acid profile. The objective of this study was to determine the emulsification properties of PPI. Particle size of PPI powders showed neither temperature (25-65°C) nor time (up to 24h) increased solubilisation of powder particles during mixing. Heating PPI dispersions (10%, w/w, protein) from 45 to 90°C led to an increase in storage modulus (G'; Pa) at 71°C, indicating the onset of protein aggregation. Gel formation occurred at 79°C (G'>1Pa). Pea protein-stabilised emulsions made using homogenization (15MPa; 1 pass) or microfluidization (50MPa; 1 pass) resulted in the formation of cold-set gels, with gel strength increasing with increasing oil concentration and fluidic pressure. Droplet size and viscosity of pea protein-stabilised emulsions decreased and increased, respectively, with increasing ultrasonication time. Overall, ultrasonication (

Composition and relative humidity (RH) can have a profound impact on the physical (flowability, stickiness) and functional (reconstitution) properties of milk powder (MP) and therefore its quality, storage stability and shelf-life. Conventional microscopic techniques are not capable of dynamically imaging the effect of RH on MP at high magnification. The aim of this study was to develop a novel method to characterise in-situ and in real time the hydration and reconstitution of five spray-dried milk protein concentrates (MPCs) using an Environmental Scanning Electron Microscope (ESEM). ESEM was employed to observe the surface microstructure of MPC powders with varying protein content (38.63%–80.94%, w/w), at various RH values ranging from 35% to over 100%. MPC powders were imaged by an ESEM without any prior preparation, and with minimal physical sample alteration, thus providing fundamental insights into MPC hydration and reconstitution. ESEM surface analysis showed particle swelling in all MPCs, and that with increasing protein content, hydration and reconstitution efficiency decreased. For the first time, dynamic particle surface fusion was observed. Such fusion can result in stickiness and caking over time. ESEM methods developed here may provide mechanistic insights into the effects of RH during storage. Surface re-arrangement was also observed in all MPCs, but was impeded in MPC70 and MPC80 thus indicating that this is the rate limiting step for MPC reconstitution. This work validates the use of an ESEM to dynamically characterise MPC powder hydration and reconstitution in-situ and in real-time, at both high magnification and spatial resolution.

The influence of diet on the water-soluble vitamin composition of skim milk powder and whey protein ingredients produced from the milk of cows fed pasture or concentrate-based diets was examined. Fifty-one Holstein-Friesian cows were randomly assigned into three diets (n=17) consisting of outdoor grazing of perennial ryegrass (GRS), perennial ryegrass/white clover (CLV), or indoor feeding of total mixed ration (TMR) for an entire lactation. Raw mid-lactation milk from each group was processed into skim milk powder and further processed to yield micellar casein whey and acid whey. Sweet whey was also produced by renneting of pasteurised whole milk from each system. The water-soluble vitamin profile of each sample was analysed using a combination of direct injection mass spectrometry and reverse-phase liquid chromatography&ndash, mass spectrometry. Vitamin B3 and B3-amide concentrations were significantly higher (p &lt, 0.05) in TMR-derived samples than in those from CLV and GRS, respectively. Vitamin B1, B2, and B7 concentrations were significantly higher in GRS and CLV-derived samples than those from TMR. Significant differences in vitamins B1, B2, and B3-amide were also observed between protein ingredient types. This study indicates that bovine feeding systems have a significant effect on B vitamin composition across a range of protein ingredient types.

The functional properties of milk protein concentrate (MPC) powders are often hindered by their poor solubility. Calcium chelating salts have been shown to improve powder solubility, but generally their action contributes to higher viscosity due to disintegration of casein micelles and higher levels of serum-phase calcium. To help mitigate increases in viscosity associated with calcium chelation, transglutaminase (TGase), an enzyme that covalently crosslinks protein, was employed in an effort to stabilise the casein micelle structure. Sodium hexametaphosphate (SHMP) was added to control (C-MPC) and TGase crosslinked MPC (TG-MPC) dispersions at concentrations of 5, 12.5 and 25 m m prior to analysis. TG-MPC dispersions had lower viscosity than C-MPC dispersions across all SHMP concentrations studied. Crosslinking limited micelle dissociation on SHMP addition and led to greater retention of the white colour of the protein dispersions, while the turbidity of C-MPC dispersions decreased with increasing SHMP addition.

peer-reviewed Thermal processing of ready-to-drink high protein beverages can have a substantial impact on the physical and sensory properties of the final product for long-life milks such as extended shelf life and ultra high temperature processed products. Direct and indirect heat treatment technologies were applied to whey protein isolate (WPI) -based beverages containing 4, 6 or 8% (w/w) protein. Lower levels of protein denaturation (66–94%) were observed using direct heating compared with indirect heating (95–99%) across protein levels and heating temperatures (121 and 135 °C final heat). Direct heat treatment resulted in significantly lower viscosity and less extensive changes to the volatile profile, compared with indirect heat treatment. Overall, the application of direct and indirect heat treatment to WPI solutions resulted in significantly different final products in terms of appearance, physical characteristics and volatile profile, with direct heating resulting in many enhanced properties compared with conventional indirect heat treatment.

peer-reviewed Acid whey (AW) is the liquid co-product arising from acid-induced precipitation of casein from skim milk. Further processing of AW is often challenging due to its high mineral content, which can promote aggregation of whey proteins, which contributes to high viscosity of the liquid concentrate during subsequent lactose crystallization and drying steps. This study focuses on mineral precipitation, protein aggregation, and lactose crystallization in liquid AW concentrates (∼55% total solids), and on the microstructure of the final powders from 2 independent industrial-scale trials. These AW concentrates were observed to solidify either during processing or during storage (24 h) of pre-crystallized concentrate. The more rapid solidification in the former was associated with a greater extent of lactose crystallization and a higher ash-to-protein ratio in that concentrate. Confocal laser scanning microscopy analysis indicated the presence of a loose network of protein aggregates (≤10 µm) and lactose crystals (100–300 µm) distributed throughout the solidified AW concentrate. Mineral-based precipitate was also evident, using scanning electron microscopy, at the surface of AW powder particles, indicating the formation of insoluble calcium phosphate during processing. These results provide new information on the composition- and process-dependent physicochemical changes that are useful in designing and optimizing processes for AW.

peer-reviewed The effects of heat treatment and protein standardisation on the physical properties of skim milk concentrates were determined. Protein standardisation was carried out by the addition of lactose or milk permeate to skim milk. Unstandardised and standardised skim milk was subjected to heat treatment temperatures of 90 or 120 °C prior to evaporation whereafter the solids content was increased to 46% (w/w). Viscosity data showed non-standardised concentrates had the highest viscosity, followed by skim standardised with milk permeate followed by that standardised with lactose. Thermal treatment at 120 °C also resulted in a higher viscosity than that at 90 °C for all concentrates. Particle size data of evaporated skim milk showed a bimodal size distribution for skim milk standardised with liquid milk permeate, compared with monomodal distribution profiles for unstandardised skim milk and lactose standardised skim milk. Overall, this study showed that protein standardisation and standardisation media significantly affected concentrate properties.

This study investigated the effects of dephosphorylation and sodium hexametaphosphate (SHMP) salt addition on the viscosity of milk protein concentrate (MPC) solutions. Dephosphorylation (DP) of casein was performed using bovine alkaline phosphatase. Nuclear magnetic resonance (NMR) spectra showed that dephosphorylation depleted the casein-bound phosphate region (CNP). SHMP addition (5 mM) had no impact on the 31P NMR spectra of DP-MPC; addition of 5 mM SHMP to control MPC (C-MPC) resulted in a shift in peaks associated with the CNP region, possibly caused by SHMP sequestering calcium, leading to swelling of micelles. DP-MPC exhibited a lower viscosity compared to C-MPC, with SHMP addition at 12.5 and 25 mM causing gelation of C-MPC and DP-MPC solutions. This work confirmed the role that phosphate residues have in maintaining micelle structural stability and provides new insights into controlling viscosity of MPC solutions.

Serum protein concentrates (SPCs) were generated from reconstituted skim milk (3.2% protein) using lab-scale tangential-flow filtration at 3–4 °C. The influence of membrane type on process performance (e.g., permeate flux) and protein-enrichment (e.g., protein profile) was assessed with polyvinylidene-difluoride membranes (0.1 μm and 0.45 μm pore-size), and a polyethersulfone membrane (1000 kDa cut-off). The 1000 kDa membrane exhibited the highest starting flux (6.7 L m −2 h −1 ), followed by the 0.1 μm (5.4 L m −2 h −1 ) and 0.45 μm (4.8 L m −2 h −1 ) membranes. Flux decreased by >40% during filtration with the 1000 kDa and 0.1 μm membranes, while the decrease was lower ( 97% of casein in SPCs from the 0.1 μm and 1000 kDa membranes. SPCs from the 0.45 μm membrane had higher β-casein:α s -casein ratios than the feed and higher levels of minor whey proteins (e.g., lactoferrin) relative to the other SPCs.

This study examined the effects of total solids (TS), preheat treatment temperature, and first- and second-stage homogenisation pressures on the stability of model infant formula emulsions, using factorial statistical design. Oil droplet size decreased with increasing first- and second-stage homogenisation pressures. The viscosity of emulsions after homogenisation was mainly affected by TS. Spray drying altered the protein profile of the interfacial layer around oil droplets compared to that posthomogenisation, but did not alter oil droplet size. This work made it possible to select optimum conditions to produce a stable infant formula emulsion, with the use of lower homogenisation pressures.

The aim of this study was to determine the effects of ultrasound on the dissolution properties of milk protein concentrate (MPC) powders. A high intensity ultrasound (20 kHz; power 70.2 W) was used to dissolve MPC powder and the dissolution rate was compared to conventional methods of dispersion (e.g., stirring). Rehydration of MPC by stirring at 50 °C complied with the 2-step dissolution model whereby the disappearance of larger particles coincided with the formation of smaller ones over time. MPC dispersal by sonication dramatically accelerated this process, achieving >90% levels of powder solubilisation. Temperature rise (>70 °C) during sonication causes protein denaturation and aggregation, but this can be alleviated using thermal dissipation. Overall, the use of a combination rehydration process for MPC powders involving (i) conventional dissolution (stirring) for 10 min at 50 °C followed by (ii) ultrasonication (

Lactoferrin and β-casein represent a large proportion of the proteins in human milk and, as a result, are important ingredients for the manufacture of infant formula. At pH 7, lactoferrin has a net positive charge, compared to the negatively charged β-casein. The effects of CaCl 2 and heat treatment on the stability of oil-in-water emulsions stabilised by lactoferrin and/or β-casein were investigated. The ζ-potential values of emulsions stabilised with β-casein or a 1:1 mixture of β-casein/lactoferrin significantly ( P 2 , while CaCl 2 had no significant ( P > 0.05) effect on the ζ-potential of lactoferrin-stabilised emulsions. Particle size of β-casein-stabilised emulsions increased significantly ( P 2 , due to flocculation, while emulsions stabilised with lactoferrin and β-casein/lactoferrin remained unaffected by CaCl 2 addition. Oscillatory rheology measurements showed that β-casein-stabilised emulsions formed a gel when CaCl 2 was added, due to calcium-bridging, compared to lactoferrin-stabilised emulsions, where a weaker gel was formed in the presence of CaCl 2 . While, 30 mM CaCl 2 did not increase the elastic modulus ( G ′) of β-casein/lactoferrin-stabilised emulsions. Lactoferrin protected β-casein from calcium-induced flocculation by: (1) binding calcium ions via sialic acid groups on lactoferrin molecules and reducing the number of free ions available to form calcium linkages between β-casein molecules; (2) electrostatically interacting with negatively charged phosphate groups on β-casein molecules, blocking calcium–phosphate interactions and (3) providing additional stability through increased steric repulsion between β-casein/lactoferrin conjugates, due to the large molecular size of lactoferrin.