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The effect of particle size on physicochemical stability, bioaccessibility, and bioactivity of bioactive compounds is important in the design of delivery systems. It is challenging to control the size of delivery systems without altering chemical composition. In the present study, the re-assembly of dissociated egg yolk granules was modulated by Ca2+ to produce recombined granules with controlled hydrodynamic diameter (Dh). Quercetin was selected as a representative bioactive compound encapsulated within recombined granules (Gra-Que). Encapsulation efficiency and loading efficiency increased with an increase in Dh until phase separation occurred at 250 µg/mL Ca2+. The thermal and photochemical stability of Gra-Que increased as Dh increased, whereas samples with the smallest Dh demonstrated the highest storage stability. Gra-Que with an intermediate Dh had the highest bioaccessibility due to a balance between the protection of quercetin and susceptibility to digestion. Smaller samples had higher bioactivity due to higher cellular uptake and greater susceptibility to digestion.

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.

Milk fat globules (MFGs) are secreted from the mammalian gland and are composed of a triacylglycerol core surrounded by a triple membrane structure, the milk fat globule membrane (MFGM). The MFGM contains complex lipids and proteins reported to have nutritional, immunological, neurological and digestive functions. Human and ruminant milk are shown to share a similar MFG structure but with different size, profile and abundance of protein and polar lipids. This review summarizes the reported data on human, bovine, caprine and ovine MFG composition and concentration of bioactive components in different MFG-size fractions. A comprehensive understanding of compositional variations between milk from different species and MFG size fractions may help promote various milk sources as targeted supplements to improve human development and health. MFG size and MFGM composition are species-specific and affected by lactation, diet and breed (or maternal origin). Purification and enrichment methods for some bioactive proteins and lipids present in the MFGM have yet to be established or are not scaled sufficiently to be used to supplement human diets. To overcome this problem, MFG size selection through fractionation or herd selection may provide a convenient way to pre-enrich the MFG fraction with specific protein and lipid components to fulfill human dietary and health requirements.

The effect of whey proteins and heat treatment (90 °C, 5 min) on pepsin-induced hydrolysis of κ-casein, and subsequent coagulation of casein micelles, was investigated at pH 6.3 and 6.0 using reverse-phase HPLC, oscillatory rheology, and confocal laser scanning microscopy. Whey proteins did not affect the hydrolysis of κ-casein but retarded the coagulation process. Heat treatment did not affect the hydrolysis kinetics in whey protein (WP)-free samples, but slightly impaired the hydrolysis rate in WP-containing samples. The coagulation process of WP-free samples was little affected by heat-treatment. However, compared with unheated WP-contained sample at the same pH, the coagulation process of the heated sample was retarded at pH 6.3 but enhanced at pH 6.0. The curd in heated samples with smaller pores had higher water holding capacity. This knowledge provides further understanding on the role of whey proteins and heat treatment on the coagulation mechanisms of milk under gastric conditions.

Milk fat globule membrane (MFGM) fractions were isolated from fresh raw cream at different temperatures and pH values. The polar lipid (PL) composition of these fractions, and of commercially produced α-serum, β-serum, and buttermilk powder samples, was determined. Lower temperature and pH during churning increased the total level of PLs in the MFGM fractions. Phosphatidylethanolamine (31–36% of total PLs), phosphatidylcholine (31–39%), and sphingomyelin (13–24%) were the major PLs in all MFGM fractions; phosphatidylserine (2–7%) and phosphatidylinositol (2–4%) were the minor ones. The β-serum fraction had the highest total PL content of the commercial samples (2.9 mg g−1 fat); buttermilk powder contained the least amount of total PL amongst all fractions (0.99 mg g−1). Processing temperature and pH can therefore influence the PL composition, likely due to how the treatments impact on the different PLs that are located within different regions within the MFGM trilayer structure.

Sphingomyelin (SM) and cholesterol complexation gives rise to detergent-resistant liquid-ordered domains. The persistence of these domains and subsequent mixed micelle formation was examined in the presence of bile under physiological digestive in vitro conditions for vesicles comprising either SM/cholesterol, porcine brain phosphatidylcholine (BPC)/cholesterol, or soy phosphatidylcholine (SPC)/cholesterol bilayers, the latter two systems having no liquid-ordered domains. Micellization of these digested phospholipid multilamellar vesicle systems was confirmed by transmission electron microscopy. Bovine bile was found to consist of large multilamellar sheets which subsumed phospholipid vesicles to form aggregated superstructures. Budding off from these superstructures were vesicle-to-micelle transition intermediates: unilamellar vesicles and cylindrical micelles. The presence of cholesterol (60/40 phospholipid/cholesterol mol/mol) delayed the initial rapid onset of digestion, but not for BPC and SPC vesicle systems. Acyl chain order/disorder before and after vesicle-to-micelle transition of all three phospholipid/cholesterol systems was examined using Raman spectroscopy. The addition of bovine bile to both PC/cholesterol vesicle systems reduced the overall ratio of acyl chain disorder to order. In SM/cholesterol vesicles with ≤ 20% mol cholesterol, only the lateral inter-acyl chain packing was reduced, whereas for SM/cholesterol vesicles with ≥ 30% mol cholesterol, a higher proportion of gauche-to-trans isomerization was apparent, demonstrating that SM/cholesterol complexes modify the acyl chain structure of micelles.

Tea consumption is practised as a tradition, and has shown potential to improve human health. Maximal uptake of tea antioxidants and milk proteins without a negative impact on tea flavor is highly desired by consumers. There is a conflicting evidence of the effect of milk addition to tea on antioxidant activity. Differences in the type of tea, the composition, type and amount of milk, preparation method of tea-milk infusions, the assays used to measure antioxidant activity, and sampling size likely account for different findings. Interactions between tea polyphenols and milk proteins, especially between catechins and caseins, could account for a decrease in antioxidant activity, although other mechanisms are also possible, given the similar effects between soy and bovine milk. The role of milk fat globules and the milk fat globule membrane surface is also important when considering interactions and loss of polyphenolic antioxidant activity, which has not been addressed in the literature.

Pulsed electric field (PEF)-treated milk (25.7 kV/cm for 34 μs after preheating to 55 °C and holding for 24 s) was microbiologically stable for 21 days at 4 °C, and similar to thermally treated milk (63 °C for 30 min or 73 °C for 15 s). Alkaline phosphatase inactivation was comparable after PEF (preheating followed by PEF) and both thermal treatments. PEF treatment initially reduced xanthine oxidase (30%) and plasmin (7%) activities, but after 21 days of refrigerated storage these activities were similar to the initial untreated milk. During refrigerated storage of PEF (preheating followed by PEF) and thermally treated milk, lipolytic activity increased and pH levels decreased.

The protein composition, redox potential (Eh), and xanthine oxidase (XO) content and activity were determined for anhydrous milk fat emulsions containing milk fat globule membrane (MFGM) fractions derived from either buttermilk or commercial sources of bovine α-serum, β-serum, and buttermilk powder (BMP). Caseins were the dominant proteins in the MFGM fractions isolated from BMP and buttermilk, whereas fractions from α- and β-serum contained higher amounts of membrane proteins. The XO content and activity was >70-fold and >700-fold higher in α- and β-serum samples, respectively, compared with the BMP fraction. The Eh values of the recombined emulsions were highest for α-serum (196 mV), and β-serum (169 mV), followed by BMP (131 mV). These positive values contrasted with the highly negative Eh of the buttermilk emulsion (−580 mV). This study demonstrates how milk-processing methods can alter the composition and functionality of the MFGM.

Two green tea polyphenols, catechin and epigallocatechin gallate (EGCG), were encapsulated in soy lecithin liposomes before being incorporated into low-fat hard cheese that was ripened for 90 days at 8 °C. Fortification of low-fat cheese with liposome-encapsulated catechin or EGCG led to a significant increase ( p in vitro gastrointestinal digestion. There was no significant effect of encapsulation on cheese composition, pH, or cheese yield from milk. Catechin and EGCG were not detected in the cheese whey, indicating complete retention in the cheese structure. About half of the initial catechin and one-third of EGCG were recovered from the cheese digesta. The process of liposomal encapsulation of phenolic compounds enabled a high level of retention in low-fat cheese with release under gastrointestinal digestive conditions to increase the antioxidative functionality of cheese.

Six types of milk fat globule membrane (MFGM) fractions were isolated from fresh raw cream using various churning conditions at different temperature (10, 15 or 20 °C) and pH values (5.5 or 6.6) and characterised for protein composition, xanthine oxidase (XO) content and activity, and oxidation–reduction potential (E h ). A greater proportion of non-membrane proteins was found at higher temperatures and higher cream pH, and the XO content decreased significantly under these conditions. XO activity was greater at lower temperatures and pH, yielding a more positive E h value for the emulsions. Storage at 4 °C for 14 d significantly reduced the Eh of the emulsions to between −320 mV and −580 mV for low pH/low temperature, and high pH/high temperature emulsions, respectively. This study suggests that it is possible to obtain MFGM fractions with specific Eh reducing ability by altering churning conditions.

Green tea extract (GTE) was incorporated into full-fat cheeses at 250, 500, and 1000 ppm to investigate the effect of green tea catechins on antioxidant properties and microstructure of cheese, and recovery of catechins. Cheeses were ripened for 90 days at 8 °C followed by simulated gastrointestinal digestion. The composition on Day 0, and pH, total phenolic content (TPC), and antioxidant activity (AA) of the cheeses on Days 0, 30, and 90, were determined. The concentrations of the major GTE catechins in the curd and from the digesta of mature cheeses were determined using HPLC. Addition of GTE significantly (p ≤ 0.05) decreased the pH of whey and curd during cheese manufacture and ripening, however there was no significant (p > 0.05) effect on moisture, protein, or fat contents. Addition of GTE increased TPC and AA at all concentrations, but in a non-linear manner. Individual catechins were selectively retained in the curd, whereas different portions were recovered from the cheese digesta. Transmission electron microscopy showed that the ripened control cheese had a regular distribution of milk fat globules entrapped in a homogeneous structure of casein proteins, which was disrupted by GTE. Interactions between green-tea catechins and cheese fat were confirmed by Fourier transform infrared spectroscopy.

A new rapid isocratic HPLC method was developed to quantify xanthine oxidase activity in several dairy products by determining both substrate (xanthine) and product (urate) concentrations at short retention times (6.76 min and 4.92 min, respectively) with high values for linearity and reliability. The impact of added green tea catechins (1000 ppm) on xanthine oxidase activity was also examined in dairy products containing fat globules using the developed HPLC method. The addition of (+)-catechin, (−)-epigallocatechin gallate (EGCG), and green tea extract significantly ( p ≤ 0.05) decreased the xanthine oxidase activity of these products. The effect of EGCG on decreasing xanthine oxidase activity of milk fat globules was stronger than for (+)-catechin, and can be attributed to different structures of green tea polyphenols, such as different numbers of OH groups in catechins. The results of this study suggest possible associations between milk fat globule surfaces and green tea catechins.

(+)-Catechin or green tea extract were encapsulated in soy lecithin nanoliposomes and incorporated into a full-fat cheese, then ripened at 8 °C for 90 days. Cheese samples were subjected to simulated gastrointestinal digestion to measure total phenolic content (TPC) and antioxidant activity of the cheese digesta, and to determine the catechin recovery after digestion by high performance liquid chromatography (HPLC). Addition of catechin or green tea extract significantly (P ≤ 0.05) increased TPC and antioxidant activity (measured by ferric reducing antioxidant power and oxygen radical absorbance capacity) of the full-fat cheese without affecting pH or proximate composition. HPLC analysis confirmed retention of encapsulated catechins in the cheese curd; however, individual catechins were recovered in differing amounts (15-52%) from cheese digesta after 6 h of digestion. Transmission electron microscopy and Fourier transform infrared spectroscopy provided evidence for association of nanoliposomes with the surface of milk fat globules inside the cheese matrix. The study shows the potential for using cheese as a delivery vehicle for green tea antioxidants.

Changes to the bovine milk fat globule membrane (MFGM) were assessed after a combination of pre-heating at 55 °C for 24 s followed by pulsed electric field (PEF) treatment at 20 kV cm−1 or 26 kV cm−1 for 34 μs, and compared to changes after thermal treatments at 63 °C or 73 °C. A decrease in milk fat globule size, increase in ζ-potential and specific surface area, and adsorption of plasma proteins onto the surface of the MFGM occurred after pre-heating and PEF and thermal treatments. The increase in ζ-potential was correlated with the surface coverage of MFGM with the plasma proteins which was further confirmed by transmission electron microscopy. PEF treatment of whole milk had less impact on the structure of milk fat compared to high temperature thermal treatments alone. This study suggests that a combination of PEF and low heat treatment at 55 °C may have less detrimental effect on the fat globule surface in whole milk.

The objective of this study was to evaluate the cytotoxicity of microemulsions prepared from glycerol monocaprylocaprate (Capmul MCM), non-ionic surfactant (Tween 80), and phosphate buffer loaded with β-carotene extracted from carrot pomace, to human intestinal epithelial (Caco-2) cells and to determine if non-cytotoxic concentrations of the natural β-carotene loaded microemulsion could protect Caco-2 cells from oxidative damage caused by exposure to H2O2. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and lactate dehydrogenase assays were used to determine mitochondria functionality and cell membrane integrity, respectively, both of which are commonly used to evaluate cell viability. In addition nitride oxide level was measured as a general indicator of cellular disruption and inflammation. Cytotoxicity of the formulations significantly decreased when lowering the microemulsion concentration. Increasing the cytotoxicity of microemulsions at concentrations higher than 0.0313% (Tween 80 concentration of 0.006%) might be the result of Tween 80 precipitation on the cell culture monolayer, and β-carotene loaded in the microemulsion did not appear to protect cells from Tween 80 associated damage. However, a β-carotene loaded microemulsion concentration of 0.0313% gave bioprotection to cells suffering oxidative damage caused by H2O2. These results show the potential of using natural β-carotene microemulsion as a delivery system at a safe level of Tween 80 for application in pharmaceutical and food sciences.

Bacterial count reduction and enzyme inactivation in bovine whole milk by pulsed electric field (PEF) processing combined with pre-heating and intermediate cooling was compared with that induced by thermal treatments (maximum of 63 °C for 30 min and 73 °C for 15 s). Milk was pre-heated to 55 °C for 24 s and PEF-treated in continuous mode at electric field intensities of 15.9–26.2 kV cm−1 for 17–101 μs. PEF treatments reduced the number of inoculated (8.3 log cfu mL−1) Escherichia coli and Listeria innocua to less than 2 log cfu mL−1. PEF treatments at 20.7–26.2 kV cm−1 reduced the total plate count and indigenous alkaline phosphatase activity to a level similar to that measured following thermal treatments. Treatment at 26.1 kV cm−1 for 34 μs, combined with pre-heating, reduced the activity of plasmin, xanthine oxidase and lipolysable fat by 12%, 32% and 82%, respectively, compared with raw milk.

Cheese microstructure, flavor, quality, and microbial growth are intricately linked. It has been argued that cheese microstructure dictates development of enzymatic flavor reactions, appearance, texture, release of nutrients under digestive conditions, and the relative populations of microbial species. New developments in advanced physical analyses have provided new insights into cheese microstructure. Milk and cheese processing and ripening conditions have profound effects upon the textural quality of the cheese. The relative location of cheese structural components dictates digestibility and ultimately the release of key nutrients, clearly showing the importance of microstructure on cheese quality.

The emulsifying properties of plant legume protein isolates (soy, pea, and lupin) were compared to a milk whey protein, β-lactoglobulin (β-lg), and a nonionic surfactant (Tween 20). The protein fractional composition was characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The following emulsion properties were measured: particle diameter, shear surface ζ-potential, interfacial tension (IT), and creaming velocity. The effect of protein preheat treatment (90 °C for 10 min) on the emulsifying behavior and the release of selected volatile organic compounds (VOCs) from emulsions under oral conditions was also investigated in real time using proton transfer reaction-mass spectrometry. The legume proteins showed comparable results to β-lg and Tween 20, forming stable, negatively charged emulsions with particle diameter d3,2 < 0.4 μm, and maintained stability over 50 d. The relatively lower stability of lupin emulsions was significantly correlated with the low protein surface hydrophobicity and IT of the emulsion. After heating the proteins, the droplet size of pea and lupin emulsions decreased. The VOC release profile was similar between the protein-stabilized emulsions, and greater retention was observed for Tween 20-stabilized emulsions. This study demonstrates the potential application of legume proteins as alternative emulsifiers to milk proteins in emulsion products.

The enzymatic activity of xanthine oxidase (XO) located within the native and recombined milk fat globule membrane (MFGM) on emulsion surfaces was investigated after successive washing with deionised water (DW) or simulated milk ultrafiltrate (SMUF). DW was more effective than SMUF at removing non-MFMG proteins from the globule surface. Surface XO activity on a protein basis increased after three washes due to loss of MFGM proteins to the serum phase. Recombined emulsions had higher surface enzymatic activity than washed native fat globule samples. The oxidation of acetaldehyde, 3-methylbutanal, 2-methylpropanol and 2-methylbutanal to the corresponding acids by XO on the globule surface was analysed. A higher proportion of aldehydes were depleted at higher XO activity when the initial aldehyde concentration was constant, and for higher initial concentrations of aldehydes. The recovery of aldehydes and acids was above 79%, indicating that the depleted aldehydes were mostly converted to the corresponding acids.

Thermodynamically stable microemulsions were used to extract β-carotene from pulsed electric field (PEF)-treated carrot pomace. In this study, a three-level Box–Behnken design was used to predict the effect of extraction time (10–110 min), extraction temperature (30–70 °C) and carrot/microemulsion ratio (1:30–1:90 w/w) on the β-carotene content, polydispersity index (PDI) and particle size of the microemulsions. The β-carotene extracted from PEF-treated carrot pomace using microemulsions was higher than untreated carrot pomace. The extraction efficiency of β-carotene using microemulsions was higher compared to 100 % hexane or 100 % glycerol monocaprylocaprate oil. A mathematical model was developed to predict the optimal extraction conditions using transparent microemulsions with high loading of β-carotene, low PDI and small microemulsion particle size. The model predicted that an extraction time of 49.4 min, temperature of 52.2 °C and carrot/microemulsion ratio of 1:70 (w/w) would result in microemulsions with β-carotene loading of 19.6 μg/g, PDI of 0.27 and particle size of 74 nm. This study demonstrates the potential of using oil-in-water microemulsions as extraction media for β-carotene.

Giant unilamellar vesicles (GUVs) were constructed using an electroformation technique to mimic the morphology of the native milk fat globule membrane (MFGM) for the purpose of structural investigation. Bovine milk derived phospholipids were selected to manufacture GUVs which were characterized by confocal laser scanning microscopy after fluorescent staining. Circular nonfluorescent dark regions were observed in a 3/7 (mol/mol) surface mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3 phosphoethanolamine. Linear shaped dark lipid domains were found in GUVs containing sphingomyelin (SM) in the absence of cholesterol. The dark regions were interpreted as a gel phase formed by a high gel–liquid phase transition temperature (Tm) of DPPC and SM. This study provides a strategy for investigating the lipid structural organization within the native MFGM using a model lipid bilayer system and reveals that a SM and cholesterol association network is not the only requirement ...

Summary The purpose of this research was to study the effect of electric field strength (0.1–1 kV cm−1) and frequency (5–75 Hz) during pulsed electric field (PEF) processing on the extractability of carotenoids in carrots, which was examined using different vegetable oils. Increasing electric field strengths up to 1 kV cm−1 at 5 Hz significantly (P

Inactivation of Gram-negative and Gram-positive bacteria in whole milk by pulsed electric field (PEF) processing with pre-heating of milk and stepwise intermediate cooling was compared with thermal pasteurisation. Electric field strengths of 18–28 kV cm −1 for 17–235 μs were applied to milk at different temperatures for 24 s. PEF treatment at 4 °C did not reduce bacterial numbers, but the effectiveness increased with increasing temperature. PEF treatments at 22–28 kV cm −1 for 17–101 μs at 50 °C gave a 5–6 log reduction, below the detection limit for Pseudomonas aeruginosa , while Escherichia coli , Staphylococcus aureus and Listeria innocua were reduced to below the detection limit at 55 °C. Gram-negative bacteria were less resistant to PEF than Gram-positive bacteria. PEF treatment with stepwise intermediate cooling after pre-heating at 55 °C for 24 s at a flow rate of 4.2 mL s −1 has the potential to pasteurise whole milk.

Thermal pasteurization ensures safety and enhances the shelf-life of milk. Exposure to heat can modify labile milk components and alter the functional properties of milk proteins. This has driven the development of non-thermal food preservation techniques such as pulsed electric field (PEF) processing, primarily for the inactivation of spoilage microorganisms. Milk components, in particular fat and protein, affect the functionality, yield and quality of dairy products, requiring a clear understanding of the structural and chemical changes occurring due to PEF processing. This review critically discusses current knowledge of the impact of PEF treatment on the functional properties of milk, namely, the physicochemical changes of milk components, changes in technological properties, shelf-life, and sensory and nutritional properties.

The proteolytic changes under in vitro digestive conditions were examined by urea-polyacrylamide gel electrophoresis, Kjeldahl determination of nitrogen, and fluorescamine analysis to evaluate the level of free amino terminal groups as an indicator of the degree of proteolysis. The protein and fat components of cheese digesta were visualized by confocal laser scanning microscopy. Cheese disintegration and subsequent release of proteins and polypeptides was quantified after each of three in vitro digestion phases: oral, gastric (pepsin, pH 2), and intestinal (pancreatic enzymes, pH 6.8). Most of the disintegration of the cheese protein matrix (˜75%), proteolysis, and protein release occurred during the intestinal digestion phase. Fat aggregate release from the cheese matrix mostly occurred in the gastric and intestinal digestion phases, and globules became more spherical after the gastric phase. Proteolysis took place primarily in the gastric and intestinal phases. These results show the importance of microstructure and the digestive environment on the release of cheese components.

The relationship between emulsion structure and the release of volatile organic compounds (VOCs) was investigated using a model mouth system under oral conditions (tongue mastication, artificial saliva, pH and salt). The VOCs were monitored on-line by proton transfer reaction mass spectrometry (PTR-MS). Two types of emulsion system were compared: primary and multilayer oil-in-water (P-O/W, M-O/W) emulsions consisting of soy oil coated by β-lactoglobulin and pectin layers. The P-O/W emulsions showed intensive flocculation at pH 5 and above 200 mM NaCl where the electrostatic repulsive charge was at a minimum. Bridging and depletion flocculation were mostly observed for P-O/W emulsions containing artificial saliva with 1 wt% mucin. The VOC release was found to increase when the emulsion droplets flocculated, thus changing the oil volume phase distribution. The adsorbed pectin layer stabilised the emulsion structure under conditions of short-time oral processing, and hindered the release of hydrophobic VOCs.

Summary The effect of (+)-catechin on total phenolic content (TPC) and antioxidant properties in low-fat hard cheese were examined over a 90-day ripening period at 8 °C. Antioxidant activity (AA) in cheese was measured by ferric reducing antioxidant power, oxygen radical absorbance capacity (ORAC) and 2,2-diphenyl-1-picrylhydrazyl assays and compared with TPC. Catechin retention coefficients in cheese curds were in the range of 0.63–0.75 and decreased the pH of cheese without affecting protein, fat or moisture content. Both TPC and AA increased during the 90-day ripening period. Oxygen radical absorbance capacity was the most suitable technique for evaluating AA in cheese due to the high correlation with TPC and suitability in both lipophilic and hydrophilic systems.

Due to their well-known health benefits, green tea catechins have received recent attention as natural additives in foods such as dairy products. However, they may present some irreversible associations with milk components (e.g. protein and milk fat globules). To investigate the behaviour of two important green tea catechins, (+)-catechin (C) and (−)-epigallocatechin gallate (EGCG), in a standard whole milk system under the conditions of cheesemaking, 250 and 500 ppm of each catechin were added to whole milk (3.3% fat). Although both C and EGCG at either concentration increased both total phenolic content and total antioxidant capacity of the subnatants obtained from the milk system, there was a less linear increase when the concentration of the catechins was doubled, whereas C or EGCG were recovered (measured by HPLC) differently. Overall, these results suggest a degree of associations between green tea catechins with milk proteins and milk fat.

Molecular integrations between green tea catechins and milk fat globules in a cheese matrix were investigated using solid-state magic angle spinning nuclear magnetic resonance spectroscopy. Full-fat cheeses were manufactured containing free catechin or free green tea extract (GTE), and liposomal encapsulated catechin or liposomal encapsulated GTE. Molecular mobility of the carbon species in the cheeses was measured by a wide-line separation technique. The (1)H evolution frequency profile of the (13)C peak at 16ppm obtained for the control cheese and cheeses containing encapsulated polyphenols (catechin or GTE) were similar, however, the spectrum was narrower for cheeses containing free polyphenols. Differences in spectral width indicates changes in the molecular mobility of --CH3- or -C-C-PO4- species through hydrophobic and/or cation-π associations between green tea catechins and cheese fat components. However, the similar spectral profile suggests that encapsulation protects cheese fat from interaction with catechins.

The impact of high methoxyl pectin adsorption on β-lactoglobulin (βLG) conformation in solution and at the interface of an oil-in-water emulsion was investigated using 6-propionyl-2-(dimethylamino)naphthalene and retinol probes to monitor βLG binding availability for hydrophobic compounds. The effects of pH (2.0–9.0) and ionic strength of NaCl (0–330 m m ) and CaCl 2 (0–1 m ) were also examined. An increase in surface hydrophobicity ( S 0 ) and retinol binding was observed for pH above 7 where the protein had a more flexible and open conformation. Pectin attachment to βLG at pH 4 had a significant impact on S 0 due to protein unfolding, confirmed by differential scanning calorimetry. Retinol binding was not affected in the closed calyx structure of βLG. Similar behaviour occurred for multilayer emulsions. The addition of salts caused a reduction in S 0 and retinol binding as the protein underwent partial aggregation in solution and at the interface of the primary emulsion.

The perception of aroma during oral processing is a complex interplay of many factors, partly related to the food matrix as well as to the oral processing conditions. The role of the tongue in transporting the bolus through the mouth by pressing it against the palate has been widely studied, however, the relationship between tongue pressures generated and volatile organic compound (VOC) release is not clear. Pressure patterns during swallowing were found to be unique across subjects which may suggest personal flavor perception. The model mouth described here is capable of reproducing actual human tongue pressure patterns by a computer controlled artificial tongue driven by an actuator. The tongue functionality is monitored by pressure and force sensors. The model was designed to incorporate oral features and conditions (e.g. temperature, saliva flow, gas flow and appropriate oral cavity volumes) with on-line VOC measurement using proton transfer reaction–mass spectrometry. Tongue material from different elastomeric materials was tested for inertness. The model will be used in follow-up studies to investigate in vitro VOC-release. Industrial relevance This paper describes the development of an innovative model mouth which has a potential industrial application as a product development evaluation tool for food and pharmaceutical companies. The model is capable of providing fast and accurate feedback on the product flavor release and its physical properties under oral conditions.

Multilayer oil-in-water (M-O/W) emulsions were compared to primary oil-in-water (P-O/W) emulsions as carriers for volatile organic compounds (VOCs) under various environmental conditions (pH and salt). The M-O/W emulsion consisted of soy oil coated with β-lactoglobulin (βLG) and pectin layers. The release of VOCs with different physiochemical properties from aqueous solutions and emulsion systems was measured using static and dynamic headspace methods. The partition coefficients (K) calculated by the phase ratio variation (PRV) method, showed different volatile release profiles between the emulsion types. An increase in VOC release was found for the unstable P-O/W emulsion at pH 5, whereas M-O/W emulsions were stable at the same pH and retained the hydrophobic VOCs. Hydrophobic interactions and hydrogen bonds with the secondary dense layer of pectin may be responsible for the improved retention. Increasing pH and ionic strength acts as a VOC release trigger to detach the pectin from the interface. The release rates from initial dynamic curves support the results under equilibrium conditions. The results of this study demonstrate the capability of using M-O/W emulsions for controlled release of VOCs, as well as an alternative system to create stable emulsions with similar VOC release profiles.

Confocal Raman microscopy was used to determine the chemical fingerprint of individual bovine milk fat globules of different sizes and from milk sourced from different breeds. No detectable level of triglycerides was found in the small milk fat globules of 1 μm diameter or less in size. These small fat globules also delivered information about the lipids of the milk fat globule membrane. In addition, the lipid composition varied according to the size of the globules with an increasing concentration of carotenoids and decreasing level of unsaturation with increasing diameter. The carotenoids content also varied according to the breed origin of the milk, with Jersey milk fat globules containing more carotenoids than the Friesian-Jersey milk fat globules. The results suggest that the milk fat globules have different properties according to their size.

Monolayers were prepared from phospholipids extracted from bovine milk and used as a model system to mimic the native milk fat globule membrane (MFGM) surface structure in various microscopic experiments. The natural complex mixtures of phospholipids were isolated from bovine raw milk, raw cream, processed whole milk, and buttermilk powder by total lipid extraction and solid-phase extraction. A Langmuir film balance mounted on an epifluorescence microscope was used to analyze the physical behavior of the monolayer films and the phase coexistence resulting from the formation of phospholipid microdomains within these films. Atomic force microscopy was used for nanometer-scale topographic resolution of the microdomains. This study allowed comparison of the behavior of phospholipid monolayers from dairy products at different stages of processing, analysis of the formation of microdomains, and the study of the effect of milk processing on lipid-lipid interactions and phase coexistence. It was observed that milk processing changes the physical behavior of phospholipid monolayers by altering the phospholipid profile and the fatty acid distribution.

The aim of this work was to assess the accuracy of different extraction methods of phospholipids and to measure the effect that processing has on phospholipid composition. Four methods of extracting phospholipids from buttermilk powder were compared to optimize recovery of sphingomyelin. Using the optimal method, the phospholipid profile of four dairy products (raw milk, raw cream, homogenized and pasteurized milk, and buttermilk powder) was determined. A total lipid extraction by the Folch method followed by a solid-phase extraction using the Bitman method was the most efficient technique to recover milk sphingomyelin. Milk processing (churning, centrifuging, homogenization, spray-drying) affected the profile of milk phospholipids, leading to a loss of sphingomyelin and phosphatidylcholine after centrifugation for cream separation. A corresponding decrease in the saturation content of the raw cream phospholipids and a loss of phosphatidylethanolamine after spray-drying to produce buttermilk powder were also observed.

This paper provides a critique of academic experiences of neoliberal economic reform at a New Zealand (NZ) university. The authors engaged in a collaborative inquiry that was based upon a developing theoretical perspective of the reform process and how this affected their academic lives. We were keen to develop an understanding of liberal educational philosophy and how neoliberalism impacts on this. In this context we examined the nature of compliance and an academic's role in society. We conclude that universities in NZ are historically liberal and that there are limits to the neoliberal project due to the relationship that individuals have with knowledge and the pressures that come from being part of a worldwide academic community that aspires to excellence in research and teaching. However, new compliance measures, such as Performance-based Research Funding, have changed academic work and made a broader societal role for academics more difficult. In serving society universities are required to accept a...

Important milestones in the understanding of cheese structure are highlighted. The development of complex instrumentation, such as transmission, scanning, cry-scanning and environmental electron microscopy, dynamic oscillatory low-strain rheology, confocal laser scanning microscopy, dynamic light scattering, and nuclear magnetic resonance have facilitated the development of structural models that can be used to predict functional properties. More recent developments in instrumentation have shown how the components interact and change during cheese ripening. The effects of pasta filata processing, high pressurisation of milk, freezing of cheese, and milk homogenisation on cheese structure and functionality are outlined. Future trends in cheese structural research are predicted.

Thermodynamics of milk components (milk fat, xanthine oxidase, caseins and whey proteins) in pulsed electric field (PEF)-treated milk were compared with thermally treated milk (63 °C for 30 min and 73 °C for 15s). PEF treatments were applied at 20 or 26 kV cm(-1) for 34 μs with or without pre-heating of milk (55 °C for 24s), using bipolar square wave pulses in a continuous mode of operation. PEF treatments did not affect the final temperatures of fat melting (Tmelting) or xanthine oxidase denaturation (Tdenaturation), whereas thermal treatments increased both the Tmelting of milk fat and the Tdenaturation for xanthine oxidase by 2-3 °C. Xanthine oxidase denaturation was ∼13% less after PEF treatments compared with the thermal treatments. The enthalpy change (ΔH of denaturation) of whey proteins decreased in the treated-milk, and denaturation increased with the treatment intensity. New endothermic peaks in the calorimetric thermograms of treated milk revealed the formation of complexes due to interactions between MFGM (milk fat globule membrane) proteins and skim milk proteins. Evidence for the adsorption of complexes onto the MFGM surface was obtained from the increase in surface hydrophobicity of proteins, revealing the presence of unfolded hydrophobic regions.

The determination of putative chemical interactions between the milk fat globule membrane and green tea catechins provided useful information about the role of milk fat globules (MFGs) in high-fat dairy systems, such as cheese, and containing bioactive compounds, such as tea catechins. Catechins from green tea (125-1,000 ppm), including (+)-catechin, (-)-epigallocatechin gallate, and green tea extract were added to washed MFGs to examine possible interactions. The addition of catechins gave a significant change in the size and ζ-potential of MFGs. The recovery of different catechins from the milk fat globule suspensions was found to vary, suggesting selective association with the milk fat globule membranes. The interactions were further investigated using transmission electron microscopy and Fourier transform infra-red spectroscopy. It is suggested that catechins are localised in association with milk fat globule membrane domains as they contain both hydrophobic and hydrophilic moieties with potential points of molecular interaction.

The stabilisation mechanisms of low-methoxy pectin, λ -carrageenan, guar gum, locust bean gum and xanthan in stirred yoghurt were investigated using dynamic oscillatory rheometry and water holding capacity measurements. As the level of low-methoxy pectin and λ -carrageenan increased, the stabilisation mechanism was consistent with the model of casein aggregates passing through a region of bridging flocculation, followed by partial steric stabilisation. For guar gum, locust bean gum and xanthan, the results were consistent with depletion flocculation at a low concentration of stabiliser, and trapped aggregated casein within a viscous polysaccharide solution at higher concentrations. A peak was observed for the phase angle of guar-stabilised yoghurt as a function of frequency, from 4.5 to 0.2 Hz as guar increased from 0.5 to 5 g L−1 for 1-day yoghurt, and from 4.5 to 2.2 Hz as the yoghurt containing 0.5 g L−1 guar gum was aged from 1 to 42 days. Results are interpreted with an understanding that the rheological behaviour is affected by the pre-sharing conditions of the stirred yogurt.

Confocal Raman microscopy was applied to detect the partitioning of a volatile compound, trans-2-hexenal, into bovine milk fat globules (MFGs). The interactions between trans-2-hexenal and individual MFGs were reflected by a change of spectral intensity of the volatile compound in the Raman shift region. At a relatively high concentration of trans-2-hexenal (5%, v/v), stronger intensities of the characteristic Raman spectra were found in the interior of the MFGs compared with the milk fat globule membrane (MFGM) region after reaching equilibrium, revealing that the MFG as a whole, rather than the MFGM, plays the major role in volatile compound absorption processes. The current study reports on an innovative instrumental method to investigate interactions among specific volatile compound and individual emulsion droplets.