Characterization of major radical scavenger species in bovine milk through size exclusion chromatography and functional assays

Antioxidant peptides, the guardian of life from oxidative stress

Reactive oxygen species (ROS) are produced during oxidative metabolism in aerobic organisms. Under normal conditions, ROS production and elimination are in a relatively balanced state. However, under internal or external environmental stress, such as high glucose levels or UV radiation, ROS production can increase significantly, leading to oxidative stress. Excess ROS production not only damages biomolecules but is also closely associated with the pathogenesis of many diseases, such as skin photoaging, diabetes, and cancer. Antioxidant peptides (AOPs) are naturally occurring or artificially designed peptides that can reduce the levels of ROS and other pro-oxidants, thus showing great potential in the treatment of oxidative stress-related diseases. In this review, we discussed ROS production and its role in inducing oxidative stress-related diseases in humans. Additionally, we discussed the sources, mechanism of action, and evaluation methods of AOPs and provided directions for future studies on AOPs.

Effect of Milk Origin and Seasonality of Yogurt Acid Whey on Antioxidant Activity before and after In Vitro Gastrointestinal Digestion

Yogurt acid whey (YAW) is a by-product of Greek strained yogurt production. The disposal of YAW constitutes an environmental problem, and given the increasing demand of Greek yogurt worldwide, its handling is a challenge. However, whey-derived peptides, resulting from microbial fermentation as well as those resulting from further hydrolysis during the digestion process, have been linked to enhanced biological activities. In this study, the antioxidant capacity of 33 samples of YAW obtained from Greek dairy companies of bovine, ovine or caprine origin was investigated using both cell-free and cell-based assays. The YAW samples, their in vitro digestion products (YAW-Ds) and a fraction of the digests (less than 3 kDa; YAW-D-P3) were assessed using four biochemical assays, namely ORAC, ABTS, FRAP and P-FRAP. Our data revealed a higher antioxidant capacity for digested samples compared with undigested samples, with all four methods. ORAC values after in vitro digestion were higher for the ovine samples compared to their bovine (YAW-D and YAW-D-P3) and caprine (YAW-D-P3) counterparts. Furthermore, the YAW-D-P3 fraction derived from samples collected in the summer months exhibited higher ORAC values when compared to the respective fraction from the winter months' samples. The cellular antioxidant activity of ovine YAW-D-P3 was improved in H2O2-treated HT29 cells compared to the control H2O2-treated cells. However, YAW-D-P3 could not trigger either the pathways involving the transcription factors NF-κB or NFE2L2 or the gene expression of SOD1, CAT and HMOX1 in LPS-challenged THP-1-derived macrophages. These results suggest that YAW, and particularly YAW from ovine origin, could be used as a natural source for its antioxidant potential in human and animal nutrition.

Sonolytic degradation kinetics and mechanisms of antibiotics in water and cow milk

Antibiotics (ABX) residues frequently occurred in water and cow milk. This work aims to understand the kinetics and mechanisms of sonolytic degradation of four ABX, i.e. ceftiofur hydrochloride (CEF), sulfamonomethoxine sodium (SMM), marbofloxacin (MAR), and oxytetracycline (OTC) in water and milk. In both water and milk, the sonolytic degradation of ABX follows pseudo-first order (PFO) kinetics well (R2: 0.951-0.999), with significantly faster ABX degradation in water (PFO kinetics constants (k1): 1.5 × 10-3-1.2 × 10-1 min-1) than in milk (k1: 3.5 × 10-4-5.6 × 10-2 min-1). The k1 values for SMM degradation in water increased by 118% with ultrasonic frequency (40-120 kHz), 174% with ultrasonic frequency (80-500 kHz), 649% with ultrasonic power (73-259 W), 22% with bulk temperature (12-40℃), and by 68% with reaction volume (50-250 mL), respectively, in other things being equal. The relevant k1 values in milk increased by 326%, 231%, 122%, 10% as well as 82% with the above same effective factors, respectively. The oxidation by free radicals generated in situ dominates ABX degradation, and the hydrophobic CEF (54.0-971.7 nM min-1) and SMM (39.2-798.4 nM min-1) underwent faster degradation than the hydrophilic MAR (33.9-751.9 nM min-1) and OTC (33.8-545.3 nM min-1) in both water and milk. Adding an extra 0.5 mM H2O2 accelerated SMM degradation by 19% in water and 33% in milk. After 130-150 min sonication of 100 mL of 2.0 mg L-1 (6.62 μM) SMM in various milk with 500 kHz and 259 W, the residue concentrations (52.9-96.3 μg L-1) can meet the relevant maximum residue limit (100 μg L-1).

Antioxidant Activity of Sweet Whey Derived from Bovine, Ovine and Caprine Milk Obtained from Various Small-Scale Cheese Plants in Greece before and after In Vitro Simulated Gastrointestinal Digestion

Whey-derived peptides have been associated with different biological properties, but most peptides are usually further hydrolyzed during the digestive process. In the present study, the antioxidant capacity of 48 samples of sweet whey (SW) derived from cheeses obtained from small-scale cheese plants made with bovine, ovine, caprine or a mixture of ovine/caprine milk was assessed using both cell-free and cell-based assays. SW digestates (SW-Ds) and a fraction (<3 kDa; SW-D-P3) thereof were obtained after in vitro digestion and subsequent ultrafiltration. Antioxidant properties using four different assays were evaluated before and after digestion. Our data showed higher values (p < 0.05) for ORAC, ABTS, FRAP and P-FRAP after in vitro digestion (SW-Ds and SW-D-P3) when compared with the corresponding values before digestion. In the non-digested SW, ORAC values were higher (p < 0.05) for the bovine SW compared with all the other samples. In contrast, the ABTS assay indicated a higher antioxidant activity for the ovine SW both before digestion and for SW-D-P3 compared with the bovine SW. The fraction SW-D-P3 of the ovine SW, using HT29 cells and H2O2 as an oxidizing agent, increased (p < 0.05) the cellular antioxidant activity. Furthermore, the same fraction of the ovine/caprine mixed SW increased, through the NF-κB pathway, the expression of SOD1 and CAT, genes implicated in the oxidative response in macrophage-like THP-1 cells. These findings indicate that SW, and particularly bovine and ovine SW, could be a candidate source for physical antioxidants in human and animal nutrition.

Biological Functions of Antioxidant Dipeptides

In the history of modern nutritional science, understanding antioxidants is one of the major topics. In many cases, food-derived antioxidants have π conjugate or thiol group in their molecular structures because π conjugate stabilizes radical by its delocalization and two thiol groups form a disulfide bond in its antioxidative process. In recent years, antioxidant peptides have received much attention because for their ability to scavenge free radicals, inhibition of lipid peroxidation, chelation of transition metal ions, as well as their additional nutritional value. Among them, dipeptides are attracting much interest as post-amino acids, which have residues in common with amino acids, but also have different physiological properties and functions from those of amino acids. Especially, dipeptides containing moieties of several amino acid (tryptophan, tyrosine, histidine, cysteine, and methionine) possess potent antioxidant activity. This review summarizes previous details of structural property, radical scavenging activity, and biological activity of antioxidant dipeptide. Hopefully, this review will help provide a new insight into the study of the biological functions of antioxidant dipeptides.

The impact of the oxidative status on the reproduction of cows and the calves’ health – a review

The profitability of cattle farming is largely determined by ensuring high-quality breeding animals for replacement and longevity in production. The provision of breeding animals requires adequate fertility of the cowherd and then intensive weight gain in the calf rearing period. For ensuring these demands, many management aspects must be considered. Continuous monitoring of the herd’s health status, including redox status, is essential. This review aims to provide a summary of relevant scientific data published in the last few decades regarding the role of oxidative stress (OS) in infertility of dairy cows and developmental diseases in calves, the major predisposing factors, and possible prevention.

Polyphenols in amaranth (A. manteggazianus) flour and protein isolate: Interaction with other components and effect of the gastrointestinal digestion

In this work, there were analysed the interaction between phenolics present in amaranth flour (F) and amaranth protein isolate (I) with other components, as well as the effect of the gastrointestinal digestion on them (Fd and Id). Extractions were performed under different conditions (temperature, acid, organic solvent, alkali). Methanol/water extracts (25 °C and 80 °C) from F showed the presence of isoquercetin/rutin, quercetin, kaempferol and two unidentified peaks (II and III). In the presence of acid (much more evident at 80 °C), the extraction of some components increased: catechin, 4-hydroxibenzoic acid, isoquercetin/rutin, II, III. When methanol/acetone/water extraction was performed, p-coumaric acid and a new unidentified peak (IV) were observed. About 15% of the total phenol -namely; p-coumaric, rutin/isoquercetin, and kaempferol- were linked to the protein fraction. After the proteins were isolated (I), the amount of some of the compounds which were originally present in a soluble form (e. g. catechin) and in the protein-bound fraction were decreased. Simulated gastrointestinal digestion of flour released some phenolics (catechin, phenolic acids) that were ligated to proteins, and they significantly incremented the ORAC and ABTS activity of most of the extracts. Isoquercetin/rutin, quercetin and kaempferol remained after digestion. Extracts from the digested protein isolate presented differences in the composition and lower ORAC and/or ABTS activities for some of them. The study of the effect of the simulated gastrointestinal digestion process on bioaccessibility and on antioxidant activity (an aspect that, to our knowledge, has not been previously studied on amaranth polyphenols) yielded promising results, which suggest that amaranth flour is a potential antioxidant functional ingredient.

Cow's milk: Composition, nutritional, biological and cardioprotective benefits

Since several years, dairy products have been at the heart of nutritional deba-tes. High-fat dairy products can aggravate dyslipidemia and the consumption of satura-ted, and trans fats is associated with an increased cardiovascular diseases risk. In this re-gard, current dietary guidelines recommend a low fat content, and a significant reduc-tion in trans fatty acid intake. However, recent controversial epidemiological studies show that high-fat dairy products consumption may reduce diabetes, metabolic syndro-me, and the risk of cardiovascular diseases. This dairy paradox has led to a dietary guidelines re-evaluation.

In vitro-digested milk proteins: Evaluation of angiotensin-1-converting enzyme inhibitory and antioxidant activities, peptidomic profile, and mucin gene expression in HT29-MTX cells

Over the past decades, several studies investigated the health-promoting functions of milk peptides. However, to date many hurdles still exist regarding the widespread use of milk-derived bioactive peptides, as they may be degraded during gastrointestinal digestion. Thus, the aim of our study was to in vitro digest intact whey protein isolate (WPI) and casein proteins (CNP), mimicking in vivo digestion, to investigate their bioactive effects and to identify the potential peptides involved. Whey protein isolate and CNP were digested using a pepsin-pancreatin protocol and ultra-filtered (3-kDa cutoff membrane). A permeate (<3 kDa) and a retentate (>3 kDa) were obtained. Soy protein was included as a control (CTR). Angiotensin-1-converting enzyme inhibitory (ACE1-I) and antioxidant activity (AOX) were assessed and compared with those observed in undigested proteins and CTR. Furthermore, the permeate was characterized by nano-liquid chromatography electrospray ionization tandem mass spectrometry (LC-nano ESI MS/MS) using a shotgun peptidomic approach, and retentate was further digested with trypsin and analyzed by MS using a shotgun proteomic approach to identify potentially bioactive peptides. Further, the effects of WPI, CNP, and CTR retentate on cell metabolic activity and on mucus production (MUC5AC and MUC2 gene expression) were assessed in intestinal goblet HT29-MTX-E12 cells. Results showed that WPI permeate induced a significant ACE1-I inhibitory effect [49.2 ± 0.64% (SEM)] compared with undigested WPI, CNP permeate, and retentate or CTR permeate (10.40 ± 1.07%). A significant increase in AOX (1.58 ± 0.04 and 1.61 ± 0.02 µmol of trolox AOX equivalents per mg of protein, respectively) upon digestion was found in WPI. Potentially bioactive peptides associated with ACE1-I and antihypertensive effects were identified in WPI permeate and CNP retentate. At specific concentrations, WPI, CNP, and CTR retentate were able to stimulate metabolic activity in HT29-MTX-E12 cells. Expression of MUC5AC was increased by CNP retentate and unaltered by WPI retentate; MUC2 expression was significantly increased by 0.33 mg/g of CNP and reduced by 1.33 mg/g of CNP. Our results confirm that milk proteins may be rich sources of bioactive compounds, with the greatest beneficial potential of CNP at the intestinal goblet cell level.

Dietary Pomegranate Pulp: Effect on Ewe Milk Quality during Late Lactation

Pomegranate pulp, a by-product of the pomegranate juice industry, contains a remarkable quantity of bioactive compounds that can favorably affect ruminant metabolism and milk quality. The present paper investigated the effect of dietary pomegranate pulp on milk yield and quality during late lactation in grazing ewes. Twenty Comisana ewes (150 ± 10 days in milk) were subdivided into control (CTRL) and pomegranate (PP) groups. The CTRL group received a corn-barley based concentrate, while the PP group received a concentrate containing 64.8% pomegranate pulp. Dietary treatment did not affect milk yield. CTRL milk had a greater percentage of β-casein and total casein, while αs1-casein percentage tended to be greater in the PP group. The PP milk showed a lower percentage of 14:0, 16:0, but a greater percentage of vaccenic, rumenic, and α-linolenic acid. Punicic acid was detected only in the PP milk. Total antioxidant capacity (ORAC) was greater in the CTRL milk as compared with the hydrophilic ORAC. Dietary pomegranate pulp increased milk health quality with no detrimental effects on milk yield. Therefore, pomegranate pulp could represent a strategy for improving milk quality and reducing feeding cost during a less profitable phases such as late lactation. Also, dietary pomegranate pulp, as an alternative to traditional feedstuffs, may lower feed-to-food competition in livestock production.

Okara residue as source of antioxidants against lipid oxidation in milk enriched with omega-3 and bioavailability of bioactive compounds after in vitro gastrointestinal digestion

The residue from soy processing (okara) was evaluated for phenolic compounds, flavonoids, radical scavenging activity and reducing power ability. The ability of okara to decelerate the oxidation of omega-3 fatty acids caused by light exposure in a milk matrix, as well as its bioavailability after in vitro digestion, were investigated. Okara contained phenolic compounds (106.7 mg gallic acid equivalents (GAE)/100 g) and flavonoids (32.7 mg quercetin equivalents/100 g) and showed antioxidant activity. The addition of okara to omega-3 fatty acids-enriched milk inhibited the production of conjugated dienes and malonaldehyde during 8 days of storage compared to the control (without okara), particularly at the higher (3 g/L) than lower inclusion concentrations studied (1 and 2 g/L). The bioavailability assay demonstrated that polyphenols (41 mg GAE/100 g) were still present after in vitro digestion and had antioxidant activity. Okara, which is considered a residue and is discarded, can potentially be used as an antioxidant ingredient for the enrichment of foods.

Redox properties of transitional milk from mothers of preterm infants

AIM

There is a discrepancy between the amount of transitional milk produced by mothers of preterm infants and the low capacity of premature infants to consume it. This milk can be used in milk banks, but previous studies found that there are large variations in the level of host-defence proteins in individual samples of milk from mothers of premature infants, which implies that large individual variations in antioxidative defence composition are also possible.

METHODS

Milk samples were collected from 20 healthy mothers of preterm infants. We determined the values for non-enzymatic antioxidative capacity parameters (oxygen radical absorbance capacity (ORAC)), static oxidation-reduction potential (ORP), activities of antioxidant defence enzymes and the amount of vitamin C in whole milk, skim and whey fractions of transitional milk.

RESULTS

The main low-molecular-weight antioxidant in transitional milk is vitamin C and most of it is contained in whey. ORAC is higher in whole transitional milk than in skim milk and whey, and ORP is lower in whole transitional milk than that in skim milk and whey. Antioxidative enzyme activities are similar in all individual samples of transitional milk from mothers of preterm infants.

CONCLUSIONS

Our results indicate that transitional milk of mothers of preterm infants shows slow individual variations in antioxidative defence composition; therefore, it can be used in human milk banks.

In silicoassessment and structural characterization of antioxidant peptides from major yolk protein of sea urchinStrongylocentrotus nudus

Sea urchin gonads have been demonstrated to contain major yolk protein (MYP), which can be hydrolyzed by enzymes to release biologically active peptides.

In vitro and in vivo antioxidant potential of milks, yoghurts, fermented milks and cheeses: a narrative review of evidence

The antioxidant potential (AP) is an important nutritional property of foods, as increased oxidative stress is involved in most diet-related chronic diseases. In dairy products, the protein fraction contains antioxidant activity, especially casein. Other antioxidants include: antioxidant enzymes; lactoferrin; conjugated linoleic acid; coenzyme Q10; vitamins C, E, A and D3; equol; uric acid; carotenoids; and mineral activators of antioxidant enzymes. The AP of dairy products has been extensively studied in vitro, with few studies in animals and human subjects. Available in vivo studies greatly differ in their design and objectives. Overall, on a 100 g fresh weight-basis, AP of dairy products is close to that of grain-based foods and vegetable or fruit juices. Among dairy products, cheeses present the highest AP due to their higher protein content. AP of milk increases during digestion by up to 2·5 times because of released antioxidant peptides. AP of casein is linked to specific amino acids, whereas β-lactoglobulin thiol groups play a major role in the AP of whey. Thermal treatments such as ultra-high temperature processing have no clear effect on the AP of milk. Raw fat-rich milks have higher AP than less fat-rich milk, because of lipophilic antioxidants. Probiotic yoghurts and fermented milks have higher AP than conventional yoghurt and milk because proteolysis by probiotics releases antioxidant peptides. Among the probiotics, Lactobacillus casei/acidophilus leads to the highest AP. The data are insufficient for cheese, but fermentation-based changes appear to make a positive impact on AP. In conclusion, AP might participate in the reported dairy product-protective effects against some chronic diseases.

Impact of legume protein type and location on lipid oxidation in fish oil-in-water emulsions: Lentil, pea, and faba bean proteins

Emulsion-based delivery systems are being developed to incorporate ω-3 fatty acids into functional foods and beverages. There is interest in formulating these delivery systems from more sustainable and label-friendly ingredients. The aim of this study was therefore to examine the impact of plant-protein emulsifiers on the oxidative stability of 1wt% fish oil-in-water emulsions. Fish oil emulsions stabilized by three types of legume protein (lentil, pea, and faba bean) were produced using a high-pressure microfluidizer. The formation of primary (peroxides) and secondary (TBARS) lipid oxidation products was measured when the emulsions were stored at 37°C under accelerated (+100μM iron sulfate) or non-accelerated (no added iron) conditions for 21 or 33days, respectively. The particle size, charge and microstructure of the emulsions were monitored during storage using light scattering and microscopy to detect changes in physical stability. Emulsions stabilized by whey protein isolate, a commonly used animal-based protein, were utilized as a control. The emulsions formed using whey protein had smaller initial particle sizes, better physical stability, and slightly better stability to lipid oxidation than the ones formed using plant-based proteins. The impact of protein location (adsorbed versus non-adsorbed) on the oxidative stability of the emulsions was also investigated. The presence of non-adsorbed proteins inhibited lipid oxidation, presumably by binding transition metals and reducing their ability to interact with ω-3 fatty acids in the lipid droplets. Overall, these results have important implications for fabricating emulsion-based delivery systems for bioactive lipids, e.g., they indicate that including high levels of non-adsorbed proteins could improve oxidative stability.

Whey protein isolate/gum arabic intramolecular soluble complexes improving the physical and oxidative stabilities of conjugated linoleic acid emulsions

Protein–polysaccharide intramolecular soluble complexes are proved to have superior emulsifying properties in stabilizing PUFAs-based emulsions.

Structure-Functional Study of Tyrosine and Methionine Dipeptides: An Approach to Antioxidant Activity Prediction

Quantum chemical methods allow screening and prediction of peptide antioxidant activity on the basis of known experimental data. It can be used to design the selective proteolysis of protein sources in order to obtain products with antioxidant activity. Molecular geometry and electronic descriptors of redox-active amino acids, as well as tyrosine and methionine-containing dipeptides, were studied by Density Functional Theory method. The calculated data was used to reveal several descriptors responsible for the antioxidant capacities of the model compounds based on their experimentally obtained antioxidant capacities against ABTS (2,2'-Azino-bis-(3-ethyl-benzothiazoline-6-sulfonate)) and peroxyl radical. A formula to predict antioxidant activity of peptides was proposed.

Lactose-hydrolyzed milk is more prone to chemical changes during storage than conventional ultra-high-temperature (UHT) milk

The enzymatic hydrolysis of lactose to glucose and galactose gives rise to reactions that change the chemistry and quality of ambient-stored lactose-hydrolyzed ultra-high-temperature (UHT) milk. The aim of the present study was to investigate and compare chemical changes in lactose-hydrolyzed and conventional UHT milk during a 9 month ambient storage period. Several complementary analyses of volatiles, free amino acids, acetate, furosine, and level of free amino terminals were concluded. The analyses revealed an increased level of free amino acids and an increased formation rate of specific compounds such as furosine and 2-methylbutanal in lactose-hydrolyzed UHT milk compared to conventional UHT milk during storage. These observations indicate more favorable conditions for Maillard and subsequent reactions in lactose-hydrolyzed milk compared to conventional UHT milk stored at ambient temperature. Furthermore, it is postulated that proteolytic activity from the lactase-enzyme preparation may be responsible for the observed higher levels of free amino acids in lactose-hydrolyzed UHT milk.

Study of oxygen transfer across milk proteins at an air-water interface with scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) combined with a Langmuir trough was used for studying oxygen transfer across protein films at an air-water interface. The method allows the comparison of the oxygen permeability of different emulsifiers without any concerns of interference of atmospheric oxygen. Two milk proteins, β-lactoglobulin and β-casein, were compared, and the permeabilities obtained were for β-casein PD ≈ 2.2 × 10(-7) cm(2)/s and for β-lactoglobulin PD ≈ 0.6 × 10(-7) cm(2)/s, which correspond to the lowest limit of the diffusion coefficients and are 2 orders of magnitude lower than the diffusion coefficient of oxygen in water, yet several orders of magnitude higher than previously reported for milk protein films. The method allows characterization of the oxygen barrier properties of liquid interfacial films, which is of crucial importance for understanding the role of the interface in the inhibition of oxygen transport and developing modified interfaces with higher oxygen blocking efficacy.

Parvalbumin as a metal-dependent antioxidant

Parvalbumin (PA) is a Ca(2+)-binding protein of vertebrates massively expressed in tissues with high oxygen uptake and respectively elevated level of reactive oxygen species (ROS). To characterize antioxidant properties of PA, antioxidant capacity (AOC) of intact rat α-PA has been explored. ORAC, TEAC and hydrogen peroxide AOC assays evidence conformation-dependent oxidation of the PA. AOC value for the apo-PA 4-11-fold exceeds that for the Ca(2+)-loaded protein. Despite folded conformation of apo-PA, it has AOC equivalent to that of the proteolized protein. The most populated under resting conditions PA form, Mg(2+)-bound PA, has AOC similar to that of apo-PA. ROS-induced changes in absorption spectrum of PA evidence an oxidation of PA's phenylalanines in the ORAC assay. Sensitivity of PA oxidation to its conformation enabled characterization of its metal affinity and pH-dependent behavior: a transition with pKa of 7.6 has been revealed for the Ca(2+)-loaded PA. Since total AOC of PA under in vivo conditions may reach the level of reduced glutathione, we propose that PA might modulate intracellular redox equilibria and/or signaling in a calcium-dependent manner. We speculate that the oxidation-mediated damage of some of PA-GABAergic interneurons observed in schizophrenia is due to a decline in total AOC of the reduced glutathione-PA pair.

Colostrum and milk selenium, antioxidative capacity and immune status of dairy cows fed sodium selenite or selenium yeast

Dietary selenium (Se) can be supplemented from organic or inorganic sources and this may affect Se metabolism and functional outcome such as antioxidative status and immune functions in dairy cows. A feeding trial was performed with 16 Holstein-Friesian dairy cows fed with a total mixed ration (0.18 mg Se/kg dry matter (DM)) either without Se supplement (Control, n = 5), or with Se from sodium selenite (Group SeS, n = 5) or Se yeast (Group SeY, n = 6). In Groups SeS and SeY, the Se supplementation amounted to an additional intake of 4 mg Se and 6 mg Se/d during gestation and lactation, respectively. The effect of both Se sources was characterised by milk Se and antioxidant levels, and the phenotyping and functional assessment of phagocytic activity of milk immune cells. Se yeast has been found to increase (p ≤ 0.001) the milk Se and antioxidant levels markedly compared to the control group. The experimental treatment did not affect the immune parameters of the cows. Lymphocyte subpopulations and phagocytosis activity of neutrophilic granulocytes were affected neither by the Se intake nor by the two different dietary supplements. It can be concluded that sodium selenite and Se yeast differ considerably in their effects on antioxidant status in dairy cows. However, the basal dietary Se concentration of 0.18 mg/kg DM seemed to be high enough for the measured immune variables.

Interannual and geographical reproducibility of the nutritional quality of milk fat from commercial grazing flocks

The objective of the present work was to study the differences in the fatty acid (FA) composition of raw sheep milk fat under commercial milk production conditions throughout lactation, in two consecutive years. Particular attention was placed on the C18:2cis-9,trans-11 isomer, C18:1trans-11 acid, and unsaturated FA as the feeding regimen of 10 commercial flocks of latxa dairy sheep changed from indoor feeding to part-time grazing conditions (from early spring) as traditionally practiced in the Basque Country (Northern Spain). Farms located at an altitude of between 600 and 700 m, in two different geographical areas with different rainfall were selected. Milk samples were collected monthly from late January (indoor feeding) until mid-, or end of, June (outdoor feeding), during two consecutive years. In spite of some interannual variability (most likely due to large differences in rainfall), the evolution of individual FA throughout lactation was comparable between years, indicating that it was reproducible under commercial milk production conditions. The average concentrations of C18:2cis-9,trans-11 isomer and C18:1trans-11 acid in milk from the commercial flocks increased about 200% during the transition period (end of March or early April until May), from indoor feeding (late January or early February until the end of March) to the outdoor period (early May to mid-June), remaining constant during the outdoor period (27·53 ± 9·32 μmol/g fat and 71·58 ± 20·53 μmol/g fat, respectively). Non-atherogenic FA comprised approximately 50% of all saturated FA at any time during lactation, whereas the milk atherogenicity index decreased significantly during the outdoor period. The Trolox-equivalent antioxidant capacity of the water-soluble milk fraction did not appear to be influenced by feeding management. The FA composition of cheeses made during the second year with milk from the indoor or outdoor periods reflected those of the corresponding milks. A principal components analysis clearly showed that differences in the milk FA composition were primarily due to outdoor grazing, with very little contribution from the geographical zone or the year.

Modifications of interfacial proteins in oil-in-water emulsions prior to and during lipid oxidation

Lipid oxidation is a major cause for the degradation of biological systems and foods, but the intricate relationship between lipid oxidation and protein modifications in these complex multiphase systems remains unclear. The objective of this work was to have a spatial and temporal insight of the modifications undergone by the interfacial or the unadsorbed proteins in oil-in-water emulsions during lipid oxidation. Tryptophan fluorescence and oxygen uptake were monitored simultaneously during incubation in different conditions of protein-stabilized oil-in-water emulsions. Kinetic parameters demonstrated that protein modifications, highlighted by decrease of protein fluorescence, occurred as an early event in the sequence of the reactions. They concerned more specifically the proteins adsorbed at the oil/water interface. The reactions led in a latter stage to protein aggregation, carbonylation, and loss of protein solubility.

Plant sterols and antioxidant parameters in enriched beverages: storage stability

Plant sterols (PS) stability, antioxidant parameters, and color were studied during 6 months of storage at 4, 24, and 37 °C in three PS-enriched functional beverages. Beverages were skimmed milk with fruit juice and PS (MFJPS), fruit juice and PS (FJPS), and skimmed milk with PS (MPS). No loss in total PS content occurred during storage observing the same values at any given storage time point. Total carotenoids decreased 36% with storage at two months and then remained stable. Total polyphenols showed fluctuations throughout the storage, remaining stable at 6 months and reaching initial values. The antioxidant capacity (TEAC method) increased 18% at 6 months, and there was an increase in color over time and temperature, probably due to Maillard reaction compound formation. The increase in total antioxidant capacity might have helped PS maintenance throughout storage, these beverages being a good PS source even after 6 months of storage.

Contribution of the interfacial layer to the protection of emulsified lipids against oxidation

The oxidative stability of oil-in-water (O/W) emulsions is highly dependent on the type of emulsifier. The purpose of this work was to investigate the specific role of the adsorbed emulsifiers on lipid oxidation of O/W emulsions. Emulsions of similar droplet size distribution stabilized by minimum amounts of proteins or surfactants were oxidized at 25 °C in the presence of equimolar iron-EDTA complex. The pH and the amount of emulsifier in the aqueous phase were also varied to investigate the role of the droplet charge and the emulsifier in the aqueous phase. Oxygen uptake, conjugated dienes (CD), and volatile compound formation demonstrated that the protein-stabilized interfaces are less efficient at protecting emulsified lipids against oxidation than surfactant-stabilized interfaces. The antioxidant effect of unadsorbed proteins was also confirmed.