Antioxidant activity of yoghurt peptides: Part 2 – Characterisation of peptide fractions

The aim of the present study was to elucidate previous findings showing that peptide fractions isolated from yoghurt had antioxidant effects. Therefore, peptides and free amino acids released during fermentation of milk were characterised. Yoghurt samples were stripped from sugars and lactic acid and subsequently fractionated by ultra filtration using membranes with cut off sizes of 30, 10 and 3 kDa. The peptides in these fractions were identified by LC–MS/MS. The identified peptides comprised a few N-terminal fragments of αs₁-, αs₂-, and κ-casein, and several fragments from β-casein. Almost all the peptides identified contained at least one proline residue. Some of the identified peptides included the hydrophobic amino acid residues Val or Leu at the N-terminus and Pro, His or Tyr in the amino acid sequence, which is characteristic of antioxidant peptides. In addition, the yoghurt contained a considerable amount of free amino acids such as His, Tyr, Thr and Lys, which have been reported to have antioxidant properties. Thus, our findings confirm that the antioxidant effects of the peptide fractions from yoghurt are due to the presence of certain peptides and free amino acids with recognised antioxidant activity in these fractions.     

Binding affinity between dietary polyphenols and β-lactoglobulin negatively correlates with the protein susceptibility to digestion and total antioxidant activity of complexes formed

Non-covalent interactions between β-lactoglobulin (BLG) and polyphenol extracts of teas, coffee and cocoa were studied by fluorescence and CD spectroscopy at pH values of the gastrointestinal tract (GIT). The biological implications of non-covalent binding of polyphenols to BLG were investigated by in vitro pepsin and pancreatin digestibility assay and ABTS radical scavenging activity of complexes formed. The polyphenol–BLG systems were stable at pH values of the GIT. The most profound effect of pH on binding affinity was observed for polyphenol extracts rich in phenolic acids. Stronger non-covalent interactions delayed pepsin and pancreatin digestion of BLG and induced β-sheet to α-helix transition at neutral pH. All polyphenols tested protected protein secondary structure at an extremely acidic pH of 1.2. A positive correlation was found between the strength of protein–polyphenol interactions and (a) half time of protein decay in gastric conditions (R² = 0.85), (b) masking of total antioxidant capacity of protein–polyphenol complexes (R² = 0.95).     

Clothing comfort and yarn packing relationship: Part II – Transmission characteristics of fabrics

The effects of ring frame process parameters affecting the packing of yarn, namely yarn twist, spindle speed and draft at ring frame, on fabric transmission characteristic have been reported in the present paper. The detailed results on the yarn characteristics and low-stress mechanical properties, due to change of these ring frame parameters, have been reported in Part I of this series. It has been observed that there is very strong evidence that by changing the above ring frame process parameters, which affect the packing factor of yarn, the transmission characteristics of the fabrics can be manipulated. The yarn packing factor is directly related with the yarn diameter. All the studied ring frame process parameters have direct relationship with air permeability, thermal conductivity and relative water vapour permeability, i.e. with the increase in these ring frame parameters the above fabric transmission parameters increase, but water retention characteristics show opposite trend. Thermal absorptivity was found to be related with the fabric surface roughness.     

The Geometry of the 2 × 2 Matt Weave Part I: Development of the Model

A study of the geometry of idealized 2×2 Matt Weave is carried out by proposing two simple models, namely point contact and distributive contact models based on a classical elastica approach, differing in the nature of the inter-yarn force active at the point of contact between bent and crossed threads. The models show that the presence of float in the weave makes the dimension of the unit cell thinner as compared to plain weave. The ratio of bending rigidities of the warp and weft threads becomes insignificant in crimp balance when the variable position of the point of contact is predominant.     

The Geometry of the 2 × 2 Matt Weave Part II: Validation of Theoretical Models

For the validation of theoretical models, experiments were suitably designed to generate a realistic set of data. Relations between the corresponding characteristic geometrical parameters exhibited a good correspondence with those of point contact model of 2×2 Matt Weave (MRP). Finally the study with distributive contact model (MRD) suggests, the necessity of a hybrid model incorporating typical features of MRP (curvature constraint) and MRD (distributive force constraint).     

Bioactivity of α-lactalbumin related to its interaction with fatty acids: a review

α-Lactalbumin (α-LA) is a whey protein that has been extensively studied for its folding properties and its ability to bind several cations. An interesting property of α-LA is its ability to interact with fatty acids, although this interaction requires the previous unfolding of the protein by removing the Ca(2+) bound. The main function of α-LA is to participate in lactose biosynthesis. However, other biological functions have been attributed to the protein in the last decade. It has been reported that a particular form of human and bovine apo-α-LA induces apoptosis in tumoral and immature cells though spares healthy differentiated cells. The conversion of α-LA to the active apoptotic form requires the unfolding of the protein and the binding of specific fatty acids, mainly unsaturated C18 fatty acids in the cis-conformation. Likewise, it has been shown that a folding variant of α-LA and also some peptidic fragments have a bactericidal activity. The proposed functions for α-LA open new perspectives for its use as a potential ingredient to be added in functional foods or in nutraceutical products. This review summarizes the current state of knowledge on the subject of the interaction of α-LA with fatty acids, and the consequences of this interaction on its bioactivity.     

Biological durability of wood in relation to end-use—Part 2: The use of an accelerated outdoor L-joint performance test

As exterior above ground testing is considered important for the assessment of treated wood intended for use in hazard class 3, reliability and reproducibility have become most relevant factors. Laboratory testing of natural durability focussing on such application has to be linked to performance, when suitability of wood species and service life are to be determined. Therefore an accelerated L-joint test has been developed to allow worst case assessment under semi-controlled outdoor circumstances. After 48 months outdoor exposure wood species could clearly be differentiated. Both, fungi isolated and mass loss figures recorded were in line with the proposed basidiomycete laboratory testing of natural durability.     

Advantages of ohmic cooking in the kilohertz range – Part II: Impact on textural changes and approaches to improve heating uniformity

The impact of ohmic heating (OH) in the low (12 kHz) and high (300 kHz) kilohertz-range on textural changes and texture uniformity of potato cubes and whole potato tubers was investigated. Potatoes were heated in aqueous NaCl solution with a conductivity of 2.5 mS/cm. Texture was characterized by cutting and puncture tests and the energy (mJ) necessary to cut or penetrate the samples was found to be a suitable indicator. The impact of the initial temperature of the surrounding liquid on the heating uniformity was analyzed by starting the cooking treatment in cold (20 ± 2 °C) and in hot (90 ± 5 °C) NaCl solution. To further improve the heating efficiency, the conductivity was adjusted during the treatment. With an increasing power input during OH, increasing texture softening rates were observed. Compared to conventional cooking, an up to 8-times faster texture softening rate occurred. Treatments at 300 kHz resulted in a better texture uniformity compared to OH at 12 kHz. Compared to the conventional cooking, OH treatments resulted in significant (p ≤ 0.05) higher weight losses and a higher texture softening at similar cooking degrees. By adjustment of the liquid conductivity and power input during the treatment, textural properties were improved, and weight loss could be reduced.Industrial relevanceOhmic heating (OH) is an alternative heating technology with the potential to reduce processing times and energy consumption. It can overcome limitations in the heat transfer particularly given for large-volume solid foods and provide a uniform heating. However, limited attention has been given to the effects of the product and process parameters on the heating uniformity during OH treatments of solid foods. The present paper highlights the importance of the electrical conductivity and the frequency of the applied electric field on the texture uniformity. The obtained results contribute to the understanding of the interaction of the electric field and the food matrix, which is the basis for the implementation of tailored and targeted processing concepts in the industry.     

Cereal fructosans: Part 2—Characterization and structure of wheat fructosans

Wheat fructosans were prepared from two different flours and separated according to degree of polymerization by gel permeation chromatography.The different fractions were quantified and characterized with regard to monomer carbohydrate composition. The tri-, tetra- and pentasaccharides made up about 50% of the total fructosan content.The structures of the trisaccharides were identified by gas chromatography/mass spectrometry. Two fructosan trisaccharides were found, neokestose and 6-kestose, along with raffinose.     

Chemical composition of the cell wall of probiotic and brewer’s yeast in response to cultivation medium with glycerol as a carbon source

The structure of cell wall of yeasts (genus Saccharomyces) is one of the factors that determine their health-promoting properties connected to the presence of β-glucans and mannoprotein. The aim of the study was to determine the influence of glycerol as a carbon source on structural polymers of cell wall (β-glucan and mannoprotein) of probiotic yeasts Saccharomyces cerevisiae var. boulardii and brewer’s yeasts S. cerevisiae R9. Significant increase of the percentage of polysaccharide content in the cell wall dry weight of S. cerevisiae R9 brewer’s yeasts was noted (in the range of 10–20 %) after cultivation in medium containing glycerol at a concentration of 2–5 % and pH 4.0. The highest content of carbohydrates in probiotic yeasts’ cell wall (58 %) was observed after cultivation in medium containing 3 % of glycerol and pH 5.0. The cell wall of probiotic yeasts was characterized by higher content of mannoprotein comparing with cell wall preparation of brewer’s yeasts S. cerevisiae R9 composed mainly of β-glucans. After cultivation in mediums with 2 and 3 % of glycerol, the cell of brewer’s yeasts contained the highest amount of β(1,3/1,6)-glucan in dry weight of the cell wall (about 36 %). Glycerol at a concentration of 3 and 5 % also intensified mannoprotein biosynthesis in cell wall of S. cerevisiae R9, approximating their content to those noted in the cells of probiotic yeasts (about 29 % (w/w) of dry weight of the cell wall) after cultivation in a medium of pH 5.0 containing 3 % of glycerol.     

The use of 2D NMR to study β-cyclodextrin complexation and debittering of amino acids and peptides

This work fully demonstrated the formation of amino acids complexes with β-cyclodextrin (β-CD) by the method of nuclear magnetic resonance with the rotating frame Overhauser effect spectroscopy (ROESY) and diffusion ordered spectroscopy (DOSY) techniques. The tested amino acids display the following decreasing order of affinity for β-CD: tryptophane > tyrosine > phenylalanine > proline > histidine > isoleucine. The influence of complexation on taste perception was determined with a trained panel to qualify taste alterations of single amino acids and quantify the debittering of soy protein hydrolysate by β-CD complexation. The results showed that β-CD complexation is effective for modifying single amino acids taste perception and debittering soy protein hydrolysate. Bitterness sensation of the latter is reduced by 90% when 5% β-CD was added, thus β-CD is recommended as a prospective additive for masking bitter taste of new functional food products.     

Characterization of traditional and exotic apple varieties from Portugal. Part 2 – Antioxidant and antiproliferative activities

Apples are known to have many health-promoting activities, especially anticancer, antiradical and antioxidant effects. Most of these actions are believed to be due to their polyphenolic components which vary greatly between different varieties.In this work, four traditional Portuguese apple cultivars (Bravo de Esmolfe, Malápio Fino, Malápio da Serra and Pêro Pipo) and five exotic varieties (Golden, Starking, Fuji, Gala Galaxy and Reineta Parda) were evaluated in terms of their bioactivity using both cell-based and cell-free assays; 17 parameters were evaluated for each sample. Results obtained were submitted to principal component analysis (PCA) and it was possible to conclude that Malápio Fino and Bravo de Esmolfe apple varieties have the highest antioxidant effect and Reineta Parda variety is the best cultivar in promoting antiproliferative effect against human colon (HT29) and gastric (MKN45) cancer cells. Correlations of the data obtained showed that among phenolic compounds catechin, epicatechin and procyanidin B1 were the major contributors to the antioxidant activity of apples whereas procyanidins (B1 and B2), phloridzin and epicatechin played an important role against human cancer cell proliferation.     

Binding of divalent metal ions to 1-25 β-caseinophosphopeptide: An isothermal titration calorimetry study

To better understand the mechanism of metal ion transport through the gastrointestinal tract to their absorption sites, isothermal titration calorimetry (ITC) was used to investigate the binding of dicationic metals to β-CN(1-25)4P, a β-casein tetraphosphorylated peptide. ITC technology was found suitable for studying weak bonds between metal ions and phosphopeptides and provided a direct means of thermodynamic and stoichiometric characterisation of complex formation. Thus, one mole of β-CN(1-25)4P binds two moles of Ca²⁺, Mg²⁺ or Zn²⁺ under experimental conditions close to those of the ileum (pH 8, 37 °C), with rather low binding affinity constants (K = 4900-11,200 M⁻¹). These low affinities should facilitate the release of metal ions during intestinal absorption. By contrast, Cu²⁺ did not bind to β-CN(1-25)4P at pH 8, despite its reported significant affinity towards β-casein and the 1-25 peptide at near-neutral pH.     

Comparison between novel and standard methods for analysis of free fatty acids in milk – Including relation to rancid flavour

A range of analytic methods for quantifying free fatty acids (FFAs) in milk were compared and further correlated to rancid flavour detected by sensory analysis. Proton transfer reaction–mass spectrometry (PTR–MS) and ¹H nuclear magnetic resonance (NMR) spectrometry were introduced as novel methods for quantifying individual short chain FFAs. Gas chromatography–mass spectrometry (GC–MS) combined with in-solution derivatisation was used for quantifying all individual FFAs, and Bureau of dairy industries (BDI), acyl-CoA-synthetase–acyl-CoA oxidase (ACS–ACOD) assay, Fourier transform infrared spectroscopy were used to estimate the total FFA concentration in 28 milk samples. High correlations (r between 0.76 and 0.86) to rancid off-flavour were found for all analytical methods, and all the individual FFAs were quantitatively inter-correlated. Furthermore, a high correlation was found between PTR–MS and GC–MS quantification of hexanoic acid. For the BDI method, the sensory thresholds rancid off-flavour in farm bulk milk were 1.95 mmol 100 g⁻¹ fat.     

Antioxidant/pro-oxidant properties of model phenolic compounds. Part II: Studies on mixtures of polyphenols at different molar ratios by chemiluminescence and LC–MS

The behaviour of four known antioxidants (quercetin, ascorbic acid, catechin and caffeic acid) and their mixtures at different molar ratios was studied in view of elaborating predictions over an eventual pro-oxidant or synergistic antioxidant activity. The Co(II)–EDTA luminol chemiluminescence showed that the mixture of quercetin and ascorbic acid at ratio 2:1 had the most pronounced antioxidant activity, while that of quercetin and caffeic acid at ratio 1:2 showed the least antioxidant activity, which may be interpreted as a strong propensity for pro-oxidant behaviour. The LC–MS analysis for the two mixtures revealed a significant amount of unoxidised quercetin in the case of quercetin with ascorbic acid, whereas in the case of quercetin with caffeic acid this amount was negligible. This observation supports the fact that the first combination was more antioxidant than the second, through efficient quercetin recycling (reduction of the quinone by ascorbic acid; redox cycling of quinones).     

Binding of ²³⁹Pu and ⁹⁰Sr to organic colloids in soil solutions: evidence from a field experiment

Colloidal transport has been shown to enhance the migration of plutonium in groundwater downstream from contaminated sites, but little is known about the adsorption of ??Sr and plutonium onto colloids in the soil solution of natural soils. We sampled soil solutions using suction cups, and separated colloids using ultrafiltration to determine the distribution of 23?Pu and ??Sr between the truly dissolved fraction and the colloidal fraction of the solutions of three Alpine soils contaminated only by global fallout from the nuclear weapon tests. Plutonium was essentially found in the colloidal fraction (>80%) and probably associated with organic matter. A significant amount of colloidal ??Sr was detected in organic-rich soil solutions. Our results suggest that binding to organic colloids in the soil solutions plays a key role with respect to the mobility of plutonium in natural alpine soils and, to a lesser extent, to the mobility of ??Sr.