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The enzyme laccase is a copper-containing oxidoreductase with the ability to oxidize a wide range of substrates, such as ferulic acid. Thus, the ferulic acid-containing sugar beet pectin (SBP) can be cross-linked through laccase-mediated oxidation. As cross-linking increases viscosity, it could be applied to stabilize SBP-containing foams. In this study, laccase-mediated cross-linking of SBP was investigated under conditions of a high-pressure foaming process. Shear, presence of CO2, and pressure were simulated in a rheometer equipped with a high-pressure cell. At rest, addition of laccase to SBP solution led to the formation of a stiff gel. Application of shear upon mixing of laccase and SBP solution decreased the storage modulus with increasing shear duration and shear rate. This can be attributed to the formation of a fluid gel. However, when shear was stopped before all available ferulic acid groups were cross-linked, a stronger and more coherent network was formed. Pressure exerted by CO2 did not affect cross-linking. Additionally, this approach was tested in a stirred high-pressure vessel where SBP was foamed through CO2 dissolution under pressure and shear followed by controlled pressure release. While pure SBP foam was highly unstable, addition of laccase decelerated collapse. Highest stability was reached when laccase and SBP were mixed prior to depressurization. At the point of foam formation, the continuous phase was thereby viscous enough to increase foam stability. At the same time, continuation of cross-linking at rest caused gel templating of the foam structure., Food & Function, 11 (3), ISSN:2042-6496, ISSN:2042-650X

Vitamin A deficiency has a widespread occurrence globally and is considered as one of the world's most serious health risk factors. Potential solutions to address this deficiency include dietary diversification or supplementation, but food fortification is generally accepted as the most cost-effective solution. The main issue with food fortification of this vitamin is related to its high instability in food matrices. Dilution of vitamin A in triglycerides is a natural and appropriate way to stabilize this compound. We show here that vitamin A palmitate stability increases with increasing concentration of triglycerides. Moreover, we found that vitamin A palmitate displays improved stability in more saturated oils. Using various temperatures, and Arrhenius plots of experiments performed at storage temperatures between 30 °C and 60 °C for oils varying by their saturation and crystallinity, we demonstrate that crystallization is not responsible for this phenomenon. Additionally, we show by centrifugation that vitamin A is preferably solubilized in the liquid phase compared to the crystalline phase, explaining that triglyceride crystallization does not stabilize vitamin A palmitate. It is proposed that unsaturated fats generate more oxidation products such as radicals and peroxides, leading to a quicker degradation of vitamin A.

The resistance of an Enterobacter pulveris strain to combined heat and supercritical carbon dioxide (scCO 2 ) treatments in different powder matrices was examined. The strain proved resistant to scCO 2 treatment up to 50MPa pressure at temperatures >73°C for at least 20min in a commercial infant formula. Water availability was shown to be important for the observed thermotolerance, because introduction of water in the scCO 2 gas flow during treatment resulted in a 1 log 10 cfu/g reduction of the initial inoculum. Interestingly, similar tolerance to heat and scCO 2 treatment was observed in a less complex matrix, a maltodextrin powder. In contrast, the bacterial strain proved sensitive to lower temperatures (55–65°C) over shorter times (≤10min) in a dextrose powder composed of crystalline particles. Therefore, the microorganism demonstrates heat sensitivity in the crystalline powder matrix closer to that of nonpowder liquid matrices. These data demonstrate the increased heat tolerance of the bacterium specifically in amorphous powders and indicate that this characteristic is not dependent on fat and other components commonly found in infant formula. The information is important in designing strategies to deal with contamination of powders with Enterobacteriacae , including pathogenic Cronobacter spp.

Fluorescence dyes Rhodamine and Fluorescein do not influence the adsorption layer properties of labelled β-lactoglobulin when used at sufficiently low concentration. However, due to interference of light absorption and emission by the dye with the registration of ellipsometric signals in surface ellipsometry experiments, errors can result. To avoid erroneous adsorption layer data, the laser light sources in ellipsometers should be selected such that the sensitivity peak of the photo detector is within a sufficient distance to the absorption and emission wavelengths of the dye.

The effect of addition of the anionic polysaccharide dextran sulfate (DS) on the properties of n -tetradecane-in-water emulsions containing sodium caseinate (CN) has been studied under different pH and ionic strength conditions. Two methods were used for preparation of the emulsions (20 vol% oil, 0.5 wt% CN, 0.1–1 wt% DS). In ‘bilayer emulsions’, the DS was added to a CN-stabilized emulsion after emulsification; in ‘mixed emulsions’, the oil was directly emulsified into the mixed biopolymer solution. At pH=6, DS was found to adsorb onto CN-coated droplets, and extensive aggregation due to bridging flocculation occurred at 0.1 wt% DS. Polymeric stabilization was observed at higher polysaccharide concentration (1 wt% DS). In the mixed emulsions, no bridging flocculation was observed at any DS concentrations. These contrasting results for the two preparation methods indicate that strong interactions are present already at a pH value above the isoelectric point of the protein, and that the structure of the adsorbed layer at the oil–water interface is different for the two sets of systems. When the pH of emulsions containing 0.5 wt% DS or less was lowered towards acidic values, precipitation was observed. The mixed and bilayer emulsions containing 1 wt% DS were found to be more stable at pH=2 than the emulsion without DS. Mixed emulsions containing 1 wt% DS exhibited good shelf-life stability on quiescent storage for 3 weeks, especially when the emulsion was prepared at low pH. Complexes were found to dissociate when 0.1 or 0.5 M NaCl was present, suggesting that associative interactions between CN and DS are mainly electrostatic.

The adsorption dynamics and equilibrium properties of hen egg-white lysozyme at the air/water interface is studied using bubble and drop profile analysis technique, ellipsometry and infrared reflection absorption spectroscopy (IRRAS). The set of equilibrium data can be described by a recently developed thermodynamic model. Using the equilibrium adsorption parameters the adsorption dynamics can be well described by a diffusion controlled mechanism at the lower concentrations and a mixed model at higher lysozyme concentrations where conformational changes in the surface layer become time determining.

Iron, vitamin A, zinc and iodine have been recognized to be the micronutrients with the largest deficiencies worldwide. Among these, iron is highly reactive and may lead to negatively perceived organoleptic changes in products such as dull colour and off-taste. The colour change originated in fortified fruit-containing food products was confirmed to be the result of the complexation of iron and polyphenols. Phenolic compounds with two or more vicinal hydroxy benzyl moieties in their structure, such as catechols and pyrogallols were investigated for their ability to give bathochromic shift phenomena when mixed with iron salts. Furthermore, strategies for limiting colour development were based on: 1) pH adjustment; 2) saturation of polyphenols with unreactive divalent metal ions; 3) suppression of iron reactivity through complexation. Some of these strategies showed a significant improvement in colour stability, with the best results achieved by the latter. The findings in model systems gave a good insight of the mechanisms involved in colour changes, and results were transferable to iron fortified banana puree.

Application of emulsifiers for water-based or water-contained heterogeneous food systems is often restricted by their very low solubility in aqueous media and, therefore, by their very low equilibrium bulk concentration. As a consequence, only very slow adsorption rates can be attained. On the other hand, the rate of adsorption from micellar solutions is found to be very fast because of the significant enhancement of matter transfer by means of micelles as containers. In this way, even surfactants with a very low critical micelle concentration (CMC) or non-micellar surfactants could be involved in such adsorption enhanced processes due to mixed micelles formation existing for many binary systems composed of substances with different micellization ability. This general mechanism of micellar promoted adsorption is realized in binary systems having great importance for applied food science and food industry.

Insoluble monolayers of commercially available sodium stearoyl lactylate (SSL) spread at the air/water interface were studied by recording pressure–area ( Π – A ) isotherms simultaneously with the morphology via Brewster angle microscopy (BAM). Whereas a strong hysteresis on the Π – A isotherms was observed for the first compression–expansion cycle, the second and further cycles show a strongly reduced hysteresis. The BAM images show significant changes in the surface textures during compression/expansion reflecting 2 D -heterogeneities in the monolayer. The most probable explanation of these phenomena can be given when taken into account the composition of the SSL sample consisting of two components of different interfacial activity—so-called SSL1 and SSL2. The less surface-active component was assumed to be pushed out of the monolayer at higher surface pressures. Additional compression experiments performed separately on the systems enriched by either of these compounds, respectively, confirm the explanation.

When using fluorescence microscopy for the investigation of β-lactoglobulin (BLG) stabilized thin liquid films and monolayers, it is necessary to label the protein sample with a fluorescent dye. In the present study, we discuss the effect of labeling β-lactoglobulin with either Rhodamine iso-thiocyanate (RITC) or Fluorescein iso-thiocyanate (FITC) on the BLG properties at the air–water interface and in thin films. RITC and FITC are the two most frequently used dyes in fluorescence microscopy. Two different Rhodamine concentrations were used, namely the concentration conventionally used in fluorescence microscopy, and a two times higher Rhodamine concentration. Interfacial tension and rheology measurements, and thin film investigations using X-ray reflectivity or the diminishing bubble method showed that the labeling procedure of the β-lactoglobulin using Rhodamine at the lowest concentration does not change the viscoelastic properties of the air–water interface, as well as the film thickness and gas permeability. However, when taking the higher Rhodamine concentration the films are thicker and more permeable for gas. Similarly, Fluorescein at a concentration equivalent to the highest concentration of Rhodamine induced also a modification of the protein film properties. However, the labeling did not influence the BLG monolayer viscoelastic characteristics. Labeling β-lactoglobulin with Rhodamine allows now using confocal fluorescence microscopy (CSLM) for the elucidation of structure formation in thin films and at water–air surfaces. As an example, images from thin films as formed in the diminishing bubble experiment and stabilized with labeled BLG show that the formed BLG aggregates are highly surface active, i.e., enriched at the water–air interface. The obtained images reveal that the aggregates are also present in the film. In general, CSLM combined with the diminishing bubble method seems to be an excellent experimental set-up to visualize the distribution of labeled components throughout a thin film and its adjacent monolayers. This is not possible using the diminishing bubble method in combination with conventional microscopy.

Monoglyceride molecules spontaneously self-assemble into various liquid crystalline structures when present in an aqueous environment. The various phases can be used to achieve different functionalities, e.g. to protect molecules from chemical degradation, to solubilize drugs and nutrients, to control release of flavours and drugs or to increase the yield in Maillard reactions. We will review (1) the typical characteristics of monoglyceride self-assembly structures, (2) the most common characterisation techniques, (3) how introduction of guest molecules influences the self-assembly structures, (4) their use for drug delivery and (5) how commercial food grade monoglycerides obtained from sunflower oil can be applied to achieve unique delivery functionalities in food systems.

The description of surface dilational rheology data by theoretical models has some general problems, essentially in the range of larger surface coverage. Typically, the dilational elasticity calculated from theoretical models increases with surfactant bulk concentration and reaches values so far not observed in any experiment. In contrast, the experimental elasticities in the high-frequency limit show an increase with concentration followed by a plateau or flat maximum. Various thermodynamic models for the state of interfacial layers are discussed with respect to the corresponding limiting dilational elasticity. With the reorientation model (Fainerman; et al. J. Phys. Chem. 1996, 100, 7669) and the additional assumption of an intrinsic compressibility of the assembled adsorption layer, the data for some oxyethylene surfactants and dodecyl dimethyl phosphine oxide are well described.

Drop and bubble shape tensiometry experiments are performed at the water/air and water/hexane interfaces in order to get more information about the differences in the adsorption layer structure of mixed protein/surfactant systems. For mixtures of β-lactoglobulin and sodium dodecyl sulphate the adsorption at the water/air interface is essentially a competitive process between protein/surfactant complexes and free surfactant molecules, while the water/oil interface is essentially covered by the complexes.

We have chemically synthesized two water-soluble forms of tocopherol succinate linked via an ester bond to hexaethylene glycol and dodecaethylene glycol. The self-assembly structure of the former in water is vesicular, whereas the latter forms elongated micelles. We treated Caco-2 cells with these compounds in these physical forms, in addition to a mixed micelle form. The intact compounds were taken up into the cells, influenced by both the chain length and the physical structure. In addition, the tocopherol derivatives were also metabolized into tocopherol succinate and tocopherol inside the cell. The total hydrolysis and uptake into the cells was two-fold higher from tocopherol hexaethylene glycol succinate in the form of mixed micelles than in vesicular form as assessed by analyzing intracellular tocopherol and tocopherol succinate. The longer polyethylene glycol chain gave a higher intracellular tocopherol succinate/tocopherol ratio. The major intracellular esterase in Caco-2 cells is carboxyl esterase 1 (EC 3.1.1.1), and in silico modelling studies show that the position of docking and hence the site of hydrolysis is influenced by the chain length. The in silico prediction is consistent with the in vitro data, since a longer chain length is predicted to favour hydrolysis of the ester bond between the succinate and polyethylene glycol moieties.

This study investigated the influence of structured fluids on Maillard-type reactions. The decomposition of xylose and the formation of volatile compounds were affected by the type of structured fluid used as reaction medium. In model systems based on xylose and glycine or leucine, xylose was preferably degraded in the hexagonal phase, compared to other mesophases and the aqueous sample. In parallel, norfuraneol was accumulated in the hexagonal phase. The data obtained indicate that molecular organisation of the reaction medium and flavour precursors can play an important role in food systems containing ingredients that tend to form self-assembly structures.

High affinity uptake of [3H](-)-norepinephrine (NE) was investigated in synaptosomes from rat cerebral cortex (Km = 360 +/- 30 nM) and hypothalamus (Km = 307 +/- 90 nM). Estrogens but not androgens, glucocorticoids or progestin interfered competitively with NE uptake. Ethinylestradiol was the most effective competitor tested, its Ki value being 200 nM in the cortex and 144 nM in the hypothalamus. Stereospecificity of the inhibitory effect of estradiol-17 beta with a preference for the 17 beta-hydroxy group was indicated by the ineffectiveness of estradiol-17 alpha and estrone as competitors. A-ring substitution of estradiol-17 beta or ethinylestradiol by hydroxyl groups in positions 2 and 4 (yielding catecholestrogens) or methyl substitution in positions 2 and 4 (yielding methylestrogens) significantly reduced the inhibitory potency of the estrogen. Methoxylation in positions 2, 4 or 11 beta completely abolished the competitive action of estradiol-17 beta or ethinylestradiol on NE uptake.

In a synaptosomal preparation from male rat cerebral cortex only 34% of total norepinephrine (NE) uptake could be inhibited by nanomolar concentrations of desmethylimipramine (DMI) with an apparent IC 50 value of 0.37 nM. The residual uptake was efficiently inhibited by micromolar concentrations of DMI (IC 50 = 4.0 μ M). In synaptosomes from the hypothalamus, 74% of total NE uptake could be blocked by DMI with an IC 50 of 0.1 nM whereas in synaptosomes from the striatum the IC 50 for DMI inhibition was 3.8 μM. It is concluded that in synaptosomes from rat cerebral cortex only 34%, and in synaptosomes from the hypothalamus 74% of total NE are taken up by noradrenergic nerve terminals whereas the residual NE uptake occurs in dopaminergic nerve endings.