Search

The present study sought to understand how the microstructure of protein gels impacts lipolysis of gelled emulsions. The selected system consisted of an oil-in-water (o/w) emulsion embedded within gelatin gels. The gelatin-gelled emulsions consisted of a discontinuous network of aggregated emulsion droplets (mesoscale), dispersed within a continuous network of gelatin (microscale). The viscoelastic properties of the gelled emulsions were dominated by the rheological behavior of the gelatin, suggesting a gelatin continuous microstructure rather than a bicontinuous gel. A direct relationship between the speed of fat digestion and gel average mesh size was found, indicating that the digestion of fat within gelatin-gelled emulsions is controlled by the ability of the gel's microstructure to slow lipase diffusion to the interface of fat droplets. Digestion of fat was facilitated by gradual breakdown of the gelatin network, which mainly occurred via surface erosion catalyzed by proteases. Overall, this work has demonstrated that the lipolysis kinetics of gelled emulsions is driven by the microstructure of protein gels; this knowledge is key for the future development of microstructures to control fat digestion and/or the delivery of nutrients to different parts of the gastrointestinal tract.

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 understanding of how foods are digested and metabolised is essential to enable the design/selection of foods as part of a balanced diet. Essential to this endeavour is the development of appropriate biorelevant in vitro digestion tools. In this work, the influence of gastric pH profile on the in vitro digestion of mixtures of β-lactoglobulin (βlg) and xanthan gum prior to and after heat induced gelation was investigated. A conventional highly acidic (pH 1.9) gastric pH profile was compared to two dynamic gastric pH profiles (initial pH of 6.0 vs. 5.2 and H(+) secretion rates of 60 vs. 36 mmol h(-1)) designed to mimic the changes in gastric pH observed during clinical trials with high protein meals. In moving away from the pH 1.9 model, to a pH profile reflecting in vivo conditions, the initial rate and degree of protein digestion halved during the first 45 minutes. After 90 minutes of gastric digestion, all three pH profiles caused similar extents of protein digestion. Given that 50% gastric emptying times of (test) meals are in range of 30-90 min, it would seem highly relevant to use a dynamic pH gastric model rather than a pH 1.9 (USP) or pH 3 model (INFOGEST) in assessing the impact of food structuring approaches on protein digestion. The impact that heat induced gelation had on the degree of gel digestion by pepsin was also investigated. Surprisingly, it was found that heat induced gelation of βlg-xanthan mixtures at 70-90 °C for 20 minutes lead to a considerable decrease in the rate of proteolysis, which contrasts many studies of dispersed aggregates and gels of βlg alone whose heating accelerates pepsin activity due to unfolding. In the present case, the formation of a dense protein network created a fine pore structure which restricted pepsin access into the gel thereby slowing proteolysis. This work not only has implications for the in vitro assessment of protein digestion, but also highlights how protein digestion might be slowed, learnings that might have an influence on the design of foods as part of a satisfying balanced diet.

Whey protein isolate was heat-treated at 85 degrees C for 15 min at pH ranging from 6.0 to 7.0 in the presence of NaCl in order to generate the highest possible amount of soluble aggregates before insolubility occurred. These whey protein soluble aggregates were characterized for composition, hydrodynamic diameter, apparent molecular weight, zeta-potential, surface hydrophobicity index, activated thiol group content, and microstructure. The adsorption kinetics and rheological properties (E', etad) of these soluble aggregates were probed at the air/water interface. In addition, the gas permeability of a single bubble stabilized by the whey protein soluble aggregates was determined. Finally, the foaming and foam-stabilizing properties of these aggregates were measured. The amount of whey protein soluble aggregates after heat treatment was increased from 75% to 95% from pH 6.0 to pH 7.0 by addition of 5 mM to 120 mM NaCl, respectively. These soluble aggregates involved major whey protein fractions and exhibited a maximum of activated thiol group content at pH6.6. The hydrodynamic radius and the surface hydrophobicity index of the soluble aggregates increased from pH 6.0 to 7.0, but the molecular weight and zeta-potential decreased. This loss of apparent density was clearly confirmed by microscopy as the soluble aggregates shifted from a spherical/compact structure at pH 6.0 to a more fibrillar/elongated structure at pH 7.0. Surface adsorption was faster for soluble aggregates formed at pH 6.8 and 7.0 in the presence of 100 and 120 mM NaCl, respectively. However, interfacial elasticity and viscosity measured at 0.01 Hz were similar from pH 6.0 to 7.0. Single bubble gas permeability significantly decreased for aggregates generated at pH6.6. Furthermore, these aggregates exhibited the highest foamability and foam liquid stability. Air bubble size within the foam was the lowest at pH 7.0. The coarsening exponent, alpha, fell within predicted values of 1/3 and 1/2, except for very dry foams where it was 1/5.

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.

Oil-in-water emulsions stabilized by sodium caseinate were frozen by the following processes: (a) Cooling to −18°C at 207 MPa, followed by slow (approximately 9 min) pressure release (SPR) or fast (approximately 3 s) pressure release (FPR), then by a freezing plateau at −0.6°C; (b) Freezing under a constant pressure of 100 MPa, at −9°C (freezing under high pressure, FUP); (c) Control freezing at atmospheric pressure and −0.6°C (freezing at atmospheric pressure, FAP). In all cases, emulsion samples were frozen in a cylindrical tubing immersed in a propanediol/water mix at −29°C. Freezing kinetics, measured with T thermocouples inserted at the sample centre or the surface, indicated very slow freezing by FUP (due to a ΔT of only 20°C). Freezing by FPR produced the shortest freezing plateau. The pressure–temperature coordinates of the sample on the phase diagram of water, determined with a fast data acquisition system, revealed moderate or extensive supercooling before nucleation for SPR or FPR, respectively. Samples were fixed by freeze substitution and the imprints of ice crystals at different sample depths were examined by light microscopy. Ice crystals resulting from FPR were small, irregularly shaped and without specific orientation, while those from FUP were larger, needle-shaped, radially oriented and with a marked size gradient from sample surface to centre. Results are consistent with enhanced supercooling and uniform ice nucleation assumed to occur upon FPR. Pressure release from 300 MPa and −16.5°C gave similar results as from 207 MPa and −18°C, while FPR from 100 MPa and −8°C resulted in less nucleation, a longer freezing plateau and some needle-shaped crystals. None of the freezing processes significantly modified the size distribution of oil droplets, as determined on thawed emulsions.

Designing food products to modulate digestion and ultimately physiological responses is a growing area of interest in the food industry. There is indeed a rising awareness toward functional foods, which can be defined as foods that, beyond their role as nutrient carriers, affect beneficially one or more target functions in the body and accordingly promote health. In the present chapter, we aim to illustrate through different examples how to tailor designed functional properties for macronutrients: proteins, lipids, and carbohydrates. Indeed, in addition to their nutritional profile, the structural and physicochemical characteristics of macronutrients within a food matrix may lead to different digest compositions, with different delivery outcomes in the gastrointestinal tract, and therefore may trigger different physiological responses. The development of different technological means of changing the structure of the main macronutrients to modulate the properties of in vitro digests and in vivo biological responses will be shown, highlighting the close link between food science, technology and nutrition and health science.

The relationship between the physical structure of espresso coffee foam, called crema, and the above-the-cup aroma release was studied. Espresso coffee samples were produced using the Nespresso extraction system. The samples were extracted with water with different levels of mineral content, which resulted in liquid phases with similar volatile profiles but foams with different structure properties. The structure parameters foam volume, foam drainage, and lamella film thickness at the foam surface were quantified using computer-assisted microscopic image analysis and a digital caliper. The above-the-cup volatile concentration was measured online by using PTR-MS and headspace sampling. A correlation study was done between crema structure parameters and above-the-cup volatile concentration. In the first 2.5 min after the start of the coffee extraction, the presence of foam induced an increase of concentration of selected volatile markers, independently if the crema was of high or low stability. At times longer than 2.5 min, the aroma marker concentration depends on both the stability of the crema and the volatility of the specific aroma compounds. Mechanisms of above-the-cup volatile release involved gas bubble stability, evaporation, and diffusion. It was concluded that after the initial aroma burst (during the first 2-3 min after the beginning of extraction), for the present sample space a crema of high stability provides a stronger aroma barrier over several minutes.

A number of lactose-binding lectins have recently been identified in the rat and mouse intestine, one of which corresponds to the C-terminal domain of IgE-binding proteins, originally identified in rat basophilic leukemia (RBL) cells and mouse 3T3 fibroblasts. In the present report, we describe the affinity purification of a rat intestinal lactose-specific lectin which binds murine IgE antibodies. This binding most likely occurs via the immunoglobulin carbohydrate chains, as it is inhibited by lactose. This intestinal lectin molecule is also immunologically related to the previously described IgE-binding protein (epsilon BP) isolated from RBL cells, since it is recognized by antibodies raised against recombinant epsilon BP. This intestinal form of epsilon BP has a molecular mass of 17.5 kDa, which is much lower than that of its RBL cell analogue (31 kDa). The attachment of IgE to the mouse intestinal epithelium was demonstrated by immunohistochemistry, along with the presence of a corresponding mouse intestinal epsilon BP. The carbohydrate-dependent nature of this attachment was established by demonstrating that IgE binding to mouse epithelium was specifically abolished by lactose (4 mM) and by a blood-group-A-active tetrasaccharide (0.2 mM), but not by mannose (10 mM). Finally, the association of IgE with the mouse intestinal epithelium was prevented by competition with the purified IgE-binding lectin isolated from rat intestine. Although the physiological function of this intestinal protein is still unknown, the finding that IgE binds to a lectin in the intestinal epithelium pinpoints a possible novel mechanism for the regulation of IgE-mediated disorders, such as food allergy.

For many years food manufacturers have been trying to meet the rising expectations of consumers for nutritionally balanced and healthy foods. The current way to address this challenge is to ‘enhance’ nutritional functionality within a product by adding to a common food base various bioactives such a...

The electrostatic complexation between beta-lactoglobulin and acacia gum was investigated at pH 4.2 and 25 degrees C. The binding isotherm revealed a spontaneous exothermic reaction, leading to a DeltaHobs = -2108 kJ mol(-1) and a saturation protein to polysaccharide weight mixing ratio of 2:1. Soluble electrostatic complexes formed in these conditions were characterized by a hydrodynamic diameter of 119 +/- 0.6 nm and a polydispersity index of 0.097. The effect of time on the interfacial and foaming properties of these soluble complexes was investigated at a concentration of 0.1 wt % at two different times after mixing (4 min, referred as t approximately 0 h and t = 24 h). At t approximately 0 h, the mixture is mainly made of aggregating soluble electrostatic complexes, whereas after 24 h these complexes have already insolubilize to form liquid coacervates. The surface elasticity, viscosity and phase angle obtained at low frequency (0.01 Hz) using oscillating bubble tensiometry revealed higher fluidity and less rigidity in the film formed at t approximately 0 h. This observation was confirmed by diminishing bubble experiments coupled with microscopy of the thin film. It was thicker, more homogeneous and contained more water at t approximately 0 h as compared to t = 24 h (thinner film, less water). This led to very different gas permeability's of Kt approximately 0 h = 0.021 cm s(-1) and Kt=24 h) = 0.449 cm s(-1), respectively. Aqueous foams produced with the beta-lactoglobulin/acacia gum electrostatic complexes or coacervates exhibited very different stability. The former (t approximately 0 h) had a stable volume, combining low drainage rate and mainly air bubble disproportionation as the destabilization mechanism. By contrast, using coacervates aged for 24 h, the foam was significantly less stable, combining fast liquid drainage and air bubble destabilization though fast gas diffusion followed by film rupture and bubble coalescence. The strong effect of time on the air/water interfacial properties of the beta-lactoglobulin/acacia gum electrostatic complexes can be understood by their reorganization at the interface to form a coacervate phase that is more fluid/viscous at t approximately 0 h vs rigid/elastic at t = 24 h.

A set of six espresso coffees with different foam characteristics and similar above cup and in-mouth flavour sensory profiles was produced by combination of two varying parameters, the extraction pressure and the filtration of the coffee beverage. The coffees were subsequently evaluated in a comparative manner by a set of analytical (headspace, nose-space) and sensory (Temporal Dominance of Sensations) techniques. The presence of espresso crema in its standard quantity was demonstrated to be associated with the optimum release of pleasant high volatiles, both in the above cup headspace and in-mouth. On the other hand, the TDS study demonstrated that increasing amount of crema was associated with increasing roasted dominance along coffee consumption. Furthermore, a parallel was established between the roasted sensory dominance and the dominant release of 2-methylfuran in the nose-space. This was, however, an indirect link as 2-methylfuran was indeed a chemical marker of roasting but does not contribute to the roasted aroma. Lowering the standard amount of crema by filtration clearly decreased the release of pleasant high volatiles and the in-mouth roasted sensory dominance. On the other hand, increasing the usual crema volume by increasing the extraction pressure did not bring any added value concerning the above cup and in-mouth release of pleasant high volatiles.