Fiona A. Husband

Interfacial Characterization of β-Lactoglobulin Networks : Displacement by Bile Salts

The competitive displacement of a model protein (beta-lactoglobulin) by bile salts from air-water and oil-water interfaces is investigated in vitro under model duodenal digestion conditions. The aim is to understand this process so that interfaces can be designed to control lipid digestion thus improving the nutritional impact of foods. Duodenal digestion has been simulated using a simplified biological system and the protein displacement process monitored by interfacial measurements and atomic force microscopy (AFM). First, the properties of beta-lactoglobulin adsorbed layers at the air-water and the olive oil-water interfaces were analyzed by interfacial tension techniques under physiological conditions (pH 7, 0.15 M NaCl, 10 mM CaCl2, 37 degrees C). The protein film had a lower dilatational modulus (hence formed a weaker network) at the olive oil-water interface compared to the air-water interface. Addition of bile salt (BS) severely decreased the dilatational modulus of the adsorbed beta-lactoglobulin film at both the air-water and olive oil-water interfaces. The data suggest that the bile salts penetrate into, weaken, and break up the interfacial beta-lactoglobulin networks. AFM images of the displacement of spread beta-lactoglobulin at the air-water and the olive oil-water interfaces suggest that displacement occurs via an orogenic mechanism and that the bile salts can almost completely displace the intact protein network under duodenal conditions. Although the bile salts are ionic, the ionic strength is sufficiently high to screen the charge allowing surfactant domain nucleation and growth to occur resulting in displacement. The morphology of the protein networks during displacement is different from those found when conventional surfactants were used, suggesting that the molecular structure of the surfactant is important for the displacement process. The studies also suggest that the nature of the oil phase is important in controlling protein unfolding and interaction at the interface. This in turn affects the strength of the protein network and the ability to resist displacement by surfactants.

High pressure, thermal and pulsed electric-field-induced structural changes in selected food allergens.

SCOPE The effects of high-pressure/temperature treatment and pulsed electric field treatment on native peanut Ara h 2, 6 and apple Mal d 3 and Mal d 1b prepared by heterologous expression were examined. METHODS AND RESULTS Changes in secondary structure and aggregation state of the treated proteins were characterized by circular dichroism spectroscopy and gel-filtration chromatography. Pulsed electric field treatment did not induce any significant changes in the structure of any of the allergens. High-pressure/temperature at 20 °C did not change the structure of the Ara h 2, 6 or Mal d 3 and resulted in only minor changes in structure of Mal d 1b. Ara h 2, 6 was stable to HPP at 80 °C, whereas changes in circular dichroism spectra were observed for both apple allergens. However, these changes were attributable to aggregation and adiabatic heating during HPP. An ELISA assay of temperature treated Mal d 3 showed the antibody reactivity correlated well with the loss of structure. CONCLUSION In conclusion, novel-processing techniques had little effect on purified allergen structure. Further studies will demonstrate if these stability properties are retained in foodmatrices.

High-pressure treatment reduces the immunoreactivity of the major allergens in apple and celeriac

SCOPE The impact of thermal and high pressure (HP) processing on the immunoreactivity of the allergens Mal d 1, Mal d 3 and Api g 1 has been investigated in apple and celeriac tissue, respectively. METHODS AND RESULTS The extracted proteins were assessed using SDS-PAGE and Western blot. The results showed that Mal d 1 was subject to loss of immunoreactivity as soon as the apple tissue was disrupted although it was remarkably resistant to both thermal and HP processing. This is in contrast to the Mal d 1 structural homolog from celeriac, Api g 1, that was susceptible to thermal processing. The other major allergen in apple, Mal d 3, was found to be resistant to chemical modification and thermal processing in apple, which is in contrast to behavior in solution. However, the combination of pressure and temperature significantly reduced its immunoreactivity. Pectin was found to protect Mal d 3 from thermal denaturation in solution and is a possible candidate for the protective effect of the fruit. CONCLUSION The conclusion to be drawn from these results is that the combination of HP and thermal processing is an effective method to reduce the allergenicity of both apple and celeriac.

Foaming properties of modified faba bean protein isolates

Abstract The foaming properties of native and modified faba bean ( Vicia faba ) protein isolates were investigated. Foam stability was studied using both a micro-conductimetric/sparging and a whipping method. Samples were defatted by either supercritical carbon dioxide or isopropanol extraction, both of which produced an increase in the foam stability. Increases in foam stability were also observed for acetylated and mechanolyzed (ball milled) samples. The latter produced the more marked effect. Samples with differing degrees of mechanolyzation were examined, the most highly mechanolyzed samples displaying the greatest foam stability. Studies using circular dichroism spectroscopy showed a correlation between the observed change in functional properties and the secondary structure of the faba bean protein. The robustness of foams formed from several of the treated samples was investigated by assessment of the stability of the foams against destabilization by competitive adsorption of the lipid analogue lysophosphatidylcholine. Again the mechanolyzed sample possessed the best foaming properties in the presence of this competitive surfactant.

Chapter 26:Role of Protein-Stabilized Interfaces on the Microstructure and Rheology of Oil-in-Water Emulsions

Emulsions have applications as wide ranging as food, pharmaceuticals, oil production, printing, agrochemicals and photography. They are incorporated into a broad range of food products, and it is estimated that over 40% of processed foods contain emulsified oils or fats. The emulsified fat is includ...