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In recent years there has been considerable interest in the development of microwave-based food processing technologies. Microwave radiation is considered to have both thermal and non-thermal effects. The thermal effects are related to the heat generated by the absorption of microwave energy by water or by organic molecules, but very little is known about the mechanisms involved in the putative non-thermal effects. It has been postulated that the latter could involve a direct energy transfer from the electromagnetic field to the vibrational modes of macromolecules, altering their conformation. In the present study, the non-thermal effects induced upon irradiation of protein solutions with microwave energy were investigated by employing Fourier transform infrared spectroscopy, circular dichroism, and fluorescence spectroscopy to elucidate the unfolding pathways of hemoglobin and beta-lactoglobulin (5% in D2O) subjected to either microwave irradiation (2450 MHz) or conventional heating. (Abstract shortened by UMI.)

Thesis (doctoral)--Uppsala University, 1983. / Includes bibliographical references (p. 29-36).

No / In this work, parameters of the steric mass-formalism SMA are optimally ascertained for a reliable determination of the adsorption isotherms of beta-lactoglobulin A and B under non-isocratic conditions. For this purpose, static batch experiments are used in contrast to the protocols based on different experimental steps, which use a chromatographic column. It is shown that parameters can already be determined for a small number of experiments by using a systematic procedure based on optimal model-based experimental design and an efficient NLP-solver. The in different works observed anti-Langmuir shape of the isotherm for small concentrations of beta-lactoglobulin A was corroborated. Moreover, we also found indications for a porosity variation with changing protein concentrations.

In this research, beta-lactoglobulin was chemically modified by attaching different levels of stearic acid to the protein. The effect of this modification on hydrophobic!ty, emulsifying and foam properties, digestibility and allergenicity of the protein was investigated. It was found that the effect of fatty acid attachment or lipophilization depended on the amount of fatty acids attached to the protein. Incorporation of the hydrophobic ligands led to increased hydrophobic interactions, resulting in a decreasing solubility with extent of incorporation. Furthermore, the surface hydrophobicity measurements showed that the two fluorescence probes 8-anilinonaphthalene-l-sulfonate (ANS) and cis-parinaric acid (CPA) used for the surface hydrophobicity measurements were not equivalent This may support the. observation by earlier workers that ANS measures aromatic hydrophobicity and CPA aliphatic hydrophobicity. The studies on surface functional properties i.e. emulsifying and foaming properties, indicated that there was some improvement in these functional properties at low and medium levels of incorporation which decreased as the extent of fatty acid attachment further increased. The improvement, of these functional properties could be attributed to improved amphiphilicity of the proteins at these levels of incorporation. This research also showed that both high solubility and high ANS surface hydrophobicity is needed for the best emulsifying properties. In vitro digestibility studies showed a decrease in digestibility of the modified proteins with increased lipophilization. From the passive cutaneous anaphylaxis experiments, it was found that the level of fatty acid attachment to the protein had a significant effect on its ability to elicit IgE antibodies. Increased ability to elicit IgE antibodies was observed at a low level of fatty acid. When a medium level of fatty acid was attached the ability to elicit antibodies was reduced and almost completely destroyed when a higher level of fatty acid was incorporated. The above observations could be explained by the fact that the low level incorporation of fatty acid led to changes in the protein structure which exposed more allergenic sites. The almost complete destruction of the allergenicity could be attributed to denaturation of the protein which reduced or destroyed available allergenic sites. The antigenicity or binding of the modified proteins to the IgG antibodies raised against the native protein was studied by both direct and competitive enzyme linked immunosorbent assay. It was found that at low and medium levels of incorporation, the proteins demonstrated increased binding ability compared to the native protein. This was attributed to the increased exposure of antigenic sites on the protein with fatty acid incorporation. However, the protein with high level of incorporated fatty acid showed decreased binding ability. / Land and Food Systems, Faculty of / Graduate