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Food and Bioprocess Technology




In this article, we report results on the behavior of selected proteins in solution and on how they could affect the overall absorption and distribution of electromagnetic energy within dielectrically heated biomaterials. Ovalbumin, bovine serum albumin (BSA), β-lactoglobulin (BLG), and lysozyme (Lys) proteins varying in molecular weight, structure, and isoelectric point were systematically screened for this study. Measurements were performed using an open-ended coaxial probe over a frequency range encompassing the industrial, scientific, and medical (ISM) bands (1–1800 MHz) at six concentration levels and 25 °C. Primary findings include discovery of an additional δ-dispersion region in addition to the previously observed two regions between the well-established β- and γ-dispersion regions for protein solutions, which we propose are a sub-set of multiple δ-dispersions in the said region. We hypothesize that the β-dispersion is a summation of these multiple δ-dispersions and their cumulative effect is manifested in the amount of heat generated within a dielectrically treated biomaterial. An individual protein’s contribution to the overall dielectric absorption was quantitatively determined to account for up to 10% of the energy absorbed by free water molecules. We derived a mixture formula that accurately predicted the dielectric constant (ε′) at the critical industrial 915 MHz frequency, which we propose to use in computational simulations for purposes of design and development of dielectric heating devices. Theoretical calculation of the local ε′ of individual proteins from their amino acid makeup resulted in an average of 2.7, closely matching previously reported results. An increase in the physical size of a protein resulted in a decrease in the overall electromagnetic absorption of the mixture. A similar effect was observed as protein concentration increased with more pronounced effects on the dielectric increments (∆ε′) and absorption decrements (∆ε″); the implication of such effect on energy absorption and heating is discussed.

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