Development of techniques for the study of protein systems

This dissertation descries work undertaken to investigate protein systems on nano- and micro-levels. The principal objective was the application of fluid dynamic gauging with simultaneous direct imaging of the changes in microstructure occurring during the cleaning of whey protein foulants. Laser confocal microscopy allowed images of the internal microstructure, on the micron and tens-of-microns scales, to be matched against the changing macro-properties of a whey protein film during cleaning, as measured by the gauge on the tens-of-microns scale. This work constitutes proof of concept; the successful capture of gauging and microscopy data displaying consistent, complementary phenomena proved the efficacy of the experimental concept. Achievement of this goal required first establishing the operating range within which use of the gauge caused minimal interference with the film being studied and, secondly, the development of a whey protein foulant that reproduced behavioural characteristics of fouling layers studied by previous researchers while also being suitable for microscopy. Both these objectives were achieved. That minimal interference range was established by comparing gauging cleaning profiles of particular deposits within duct flows against alternative cleaning profiles obtained by measuring the changing thermal resistances of the deposits. It was shown that the suitability of the operating regime was dependent on the capacity of the deposit to resist the suction pressure of the gauge. Stresses that exceed the cohesive and adhesive strengths of a deposit were used to explore in more detail the adhesive properties of foulant layers, using dried tomato purée as a model system. A quasi-stagnant system was used, in which the only flow present was that through the gauge. Thus the gauge was the source of all stresses imposed on the deposit by flow; this enabled accurate inference of the imposed normal stress.