Browsing by Author "Archer, Richard Hamilton"
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- ItemHydrolysis of bile acid conjugates and dehydroxylation of cholic acid by Clostridium bifermentans : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biotechnology(Massey University, 1980) Archer, Richard HamiltonThe transformation of bile acids by Clostridium bifermentans was studied with a view to developing a process whereby the bile acid conjugates of New Zealand mutton and beef gall may be converted to deoxycholic acid. Statistically designed experiments were employed to maximise 7α-dehydroxylation of cholic acid to deoxycholic acid and to minimise the 7α-dehydrogenation of cholic acid to 7-ketodeoxycholic acid. Both transformations showed optima near pH 7. High deoxycholate yields were associated with conditions less favourable to strong growth and with relatively high electrode potentials. 7-ketodeoxycholic acid production was not as sensitive to environmental factors as was 7α-de-hydroxylation and could not be eliminated merely by manipulating fermentation variables. Studies on the 7α-dehydrogenation of cholic acid with washed resting-stage cells of Cl. bifermentans indicated several means of manipulating 7-ketodeoxycholate yields which were then tested using batch fermentation. In the presence of Zn++ions, 7-ketodeoxycholate yields were reduced but dehydroxylation was completely inhibited. In the presence of EDTA, 7α-dehydrogenation was almost quantitative but deoxycholate yields were again nil. Both transformations were enhanced during aerobic incubation. The highest deoxycholate yield observed during the work (50 molar %) was obtained by sweeping the fermenter headspace with air. Growing cells of Cl. bifermentans effected the near-quantitative hydrolysis of glycodeoxycholate, taurodeoxycholate and taurocholate within 48 h whilst glycocholate was 90% deconjugated. At substrate concentrations greater than 0.1% w/v however, taurine conjugates were less well hydrolysed.
- ItemRate controlling mechanisms in atmospheric freeze drying : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemical and Bioprocess Engineering at Massey University, Manawatū, New Zealand(Massey University, 2023) Mathew, MeritAtmospheric freeze drying (AFD) can be considered a cost-effective alternative to vacuum freeze drying (VFD) but the very slow drying rate associated with it limits industrial scale adoption. Nevertheless, there are applications, particularly with thin sections such as sliced fruit or leaves, for which hops is an example, where the rate of AFD is relatively high. Therefore, it is important to understand the rate-controlling mechanisms in AFD and how it is affected by the structure of the fruit or leaf. Such understanding will help identify the bottlenecks of the process and thus the steps that may be taken to overcome them. This project has developed a mathematical model for AFD by considering the intrinsic material properties and the theoretical principles of heat and mass transfer. This could help the end-users to run simulations of AFD for different products and arrive at the best drying strategies to achieve faster drying rates before doing time-consuming and expensive experiments. In this work, hops are considered as the model system for the model development. The study needed high-quality experimental data for continuous in-situ weight loss measurements during AFD and there was a lack of such data in the literature reviewed. To deliver this, part of the project has developed a new experimental apparatus. The experimental apparatus developed is capable of continuous weight-loss measurement and data logging temperature and RH of the air in the drying chamber. Temporal weight-loss trial data are used to fit parameters and predict the drying rate and product weight loss. During the study it was found that AFD of hops is a mass transfer limited process. The drying rate was found to increase with process temperature and the adsorbent to hops ratio. Air circulation also helped in increasing the drying rate. The one-dimensional model developed to simulate AFD of hops was able to predict the drying behaviour based on the process parameters and the fitting factors for the hops. Ice sublimation was also studied in this project, based on the hypothesis that the AFD of hops is a type of pure ice sublimation with an additional layer of resistance to mass transfer. This hypothesis was found to be true for the present case and the model was development based on this.