Theses and dissertations (Applied Sciences)

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Microencapsulation of Bifidobacterium animalis and Lactobacillus casei using resistant starch from Vigna unguiculata
(2020) Rengadu, Danielle; Mellem, John Jason
The use of functional foods is increasing globally with individuals aiming to maintain a healthy gut causing an increasing trend associated with probiotics in the health sector. Probiotics are live microorganisms that aid in improving the digestive system and gut health, however, the main problem associated with probiotics are ensuring a safe delivery through transition to the colon in harsh gastrointestinal conditions. For probiotics to be considered effective to the host a growth of Log 7 is essential in the colon, thus the need for microencapsulation. Therefore, this study was aimed at analysing resistant starch isolated from cowpea as an encapsulation material for Lactobacillus casei and Bifidobacterium animalis, for beverage application. Five different cultivars of cowpea (Bechuana white, Fahari, PAN 311, TVU 11424 and DT129-4) were analysed to determine the amount of resistant starch yielded as well as structural and physicochemical properties to determine the most suitable cultivar for the encapsulation process. The resistant starch percentage obtained was found in the range of 9.42-13.74%, with DT129-4 yielding the most resistant starch. The structural and physicochemical results obtained showed that the resistant starch isolated from cowpea has the potential for microencapsulation with cultivar DT129-4 exhibiting the most favourable results. Resistant starch was used as an encapsulating medium for Lactobacillus casei (RSL), Bifidobacterium animalis (RSB) and for a combination of the two probiotic microorganisms (RSLB) at a ratio of 1:1. The encapsulation yield after freeze drying were between 81.55-88.78% with the viability of the microcapsules under simulated gastrointestinal conditions also observed. The microcapsules were added to apple juice and the viability and stability of the microcapsules examined over 28 d. The final viability for microcapsules in the juice at the end of 28 d for RSL, RSB and RSLB were 7.53, 6.98 and 7.46 Log CFU/mL. This study shows that that resistant starch from cowpea has great potential as an encapsulating membrane within the nutraceutical beverage manufacturing industry.
Molecular interactions of binary mixtures of deep eutectic solvents with organic solutes
(2024-05) Molefi, Reitumetse Precious; Kabane, Bakusele; Deenadayalu, Nirmala
Deep eutectic solvents are the new emerging solvents formed by the combination of hydrogen bond acceptor and hydrogen bond donor. This type of solvent is still under development for possible industrial application including in chemistry, biotechnology, and pharmaceutical processes. The deep eutectic solvents have attracted much attention because they are characterized as greener solvents when compared to the currently used volatile organic solvents. Deep eutectic solvents are to replace the ionic liquids, which are posed as green solvents, however, their toxic nature has turned to be its drawbacks. The deep eutectic solvents attracted great interest due to their unique properties such as biodegradability, thermal stability, less toxicity, easy and cheap to prepare. This work explores the activity coefficients at infinite dilution of deep eutectic solvents. The deep eutectic solvents under investigation were carefully synthesized using hydrogen bond donors (HBD) and hydrogen acceptors (HBA) at a specific ratio. The analysis of these prepared deep eutectic solvents were analysed using spectroscopic techniques (FTIR and NMR) to confirm the formation of deep eutectic solvents and the type of interaction occurring between the HBD and the HBA. Additionally, thermal stability of the prepared deep eutectic solvents was investigated. The DESs were then used to measure the activity coefficients at infinite dilution for volatile organic compounds (alkanes, alkene, alkynes, aromatic hydrocarbons, ketones, acetonitrile, tetrahydrofuran, alcohols and thiophene) using the chromatography technique. The activity coefficients at infinite dilutions were conducted over a range of temperature (313.15 - 353.15) K. The prepared deep eutectic solvents for this include.  DES1 {1- butyl-2,3-dimethylimidazolium chloride + ethylene glycol (1:3)}  DES2 {1-butyl-2,3-dimethylimidazolium chloride + diethylene glycol (1:2)}  DES3 {1-butyl-2,3-dimethylimidazolium tetrafluoroborate + ethylene glycol (1:3)}  DES4 {1 -butyl-2,3-dimethylImidazolium tetrafluoroborate + diethylene glycol (1:3)) The study also focuses on understanding the behaviour of these DES through a comprehensive analysis of their thermophysical characteristics and their ability to dissolve solutes at infinite dilution. The investigation revealed intriguing trends in the solvation behaviour of different classes of solutes within the DES. Alkanes exhibited higher activity coefficients, with a clear dependence on the alkyl chain length. Cyclic hydrocarbons showed distinct behaviour due to stronger interactions with the imidazolium ring. Alkynes demonstrated the lowest activity coefficients, attributed to the presence of triple bonds influencing solute-solvent interactions. Aromatic hydrocarbons exhibited unique solvation behaviour influenced by the delocalized pi- π- electrons on the benzene ring. To use the deep eutectic solvents at an industrial level, it is highly imperative to understand the intermolecular interactions and properties of the pure deep eutectic solvents and their mixtures with volatile organic solutes. The prepared deep eutectic solvents for thermophysical properties include.  DES5 (1-butyl-1-methylpyrrolidinium bromide + ethylene glycol)  DES6 (1-butyl-3-methylimidazolium chloride + ethylene glycol) Thermophysical properties, such as densities, speed of sound, and refractive indices were measured as a function of temperature. The study investigated the binary mixtures containing (DES5 + acetic acid or ethanol) and (DES 6 + acetic acid or ethanol). These were investigated at temperatures ranging between (293.15 and 313.15) K and at atmospheric pressure (0.1MPa) over a range of mole fraction (𝑥1= 0 to 1) as a function of DES. The measured property values were used to compute the excess properties such as excess molar volumes, isentropic compressibilities, deviation in refractive indices, deviation in isentropic compressibilities and intermolecular free length. The data obtained provides insights into the molecular interactions within the DESs, shedding light on their structural arrangements and overall stability. This study contributes to the fundamental understanding of deep eutectic solvents, offering a detailed exploration of their thermophysical properties and their solvation behaviour at infinite dilution. The findings have implications for the design and optimization of DESs for various applications, including their use as green solvents in chemical processes and separations.
Oxidative dehydrogenation of n-octane using dealuminated faujasite zeolites
(2024-09) Mpotulo, Archie Sifundo; Friedrich, HB; Ndlela, SS
Commercially obtained NaY was modified by a dealumination process using different solutions containing specific concentrations of citric acid, ethylenediaminetetraacetic acid disodium (EDTA-2Na), and a mixture of both EDTA-2Na and citric acid. The three prepared catalysts were then used to study the effect of dealumination on oxidative dehydrogenation (ODH) of n-octane. Dealumination was carried out to strengthen the zeolites acid sites, which will lead to an increased activity towards the oxidation of n-octane. Results from these showed that removing the framework and extra framework aluminium in the NaY zeolites increases the intrinsic acidity, which then led to increased conversion in the ODH of n-octane, with the catalyst prepared by the mixture of both EDTA-2Na and citric acid recording the highest conversion of just above 10 %. The conversion was ascribed to the removal of both the non- and framework aluminium, which leads to improved pore volumes and surface area. All the three prepared catalysts were mostly selective towards the carbon oxides (COx) products which was due to the absence of the ODH promoting metal. To induce the ODH promoting properties on the prepared catalysts (NaY[AL] for acid leaching using citric acid, NaY[CAT] for chelating agent treatment using EDTA-2Na and NaY[CT] for complex treatment using citric acid and EDTA-2Na), they were then further modified by introducing gallium using a modified ionic exchange procedure. Gallium has been shown by previous studies to be a promising ODH active metal. All the prepared catalysts were exchanged by 2 %wt of gallium which contributed to the increase of about 2 % for all the prepared catalysts when they tested were under similar ODH conditions with the first three batches of dealuminated NaY. The introduction of framework gallium also decreased side reactions such as the cyclization and cracking reactions, due to the reduction in medium to strong acid sites. The COx selectivity for the catalysts decreased from above 90 % to just below 85 %. This was not the case for the highest acidic NaY[AL], which showed no decrease in the COx selectivity. Though there was a slight improvement on the olefins selectivity after gallium introduction, COx production was still favoured by the catalysts. To mitigate this, barium, a basic metal was also introduced into the prepared Ga-NaY catalysts. Barium was also introduced using ionic exchange, and 1.5 %wt was introduced. Barium is known for inducing basic sites which facilitates the quick desorption of ODH products, leading to suppressed overoxidation. Due to subsequent ionic exchange procedures done on the catalysts, the morphology of the catalysts was altered, with the NaY zeolites losing their cubic shape and also clustering. The effect of Ba for all the catalysts was not much, as only BaGa-NaY[CT] showed a 4 % decrease in the COx activity. All the catalysts showed increased cracked products and oxygenates, but not much improvement in the olefins and aromatic products. The findings of this study showed that the behavior of the zeolite catalysts in the ODH of alkanes depends both on the physical and chemical properties of the catalyst. Acidity is a big factor when dealing with zeolites, as the activity and selectivity of the catalysts depends on the alteration of this feature. A high concentration of strong acid sites alone can activate the paraffin of interest, however Lewis acid sites induced by a reducible gallium metal are responsible for improved octene activity, selectivity and stability of the catalysts through the facilitation of coke burning on the surface of the catalyst.